Applied Geochemistry (v.26, #S)

A simple mass balance model has been developed to assess the planetary boundary for P supply in relation to use by human society. Phosphorus sources used by humans are from fossil reserves. The model takes into account resource use rate and reserves, consumption, phosphate to food production, environmental degradation, waste and recycling. Various policy scenarios are tested from current end of pipe solutions to clean production and pollution prevention, sustainable consumption and production polices and sustainable population policy. In order to get an overview of possible future scenarios it is necessary to close nutrient cycles and formulate a sustainable population policy. The outcome of systems dynamics based modeling for four scenarios are given in a sister paper in this issue. Results show that effective population and P recycling policies are crucial to avoid world hunger.

► Peak phosphorus supply behaviour. ► Recycling essential for phosphorus supply. ► Phosphorus supply is connected to food security.A systems dynamics model was developed to assess the planetary boundary for P supply in relation to use by human society. It is concluded that present day use rates and poor recycling rates of P are unsustainable at timescales beyond 100+ a. The predictions made suggest that P will become a scarce and expensive material in the future. The study shows clearly that market mechanisms alone will not be able to secure an efficient use before a large part of the resource will have been allowed to dissipate into the natural environment. It is suggested that population size management and effective recycling measures must be planned long term to avoid unpleasant consequences of hunger and necessary corrections imposed on society by mass balance and thermodynamics.

Land–sea carbon and nutrient fluxes and coastal ocean CO2 exchange and acidification: Past, present, and future by Fred T. Mackenzie; Andreas J. Andersson; Rolf S. Arvidson; Michael W. Guidry; Abraham Lerman (S298-S302).
► Seawater CO2-carbonic acid system chemistry and epochs of ocean acidification have varied nearly in concert with atmospheric CO2 changes at various time scales during the Phanerozoic. ► Long-term geologic changes in atmospheric CO2 and ocean carbon chemistry largely reflect both plate tectonic mechanisms and biological evolution. ► From the Last Glacial Maximum to late preindustrial time, as sea level and atmospheric CO2 rose and the climate warmed, riverine fluxes of DIC, total alkalinity, and N and P nutrients increased and the pH and carbonate saturation state of the global coastal ocean fell. ► Nominal modeling of the future state of the global coastal ocean forecasts profound changes in its land-derived nutrient subsidies, and acidity, carbonate saturation state, magnitude and direction of air-sea CO2 exchange and trophic status of its waters due primarily to anthropogenic activities.Epochs of changing atmospheric CO2 and seawater CO2–carbonic acid system chemistry and acidification have occurred during the Phanerozoic at various time scales. On the longer geologic time scale, as sea level rose and fell and continental free board decreased and increased, respectively, the riverine fluxes of Ca, Mg, DIC, and total alkalinity to the coastal ocean varied and helped regulate the C chemistry of seawater, but nevertheless there were major epochs of ocean acidification (OA). On the shorter glacial–interglacial time scale from the Last Glacial Maximum (LGM) to late preindustrial time, riverine fluxes of DIC, total alkalinity, and N and P nutrients increased and along with rising sea level, atmospheric PCO2 and temperature led, among other changes, to a slightly deceasing pH of coastal and open ocean waters, and to increasing net ecosystem calcification and decreasing net heterotrophy in coastal ocean waters. From late preindustrial time to the present and projected into the 21st century, human activities, such as fossil fuel and land-use emissions of CO2 to the atmosphere, increasing application of N and P nutrient subsidies and combustion N to the landscape, and sewage discharges of C, N, P have led, and will continue to lead, to significant modifications of coastal ocean waters. The changes include a rapid decline in pH and carbonate saturation state (modern problem of ocean acidification), a shift toward dissolution of carbonate substrates exceeding production, potentially leading to the “demise” of the coral reefs, reversal of the direction of the sea-to-air flux of CO2 and enhanced biological production and burial of organic C, a small sink of anthropogenic CO2, accompanied by a continuous trend toward increasing autotrophy in coastal waters.

Compatibility of space and time for modeling fluvial HCO 3 - fluxes – A comparison by Nils Moosdorf; Jens Hartmann; Ronny Lauerwald (S295-S297).
► Distributed lumped models predict HCO3 - flux time series well. ► HCO3 - concentration in general decreases with increasing runoff. ► HCO3 - concentration variation has less impact on HCO3 - flux than runoff variation.Empirical matter-flux models calibrated on a large number of catchments (“distributed lumped models”) are regularly used to analyze fluvial HCO 3 - fluxes. Despite the demonstrated applicability for spatial predictions, the applicability of distributed lumped models for historic reconstructions or future projections needs validation. Here, as a first evaluation, predictions of a published distributed lumped HCO 3 - flux model will be compared to observed HCO 3 - flux time series of individual catchments and additionally to models which were calibrated using those time series. The distributed lumped model, which was calibrated by regional data, predicts the time-series of single catchments well. Additionally, the results and parameters of models calibrated on time series of the single catchments are within the range that is covered by the distributed lumped model. The evaluation hints at the applicability of distributed lumped models, calibrated by annual flux data of a large number of catchments, for historic reconstructions and future projections of fluvial HCO 3 - flux at the regional scale.

Atmospheric CO2 sink: Silicate weathering or carbonate weathering? by Zaihua Liu; Wolfgang Dreybrodt; Huan Liu (S292-S294).
It is widely accepted that chemical weathering of Ca–silicate rocks could potentially control long-term climate change by providing feedback interaction with atmospheric CO2 drawdown by means of precipitation of carbonate, and that in contrast weathering of carbonate rocks has not an equivalent impact because all of the CO2 consumed in the weathering process is returned to the atmosphere by the comparatively rapid precipitation of carbonates in the oceans. Here, it is shown that the rapid kinetics of carbonate dissolution and the importance of small amounts of carbonate minerals in controlling the dissolved inorganic C (DIC) of silicate watersheds, coupled with aquatic photosynthetic uptake of the weathering-related DIC and burial of some of the resulting organic C, suggest that the atmospheric CO2 sink from carbonate weathering may previously have been underestimated by a factor of about 3, amounting to 0.477 Pg C/a. This indicates that the contribution of silicate weathering to the atmospheric CO2 sink may be only 6%, while the other 94% is by carbonate weathering. Therefore, the atmospheric CO2 sink by carbonate weathering might be significant in controlling both the short-term and long-term climate changes. This questions the traditional point of view that only chemical weathering of Ca–silicate rocks potentially controls long-term climate change.

The mechanical breakdown of rock by physical weathering exerts a significant control on chemical weathering rates because it produces surface area. During periods of icehouse conditions on Earth, the grinding of rock by glacial processes should lead to faster chemical weathering of the continents, perhaps particularly during periods of pronounced climatic variability, like the Quaternary. Evidence is reviewed here for both high and cyclical chemical weathering rates during the Quaternary, and the implications for both marine geochemical budgets and climate-chemical weathering feedbacks are discussed.

Assessing Cd, Co, Cu, Ni, and Pb Sorption on montmorillonite using surface complexation models by Martin M. Akafia; Thomas J. Reich; Carla M. Koretsky (S154-S157).
► Cd, Co, Cu, Ni, and Pb sorption on montmorillonite is measured at 6 distinct conditions. ► The data are used to develop a diffuse layer model with variable charge and fixed charge sites. ► The DLM lacked the robustness to accurately predict adsorption at all conditions.Cadmium, Co, Cu, Ni and Pb adsorption is measured on montmorillonite as a function of pH (3–11), ionic strength (0.001–0.1 M NaNO3), and sorbate concentration (0.1–10 μM metal on 0.5 g/L solid). Sorption of all metals shows strong dependence on ionic strength and sorbate concentration, as well as a break in the slope of the edge, indicative of a 2-site interaction with montmorillonite. The resulting adsorption edges are used to parameterize diffuse layer surface complexation models (DLMs) for each metal. A 2-site DLM with a bidentate variable charge surface hydroxyl site and a bidentate permanent charge exchange site produced good fits for the individual experiments, but lacked the robustness to accurately predict adsorption across the entire experimental range. Other models, such as CCM, TLM, or CD-MUSIC may be required for more accurate predictions across broad ranges of solution conditions.

Impact of the addition of a compound fertilizer on the dissolution of carbonate rock tablets: A column experiment by Song Chao; Liu Changli; Wang Junkun; Zhang Yun; Hou Hongbing (S170-S173).
► Impact of compound fertilizer on carbonate dissolution is studied by columns. ► Compound fertilizer reduced soil pH and increased the leach of ions. ► Carbonate dissolution accelerated due to compound fertilizer application. ► Impact of fertilizer on the budget of CO2 sink cannot be disregarded.The chemical weathering dynamics of carbonate and the C cycle are strongly influenced by anthropogenic perturbations such as agricultural fertilization. In this study, two columns (a control column and a fertilizer column) with carbonate rock tablets in the bottom of each were established to explore the impact of the addition of a compound fertilizer on the dissolution of carbonate rock tablets. The impacts were assessed from hydro-chemical analyses of the leachates from the two columns and comparison of the amount of dissolution of the carbonate rock tablets. The results showed that NH 4 + , free CO2, HCO 3 - , HPO 4 2 - and COD increased in the leachate after addition of the compound fertilizer, whereas the pH decreased. The pH decrease was attributed to the release of protons from the nitrification reaction. The amount of dissolution of limestone and dolomite tablets decreased as a result of the compound fertilizer application. Furthermore, the calculated results using Phreeqci software showed that the compound fertilizer reduced the saturation index of calcite and dolomite. Thus, the impact of a compound fertilizer, especially an ammonium fertilizer, on the budget of the CO2 sink cannot be disregarded on either a regional or a global scale.

Responses of soil and water chemistry to mountain pine beetle induced tree mortality in Grand County, Colorado, USA by David W. Clow; Charles Rhoades; Jennifer Briggs; Megan Caldwell; William M. Lewis (S174-S178).
► Soil and water chemistry responses to a mountain pine beetle epidemic were studied. ► Soil moisture and soil N increased, reflecting reduced uptake of water and N. ► Total N and total P in stream water increased, but there was no change in nitrate. ► Stream water NO3 and DOC were strongly influenced by % forest in the study basins.Pine forest in northern Colorado and southern Wyoming, USA, are experiencing the most severe mountain pine beetle epidemic in recorded history, and possible degradation of drinking-water quality is a major concern. The objective of this study was to investigate possible changes in soil and water chemistry in Grand County, Colorado in response to the epidemic, and to identify major controlling influences on stream-water nutrients and C in areas affected by the mountain pine beetle. Soil moisture and soil N increased in soils beneath trees killed by the mountain pine beetle, reflecting reduced evapotranspiration and litter accumulation and decay. No significant changes in stream-water NO 3 - or dissolved organic C were observed; however, total N and total P increased, possibly due to litter breakdown or increased productivity related to warming air temperatures. Multiple-regression analyses indicated that % of basin affected by mountain pine beetles had minimal influence on stream-water NO 3 - and dissolved organic C; instead, other basin characteristics, such as percent of the basin classified as forest, were much more important.

Composition, stability, and measurement of reduced uranium phases for groundwater bioremediation at Old Rifle, CO by K.M. Campbell; J.A. Davis; J. Bargar; D. Giammar; R. Bernier-Latmani; R. Kukkadapu; K.H. Williams; H. Veramani; K.-U. Ulrich; J. Stubbs; S. Yabusaki; L. Figueroa; E. Lesher; M.J. Wilkins; A. Peacock; P.E. Long (S167-S169).
► Diffusion, biomass and groundwater solutes retard in-well oxidative dissolution of biogenic UO2. ► Kinetic limitations and redox buffering may extend the lifetime of U(IV) in the subsurface. ► Oxidants other than O2 (e.g., Fe(III)), may be important when considering field-scale U(IV) stability.Reductive biostimulation is currently being explored as a possible remediation strategy for U-contaminated groundwater, and is being investigated at a field site in Rifle, CO, USA. The long-term stability of the resulting U(IV) phases is a key component of the overall performance of the remediation approach and depends upon a variety of factors, including rate and mechanism of reduction, mineral associations in the subsurface, and propensity for oxidation. To address these factors, several approaches were used to evaluate the redox sensitivity of U: (1) measurement of the rate of oxidative dissolution of biogenic uraninite (UO2(s)) deployed in groundwater at Rifle, (2) characterization of a zone of natural bioreduction exhibiting relevant reduced mineral phases, and (3) laboratory studies of the oxidative capacity of Fe(III) and reductive capacity of Fe(II) with regard to U(IV) and U(VI), respectively.

Remediation of coal-mine drainage by a sulfate-reducing bioreactor: A case study from the Illinois coal basin, USA by Paul T. Behum; Liliana Lefticariu; Kelly S. Bender; Yosief T. Segid; Andrew S. Burns; Charles W. Pugh (S162-S166).
This study reports changes in coal-mine drainage constituent concentrations through an anaerobic SO4-reducing bioreactor monitored over a 3-a period. The purpose of the study was to identify and monitor over time the biogeochemical mechanisms that control the attenuation of toxic compounds in the mine drainage. This information is needed to investigate bioreactor performance and longevity. The water treated at the case example site, the Tab-Simco Mine, was highly acidic with an average pH of 2.9, a net acidity of 1674 mg/L CaCO3 equivalent-CCE, and high levels of dissolved SO 4 2 - , Al, Fe and Mn. The results of this study indicated that the treatment system increased the pH of the acid mine drainage (AMD) to 6.2 and decreased the median acidity to 22.7 mg/L CCE, SO 4 2 - from 2981 to 1750 mg/L, Fe from 450.6 to 1.76 mg/L, Al from 113 to 0.42 mg/L, and Mn from 36.4 to 23.3 mg/L. Geochemical modeling indicates that the bioreactor discharge is saturated with respect to the minerals alunite, gibbsite, siderite, rhodochrosite, jarosite, and Fe hydroxide precipitates. The observed trends also include seasonal variations in SO 4 2 - reduction and a general decline in the amount of alkalinity produced. The average δ 34S value of the SO 4 2 - in the untreated AMD was +7.3‰. In the bioreactor, δ 34S value of SO 4 2 - increased from an average of +6.9‰ to +9.2‰, suggesting the presence of bacterial SO4 reduction processes. Preliminary results of a bacterial community analysis show that DNA sequences corresponding to bacteria capable of SO4 reduction were present in the bioreactor outflow sample. However, these sequences were outnumbered by sequences similar to bacteria capable of reoxdizing reduced sulfur species. This study illustrates the dynamic nature of metal removal in SO4-reducing bioreactor-based treatment systems.

Uranium(VI) sorption onto kaolinite was investigated as a function of pH (3–12), sorbate/sorbent ratio (1 × 10−6–1 × 10−4  M U(VI) with 2 g/L kaolinite), ionic strength (0.001–0.1 M NaNO3), and pCO2 (0–5%) in the presence or absence of 1 × 10−2–1 × 10−4  M citric acid, 1 × 10−2–1 × 10−4  M EDTA, and 10 or 20 mg/L fulvic acid. Control experiments without-solids, containing 1 × 10−6–1 × 10−4  M U(VI) in 0.01 M NaNO3 were used to evaluate sorption to the container wall and precipitation of U phases as a function of pH. Control experiments demonstrate significant loss (up to 100%) of U from solution. Although some loss, particularly in 1 × 10−5 and 1 × 10−4  M U experiments, is expected due to precipitation of schoepite, adsorption on the container walls is significant, particularly in 1 × 10−6  M U experiments. In the absence of ligands, U(VI) sorption on kaolinite increases from pH ∼3 to 7 and decreases from pH ∼7.5 to 12. Increasing ionic strength from 0.001 to 0.1 M produces only a slight decrease in U(VI) sorption at pH < 7, whereas 10% pCO2 greatly diminishes U(VI) sorption between pH ∼5.5 and 11. Addition of fulvic acid produces a small increase in U(VI) sorption at pH < 5; in contrast, between pH 5 and 10 fulvic acid, citric acid, and EDTA all decrease U(VI) sorption. This suggests that fulvic acid enhances U(VI) sorption slightly via formation of ternary ligand bridges at low pH, whereas EDTA and citric acid do not form ternary surface complexes with the U(VI), and that all three ligands, as well as carbonate, form aqueous uranyl complexes that keep U(VI) in solution at higher pH.

► Si–C coupled biogeochemical cycle. ► Human perturbations. ► River delivery. ► Global primary production.We present a model of the global biogeochemical cycle of silicon (Si) that emphasizes its linkages to the carbon cycle and temperature. The Si cycle is a crucial part of global nutrient biogeochemistry regulating long-term atmospheric CO2 concentrations due to silicate mineral weathering reactions involving the uptake of atmospheric CO2 and production of riverine dissolved silica, cations and bicarbonate. In addition and importantly, the Si cycle is strongly coupled to the other nutrient cycles of N, P, and Fe; hence siliceous organisms represent a significant fraction of global primary productivity and biomass. Human perturbations involving land-use changes, burning of fossil fuel, and inorganic N and P fertilization have greatly altered the terrestrial Si cycle, changing the river discharge of Si and consequently impacting marine primary productivity primarily in coastal ocean waters.

Ocean acidification during the Cenozoic by Bärbel Hönisch; Katherine Allen; Orit Hyams; Donald Penman; Markus Raitzsch; Janina Ruprecht; Ellen Thomas; James Zachos (S288).

The effect of methanogenesis on the geochemistry of low temperature water–Fe0–basalt reactions by Lisa E. Mayhew; Graham E. Lau; Tom M. McCollom; Sam Webb; Alexis S. Templeton (S318).
Hydrogen gas produced in the subsurface from the hydration of mafic rocks is known to be a major energy source for chemolithotrophic life in extreme environments such as hydrothermal vents. The possibility that in situ anaerobic microorganisms present in the deep subsurface are sustained by low temperature H2-generating water–rock reactions taking place around them is being investigated. Whether the growth and activity of H2-utilizing microbes directly influences aqueous geochemistry, rates of mineral dissolution, and the chemical composition of the alteration products is also being quantitatively evaluated.To explore how microorganisms are affected by water–rock reactions, and how their activity may in turn affect reaction progress, laboratory experiments have been conducted to monitor the growth of a methanogenic Archaea in the presence of H2(g) produced from low temperature water–Fe0–basalt reactions. In these systems, the conversion of Fe(II) to Fe(III) and subsequent hydrolysis of water is responsible for the production of H2(g). To characterize key components of the geochemical system, time series measurements of H2 and CH4 gas concentrations, Fe and Si aqueous concentrations, and spatially resolved synchrotron-based analyses of microscale Fe distribution and speciation were conducted. Culture experiments were compared with an abiotic control to document changes in the geochemistry both in the presence and absence of the methanogen.In the control abiotic batch experiment, H2 was continuously produced, until the headspace became saturated, while in the biotic experiments, microbial consumption of H2 for methanogenesis draws H2 down and produces CH4. Purging the headspace gas reinitiates H2 and CH4 production in abiotic and culture experiments, respectively. Mass balance analysis of the amount of CH4 produced suggests that the total H2 production in microbial experiments does not exceed the abiotic experiment. Soluble Si concentrations, while buffered to relatively constant values, were higher in culture experiments than the abiotic control.Iron(aq) concentrations appear to respond to perturbations of H2 and CH4 gas concentrations in both culture experiments and the abiotic control. A pulse of Fe preceded the rise in either H2 or CH4 production, and as the gas concentrations increased the Fe(aq) decreased. Iron-bearing mineral assemblages change with increasing reaction time and mineral assemblages vary between culture experiments and the abiotic control. These geochemical trends suggest that there are different reaction paths between the culture experiments and the abiotic control.The hydration of mafic rocks is a common geologic reaction and one that has taken place on Earth for the majority of its history and is postulated to occur on Mars. These reactions are important because of their effect on the rheology and geochemistry of the ocean crust. While most often studied at temperatures of ∼250 °C, this work suggests that at lower temperatures microorganisms may have a profound effect on what has long been thought to be solely an abiotic reaction, and may produce diagnostic mineral assemblages that will be preserved in the geological record.

By design: The architecture of microbial redox cycling by Lesley A. Warren; Kelsey I.L. Norlund; Adam P. Hitchcock (S322).
► Organized microbial cooperation is important in environmental geochemical processes. ► Environmental microbes create macrostructures (pods) that enable coupled metabolic function. ► The pod structure enables microbial participants to carry out reactions not predicted by bulk system geochemistry. ► Novel pod discoveries from mine waters for (1) acid mine drainage (AMD) biofilm metal dynamics and (2) mine water sulfur redox cycling and associated acid generation indicate the importance of ecological partnerships in system geochemical behaviour.The authors’ work on mine systems, combines field and laboratory integrated microbial geochemical investigation with high-resolution techniques enabling characterization and visualization at the bacterium scale (i.e. STXM). The results indicate a repeated motif of socially organized microbial cooperation occurring within microbial consortial macrostructures (pods). The pod structure directly enables the specific geochemical processes linked to the metabolic function of the consortial members. These microbially linked geochemical processes have important ramifications for bulk system geochemistry that were previously unknown. Results from two examples: (1) microbial metal interactions within AMD biofilms and (2) sulfur redox cycling by a novel consortia within mine waters, illustrate how the ecology of the pod consortia is linked to pod biogeochemical macrostructure as well as to the resulting geochemistry associated with pod metabolism. In both instances the pod structures enabled the associated consortia to carry out reactions not predicted by classic geochemical understanding of these systems. Investigation of AMD biofilm biogeochemical architecture capturing the micro-scale linkages amongst geochemical gradients, metal dynamics and depth resolved micro-organism community structure, illustrated a novel biomineralization process driven by biofilm associated pods controlling biofilm metal capture. Similarly, the groups’ recent discovery of an environmental S redox cycling, pod-forming, consortium revealed ecologically driven S cycling with previously unknown implications for both AMD mitigation and AMD carbon flux modeling. These results highlight how microbes cooperatively orchestrate their geochemical environment, underscoring the need to consider syntrophic community activity in environmental processes and the requirement for integrated, high-resolution techniques spanning geochemistry, molecular microbiology and imaging to reveal the biogeochemistry involved.

Arsenic redox transformation by humic substances and Fe minerals by Andreas Kappler; Katja Amstaetter; Thomas Borch; Philip Larese-Casanova; Jie Jiang; Iris Bauer; Andrea Paul (S317).
► As(III) oxidation by reduced humic substance model quinone (AQDS) containing semiquinone radicals. ► As(III) oxidation by reactive Fe(II)-goethite systems. ► Potential explanation for the presence of As(V) in reduced groundwater aquifers.The toxicity and mobility of the redox-active metalloid As strongly depends on its oxidation state, with As(III) (arsenite) being more toxic and mobile than As(V) (arsenate). It is, therefore, necessary to know the biogeochemical processes potentially influencing As redox state to understand and predict its environmental behavior. The first part of this presentation will discuss the quantification of As redox changes by pH-neutral mineral suspensions of goethite [α-FeIIIOOH] amended with Fe(II) using wet-chemical and synchrotron X-ray absorption (XANES) analysis (). First, it was found that goethite itself did not oxidize As(III). Second, in contrast to thermodynamic predictions, Fe(II)–goethite systems did not reduce As(V). However, surprisingly, rapid oxidation of As(III) to As(V) was observed in Fe(II)–goethite systems. Iron speciation and mineral analysis by Mössbauer spectroscopy showed rapid formation of 57Fe–goethite after 57Fe(II) addition and the formation of a so far unidentified additional Fe(II) phase. No other Fe(III) phase could be detected by Mössbauer spectroscopy, EXAFS, scanning electron microscopy, X-ray diffraction or high-resolution transmission electron microscopy. This suggests that reactive Fe(III) species form as an intermediate Fe(III) phase upon Fe(II) addition and electron transfer into bulk goethite but before crystallization of the newly formed Fe(III) as goethite.The second part of the presentation will show that semiquinone radicals produced during microbial or chemical reduction of a humic substance model quinone (AQDS, 9,10-anthraquinone-2,6-disulfonic acid) can react with As and change its redox state (). The results of these experiments showed that these semiquinone radicals are strong oxidants and oxidize arsenite to arsenate, thus decreasing As toxicity and mobility. The oxidation of As(III) depended strongly on pH. More arsenite (up to 67.3%) was oxidized at pH 11 compared to pH 7 (12.6% oxidation) and pH 3 (0.5% oxidation). In addition to As(III) oxidation by semiquinone radicals, hydroquinones that were also produced during quinone reduction, reduced As(V) to As(III) at neutral and acidic pH values (less than 12%) but not at alkaline pH. In an attempt to understand the observed redox reactions between As and reduced/oxidized quinones present in humic substances, the radical content in reduced AQDS solutions was quantified and Eh-pH diagrams were constructed. Both the radical quantification and the Eh-pH diagram allowed explaining the observed redox reactions between the reduced AQDS solutions and the As.In summary these studies indicate that in the simultaneous presence of Fe(III) oxyhydroxides, Fe(II), and humic substances as commonly observed in environments inhabited by Fe-reducing microorganisms, As(III) oxidation can occur. This potentially explains the presence of As(V) in reduced groundwater aquifers.

► Controlled laboratory experiments studied biological weathering of basalt and granite. ► Relationship of plant rooting depth and mycorrhizal type (AM or EM) to rock weathering assessed. ► Biological weathering experiments replicated at both ambient and elevated atmospheric CO2. ► Biological and geochemical analysis suite quantitatively links C flow to rock weathering.The rise of vascular land plants in the Paleozoic is hypothesized to have driven lower atmospheric CO2 levels through enhanced weathering of Ca and Mg bearing silicate minerals and rocks. However, this view overlooks the co-evolution of roots and mycorrhizal fungi, with many of the weathering processes ascribed to plants potentially being driven by the combined activities of roots and fungi. Here mesocosm scale controlled laboratory experiments quantifying the effects of plant and fungal evolution on silicate rock weathering under ambient and elevated CO2 concentrations are described. A snapshot is presented of C allocation through roots and mycorrhizal fungi and biological activity associated with geochemical changes in weathered mineral substrates via transfer of elements from solid phases into solution.

Methods for evaluating in-stream attenuation of trace organic compounds by Jeffrey H. Writer; Steffanie K. Keefe; Joseph N. Ryan; Imma Ferrer; Michael E. Thurman; Larry B. Barber (S344-S345).
► Coordinating water quality sampling with hydrologic analysis is essential to understand the fate and transport of trace organic compounds in surface waters. ► Steroidal hormones, anti-depressants and other bio-active organic compounds are consistently identified at concentrations known to elicit biological responses several kilometers downstream from confirmed sources. ► Identification of steroidal hormones and other bio-active organic compounds above wastewater treatment plants confirms not only their environmental persistence, but the existence of multiple sources.Wastewater treatment plants are often the most substantial contributor of trace organic compounds including pharmaceuticals, steroidal hormones, and surfactants to surface waters. Studying stream reaches below wastewater treatment plants provide valuable information on the environmental persistence of these compounds. Three methods for conducting field investigations to evaluate in-stream attenuation of trace organic compounds are presented: (1) using intrinsic tracers in wastewater, (2) environmental sampling coupled with dye studies to assess travel times between sample locations, and (3) Lagrangian sampling. Advantages and limitations of each method are discussed, along with key findings from several investigations.

Bioenergetics of microbial sulfur-redox reactions in a glacial environment by Katherine E. Wright; Stephen E. Grasby; Charles Williamson; John Spear; Alexis S. Templeton (S323).
► Do bioenergetic calculations predict which sulfur redox reactions microbes use?. ► Sulfur redox reactions appear to be the dominant energy source at this site. ► The energy available from these reactions at this site has been calculated. ► DNA has been extracted from the same environment. ► This DNA is being analyzed for sulfur redox genes.The authors are studying microbial sulfur redox metabolisms in a glacial environment. The energy available from sulfur redox reactions at this site has been calculated using geochemical data obtained from the site. DNA has been extracted from the same site and is being analyzed for the presence and relative quantities of sulfur redox genes, to determine whether bioenergetic calculations can predict the sulfur redox reactions that microbes are in fact utilizing.

Selenite oxyanions are readily assimilated by microorganisms for the synthesis of selenoproteins. However, at elevated concentrations, selenite becomes highly toxic due to the intracellular formation of reactive oxygen species. Remarkably, some microorganisms have evolved the ability to not only survive toxic levels of selenite, but to flourish in its presence. The cultivation and genomic sequencing of dissimilatory selenite-respiring Bacteria and Archaea have begun to help elucidate the molecular mechanisms of selenite respiration.

► Identification of sources of weathering fluxes by coupling geochemical and lithological information. ► Distinguishing weathering rates of silicate and non-silicate minerals at the regional scale. ► Quantification of the Ca/Na-release ratio by chemical weathering.Lithological maps have been proved to be a useful tool to evaluate regional and global matter fluxes from chemical weathering. However, lithological classes provide aggregated information of mineralogical, geochemical, sedimentary or diagenetic properties. Thus, using a limited number of lithological classes introduces by their definition a bias to the analysis of weathering fluxes, specifically in the case of multilithological catchments. Here it is shown that the coupling of geochemical with lithological information may help to better identify the sources of the weathering fluxes, using the example of dissolved Ca to better distinguish weathering rates of silicate and non-silicate minerals.

Erosion-driven drawdown of atmospheric carbon dioxide: The organic pathway by Niels Hovius; Albert Galy; Robert G. Hilton; Robert Sparkes; Joanne Smith; Kao Shuh-Ji; Chen Hongey; Lin In-Tian; A. Joshua West (S285-S287).
► Mass wasting and distributed surface runoff harvest particulate organic carbon. ► All grades of fossil POC are resilient in transport through short routing systems. ► Turbidites are a primary facies for trapping and preservation of POC.Rapidly eroding, coastal mountain belts, where steep rivers and submarine channels connect upland sources to nearby marine sinks are hotspots of organic carbon transfer from life biomass, soil and exhumed bedrock into geological storage. Using observations from the Southern Alps of New Zealand, and Taiwan, we have mapped this organic pathway to geological carbon sequestration, and can evaluate the magnitude and efficiency of transfers between sources and sinks. We demonstrate that POC is harvested by landsliding, but importantly also by common and widespread surface runoff on steep hillslopes. Although terrestrially sourced POC is found in many sedimentary environments associated with mountain belts and frontier basins, it appears to be most abundantly trapped and preserved in marine turbidites. The loss of all forms of POC in onward transport through short, steep routing systems to this repository is limited. This is in marked contrast to larger routing systems, in which only the most resilient forms of POC survive into long-term deposition.

Clumped-isotope geochemistry of carbonates: A new tool for the reconstruction of temperature and oxygen isotope composition of seawater by Stefano M. Bernasconi; Thomas W. Schmid; Anna-Lena Grauel; Joerg Mutterlose (S279-S280).
► Clumped-isotope thermometry of carbonates is discussed. ► Clumped isotopes of Belemnites show higher sea surface temperatures than commonly assumed for the lower Cretaceous. ► The potential of clumped-isotope measurement on foraminifera is discussed.Clumped-isotope geochemistry deals with the state of ordering of rare isotopes in molecules, in particular with their tendency to form bonds with other rare isotopes rather than with the most abundant ones. Among its possible applications, carbonate clumped-isotope thermometry is the one that has gained most attention because of the wide potential of applications in many disciplines of the earth sciences. In particular, it allows reconstructing the temperature of formation of carbonate minerals without knowledge of the isotopic composition of the water from which they were formed. In addition, the O isotope composition of the waters from which they were formed can be calculated using the δ18O of the same carbonate sample. This feature offers new approaches in paleoclimatology for reconstructing past global geochemical cycles. In this contribution two applications of this method are presented. First the potential of a new analytical method of measurement of clumped isotopes on small samples of foraminifera, for high-resolution SST and seawater δ18O reconstructions from marine sediments is shown. Furthermore the potential of clumped isotope analysis of belemnites, for reconstructing seawater δ18O and temperatures in the Cretaceous is shown.

► Biotic enhancement of weathering is modeled for two contrasting weathering regimes. ► In one regime climate and thus eco-hydrological conditions rule. ► The other regime is characterized by supply limitation. ► Only areas that are not supply limited are susceptible to biotic enhancement of weathering. ► The potential for biotic enhancement of weathering thus depends directly on crustal uplift.Biotic enhancement of weathering (BEW) has been proposed to substantially alter the geologic C cycle but the large scale impact of small scale biotic processes remains elusive, especially when compared to large scale drivers of weathering such as climate and crustal uplift. A global land surface model was used to estimate the potential strength of BEW for two contrasting types of weathering regimes that are either limited by the supply of fresh parent material by uplift or controlled by the climatic and eco-hydrological conditions. The biospheric effect on soil CO2 in the model was then removed in order to determine the reduction of weathering rates and thereby to infer BEW. It was found that only those areas that are not supply limited are susceptible to biotic enhancement. This indicates that the potential for BEW depends directly on the supply of fresh material and thus on crustal uplift.

Microbial community and activity shifts after soil transplantation in a glacier forefield by Anita Zumsteg; Stefano M. Bernasconi; Josef Zeyer; Beat Frey (S326-S329).
The majority of Alpine glaciers are currently receding because of global warming. Their forefields have become interesting sites to study primary microbial colonisation and microbial adaptation. Here, the structure and enzyme activity of microbial communities in exposed rock substrates and their changes in a gradient of temperature and soil moisture conditions within the forefield of the Damma glacier in the Swiss Central Alps are discussed. The temperature at the sites differed in the course of a day and also showed differing mean temperatures over the summer. Distinct bacterial communities inhabit the differing sites at the beginning of the experiment and even after transplantation they stay distinct. But a seasonal shift in the communities could be observed, which followed the same pattern for all the samples. Interestingly, microbial enzyme activity was highest at the site with the smallest temperature shifts.

► Research on five nested catchments and bulk deposition in a rural area is presented. ► Seasonal patterns of some components display a strong correlation with the amount of precipitation. ► Lithological differences in the catchments and contamination affect the observed compositional patterns.259 stream water and 21 bulk precipitation samples have been studied between April 2008 and December 2010 in order to assess baseline hydrochemical conditions in a rural area of NW Spain. Stream waters are related to five nested catchments (<10 km2) with apparent low mean residence times. Their hydrochemical characteristics are closely related to bulk precipitation although clear evidences of seasonal (flushing, dilution, sediment desorption, etc.), lithological (schist vs. granite substrate) and anthropogenic (land use, contamination) effects are also described.

Land use and land cover changes can cause variations in terrestrial energy, water balance and availability of nutrients. To understand the role of vegetation in regulating the hydrochemistry of karst hillslopes, overland flow and soil seepage water from two hillslopes covered with and without vegetation were studied in the Huanjiang Observation and Research Station for Karst Ecosystems, Guangxi, SW China. Dissolved major ions, as well as isotopic compositions of dissolved inorganic C (DIC) were examined. Water from the vegetated control slope had higher solute concentrations (except NO 3 - ) and lower δ13C values than water from the disturbed slope. The dynamics of K+ and NO 3 - in soil water sampled in time-sequence from the control slope was different from the disturbed slope. Specifically, K+ and NO 3 - concentrations of the control slope decreased gradually over time, while K+ and NO 3 - concentrations of the disturbed slope increased, and other ionic concentrations increased in both of the slopes.

A national-scale geochemical and mineralogical survey of soils of the conterminous United States by David B. Smith; William F. Cannon; Laurel G. Woodruff (S250-S255).
► Sampling for national-scale soil geochemical and mineralogical survey completed for conterminous USA. ► Natural variation for most elements is approximately three orders of magnitude. ► Composition of soil parent material is the major controlling factor. ► Climate (average annual precipitation) is also an important controlling factor for some elements. ► Sample archive (4800 sites) available for future investigations.In 2007, the US Geological Survey initiated a low-density (1 site per 1600 km2, c. 4800 sites) geochemical and mineralogical survey of soils of the conterminous USA. The ideal sampling protocol at each site includes a sample from 0–5 cm depth, a composite of the soil A horizon, and a sample from the soil C horizon. The <2-mm fraction of each sample is analyzed for Al, Ca, Fe, K, Mg, Na, S, Ti, Ag, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Ga, In, La, Li, Mn, Mo, Nb, Ni, P, Pb, Rb, Sb, Sc, Sn, Sr, Te, Th, Tl, U, V, W, Y and Zn by inductively coupled plasma-mass spectrometry and inductively coupled plasma-atomic emission spectrometry following a near-total digestion in a mixture of HCl, HNO3, HClO4 and HF. Separate methods are used for As, Hg, Se and total C on this same size fraction. The major mineralogical components are determined by a quantitative X-ray diffraction method. Sampling was completed in 2010 with chemical and mineralogical analysis currently underway. Preliminary results for a swath from the central USA to Florida clearly show the effects of soil parent material and climate on the chemical and mineralogical composition of soils. A sample archive will be established and made available for future investigations.

► Nitrate retention is a linear function of hydrologic flux. ► Submerged aquatic vegetation seasonally restrict tidal channel hydrologic flux. ► Laboratory derived NO3- loss rates overestimate in situ NO3- retention.Tidal freshwater wetlands are highly complex ecosystems that are important sites for nutrient retention. Although marsh surfaces have been identified as important sites for N processing, temporal and spatial variability is not well understood. Previous research has focused on measuring denitrification rates in sediment cores, sampled along marsh vegetation or salinity gradients, through laboratory experiments or plot studies. Extending these results to the ecosystem scale requires that we know whether ecosystem denitrification is kinetically-limited or transport-limited. The purpose of this study is to examine this question in freshwater tidal marshes. A multi-scale, mass balance approach was used to measure tidal NO 3 - retention and loss in freshwater tidal wetlands. Geomorphic characteristics (marsh surface area and channel inlet characteristics) were examined within the freshwater tidal ecosystem of the Patuxent River, Maryland. From the measured range of geomorphic characteristics in the ecosystem, individual marshes were selected for mass balance studies of hydrologic fluxes and NO 3 - retention. The data indicated that net NO 3 - retention per water volume is constant for marshes of different sizes, whereas NO 3 - retention per marsh surface area decreases with an increase in marsh size. These data suggest that NO 3 - retention is transport, not kinetically-limited in this freshwater tidal marsh ecosystem. This hydrologic limitation is likely due to the effects of macrophyte vegetation on flow resistance in tidal channels and on marsh surfaces, which produces non-synchronous flooding of marsh surfaces of equal elevation, particularly in large marshes. The reported measurements are for high tidal stages in autumn, but transport limitations on denitrification rates should be significant throughout the growing season when macrophytes are present.

► Four sites with different lithology (syenite, gneiss, granite, sedimentary rocks), formerly glaciated terrain, Oslo, Norway. ► Variations with depth of grain-size, total organic C, Pb concentration, Pb isotope ratio. ► Content of anthropogenic Pb in podzolic forest soil. ► Comparison of three methods for calculating anthropogenic Pb input. ► Amounts of anthropogenic Pb in upper 20 cm calculated to be 1–6 t/km2.Lead has been exploited by man over thousands of years for a variety of metallurgical, medicinal, and industrial purposes. The cumulative output of Pb from mining is estimated to be 260 million metric tonnes and 85% of this has occurred over the last two centuries. Global annual production of Pb from mining was about 3 million tonnes at the turn of the millenium. Terrestrial ecosystems all over Norway have been contaminated moderately to strongly by Pb and other trace elements from atmospheric deposition. With the aim of developing a method for mapping the accumulated content of anthropogenic Pb and how deep in the soil profile the atmospherically deposited Pb has penetrated, the concentration of Pb and the 206Pb/207Pb ratio has been studied in podzolic forest soils at four locations with different lithology, i.e. age and type of bedrock, in the Oslo area. The concentrations of Pb in the soil profiles are 6.6–38.1 mg/kg (median 10.3). The 206Pb/207Pb ratio ranges between 1.168 and 1.314 (median 1.267) over the entire profile. In the upper 5 cm the range is 1.168–1.191, similar to ratios determined in recent atmospheric deposition. Applying three different methods, the amount of anthropogenically deposited Pb is estimated at 1–6 t/km2.

The contribution of organic and mineral colloidal nanoparticles to element transport in a podzol soil by Inge C. Regelink; Liping Weng; Willem H. van Riemsdijk (S241-S244).
► Mobile nanoparticles are organic matter and clay particles with associated iron-(hydr)oxides. ► Both organic- and mineral particles contribute to transport of Al, Fe, trace metals and P. ► Mineral nanoparticles can contribute significantly to the transport of especially Zn, Pb and P.The aim of this work is to analyze the size-distribution and composition of nanoparticles in a water-extract of a podzol B horizon. AsFlowFFF coupled to ICP–MS and a UV/VIS detector was used for particle fractionation and simultaneous measurement of the composition of the nanoparticles. Detected nanoparticles were organic and mineral particles; the mineral particles were dominated by clay and Fe-(hydr)oxides. Both organic- and inorganic particles contributed to the mobility of Fe, Al, trace metals and P. For Zn, Pb and P respectively 73%, 92% and 72% of the colloidal concentrations were associated with clay minerals. The large contribution of clay particles to the mobility of trace metals and P can be partly explained by the high amount of dispersed clay due to drying, sieving and rewetting of the soil. Inorganic nanoparticles can contribute significantly to the mobility of metals and P in soils.

Pollutants, human health and the environment – A risk-based approach by Jane A Plant; James Bone; Kristin Vala Ragnarsdottir; Nickalaos Voulvoulis (S238-S240).
Over the last 50 a there has been mounting unease about the risk of synthetic chemicals to human health. Publication of Rachel Carson’s Silent Spring in 1962 catalyzed public concern about chemicals. There is now a vast range of synthetic substances in the environment and their potential cocktail as well as the effects of chronic exposure is of concern. Concerns about pollution are not restricted to toxic chemicals, with radioactivity being an issue that continues to be emotive, and exposure to substances such as particulates has been seen to cause health problems. Improved understanding of chemical risks to the environment and human health suggest that a precautionary approach is adopted, with new approaches demonstrating how nature uses thousands of sustainable, non-toxic processes, which can be copied by industry. Policy has evolved from the prevention of local pollution to the holistic management of environmental quality. Regulation is now increasingly underpinned by risk assessment and responsibility for understanding and managing chemical risk is being transferred progressively to manufacturers and users. There is now an increased emphasis on individual responsibilities which requires a debate about the risks and benefits of chemicals in which all members of society can participate.

Historical influence of soil and water management on sediment and carbon budgets in the United States by Eric T. Sundquist; Katherine Visser Ackerman; Robert F. Stallard; Norman B. Bliss (S259).

Colloidal arsenic composition from abandoned gold mine tailing leachates in Nova Scotia, Canada by Kathryn Tindale; Pritesh Patel; Dirk Wallschläger (S260-S262).
Asymmetric-Flow Field-Flow Fractionation (AsFlFFF) coupled to an inductively coupled plasma-mass spectrometer (ICP-MS) was used to determine whether colloidal As exists in mine tailings from abandoned Au mine sites in Nova Scotia. Using this technique, the chemical composition and the size of the colloidal material was determined. Tailings samples were collected from the sites and leachates were analyzed. The resulting fractograms showed the presence of colloidal As. Arsenic co-elutes with Fe and Al suggesting that the As is associated with colloids containing these elements. The colloidal material present in the samples has a calculated median size of 7 nm. The leachates were also analyzed for totalAs, Fe and Al using ICP-MS. The colloidal fraction was determined to account for approximately 20% of the total dissolved As present in these samples. Dissolved As concentrations at the selected mine sites are very high and the arbitrary cutoff for dissolved still incorporates colloidal material. Therefore. it is important to distinguish between truly dissolved and colloidal As as the speciation will affect the toxicity and mobility of As at these locations.

Geochemistry of the Earth’s Surface by Suzanne Anderson; Sigurdur Gislason (S1-S2).

Copper isotope fractionation by desert shrubs by Jesica U. Navarrete; Marian Viveros; Joanne T. Ellzey; David M. Borrok (S319-S321).
Copper has two naturally occurring stable isotopes of masses 63 and 65 which can undergo mass dependent fractionation during various biotic and abiotic chemical reactions. These interactions and their resulting Cu isotope fractionations can be used to determine the mechanisms involved in the cycling of Cu in natural systems. In this study, Cu isotope changes were investigated at the organismal level in the metal-accumulating desert plant, Prosopis pubescens. Initial results suggest that the lighter Cu isotope was preferentially incorporated into the leaves of the plant, which may suggest that Cu was actively transported via intracellular proteins. The roots and stems show a smaller degree of Cu isotope fractionation and the direction and magnitude of the fractionations was dependent upon the levels of Cu exposure. Based on this and previous work with bacteria and yeast, a trend is emerging that suggests the lighter Cu isotope is preferentially incorporated into biological components, while the heavier Cu isotope tends to become enriched in aqueous solutions. In bacteria, plants and animals, intracellular Cu concentrations are strictly regulated via dozens of enzymes that can bind, transport, and store Cu. Many of these enzymes reduce Cu(II) to Cu(I). These initial results seem to fit into a broader picture of Cu isotope cycling in natural systems where oxidation/reduction reactions are fundamental in controlling the distributions of Cu isotopes.

► The spatial distribution of arsenic in Gangdese belt shows a complex and mixed pattern. ► The spectrum-area fractal model (S-A) is a powerful tool to decompose a mixed pattern. ► The arsenic anomalies may related to Cu mineralization because the areas with high anomaly of arsenic mainly are located surrounding known Cu deposits.Decomposing mixed geochemical patterns is a challenge in geochemical exploration and environmental assessment. In this paper, the spectrum–area technique (SA) is used to decompose a mixed pattern of arsenic in Gangdese belt based on stream sediment data. SA is a multifractal model based on power–law relationships between area of the set consisting of wave numbers with spectral energy density above S[A(>S)] on the 2D frequency domain. The original spatial distribution map of arsenic obtained by inverse distance weighted (IDW) shows a mixed pattern due to superposition of different geological processes or events and is converted into the frequency domain by means of Fourier transformation. Two components, including power spectrum density and phases, are obtained. The spectrum energy density (S) and the area (A) enclosed by the above-threshold spectrum energy density is plotted on a log–log scale. Two cutoff values determined by three straight lines define three filters which decompose the original map of arsenic into background, anomalous, and high frequency (noise) components. The areas with high anomaly of arsenic mainly are located surrounding known Cu deposits, indicating that arsenic anomalies may be related to Cu mineralization.

Economic reform in China since 1978 has accelerated economic development nationwide hugely, but has also brought about some environmental pollution. In order to identify the primary Pb source to the atmosphere in the central Guizhou region, Pb isotopic ratios in the acid soluble fraction of sediment from Hongfeng Lake were investigated. Lead isotopes in the lake sediments record the history of regional atmospheric Pb pollution. Before the economic reform in 1978, the 208Pb/206Pb and 206Pb/207Pb ratios in the leachates of lake sediments were constant, with a range of 2.0060 to 2.0117 and of 1.2314 to 1.2355, respectively. In the early period of economic reform (1978 to 1988), with the rapid industrial growth in Guizhou province, the acid soluble Pb isotope ratios in the lake sediments changed sharply: the 208Pb/206Pb ratios increased from 2.0212 to about 2.05, while the 206Pb/207Pb ratios decreased from 1.2251 to 1.2060. Emissions from Pb-ore-related industries are suggested to be the major pollution source of Pb in this period. Due to output from a local power plant since 1988, the isotope ratios of the acid soluble Pb in sediments in 1990s are characterized by a little higher radiogenic Pb (208Pb/206Pb = 2.0340–2.0400; 206Pb/207Pb = 1.2122–1.2158) than for the 1980s.

Leaching of metals from copper smelter flue dust (Mufulira, Zambian Copperbelt) by Martina Vítková; Vojtěch Ettler; Jiri Hyks; Thomas Astrup; Bohdan Kříbek (S263-S266).
► The leaching behaviour of Cu smelter flue dust is pH-dependent. ► Maximum concentrations of metals were released at pH 3-4.5. ► Primary chalcanthite was dissolved and secondary Cu sulphates were formed. ► Potential risk of contamination of dust-polluted acidic soils near the smelter.The leaching behaviour of electrostatic precipitator dust from the Mufulira Cu smelter (Copperbelt, Zambia) was studied using a 48-h pH-static leaching experiment (CEN/TS 14997). The release of metals (Cd, Co, Cu, Ni, Pb and Zn) and changes in mineralogical composition using X-ray diffraction and PHREEQC-2 modelling were investigated in the pH range of 3–7. The highest concentrations of metals were released at pH 3–4.5, which encompasses the natural pH of the dust suspension (∼4.3). About 40% of the total Cu was leached at pH 3, yielding 107 g/kg. Chalcanthite (CuSO4·5H2O), magnetite (Fe3O4) and delafossite (CuFeO2) represented the principal phases of the studied dust. In contact with water, chalcanthite was dissolved and hydrated Cu sulphates precipitated at pH 4–7. Gypsum (CaSO4·2H2O) and secondary Fe or Al phases were observed in the leached residues. Serious environmental impact due to leaching may occur in dust-contaminated soil systems in the vicinity of the smelting plants.

► P cycling in an oxygenated lake. ► Internal P loading during summer thermal stratification. ► Release of P from oxyhydroxide phases during periods of low dissolved oxygen.Irondequoit Bay, adjacent to Rochester, New York, is one of the larger embayments along the southern coast of Lake Ontario. Since the 1980s, management activities have been focused on improving water quality and the trophic status of the bay, including a program of hypolimnetic oxygenation. During the summers of 2003, 2004 and 2009, a program of basic water quality parameter profiles and sediment sampling completed. Results of these surveys show an increase in hypolimnetic P throughout each summer season. The increase in P is concordant with decreasing dissolved O2 concentrations. Although the dissolved O2 levels are persistent in the suboxic range for most of the summer season, the oxygenation program prevents anoxic conditions, limiting the release of P to that associated with Mn oxyhydroxides. Longer-term trends show an upward linear trend in metalimnetic P which is associated with the trophic status of the bay. This upward trend may be linked to cycling and enrichment of the near surface sediment in P.

Human impacts on soils: Tipping points and knowledge gaps by Nikolaos P. Nikolaidis (S230-S233).
► Evidence suggesting impeding soil ecosystem shift in areas impacted by climate change. ► Maintaining soil ecosystem services requires substantial input of organic matter. ► Holistic management ensures soil fertility and sustainable food production.Soil ecosystem functions are derived from plant, animal and microorganism communities and the non-living environment interacting as a unit. Human activities have affected soil ecosystem functions and in many cases caused soil ecosystem collapse. This review provides a synthesis of current knowledge of human impacts on soil ecosystems, with a special focus on knowledge gaps regarding soil ecosystem shifts and tipping points, using the island of Crete, Greece as an example. Soil ecosystem shifts are abrupt changes that occur at “tipping points” and have long-lasting effects on the landscape and both the biotic and abiotic structure of the soil. These shifts can occur due to climate change, land use change, fertilization, or above-ground biodiversity decline. The environmental pressures in the agricultural land of Crete, place the island very close to tipping points, and make it an “ideal” area for soil ecosystem shifts. Reversing the trend of the shift while using the soil ecosystem services, means that significantly more organic matter needs to be added to the soil compared to the amount added under set-aside conditions. Potential nutrient supply and demand calculations indicate that fertilizer demand in Crete can be satisfied by recycling of bio-residue and livestock excreta produced on the island. Soil fertility improves faster if, in addition to bio-fertilization, farmers use traditional agricultural practices such as crop rotations and legume row plantings within olive trees and orchards. A renewed soil fertility paradigm shift requires a “holistic” management of biotic-soil–water resources in order to provide sufficient and an appropriate type of organic matter to the plant–microorganism system to maximize food production.

Tillage and farm manure affect root growth and nutrient uptake of wheat and rice under semi-arid conditions by Muhammad Ibrahim; Muhammad Yamin; Ghulam Sarwar; Alia Anayat; Fareeha Habib; Sami Ullah; Saif-ur-Rehman (S194-S197).
► Organic residues improve soil quality and rooting conditions. ► Tillage operations directly influence root growth and nutrient uptake. ► Root length density is good indicator of crop growth and quality. ► Tillage and manure had direct impact on growth of wheat-rice under semi-arid conditions.Tillage systems affect soil properties, crop growth and nutrient uptake under various agro-ecological conditions. The uptake of water and nutrients are largely dependent on the root systems of wheat (Triticum aestivum L.) and rice (Oryza sativa L.). The application of manure has direct influence on the nutrient uptake by the crop plants. A 2 year field experiment was conducted to evaluate the impact of tillage and farm manure on root growth by measuring the root length density on a sandy clay loam (Typic calciargid soil). Three tillage systems were used; (i) minimum tillage (MT), (ii) deep tillage (DT) and (iii) conventional tillage (CT). Three farm manure levels were used; (i) FM0 (only chemical fertilizers), (ii) FM15 (farm manure at 15 Mg ha−1) and (iii) FM30 (farm manure at 30 Mg ha−1). The incorporation of farm manure into soil markedly improved the root length density (RLD) of both wheat and rice crops. For wheat, the application of FM30 increased RLD by 16% and 9% in cases of deep tillage and minimum tillage, respectively. For rice, the increase in RLD at the same farm manure rate (FM30) was 13% and 17%, during first and second year, respectively. Averaged across tillage, the trend of RLD for both wheat and rice was DT > CT > MT. The incorporation of FM has increased the uptake of N, P and K significantly (P  < 0.05), thereby increasing the agronomic parameters. The manure may be used to ameliorate the deleterious effects of tillage for sustainable crop yield.

Influence of NaCl and CaCl2 on lake sediment biogeochemistry by Seon-young Kim; Carla Koretsky (S198-S201).
► We assess the effect of NaCl and CaCl2 addition on lake sediment geochemistry. ► Addition of NaCl or CaCl2 stimulates ion exchange. ► Addition of NaCl, and especially CaCl2, stimulates anaerobic respiration of Fe and Mn.The influence of two commonly used road salt deicers, NaCl and CaCl2, on sediment biogeochemistry was investigated using a series of core incubations. Sediment cores collected in fall 2009 and spring 2010 were incubated for 100 days in 1 or 5 g/L CaCl2·2H2O, 5 g/L NaCl or DI water (control). For each treatment, 3 cores were sacrificed every month, sliced into three intervals (0–5, 5–10 or 10–15 cm depth) and the pore waters analyzed for pH, total alkalinity, dissolved Fe(II), Mn(II), NH 4 + , PO 4 3 - , SO 4 2 - , sulfide, Na, Mg, K and Ca. Addition of NaCl, and especially 5 g/L CaCl2·H2O, resulted in the growth of microbial mats on the surfaces of the cores and stimulated anaerobic production of dissolved Mn(II) and Fe(II) in the sediment pore waters. This is hypothesized to be the result of nutrient release (e.g., K, Ca, trace elements) via ion exchange processes, which fueled primary production and subsequent organic matter degradation in the cores treated with NaCl or CaCl2. Such processes may be significant in wetland sediments impacted by large loadings of salt from road deicers.

Assessing the redox properties of iron-bearing clay minerals using homogeneous electrocatalysis by Christopher A. Gorski; Michael Sander; Michael Aeschbacher; Thomas B. Hofstetter (S191-S193).
Iron-bearing clay minerals are ubiquitous in the environment and have been shown to play important roles in several biogeochemical processes. Previous efforts to characterize the Fe2+–Fe3+ redox couple in clay minerals using electrochemical techniques have been limited by experimental difficulties due to inadequate reactivity between clay minerals and electrodes. The current work overcomes this limitation by utilizing organic electron transfer mediators that rapidly transfer electrons with both the Fe-bearing clay minerals and electrodes. Here, an Fe-rich source clay mineral (ferruginous smectite, SWa-1) is examined with respect to what fraction of structural Fe participates in oxidation/reduction reactions and the relationship between bulk Fe2+/Fe3+ ratios to the reduction potential (Eh ).

Volcanic ash from the 2010 Eyjafjallajökull eruption by S.R. Gislason; H.A. Alfredsson; E.S. Eiriksdottir; T. Hassenkam; S.L.S. Stipp (S188-S190).
► The April 2010 eruption of Eyjafjallajökull volcano created major disruption to European air traffic. ► The main uncertainty in predicting the volcanic ash distribution in air space was the nature of the eruption plume including the grain size of the volcanic ash. ► Volcanic ash particles, less than about 63 μm in diameter, can travel for days suspended in air. ► Up to 70 wt% of the Eyjafjallajökull ash, 50 km from the source, was less than 60 μm in diameter.The April 2010 eruption of Eyjafjallajökull volcano created major disruption to European air traffic. The main uncertainty in predicting the volcanic ash distribution in air space was the nature of the eruption plume including the grain size of the volcanic ash. The volcanic ash samples collected in the vicinity of the volcano on April 15th 2010, the first day of air traffic disruption in Europe, reveal that up to 70% of the mass was less than 60 μm in diameter. This fine grained ash could remain suspended in the atmosphere for days, posing threats to air traffic.

This paper presents hydrogeochemical and S isotopic characteristics of karstic surface and ground water in the karstic aquifers of Zunyi city of Guizhou Province, SW China. The average δ34S value of SO4 is +2.2‰ (n  = 28) in ground waters and +7.0‰ (n  = 15) in surface waters in the low flow season, while in the high flow season it is +1.0‰ in ground waters and +2.8‰ in surface waters. Natural and anthropogenic sources of the dissolved SO 4 2 - can be discriminated by a combined approach using water chemistry and stable S isotope data. A pollutant source of SO4 is estimated to have very high TDS contents and a narrow range of δ34S values (0‰ to +5.0‰). The water with a distinctively high δ34S value of +30.5‰ originates from an evaporite (gypsum and anhydrite)-bearing aquifer, and the δ34S values lower than −10‰ suggest an origin by oxidation of sulfide minerals in coal seams with intermediate TDS contents.

Mineralogical and geochemical diversity in cryoconite granules from Aldegondabreen glacier was investigated using FTIR spectroscopy. Results suggest that the technique is an effective tool for investigating mineralogy and identifying spatial differences in geochemistry, based upon characteristic spectral signatures.

What controls selenium release during shale weathering? by Adriana Matamoros-Veloza; Robert J. Newton; Liane G. Benning (S222-S226).
► Quantification of selenium distribution in shales using various sequential extractions. ► Prime selenium host phases are organic matter and sulphides. ► Even low pyrite contents outcompete the organic matter for available Selenium. ► Pyrite oxidation controls the release of selenium during shale weathering.This study demonstrates that only a combination of a chromous chloride reduction with dual sequential extraction schemes can clearly separate the proportions of Se present in the sulphide versus the organic pools in shales. The data reveals that even small amounts of pyrite outcompete the organic matter for the available Se and pyrite oxidation will control the release of selenium during shale weathering.

Electrical conductivity method for natural waters by R. Blaine McCleskey; D. Kirk Nordstrom; Joe N. Ryan (S227-S229).
► A new method for calculating the electrical conductivity of natural waters is presented. ► The method can be used to determine the transport number of major ions. ► The method can be used, in conjunction with charge balance, as a analytical QAQC method.A new method is presented for calculating the electrical conductivity of a wide range of natural waters including acid mine waters, geothermal waters, seawater, dilute mountain waters, and river water impacted by municipal wastewater. The method has several advantages over previously published methods. New electrical conductivity measurements for electrolytes commonly found in natural waters provide a basis for improved calculation of ionic molal conductivities. In addition, the method is coupled to a geochemical speciation model that is used to calculate the speciated concentrations required for accurate conductivity calculations. The method can be used to calculate the electrical conductivity of most natural water compositions and is accurate over a large range of effective ionic strengths (0.0004–0.7 m), temperature (0–95 °C), pH (1.0–9.8), and conductivity (30–70,000 μS cm−1). For the wide range of natural waters tested in this study, transport numbers were calculated and the ions that contribute significantly to the specific conductance were identified as H+ . Na+, Ca2+, Mg2+, NH 4 + , K+, Cl, SO 4 2 - , HCO 3 - , CO 3 2 - , F, Al3+, Fe2+, NO 3 - and HSO 4 - .Transport numbers can also be used to better predict the concentrations of ions in natural waters. Another important application of the specific conductance method is checking the accuracy of water analyses by coupling charge imbalance and specific conductance imbalance. Either the major cation or anion concentrations for 50 different water samples were artificially adjusted and the constituent most likely in error was easily identified. Considering the importance of accurate chemical analyses, the ability to identify inaccurate determinations is critical.

Biochar application in a tropical, agricultural region: A plot scale study in Tamil Nadu, India by Utra Mankasingh; Poon-Chung Choi; Vala Ragnarsdottir (S218-S221).
► Biochar from several locally available feedstocks were analysed as proposed soil amendments. ► All biochars contained >20% C and were high in macro- and micronutrients. ► The results suggest that application of 6.6 tonnes ha-1 cassia biochar initiated C-accumulation. ► This is reflected in an increase in OM and a net reduction in soil bulk density.A plot-scale evaluation of biochar application to agricultural soils was conducted in Tirunelveli, Tamil Nadu, India, to investigate the potential of biochar to improve soil fertility and moisture content. Biochar feedstocks need to be sustainably sourced: several locally available feedstocks (rice husk, cassia stems, palm leaves and sawdust) were analysed as proposed soil amendments so that no single biomass material is depleted to maintain biochar addition. The biochars from different biomass feedstock contained >20% C and were high in macro- and micronutrients. The results suggest that an application rate of 6.6 metric tonnes ha−1 cassia biochar was enough to initiate C-accumulation, which is reflected in an increase in OM and a net reduction in soil bulk density.

Eutrophication and salinization of urban and rural kettle lakes in Kalamazoo and Barry Counties, Michigan, USA by Andrew MacLeod; Ryan Sibert; Christine Snyder; Carla M. Koretsky (S214-S217).
► Eutrophication was compared in urban and rural lakes in Michigan, USA. ► Salinization of urban and rural lakes in Michigan, USA was compared. ► Urban lakes contained significantly higher Na and Cl then a rural lake. ► All lakes studied showed were eutrophic and redox-stratified.Salinization and eutrophication caused by runoff of road salt and nutrients was assessed in three kettle lakes, two (Woods and Asylum Lakes) located in urban Kalamazoo, MI, and one (Brewster Lake) in rural Hastings, MI. Profiles of dissolved O2, conductivity, pH, and temperature were measured in situ, at half meter intervals. Water samples were collected at discrete depth intervals of 1 m and analyzed for Fe(II), Mn(II), ammonium, alkalinity, Cl, Na, Mg, K and Ca. Results of this study indicate that all three lakes are eutrophic with anoxic bottom waters. Conductivity was much greater, and Cl levels were more than 100 times greater, in the two urban lakes compared to the rural lake, demonstrating the significant impact of road salt deicers on urban lake water chemistry.

Using a dual isotopic approach to trace sources and mixing of sulphate in Changjiang Estuary, China by Si-Liang Li; Cong-Qiang Liu; Sivaji Patra; Fushun Wang; Baoli Wang; Fujun Yue (S210-S213).
► Changjiang Estuary plays an important role in transportation of the water and solute. ► The dual isotopic method could be used to understand sulfate biogeochemistry in estuaries. ► Mixing processes should be a major factor involved in the distribution of water and sulphate. ► Sulphate in the Changjiang River mainly derived from atmospheric deposition, evaporite dissolution and sulphide oxidation.The dual isotopic compositions of dissolved SO 4 2 - in aquatic systems are commonly used to ascertain SO 4 2 - sources and possible biogeochemical processes. In this study, the physical parameters, major anions and isotopic compositions of SO 4 2 - in water samples from Changjiang River (Nanjin) to the East Sea in Changjiang Estuary were determined. The salinity ranged from 0‰ to 32.3‰ in the estuary water samples. The Cl - , SO 4 2 - concentrations and δ18O–H2O values followed the salinity variations from freshwater to seawater, which indicated that mixing processes might be a major factor involved in the distribution of water and solutes. The contents and isotopic compositions of SO 4 2 - suggested that atmospheric deposition, evaporite dissolution and sulphide oxidation were the major sources of dissolved SO 4 2 - in the freshwater of Changjiang River. In addition, the mixing model calculated by contents and isotopic compositions of SO 4 2 - indicated that the mixing of freshwater and sea water was the major factor involved in SO 4 2 - distribution in Changjiang Estuary. However, slightly elevated δ18O–SO4 values were observed in the turbidity maximum zone, which suggested that biological processes might affect the O isotopic compositions of SO 4 2 - there.

Dissolved organic nitrogen as an indicator of livestock impacts on soil biochemical quality by Fotini E. Stamati; Nikolaos P. Nikolaidis; Danae Venieri; Eleftheria Psillakis; Nicolas Kalogerakis (S340-S343).
► Evidence linking the DON river export to livestock grazing intensity. ► De-vegetation due to overgrazing affects soil biochemical quality. ► DON is a reliable indicator for livestock grazing impacts.Soil degradation in the Mediterranean and other arid and semi-arid regions of the world is caused mainly by cultivation and grazing. A consequence of de-vegetation due to overgrazing has been a decrease in organic matter (litter) input to soil and a decrease of aggregate size and stability making soils more susceptible to erosion and to organic matter losses. This study provided evidence linking the Dissolved Organic Nitrogen (DON) export from river basins to livestock grazing intensity and the resulting decrease in vegetation. Koiliaris River Basin in Crete was selected to study the effects of livestock grazing on water quality because it offers a unique morphologic situation due to its karstic hydrogeology draining the upland grazing areas through karstic springs. Mass balance calculations of N loads indicated that organic N is behaving as a conservative substance. It is postulated that the two potential mechanisms of Mineralization–Immobilization-Turnover and Direct Uptake did not operate in the degraded soils of the karst and arguments are presented justifying the hypothesis. De-vegetated soils of the area had lower C and N content, the same bacterial count, but lower microbial activity, lower fungi counts and species richness and lower mineralizable N compared to naturally vegetated soils. DON was the predominant N species in both extracted soluble N pools. De-vegetated soils had lower decomposition potential compared to vegetated soils. Mineralization and plant uptake appeared to be restricted and leaching of soluble low aromaticity organic matter was favored. A linear relationship between DON export and livestock N load was obtained for five Greek basins suggesting a mechanism that operates on regional scales. The de-vegetation of grazing lands in Koiliaris River highland calcaric leptosols was shown to be a primary factor causing the decline of soil biochemical quality and DON can be used as a reliable indicator for livestock grazing impacts to soil biochemical quality.

► Ecotoxicology is an important component of water quality assessment. ► Linking molecular effects to outcomes in organisms and populations is a key challenge. ► Cooperation with geosciences can provide new insight into chemical-environment interactions.Thousands of chemicals are in daily use; many of these reach the aquatic environment, which serves as a medium of transport and deposition into sediment and organisms. It is often unknown which effects these contaminants, alone or in combination with other stressors, may have on organisms, populations and communities in the aquatic environment. Ecotoxicology strives to identify and mechanistically understand contaminant–biota interactions with the ultimate goal to predict potential adverse effects. There are two general routes to addressing this goal. The first is to understand how organisms and populations respond according to anticipated exposure routes, organisms’ genome and physiology, and structure- physico-chemical properties of chemicals. This knowledge should lead to improved criteria for chemical design and approval. The second general route is to identify the cause–effect relationships of effects detected in the environment without prior knowledge on the chemical’s identity. This approach serves to pinpoint critical chemicals in complex environmental samples to enable decisions or technologies for their reduction or removal. An example will be presented in which biological effect assessment contributed to a better understanding of groundwater contamination.

Soil pH governs production rate of calcium carbonate secreted by the earthworm Lumbricus terrestris by D.C. Lambkin; K.H. Gwilliam; C. Layton; M.G. Canti; T.G. Piearce; M.E. Hodson (S64-S66).
► Some species of earthworm secrete calcium carbonate granules. ► Maximum granule production rates measured for Lumbricus terrestris were 4.3 mgCaCO3 earthworm-1 day-1. ► Granule production rate increased with increasing soil pH. ► Granules may represent a significant pool of calcium carbonate in soils. Lumbricus terrestris earthworms exposed to 11 soils of contrasting properties produced, on average, 0.8 ± 0.1 mgCaCO3  earthworm−1  day−1 in the form of granules up to 2 mm in diameter. Production rate increased with soil pH (r 2  = 0.68, p  < 0.01). Earthworms could be a significant source of calcite in soils.

Exploring links between vadose zone hydrology and chemical weathering in the Boulder Creek critical zone observatory by Abigail L. Langston; Gregory E. Tucker; Robert S. Anderson; Suzanne P. Anderson (S70-S71).
Understanding the relationship between subsurface flow paths on hillslopes and chemical weathering of bedrock is fundamental to understanding the timing and mechanisms that weather bedrock to saprolite. The link between chemical weathering of bedrock and contact time with reactive water along flow paths motivates this study. Water drives the chemical alteration of rock into saprolite, yet connected porosity generally declines with depth into the weathered profile. Saprolite formation, therefore, reflects coupled weathering and permeability development over time. This study uses numerical modeling and soil-moisture monitoring to explore the hydrology of the unsaturated zone and the influence of fracture density, hillslope gradient, and permeability contrasts within the saprolite development horizon on saprolite development.

Dissolution rates of earthworm-secreted calcium carbonate by D.C. Lambkin; M.G. Canti; T.G. Piearce; M.E. Hodson (S67-S69).
► Earthworms secrete granules of calcium carbonate. ► Rates of granule dissolution increase with decreasing soil pH. ► Granule dissolution rate increases with decreasing proportion of exchange sites occupied by Ca. ► Extrapolating measured dissolution rates indicates granules can survive in soils for significant periods of time. ► Granules may represent a significant calcium carbonate pool in soils.The dissolution of CaCO3 granules secreted by earthworms in soil leaching columns was governed by soil pH and exchange sites available for Ca. Results indicate that granules could last for significant periods of time in soils and that, therefore, granules could be an important source of soil calcite.

Soil erosion and depositon are often considered to generate an unintentional, but significant sink sink for atmospheric GHGs. This study highligts the need for a full account of all emissions associated with agriculture when assessing the impact of soil erosion on climate.

Climate change effects on snow melt and discharge of a partly glacierized watershed in Central Switzerland (SoilTrec Critical Zone Observatory) by Florian Kobierska; Tobias Jonas; Jan Magnusson; Massimiliano Zappa; Mathias Bavay; Thomas Bosshard; Frank Paul; Stefano M. Bernasconi (S60-S62).
A comprehensive hydrological modeling study in the drainage area of a hydropower reservoir in central Switzerland is presented. Two models were tested to reproduce the measured discharge dynamics: (1) a detailed energy-balance model (ALPINE3D) primarily designed for snow simulations; (2) a conceptual runoff model system (PREVAH), including a distributed temperature-index snow and ice melt model. Considerable effort was put into distributing available meteorological station data to the model grids as forcing data. The recent EU regional climate modeling initiative ENSEMBLES provided up-to-date climate predictions for two 30-a periods in mid and late 21st century. These were used to estimate evolutions in the water supply of the hydropower reservoir in response to expected climate changes. The simulations suggest a shift of spring peak-flow by almost two months for the end of the century. Warmer winter temperatures will cause higher winter base-flow. Due to glacier retreat, late-summer flow will decrease at the end of the century.

Characteristics of a paleosol and its implication for the Critical Zone development, Rocky Mountain Front Range of Colorado, USA by Matthias Leopold; Jörg Völkel; David Dethier; Juliane Huber; Markus Steffens (S72-S75).
► We dated a sediment section (USA) including an 8000 years old paleosol by OSL and Radiocarbon. ► Nuclear magnetic resonance spectroscopy is used to characterize the paleosols’ organic matter. ► High amounts of aromatic structures (charcoal) indicate fire events that influenced the soil. ► The section represents geomorphic stability and instability phases. ► We use these geomorphic changes to reconstruct the Critical Zone development.Activity and stability phases as well as geomorphic processes within the Critical Zone are well known. Erosion and deposition of sediments represent activity; soils represent geomorphic stability phases. Data are presented from a 4 m deep sediment section that was dated by luminescence techniques. Upslope erosion and resulting sedimentation started in the late Pleistocene around 18 ka until 12 ka. Conditions at the study site then changed, which led to the formation of a well-developed soil. Radiocarbon dating of the organic matter yielded ages between 8552 and 8995 cal. BP. From roughly 6.2 to 5.4 ka another activity phase accompanied by according sediment deposition buried the soil and a new soil, a Cambisol, was formed at the surface. The buried soil is a strongly developed Luvisol. The black colors in the upper part of the buried soil are not the result of pedogenic accumulation of normal organic matter within an A-horizon. Nuclear magnetic resonance spectroscopy clearly documents the high amount of aromatic components (charcoal), which is responsible for the dark color. This indicates severe burning events at the site and the smaller charcoal dust (black carbon) was transported to deeper parts of the profile during the process of clay translocation.

Boron isotope ratios of surface waters in Guadeloupe, Lesser Antilles by Pascale Louvat; Jérôme Gaillardet; Guillaume Paris; Céline Dessert (S76-S79).
► Rivers outer of hydrothermal areas have d11B around 40‰ and [B] of 10–31 μg/L. ► Thermal springs have d11B of 8–15‰ and [B] between 250 and 1000 μg/L. ► With Na, SO4 and Cl, boron shows mixing of rain, low and high-T weathering inputs. ► Guadeloupe rivers and thermal springs have d11B 20–40‰ higher than the local rocks. ► Solid–solution fractionation during weathering pathways may explain this gap of d11B.Large variations are reported in the B concentrations and isotopic ratios of river and thermal spring waters in Guadeloupe, Lesser Antilles. Rivers have δ11B values around 40‰ and B concentrations lower than 30 μg/L, while thermal springs have δ11B of 8–15‰ and B concentrations of 250–1000 μg/L. River samples strongly impacted by hydrothermal inputs have intermediate δ11B and B contents. None of these surface water samples have δ11B comparable to the local unweathered volcanic rocks (around 0‰), implying that a huge isotopic fractionation of 40‰ takes place during rock weathering, which could be explained by preferential incorporation of 10B during secondary mineral formation and adsorption on clays, during rock weathering or in the soils. The soil-vegetation B cycle could also be a cause for such a fractionation. Atmospheric B with δ11B of 45‰ represents 25–95% of the river B content. The variety of the thermal spring chemical composition renders the understanding of B behavior in Guadeloupe hydrothermal system quite difficult. Complementary geochemical tracers would be helpful.

Deep groundwater flow as the main pathway for chemical outputs in a small headwater watershed (Mule Hole, South India) by J.C. Maréchal; J. Riotte; C. Lagane; S. Subramanian; C. Kumar; L. Ruiz; S. Audry; M.R.R. Varma; J.J. Braun (S94-S96).
► Water and chemical cycles of a small forested head catchment are studied. ► High evapotranspiration rate of forest induces low recharge to the aquifer. ► Water table is disconnected from the stream. ► Deep groundwater flow occurs below the weir at the outlet. ► Groundwater flow is the main pathway for chemical outputs.This study examined the water and chemical cycles of a small forested head catchment. Application of Cl mass balance lead to the identification of a groundwater baseflow located into the active zone of the crystalline aquifer, below the weir. These findings indicate that groundwater contributes to a large part of chemical outputs at the catchment scale. This study shows that groundwater should not be ignored in most small watershed studies because this flow path and associated solutes are strongly significant for chemical balance assessment.

Using stable isotopes to understand hydrochemical processes in and around a Prairie Pothole wetland in the Northern Great Plains, USA by Christopher T. Mills; Martin B. Goldhaber; Craig A. Stricker; JoAnn M. Holloway; Jean M. Morrison; Karl J. Ellefsen; Donald O. Rosenberry; Roland S. Thurston (S97-S100).
► A stable isotope study of the hydrochemistry of a Prairie Pothole wetland system. ► δ18OH2O and δ2HH2O values show salt concentration by transpiration at wetland edge. ► A range of δ34SSO4 values indicate SO4 source and reduction processes. ► Isotopic mixing lines show interaction of surface and groundwater at wetland edge.Millions of internally drained wetland systems in the Prairie Potholes region of the northern Great Plains (USA and Canada) provide indispensable habitat for waterfowl and a host of other ecosystem services. The hydrochemistry of these systems is complex and a crucial control on wetland function, flora and fauna. Wetland waters can have high concentrations of SO 4 2 - due to the oxidation of large amounts of pyrite in glacial till that is in part derived from the Pierre shale. Water chemistry including δ18OH2O, δ2HH2O, and δ34SSO4 values, was determined for groundwater, soil pore water, and wetland surface water in and around a discharge wetland in North Dakota. The isotopic data for the first time trace the interaction of processes that affect wetland chemistry, including open water evaporation, plant transpiration, and microbial SO4 reduction.

► Statistical analysis on element concentrations of bedrock, regolith, and sediments. ► Element groups with different geochemical behaviors during soil formation. ► Mineralogical, cycling, and geochemical controls during chemical weathering.Major and trace element concentrations were measured in bedrock, regolith and stream sediments from a first-order catchment developed entirely on grey shale in central Pennsylvania, USA. These elements can be classified into five major groups based on statistical data analysis. The presence of different elemental groups is due to the mineralogical origin, cycling processes, and geochemical properties of these elements during soil formation. A better understanding of the behaviors of these elements during chemical weathering would allow for their possible use as natural tracers in Critical Zone processes.

Carbon–mineral interactions along an earthworm invasion gradient at a Sugar Maple Forest in Northern Minnesota by Amy Lyttle; Kyungsoo Yoo; Cindy Hale; Anthony Aufdenkampe; Stephen Sebestyen (S85-S88).
► We investigated the population dynamics of earthworm invasion and its impact on soil carbon storage in a northern hardwood forest in Minnesota. ► With increasing earthworms’ biomass and particularly with the arrival of endogenic species, leaf litter biomass is significantly reduced. ► Earthworms vertically redistribute organic matter throughout the soil profile and thus significantly affect the soil carbon storage. ► Earthworms increase the soil specific mineral surface area in the A and E horizon.The interactions of organic matter and minerals contribute to the capacity of soils to store C. Such interactions may be controlled by the processes that determine the availability of organic matter and minerals, and their physical contacts. One of these processes is bioturbation, and earthworms are the best known organisms that physically mix soils. Earthworms are not native species to areas previously glaciated, and the introduction of earthworms to these regions has been associated with often dramatic changes in soil structure and geochemical cycles. The authors are studying C mineral interaction along an approximately 200 m long earthworm invasion transect in a hardwood forest in northern Minnesota. This transect extends from the soils where earthworms are absent to soils that have been invaded by earthworms for nearly 30–40 years. Pre-invaded soils have an approximately 5 cm thick litter layer, thin (∼5 cm) A horizon, silt rich E horizon, and clay-rich Bt horizons. The A and E horizons formed from aeolian deposits, while the clay-rich Bt horizons probably developed from underlying glacial till. With the advent of earthworm invasion, the litter layer disappears and the A horizons thicken at the expense of the O and E horizons. In addition, organic C contents in the A horizons significantly increase with the arrival of earthworms. Simultaneously, measured mineral specific surface areas suggest that minerals’ capacities to complex the organic matter appear to be greater in soils with active earthworm populations. Based on the data from two end member soils along the transect, mineral specific surface areas in the A and E horizons are larger in the earthworm invaded soil than in the pre-invasion soil. Additionally, within < 5 a of earthworm invasions, A horizon materials are turned from single grain to a strong medium granular structure. While A horizon organic matter content and organic C-mineral complexation increase after earthworm invasion, they are also more vigorously mixed. This growing data set, when ultimately combined with ongoing measurements of (1) the population dynamics of earthworms along the invasion transect, (2) C-mineral association (via surface adsorption and physical collusion in mineral aggregates) and (3) dissolved organic C will show how and how much soil capacity to store C is affected by burrowing organisms, which are often the keystone species of given ecosystems.

► Depth to paralithic contact generally increased with elevation. ► Q/P ratios were higher in divergent landscape positions compared to adjacent convergent hollows. ► Clay mineral assemblages changed as a function of elevation. ► Climate, landscape position and erosion interactively control soil and regolith development.Understanding the interactions of climate, physical erosion, chemical weathering and pedogenic processes is essential when considering the evolution of critical zone systems. Interactions among these components are particularly important to predicting how semiarid landscapes will respond to forecasted changes in precipitation and temperature under future climate change. The primary goal of this study was to understand how climate and landscape structure interact to control chemical denudation and mineral transformation across a range of semiarid ecosystems in southern Arizona. The research was conducted along the steep environmental gradient encompassed by the Santa Catalina Mountains Critical Zone Observatory (SCM-CZO). The gradient is dominated by granitic parent materials and spans significant range in both mean annual temperature (>10 °C) and precipitation (>50 cm a−1), with concomitant shift in vegetation communities from desert scrub to mixed conifer forest. Regolith profiles were sampled from divergent and convergent landscape positions in five different ecosystems to quantify how climate-landscape position interactions control regolith development. Regolith development was quantified as depth to paralithic contact and degree of chemical weathering and mineral transformation using a combination of quantitative and semi-quantitative X-ray diffraction (XRD) analyses of bulk soils and specific particle size classes. Depth to paralithic contact was found to increase systematically with elevation for divergent positions at approximately 28 cm per 1000 m elevation, but varied inconsistently for convergent positions. The relative differences in depth between convergent and divergent landscape positions was greatest at the low and high elevation sites and is hypothesized to be a product of changes in physical erosion rates across the gradient. Quartz/Plagioclase (Q/P) ratios were used as a general proxy for bulk regolith chemical denudation. Q/P was generally higher in divergent landscape positions compared to the adjacent convergent hollows. Convergent landscape positions appear to be collecting solute-rich soil–waters from divergent positions thereby inhibiting chemical denudation. Clay mineral assemblage of the low elevation sites was dominated by smectite and partially dehydrated halloysite whereas vermiculite and kaolinite were predominant in the high elevation sites. The increased depth to paralithic contact, chemical denudation and mineral transformation are likely functions of greater water availability and increased primary productivity. Landscape position within a given ecosystem exerts strong control on chemical denudation as a result of the redistribution of water and solutes across the landscape surface. The combined data from this research demonstrates a strong interactive control of climate, landscape position and erosion on the development of soil and regolith.

Soil aggregation estimates in CZO-Fuchsenbigl by Milena Kercheva; Svetla Rousseva; Emil Dimitrov; Martin Nenov; Toma Shishkov (S57-S59).
► Strong relationships between soil aggregation estimates (composite versus single samples). ► The method applied is sensitive to vertical and horizontal changes of water stable aggregates (WSA). ► WSA in 1–3 mm size dry aggregates in the upper layer vary from 44% to 76% under native vegetation. ► WSA in 1–3 mm size dry aggregates in the upper layer drop to 1% under intensively cultivation.The study presents results on the informativity and spatial variation of soil aggregation characteristics in one of the Critical Zone Observatories (CZO) in Europe – Fuchsenbigl, Austria. Water stable aggregates of different size were measured, and strong relationships between soil aggregation estimates were found. The horizontal variation of water stable aggregates at particular depths can be explained by certain vertical heterogeneity of the soil profiles in space. The water stable aggregates in 1–3 mm size dry aggregates in the upper layer vary from 44% to 76% under native vegetation, drop to 1% under intensive cultivation, and comprise 19% in land not tilled for 5 years. The results allow linking the characteristics of soil structure with other biotic and chemical properties for better estimation of the driving forces for soil aggregate formation.

► Soils in a swale are controlled by weathering and colluvium sediment transport. ► Plagioclase and clay dissolution dictates elemental profiles at Shale Hills soils. ► Swales at Shale Hills are wetter but oxic, evidenced by the positive Ce anomaly.Soil chemistry data (major and REEs) are presented from a swale transect for comparison to similar measurements on a planar transect published previously for the Susquehanna/Shale Hills Critical Zone Observatory. Similar reaction fronts are observed: plagioclase dissolution is indicated by Na and Ca depletion and a negative Eu anomaly; clay dissolution followed by particle loss is accompanied by depletion of Mg, K, Fe, Al and Si. However, in contrast to the planar transect, soils along the swale transect, especially in the topographically depressed site, do not show smooth elemental profiles. This documents both residuum soils and accumulation of colluvium sediments. The soils in the swale transect are thicker and on average wetter than those along the planar transect; however, the Ce anomaly observed in the swale soils is consistent with a generally oxic environment. Thus, preferential flowpaths are an important mechanism for water transport, preventing swale soils from water saturation.

Understanding the fate of iron in a modern temperate estuary: Leirárvogur, Iceland by Gemma M. Byrne; Richard H. Worden; David M. Hodgson; David A. Polya; Paul R. Lythgoe; Craig D. Barrie; Adrian J. Boyce (S16-S19).
► Fluvial Fe (aq) and Fe (total) concentrations drop upon mixing with seawater in estuaries. ► The majority of Fe in estuaries is lost in the bay-head delta. ► Our results suggest that the bay-head delta is a key location in Fe-mineral formation. ► Isotopic variation in estuarine waters may play a role in the formation of Fe-minerals.Fluvial dissolved Fe concentrations decrease upon mixing with seawater, resulting in the formation of Fe-floccules. However, a clear understanding of the fate of these floccules has yet to be established. Assessing how tidal processes affect the formation of Fe-colloids in the Leirárvogur estuary, SW Iceland, is an important step in understanding the formation and potential deposition of estuarine Fe-rich minerals within this estuarine system. The Leirárvogur estuary drains predominately Fe-rich basalt, increasing the likelihood of detecting changes in Fe-phases. Fluvial waters and local lake waters that drain into the estuary were compared and the effects of seasonal changes were considered, in an attempt to understand how varying end-members and external factors play a role in Fe-rich mineral formation. Aqueous and colloidal Fe concentrations were found to be greater towards the head of the Leirárvogur estuary, suggesting that potential Fe-rich minerals and complexes are forming at sites of fluvial input. Increasing suspended colloidal Fe towards the estuary mouth suggests that Fe-colloids are readily transported seaward.

Determination of chemical weathering rates from U series nuclides in soils and weathering profiles: Principles, applications and limitations by François Chabaux; Lin Ma; Peter Stille; Eric Pelt; Mathieu Granet; Damien Lemarchand; Raphael di Chiara Roupert; Susan L. Brantley (S20-S23).
► Determination of weathering front propagation rates. ► Mathematical models, parameters and required assumptions. ► Limitations of the modelling approaches.The development of U-series nuclides for investigating weathering processes has been significantly stimulated by the analytical improvement made over the last decades in measuring the 238U series with intermediate half-lives (i.e., 234U–230Th–226Ra). It is proposed in this paper to present principles and methods that are now being developed to determine weathering rates from the study of U-series nuclides in soils and weathering profiles. Mathematical approaches, developed to calculate such rates, are based on some implicit assumptions that are also presented and must be kept in mind if one wants to correctly interpret the obtained ages.

Investigating the complex interface where bedrock transforms to regolith by S.L. Brantley; H. Buss; M. Lebedeva; R.C. Fletcher; L. Ma (S12-S15).
► Rates of weathering and erosion are documented in regolith depth profiles of chemistry and rock fragment size.The interface where bedrock transforms to regolith is not planar but rather has a roughness that varies with the scale of observation. The complexity of this surface is manifested in both element-depth and fragment size-depth distributions and may sometimes be related to the longitudinal profiles of watershed streams. The fractal nature of the bedrock-regolith interface means that the interface has a “thickness” which is >20 m in two ridgetop examples from Pennsylvania and Puerto Rico. Such weathering thicknesses, modeled as a function of one-dimensional fluid flow, are affected by the balance between rates of weathering and erosion. One-dimensional models are consistent with weathering advance rates that vary with equilibrium solubility and porefluid velocities (and not reaction kinetics). However, fluid flow is not strictly downward and one-dimensional. Permeability of regolith changes as particle size and bulk density changes with depth. Thus, both downward and lateral flow occurs especially at reaction fronts where reactions change permeability. The rate of weathering advance is, therefore, affected by the 3-dimensional distribution of reaction zones that affect permeability across the watershed. Quantitative models of such phenomena over a range of spatial and temporal scales are needed.

► High field strength (HFS) elements used to index weathering may be mobile in suspension. ► Redistribution can be quantified using HFS element ratios of weathering system components. ► Corrections can be made to HFS element concentrations used to index weathering.Evidence shows that high field strength (HFS) elements commonly used to index chemical weathering are variably mobile. This mobility may be linked to redistribution of suspended solids. A mass-balance model is presented that can quantify such redistribution without assuming immobility for any single element. Two tropical weathering profiles on quartz diorite and basalt are examined and redistribution of the HFS elements Zr and Ti is documented, along with potential corrections for the resulting changes in measured concentrations.

► Only minor effects of climate change on stream water chemistry are expected. ► Stream chemistry will be dominantly controlled by high historical acidic deposition. ► The runoff and soil water storage will decrease significantly in summer.The aim of this study was to estimate future water balance and streamwater chemistry changes, according to different climate change scenario, in a forested acid-sensitive catchment. The investigated Czech catchment was affected by large anthropogenic acidification in the 20th century. Runoff for the year 2070 and streamwater chemistry for the period 1860–2070 were simulated by the models Brook90 and MAGIC, respectively. The runoff would change from 450 mm a−1 (1990–2006) to 320–402 mm a−1 for the year 2070 according to Brook90 simulations with bias-corrected regional climate model (RCAO) data with A2 emission scenario. Future streamwater SO 4 2 - concentration would maintain at the current level of approximately 90 μeq L−1 (2008–2009) in the case of minimum or no change in runoff, or would increase by 10–30% as a result of projected runoff decrease. The runoff change would increase the concentration of base cations of a similar magnitude compared to the measured 160 μeq L−1 (2008–2009). According to both scenarios, the effect of climate change on pH would be small and would lead to slight re-acidification of streamwater compared to the measured 4.2 (2008–2009). The climate change influence to streamwater chemistry would be small compared to the influence of atmospheric acid deposition. The environmental condition of the stream will probably remain unsatisfactory until the 2070s.

► The uranium-series isotope composition of regolith material can be used to determine the soil residence time. ► Soil residence times up to 30 and 90 kyr are calculated for Frogs Hollow and Bisley, respectively. ► Production rates are relatively similar for granitic and shale lithologies, but much higher over volcanic parent rock. ► Soil production matches erosion in soil-mantled landscapes, demonstrating quantitatively that this type of landscape results from a balance between these two processes ► Soil production is up to two orders of magnitude slower than erosion in cultivated areas.The diversity in landscapes at the Earth’s surface is the result, amongst other things, of the balance (or imbalance) between soil production and erosion. While erosion rates are well constrained, it is only recently that we have been able to quantify rates of soil production. Uranium-series isotopes have been useful to provide such estimates independently of erosion rates. In this study, new U-series isotope are presented data from weathering profiles developed over andesitic parent rock in Puerto Rico, and granitic bedrock in southeastern Australia. The site in Australia is located on a highland plateau, neighbouring a retreating escarpment where soil production rates between 10 and 50 mm/kyr have been determined. The results show that production rates are invariant in these two regions of Australia with values between 15 and 25 mm/kyr for the new site. Andesitic soils show much faster rates, about 200 mm/kyr. Overall, soil production rates determined with U-series isotopes range between 10 and 200 mm/kyr. This is comparable to erosion rates in soil-mantled landscapes, but faster than erosion in cratonic areas and slower than in alpine regions and cultivated areas. This suggests that soil-mantled landscapes maintain soil because they can: there is a balance between production and erosion. Similarly, thick weathering profiles develop in cratonic areas because, despite slow erosion rates, soil production is still significant. Bare landscapes in Alpine regions are probably the result of the inability of soil production to catch up with fast erosion rates, although this needs testing by U-series isotope studies of these regions. Finally, the range of production rates is up to several orders of magnitude lower than erosion rates in cultivated areas, demonstrating quantitatively the fast depletion of soil resources with common agricultural practices.

Soil evidence for historical human-induced land degradation in West Iceland by Guðrún Gísladóttir; Egill Erlendsson; Rattan Lal (S28-S31).
► Environmental change in W-Iceland over the last 2700 years is studied from two soil cores. ► The Norse settlement around AD 870 caused depletion of vegetative coverage and biomass. ► Vegetation degradation induced soil erosion which successively caused a decline in soil quality.Human impacts have been severe on Icelandic soils and vegetation. In order to assess human impact on soils soil quality, soil organic C (SOC), soil bulk density (BD), soil moisture content (SMC), soil mass, and SOC sequestration were measured from two Histosol cores in West Iceland. The cores cover a period from around 665 BC to present, capturing the initial human settlement of Iceland in AD 871. Tephrochronology allowed for a reliable correlation and comparison between the two cores. The initial settlement had profound impacts on the soil quality, causing decreased SOC concentration and SMC, and increased vegetation degradation, soil exposure, eolian deposition, and BD. The total SOC pool was 34.6 kg C m2 at one of the sites, of which 60.1% was formed during historic times, driven by increased soil mass deposition from surrounding eroded areas. The SOC pool was 43.7 kg C m2 at the other site, of which 31.4% was formed during historic time, constrained by water cycling and decomposition.

Carbon and nitrogen biogeochemistry of a Prairie Pothole wetland, Stutsman County, North Dakota, USA by JoAnn M. Holloway; Martin B. Goldhaber; Christopher T. Mills (S44-S47).
► Wetland nitrogen and carbon are derived from nitrogen fixation and photosynthesis with subsequent decay of wetland vegetation and algae. ► Ground water nitrogen and carbon are derived in part from dissolution of organic rich Pierre Shale, which makes up part of the underlying glacial till aquifer. ► Trends in SUVA254 with pH in wetlands may reflect differences in vegetation communities. ► Ammonium is the dominant inorganic nitrogen species, indicating a highly reducing environment in both surface and ground water.The concentration and form of dissolved organic C (DOC) and N species ( NH 4 + and NO 3 - ) were investigated as part of a larger hydrogeochemical study of the Cottonwood Lake Study Area within the Prairie Potholes region. Groundwater, pore water and surface wetland water data were used to help characterize the relationships between surface and groundwater with respect to nutrient dynamics. Photosynthesis and subsequent decomposition of vegetation in these hydrologically dynamic wetlands generates a large amount of dissolved C and N, although the subsurface till, derived in part from organic matter rich Pierre Shale, is a likely secondary source of nutrients in deeper groundwater. While surface water DOC concentrations ranged from 2.2 to 4.6 mM, groundwater values were 0.15 mM to 3.7 mM. Greater specific UV absorbance (SUVA254) in the wetland water column and in soil pore waters relative to groundwater indicate more reactive DOC in the surface to near-surface waters. Circumneutral wetlands had greater SUVA254, possibly because of variations in vegetation communities. The dominant inorganic nitrogen species was NH 4 + in both wetland water and most ground water samples. The exceptions were 3 wells with NO 3 - ranging from 38 to 115 μM. Shallow groundwater wells (Well 28 and Well 13S) with greater connection to wetland surface water had greater NH 4 + concentrations (1.1 mM and 120 μM) than other well samples (3–90 μM). Pore water nutrient chemistry was more similar to surface water than ground water. Nitrogen results suggest reducing conditions in both groundwater and surface water, possibly due to the microbial uptake of O2 by decaying vegetation in the wetland water column, labile organic C available in shallow groundwater, or the oxidation of pyrite associated with the subsurface.

Landscape response to tipping points in granite weathering: The case of stepped topography in the Southern Sierra Critical Zone Observatory by Barbara S. Jessup; W. Jesse Hahm; Scott N. Miller; James W. Kirchner; Clifford S. Riebe (S48-S50).
► This work tests a decades-old hypothesis in which relief development in the southern Sierra Nevada is attributed to differential weathering of bare and soil-mantled granite. ► Terrain analysis shows that the landscape is organized into a sequence of steep steps and gentle treads, consistent with the hypothesis. ► Cosmogenic nuclides show that bare granite erodes more slowly than its soil-mantled counterparts, as required by the hypothesis.However, steps erode more quickly than treads, undermining the explanation for the origins of the stepped topography.The dynamics of granitic landscapes are modulated by bimodal weathering, which produces patchy granular soils and expanses of bare rock ranging from meter-scale boulders to mountain-scale domes. We used terrain analysis and with cosmogenic nuclide measurements of erosion rates to quantitatively explore Wahrhaftig’s decades-old hypothesis for the development of “stepped topography” by differential weathering of bare and soil-mantled granite. According to Wahrhaftig’s hypothesis, bare granite weathers slower than soil-mantled granite; thus random erosional exposure of bare rock leads to an alternating sequence of steep, slowly weathering bedrock “steps” and gently sloped, but rapidly weathering, soil-mantled “treads.” Our investigation focused on the terrain surrounding the Southern Sierra Critical Zone Observatory (CZO), which is underlain by granitic bedrock and lies outside the limits of recent glaciation, in the heart of the stepped topography described by Wahrhaftig. Our digital terrain analysis confirms that steep steps often grade into gentle treads, consistent with Wahrhaftig’s hypothesis. However, we observe a mix-and-match of soil and bare rock on treads and steps, contrary to one of the hypothesis’ major underpinnings – that bare rock should be much more common on steps than on treads. Moreover, the data show that bare rock is not as common as expected at step tops; Wahrhaftig’s hypothesis dictates that step tops should act as slowly eroding base levels for the treads above them. The data indicate that, within each landscape class (i.e., the steps and treads), bare rock erodes more slowly than surrounding soil. This suggests that the coupling between soil production and denudation in granitic landscapes harbors a tipping point wherein erosion rates decrease when soils are stripped to bedrock. Although broadly consistent with the differential weathering invoked by Wahrhaftig, the data also show that steps are eroding faster than treads, undermining Wahrhaftig’s explanation for the origins of the steps. The revised interpretation proposed here is that the landscape evolves by back-wearing of steps in addition to differential erosion due to differences in weathering of bare and soil-mantled granite.

Movement of manganese contamination through the Critical Zone by Elizabeth M. Herndon; Susan L. Brantley (S40-S43).
► Soils throughout the United States and Europe are enriched in Mn near zones of industrial input. ► The decline of Mn in rivers reflects the decline of Mn in air since the mid-20th century. ► River chemistry can be used to evaluate the removal of Mn from soils. ► Rapid biocycling contributes to the retention of Mn in affected ecosystems.Humans have transferred large quantities of metals from the lithosphere to the Earth’s surface, drastically altering the natural flow of these elements. The geographic dispersal of many metals and their impacts on the environment are unknown. Here, existing datasets are compiled to assess how anthropogenic inputs of Mn to the air have altered soil and water chemistry over time. Although levels of Mn in the air have declined in recent decades, soils throughout the USA and Europe are enriched in Mn, revealing past contamination near zones of industrial input. Examination of river chemistry indicates a similar decline in Mn and can be used to evaluate the removal of Mn from soils. We use a small watershed, the Susquehanna/Shale Hills Critical Zone Observatory, as a focus site to investigate geochemical mass balance models and find that rapid biocycling contributes to the retention of Mn in this affected ecosystem.

► Climate exerts control, through infiltration, on weathering depth and intensity. ► The potential vadose zone extent and weathering depth appear to be set by local base level. ► Key weathering reactions and type of resulting saprolite depend upon vadose zone hydrology.An investigation of vadose zone weathering processes has been undertaken on grussic saprolites developed on Californian granitoids. Preliminary results indicate strong climatic control, through infiltration, on the depth and intensity of weathering. At sites with higher infiltration, the vadose zone is comprehensively altered to grussic saprolite and saprock. Conversely, lower infiltration sites display only thin grussic saprolites, strongly influenced by rock texture. Both vadose zone and weathering depth appear to be governed by local base level, and vadose zone hydrology exerts a fundamental control on the effective operation and relative dominance of the key weathering reactions. In zones of matrix permeability, oxidation of biotite comprehensively disaggregates the rock but results in little mass loss and clay mineral formation. Conversely, the higher transient flow rates that characterize zones of fracture permeability result in plagioclase hydrolysis, significant mass losses and accompanying clay mineral formation. A variable hydrological regime may also contribute to high partial pressures of O2 in vadose zone pore waters and pore spaces, thereby enhancing the oxidative environment and further predisposing grussic saprolite formation.

The role of critical zone processes in the evolution of the Prairie Pothole Region wetlands by M.B. Goldhaber; C. Mills; C.A. Stricker; J.M. Morrison (S32-S35).
► The geochemistry of Prairie Pothole wetlands in ND is governed by oxidation of pyrite. ► Pyrite oxidation progressively leads to sulfate dominated wetland and ground waters. ► The source of the pyrite is a component of glacial till derived from Cretaceous shale. ► The interval of pyrite oxidation is marked by a brown to grey color transition in the till. ► Pyrite oxidation is a slow process that has taken place over atleast a thousand years.The Prairie Pothole Region, which occupies 900,000 km2 of the north central USA and south central Canada, is one of the most important ecosystems in North America. It is characterized by millions of small wetlands whose chemistry is highly variable over short distances. The study involved the geochemistry of surface sediments, wetland water, and groundwater in the Cottonwood Lakes area of North Dakota, USA, whose 92 ha includes the dominant wetland hydrologic settings. The data show that oxygenated groundwater interacting with pyrite resident in a component of surficial glacial till derived from the marine Pierre Shale Formation has, over long periods of time, focused SO 4 2 - -bearing fluids from upland areas to topographically low areas. In these low areas, SO 4 2 - -enriched groundwater and wetlands have evolved, as has the CaSO4 mineral gypsum. Sulfur isotope data support the conclusion that isotopically light pyrite from marine shale is the source of SO 4 2 - . Literature data on wetland water composition suggests that this process has taken place over a large area in North Dakota.

Cluster analysis of a regional-scale soil geochemical dataset in northern California by Jean M. Morrison; Martin B. Goldhaber; Karl J. Ellefsen; Christopher T. Mills (S105-S107).
► Over 1300 soil samples were chemically analyzed for 42 elements as part of a geochemical landscape study in northern California. ► Two types of cluster analyses were applied to identify groups of elements whose spatial patterns could be related to specific geologic sources. ► Hierarchical clustering of Sacramento Valley soils showed element groupings associated with source rocks. ► Non-hierarchical clustering revealed spatial patterns relating source rock distributions in valley soils. ► Geochemical intuition must be used in interpreting cluster analysis results on large datasets.A regional-scale soil geochemical study was conducted within a 22,000 km2 area in northern California including the Sierra Nevada, Sacramento Valley, and northern Coast Range. Over 1300 soil samples were chemically analyzed for 42 elements. The distribution of distinct groups of elements demonstrates the interplay of geologic, hydrologic, geomorphologic and anthropogenic factors; however, it is difficult to fully appreciate the complexity of geochemical transport and weathering processes on a landscape-scale in an area of very complex geology with such a large dataset containing more than 40 variables. To examine the data from a perspective of multi-element groupings, cluster analyses were applied to the dataset. The analysis identified several groups of elements whose spatial patterns could be related to specific geologic sources.

CZChemDB and EarthChem: Advancing management and access of critical zone geochemical data by Xianzeng Niu; Kerstin A. Lehnert; Jennifer Williams; Susan L. Brantley (S108-S111).
Multiple Critical Zone Observatories (CZO) have been established in recent years in the USA and other international settings to conduct collaborative research on processes that occur at and near Earth’s surface, also known as the Critical Zone (CZ). Data documentation and data sharing are two persistent problems facing the CZOs that impede the ability for cross-site comparisons and integrated analysis. In this study, a relational database was developed for CZ rock and regolith geochemical data – CZChemDB. There are a total of 24 interrelated tables in the database, each representing different aspects of CZ features. The main data group includes tables of locations, sites, samples, subsamples, preparation/treatments, laboratory-analysis and data values. The meta-data group includes tables of methods, references, and data quality. Lookup tables (variables, units, etc.) contain lists of “controlled” vocabularies. The CZChemDB is currently implemented in the MS Access database management system. It is expected to be integrated into the EarthChem portal by summer of 2011 for broader online accessibility and usability. This integration also complements the EarthChem’s global geochemistry database with CZ regolith data. The structure of the CZChemDB is simple, straightforward, and flexible so that it has potential to accommodate other chemical data collected from CZOs, such as pore fluid data. Furthermore, the development of CZChemDB represents the first attempt toward the standardization of geochemical data documentation and data sharing among CZOs. This effort will establish a model to bridge the connections between data acquisition, data management, data sharing, and data searching/discovering that are all essential but weak in terms of linkages within most geoscience research projects.

Importance of weathering and human perturbations on the riverine transport of Si by Jean-Dominique Meunier; Jean-Jacques Braun; Jean Riotte; Chikkakenchaiah Kumar; Muddu Sekhar (S360-S362).
► The factors that have been identified for increasing the riverine transport of dissolved silica (DSi) are elevated temperature, a high content of weatherable silicate minerals, steep slopes and deforestation. ► Low temperatures, lack of weatherable silicate, flat surfaces, diatom bloom and vegetation growth, urbanization, agriculture, eutrophication and damming favor low riverine DSi. ► Preliminary data along the Kaveri river (India) suggest that DSi is controlled by a combined effect of chemical weathering, damming and groundwater recharge.The global Si cycle is strongly controlled by riverine input. Over the last decade two parameters have been shown to play a significant role in the control of dissolved Si (DSi): biology, through the effects of diatom blooms and vegetation growth, and human activity, through the effects of eutrophication, urbanisation, agriculture, deforestation and damming. Human perturbations should now be better quantified when modelling the global Si cycle and particularly in the tropics. A case study is presented based on preliminary data along the Kaveri river (India) strongly impacted by dams. It is suggested that DSi is controlled by a combined effect of chemical weathering, damming and groundwater recharge.

► Discharge and water quality (organic carbon, nutrients, major ions, and metals) are being measured upstream, within, and downstream of the burned area. ► Downstream samples collected during the first major post-fire precipitation event showed brief increases in specific conductance, nitrate, and carbon. ► Water samples are being collected several times a week during snowmelt, and will be collected on an event basis during summer convective storms.The impacts of a September 2010 wildfire on hydrologic and biogeochemical processes are being evaluated in a Colorado Front Range stream.

The Li isotope geochemistry of the Jinshajiang (upper reach of the Changjiang), Lancangjiang (Meckong) and the Nujiang (Salween) rivers have been studied to better understanding the weathering of continental crust. The three rivers show different water geochemistry, the Jinshajiang followed by the Lancangjiang contains much solute from dissolution of evaporites; the Jinshajiang has the highest average Li content and δ7Li values. The relatively low δ7Li values (+4.74∼+12.9‰) of the river waters, compared to those of large rivers in the world, probably reflect less weathering intensity in this arid and cold region. The Jinshajiang water has relatively high and constant δ7Li values, and is considered to be affected by evaporite dissolution and the high δ7Li values indicating that precipitation of salt minerals might have resulted in enrichment of 7Li in the remaining water. It is thought that H2SO4 has been involved in crustal weathering in the region, especially in the Nujiang basin.

Characterization and source determination of stream suspended particulate material in White Clay Creek, USA by Diana L. Karwan; Rolf Aalto; Anthony K. Aufdenkampe; J. Denis Newbold; James E. Pizzuto (S354-S356).
► Sediment fingerprinting will be used to determine the source of suspended particulate material to nested first- through fourth-order watersheds of mixed agriculture, forest, and urban land use. ► This study is conducted as a part of the Christina River Basin Critical Zone Observatory (CRB CZO).The material exported from a watershed reflects its origin and the processes it undergoes during downhill and downstream transport. Due to its nature as a complex mixture of material, the composition of suspended particulate material (SPM) integrates the physical, biological and chemical processes effecting watershed material. This study will (1) use a sediment fingerprinting approach to quantify the composition and sources of SPM in the White Clay Creek Watershed in SE Pennsylvania and Delaware, USA, (2) examine longitudinal trends in SPM composition and source in first to fourth reaches of the White Clay Creek, (3) quantify the differences in composition and source with hydrologic variations produced by storms and seasonality.

Rivers from Volcanic Island Arcs: The subduction weathering factory by Jérôme Gaillardet; Pascale Louvat; Eric Lajeunesse (S350-S353).
Here the focus is on the geochemistry of rivers draining volcanic arc regions. Although data are rather sparse, first order estimates show that volcanic arc settings are amongst the faster eroding regions of the Earth because they combine high precipitation regimes with high hydrothermal contributions in which increased temperature and increased acidity favor water–rock interaction. The hydrothermal contribution tends to obliterate the effect of climate and shows the importance of better evaluating the hydrothermal input from subduction zones, and the parameters that control it.

The role of riverine particulate material on the global cycles of the elements by Eric H. Oelkers; Sigurdur R. Gislason; Eydis Salome Eiriksdottir; Morgan Jones; Christopher R. Pearce; Catherine Jeandel (S365-S369).
► Particulate transport dominates dissolved transport of the elements to the ocean. ► Particulate material readily dissolves in sea water releasing its elements. ► Particulate element release can rapidly affect the isotopic composition of seawater. ► Ocean Nd, Fe, Si, and Sr isotopic ratios are likely affected strongly by this process.A review of the relative masses of continental weathering products transported to the oceans indicates that particulate fluxes dominate dissolved fluxes for most elements. The degree to which this particulate material plays a role in the compositional evolution of seawater depends on its dissolution rate, which appears to be rapid due to its high surface area. Consideration of the results of batch experiments and mineral saturation state calculations suggest that much of the mass dissolved into seawater from particulate material dissolution is rapidly removed by the precipitation of secondary minerals. Although this process limits the degree to which the overall concentration of elements in seawater are affected by the addition of particulate material, the dissolution of isotopically distinct particulate phases may affect the isotopic composition of seawater over remarkably short timescales.

► Adjusted yields of silica, calcium, sodium, chloride, and dissolved organic carbon demonstrate little preferential influence by geology or land cover. ► Adjusted yields of magnesium, dissolved inorganic carbon, and sulfate differ in manners consistent with watershed geology. ► Adjusted yields of biologically active constituents (potassium, nitrate, ammonia, phosphate) and particulate constituents were considerably greater for developed landscapes compared to forested watersheds. ► Particulate organic carbon is the only aspect of fluvial carbon export that demonstrates a significant increase due to human activities or environmental change.The U.S. Geological Survey Water, Energy, and Biogeochemical Budgets Program in eastern Puerto Rico involves a double pair-wise comparison of humid-tropical montane streams on granitic bedrock and fine-grained volcaniclastic bedrock. For each bedrock type, one catchment is covered with mature rainforest, and the other catchment is affected by grazing, cropping, and minor urbanization. Biogeochemical budgets were monitored for fifteen years and included water, major dissolved constituents, nutrients, carbon, and sediment. To adjust for differences in runoff, the relation between annual runoff and annual yield were used to project the yields for all the rivers to an intermediate common runoff. Observed and adjusted rates of physical denudation greatly exceed rates expected for a dynamic equilibrium, except for the forested river on volcaniclastic bedrock. Deforestation and agriculture can explain the accelerated physical erosion in the two developed catchments. Something else, possibly climate or forest-quality change, must explain the excessive erosion in the forested river on granitic bedrock. Particulate organic carbon yields are closely linked to sediment yields, which are in turn, far in excess of equilibrium yields. This implies that much of the particulate carbon transport in the four rivers is being caused by enhanced erosion perhaps due to human activities or environmental change. Dissolved organic and inorganic carbon show a weak runoff signal, and there is no evidence of human perturbations to dissolved carbon production or silicate weathering in the four watersheds.

► The fate of nitroaromatic and nitro-triazine compounds in soils is commonly modeled using highly empirical partition coefficients (KD ). ► Theoretical considerations are discussed in terms of refining KD predictions through the development of mathematical functions with respect to soil properties. ► Solute sorption can vary with changes in sample handling and experimental procedures. ► Preliminary steady state transport experiments point to a link between the fate of munition constituents and soil fertility.This paper focuses on the chemistry of DoD-relevant organic contaminants in soil. Most of the work presented here is based on the author’s experience with the environmental fate of the munition constituents, TNT and RDX, for DoD related issues. The principles and challenges of understanding the transport of nitrobenzene and triazine compounds in the environment are captured. In this work, disparities in the current scientific literature with respect to the construction of sorption experiments are discussed, in terms of soil sample handling, dispersion state of the soil, and sorption hysteresis/equilibrium. Here is discussed the concept of environmentally formulated compounds and its implications toward reduced accuracy of predicting the environmental fate of munition constituents. Also, further research linking simple but oft-forgotten basic concepts of soil fertility to the transport and environmental fate of munition constituents are discussed.

Tracking transformation processes of organic micropollutants in aquatic environments using multi-element isotope fractionation analysis by Thomas B. Hofstetter; Jakov Bolotin; Marita Skarpeli-Liati; Reto Wijker; Zohre Kurt; Shirley F. Nishino; Jim C. Spain (S334-S336).
The quantitative description of enzymatic or abiotic transformations of man-made organic micropollutants in rivers, lakes, and groundwaters is one of the major challenges associated with the risk assessment of water resource contamination. Compound-specific isotope analysis enables one to identify (bio)degradation pathways based on changes in the contaminants’ stable isotope ratios even if multiple reactive and non-reactive processes cause concentrations to decrease. Here, we investigated how the magnitude and variability of isotope fractionation in some priority pollutants is determined by the kinetics and mechanisms of important enzymatic and abiotic redox reactions. For nitroaromatic compounds and substituted anilines, we illustrate that competing transformation pathways can be assessed via trends of N and C isotope signatures.

► Chaohu Lake is one of the five largest freshwater lakes in China. ► Eutrophication has become the most serious problems since the 1990s. ► Chemical and Sr isotopic compositions were determined to quantify the contributions of different sources to the dissolved load.As one of the five largest freshwater lakes in China, the Chaohu Lake is polluted by many kinds of pollutants. Chemical and Sr isotopic compositions of river waters in the Zhegao River sub-catchment have been determined with the main purpose of understanding the contribution of chemical weathering and anthropogenic inputs to solutes. The major ion compositions of the river waters are characterized by the dominance of Ca2+ and HCO 3 - , followed by Mg2+ and SO 4 2 - . The chemical and Sr isotopic analyses indicate that three major reservoirs (carbonate, silicate and human activities) contribute to the dissolved load. The calculated results show that the dissolved load is dominated by carbonate weathering. The contribution of the anthropogenic inputs is estimated to be from 1.64% to 31.8%, with an average of 15.6%, demonstrating the strong impacts of human activities on water chemistry. The total chemical denudation flux of the Zhegao sub-catchment is about 127.7 ton km−2  a−1, with carbonate and silicate weathering rates of 97.5 ton km−2  a−1 and 30.2 ton km−2  a−1, respectively.

Disrupting the riverine DIC cycling by series hydropower exploitation in Karstic area by Fushun Wang; Cong-Qiang Liu; Baoli Wang; Xiaolong Liu; Ganrong Li; Jin Guan; Chenchen Yao; Yiying Wu (S375-S378).
► Series hydropower exploitation disrupt riverine DIC cycling. ► Hypoliminion introduction for hydropower lead to discontinuity of water chemistry. ► Deep water released from reservoir can cause CO2 evasion.Two reservoirs in series in a Karst area were investigated in this study to understand the impact of river damming on riverine C cycling. Monthly sampling strategy was performed in Hongfeng and Baihua reservoirs, from July, 2007 to June, 2008. DIC and its isotopic compositions were determined. pCO2, and calcite saturation index (SIc) were then calculated. Results show that δ13C-DIC in surface water of these reservoirs responded clearly to the transformation between photosynthesis and respiration, which also changes the inorganic C equilibrium. Based on monthly monitoring data, the major biogeochemical processes along the water column in these reservoirs, was also discussed. It is noted that hypoliminion introduction for hydropower generation and then release can lead to the discontinuity of water chemistry along a river course, and has adverse effects on the downstream environment.

Global sediment fluxes to the Earth’s coastal ocean by James P.M. Syvitski (S373-S374).
► Sediment load is determined by drainage area, relief, climate and geology. ► Sediment yield decreases with increasing size of the basin. ► Human activities can strongly increase or decrease a river’s effective load. ► Human activities can pre-condition river making them susceptible to climate events.A river’s sediment load is influenced by the rates of chemical and physical erosion within the drainage basin. These erosion rates are in turn influenced by the location of a river basin (geography), the geological and tectonic setup conditions, and the magnitude and vector of human influence. Scaling analysis is an important tool for understanding this magnitude and variability of a river’s load.

Does runoff or temperature control chemical weathering rates? by Eydis Salome Eiriksdottir; Sigurdur Reynir Gislason; Eric H. Oelkers (S346-S349).
► The rate chemical weathering is affected by both temperature and runoff. Separating out these two factors is challenging because runoff tends to increase with increasing temperature. ► In this study, natural river water samples collected on basaltic catchments over a five year period are used together with experimentally derived dissolution rate model for basaltic glass to pull apart the effects of runoff and temperature. ► This study shows that the rate of chemical denudation is controlled by both temperature and runoff, but is dominated by runoff.The rate of chemical denudation is controlled by both temperature and runoff. The relative role of these two factors in the rivers of NE Iceland is determined through the rigorous analysis of their water chemistry over a 5-a period. River catchments are taken to be analogous to laboratory flow reactors; like the fluid in flow reactors, the loss of each dissolved element in river water is the sum of that of the original rainwater plus that added from kinetically controlled dissolution and precipitation reactions. Consideration of the laboratory determined dissolution rate behaviour of basalts and measured water chemistry indicates that the maximum effect of changing temperature on chemical denudation in the NE Icelandic rivers was 5–25% of the total change, whereas that of runoff was 75–95%. The bulk of the increased denudation rates with runoff appear to stem from an increase in reactive surface area for chemical weathering of catchment solids.

Identification of hydrologic and geochemical pathways using high frequency sampling, REE aqueous sampling and soil characterization at Koiliaris Critical Zone Observatory, Crete by Daniel Moraetis; Fotini Stamati; Manolis Kotronakis; Tasoula Fragia; Nikolaos Paranychnianakis; Nikolaos P. Nikolaidis (S101-S104).
► Identification of hydrological and geochemical pathways within a complex watershed. ► Water increased N-NO3 concentration and E.C. values during flash flood events. ► Soil degradation and impact on water infiltration within the Koiliaris watershed. ► Analysis of Rare Earth Elements in water bodies for identification of karstic water.Koiliaris River watershed is a Critical Zone Observatory that represents severely degraded soils due to intensive agricultural activities and biophysical factors. It has typical Mediterranean soils under the imminent threat of desertification which is expected to intensify due to projected climate change. High frequency hydro-chemical monitoring with targeted sampling for Rare Earth Elements (REE) analysis of different water bodies and geochemical characterization of soils were used for the identification of hydrologic and geochemical pathways. The high frequency monitoring of water chemical data highlighted the chemical alterations of water in Koiliaris River during flash flood events. Soil physical and chemical characterization surveys were used to identify erodibility patterns within the watershed and the influence of soils on surface and ground water chemistry. The methodology presented can be used to identify the impacts of degraded soils to surface and ground water quality as well as in the design of methods to minimize the impacts of land use practices.

Age of river basins in Guadeloupe impacting chemical weathering rates and land use by Sétareh Rad; Olivier Cerdan; Karine Rivé; Gilles Grandjean (S123-S126).
The Lesser Antilles have very high chemical weathering rates, with values that can reach 1290 t/km2/a. The tropical environment induces high precipitation rates, high temperature, dense vegetation, with sharp relief and thick soils. Because of volcanic activity, frequent pyroclastic flows produce very erodible and porous materials. In addition, agriculture induces important land use changes which replace existing native forest cover with banana and sugar cane plantations. Their surface can cover as much as 40% of the total area of a river basin. The aim of this study is to identify key parameters, either natural or anthropogenic, that control chemical weathering rates. Among the combined impact of all parameters (climate, runoff, slopes, vegetation etc.), basin age seems to be the control parameter: the younger the basin, the higher the weathering rate. A correlation between the chemical weathering rate and the basin age suggests that young volcanic rocks are more easily weathered than old ones: young fresh material is easily mobilized by erosion, while for older rocks with thick soil covers, chemical rates are much lower. A combined effect between the higher erodibility and a higher climate erosivity of the younger relief could be observed. Moreover, a correlation between banana plantations and the chemical weathering rates that can be explained by an increase of infiltration, due to stem flow processes is shown here. Banana plantations also have a correlation with the basin age, older basins being more favorable terrains for cultivation.

Elemental and mineralogical changes in soils due to bioturbation along an earthworm invasion chronosequence in Northern Minnesota by Kathryn Resner; Kyungsoo Yoo; Cindy Hale; Anthony Aufdenkampe; Alex Blum; Stephen Sebestyen (S127-S131).
Minnesota forested soils have evolved without the presence of earthworms since the last glacial retreat. When exotic earthworms arrive, enhanced soil bioturbation often results in dramatic morphological and chemical changes in soils with negative implications for the forests’ sustainability. However, the impacts of earthworm invasion on geochemical processes in soils are not well understood. This study attempts to quantify the role of earthworm invasion in mineral chemical weathering and nutrient dynamics along an earthworm invasion chronosequence in a sugar maple forest in Northern Minnesota. Depth and rates of soil mixing can be tracked with atmospherically derived short lived radioisotopes 210Pb and 137Cs. Their radioactivities increase in the lower A horizon at the expense of the peak activities near the soil surface, which indicate that soil mixing rate and its depth reach have been enhanced by earthworms. Enhanced soil mixing by earthworms is consistent with the ways that the vertical profiles of elemental and mineralogical compositions were affected by earthworm invasion. Biologically cycled Ca and P have peak concentrations near the soil surface prior to earthworm invasion. However, these peak abundances significantly declined in the earthworm invaded soils presumably due to enhanced soil mixing. It is clear that enhanced soil mixing due to earthworms also profoundly altered the vertical distribution of most mineral species within A horizons. Though the mechanisms are not clear yet, earthworm invasion appears to have contributed to net losses of clay mineral species and opal from the A horizons. As much as earthworms vertically relocated minerals and elements, they also intensify the contacts between organic matter and cations as shown in the increased amount of Ca and Fe in organically complexed and in exchangeable pools. With future studies on soil mixing rates and elemental leaching, this study will quantitatively and mechanically address the role of earthworms in geochemical evolution of soils and forests’ nutrient dynamics.

Is silt the most influential soil grain size fraction? by S.A. Parry; M.E. Hodson; E.H. Oelkers; S.J. Kemp (S119-S122).
► Contribution of grain size fractions to bulk soil surface area and reactivity. ► Influence of amorphous and free Fe oxides phases on soil surface area. ► 63–2 μm fraction may be the most influential for soil elemental release rates.The contribution of individual grain size fractions (2000–500, 500–250, 250–63, 63–2 and < 2 μm) to bulk soil surface area and reactivity is discussed with reference to mineralogical and oxalate and dithionite extractions data. The 63–2 μm fraction contributed up to 56% and 67% of bulk soil volume and BET surface area, respectively. Consideration of these observations and the mineralogy of this fraction suggest that the 63–2 μm fraction may be the most influential for the release of elements via mineral dissolution in the bulk soil.

Silicon isotopes in allophane as a proxy for mineral formation in volcanic soils by S. Opfergelt; R.B. Georg; K.W. Burton; R. Guicharnaud; C. Siebert; S.R. Gislason; A.N. Halliday (S115-S118).
► The fate of dissolved Si in volcanic soils strongly depends on Al availability. ► Lighter δ30Si ratios in allophane relative to the basalt reflect weathering processes. ► Heavier δ30Si ratios in allophane indicate Si precipitation as Al is humus-complexed. ► Allophane δ30Si ratios could be useful in paleo-environmental reconstruction.Weathering of basaltic ash in volcanic areas produces andosols, rich in allophane and ferrihydrite. Since the rate of mineral formation is very useful in climate and geochemical modelling, this study investigates Si isotope compositions of allophane as a proxy for mineral formation. Allophane formed in contrasting conditions in five Icelandic soil profiles displays silicon isotope signatures lighter than the basalt in less weathered soils (−0.64 ± 0.15‰), and heavier in more weathered organic-rich soils (+0.23 ± 0.10‰). The fate of the dissolved Si in those volcanic soils strongly depends on Al availability. In organic-rich soils, most of Al is humus-complexed, and the results support that Si precipitates as opaline silica by super-saturation, leaving an isotopically heavier dissolved Si pool to form allophane with uncomplexed Al. This study highlights that Si isotopes can be useful to record successive soil processes involved in mineral formation, which is potentially useful in environmental paleo-reconstruction.

Many etch-pits on olivine grains occur as a pair of cone-shaped pits sharing a base, which consequently appear as diamond-shaped etch-pits in cross-section. Quantitative image analysis of back-scattered electron images establishes empirical dimensions of olivine etch-pits in naturally weathered samples from Hawaii and North Carolina. Images of naturally etched olivine were acquired from polished thin-sections by scanning electron microscopy. An average cone-radius-to-height ratio (r:h) of 1.78 was determined for diamond-shaped cross-sections of etch-pits occurring in naturally weathered olivine grains, largely consistent with previous qualitative results. Olivine etch-pit shape as represented by r:h varies from slightly more than half the average value to slightly more than twice the average. Etch-pit shape does not appear to vary systematically with etch-pit size.

Seasonal dynamics of CO2 profiles across a soil chronosequence, Santa Cruz, California by Marjorie Schulz; David Stonestrom; Guntram Von Kiparski; Corey Lawrence; Carrie Masiello; Art White; John Fitzpatrick (S132-S134).
► Soil CO2 concentrations and CO2 efflux were measured in a marine terrace soil chronosequence. ► The argillic horizon, causes a two-tier soil gas profile in the older terrace soils. ► Above the argillic horizon seasonal variations in soil CO2 occurred. ► Soils with an argillic horizons maintain a year round ∼1 %CO2 below the argillic horizon. ► The CO2 efflux during the growing season is higher on the older terraces.Concentrations of CO2 in soil atmosphere and CO2 efflux were measured across a marine terrace soil chronosequence near Santa Cruz, California. Soil development, specifically the formation of an argillic horizon, has created a two-tier soil gas profile in the older terrace soils. The soil above the argillic horizon has seasonal variations in soil CO2 associated with plant respiration. The older soils with dense argillic horizons maintain a year round ∼1%CO2 below the argillic horizon. The CO2efflux during the growing season is higher on the older terraces.

► Newly discovered paleosols. ► Indicate a seasonal paleoclimate. ► Suggests role of paleotopography.Paleosol (fossilized soil) geochemistry can provide a record of paleoclimatic conditions due to the relationships between pedogenic processes and climate. In this study, paleosols from the late Paleocene Goler Formation of Southern California were used to determine the paleoclimatic conditions active during pedogenesis. The enrichment and retention of soluble elements (Ca, Mg and Na) and the mobilization of Fe and Mn within the paleosol profiles suggest a climate with strongly seasonal precipitation. Similarly, variations in the Mn content and δ13C ratio of pedogenic carbonate nodules also reflect seasonal precipitation. Regional paleotopography was likely an important control on the paleoclimate of the Goler Formation due to rain shadow effects. Although the size and location of these ancient mountains are poorly constrained, the identification of climatic effects specifically associated with these variables provides new constraints.

► At our field site, most meteoric 10Be remains in the uppermost decimeters of soil. ► Meteoric 10Be inventories suggest that ridge top soils are Holocene. ► Meteoric 10Be inventories suggest a ridge top erosion rate of 19.4 m/Ma. ► The downslope increase in 10Be suggests relatively slow downslope transport of soil.This study seeks to quantify the rate and timing of regolith generation in the Critical Zone at the Susquehanna Shale Hills Critical Zone Observatory (SSHO). Meteoric 10Be depth profiles were determined using measurements from 30 hillslope soil and bedrock core samples in an effort to constrain 10Be inventories. The SSHO is located in the temperate climate zone of central Pennsylvania and comprises a first-order watershed developed entirely on a Fe-rich, organic-poor, Silurian-aged shale. Two major perturbations to the landscape have occurred at SSHO in the geologically recent past, including significant and sustained periglacial activity until after the retreat of the Laurentide ice sheet (∼21 ka) and deforestation during early colonial land-use. Bulk soil samples (n  = 16) were collected at three locations along a planar hillslope on the southern ridge of the catchment, representing the ridge top, mid-slope and valley floor. Rock chip samples (n  = 14) were also collected from a 24 m deep core drilled into the northern ridge top. All meteoric 10Be concentration profiles show a declining trend with depth, with most of the 10Be retained in the uppermost decimeters of the soil. Meteoric 10Be inventories are higher at the mid-slope and valley floor sample sites, at 3.71 ± 0.02 × 1010  at/cm2 and 3.69 ± 0.02 × 1010  at/cm2, than at the ridge top site (1.90 ± 0.01 × 1010  at/cm2). The 10Be inventory at the convex ridge top site implies a minimum residence time of ∼10.6 ka, or if erosion is steady, an erosion rate of 19.4 ± 0.2 m/My.

Evolution of hillslope soils: The geomorphic theater and the geochemical play by Kyungsoo Yoo; Beth Weinman; Simon Marius Mudd; Martin Hurst; Mikael Attal; Kate Maher (S149-S153).
► We ask “how and how fast do hillslope soils form as the landscape’s morphology changes over time?”. ► Over wide range of denudation rates, soil thicknesses do not vary significantly. ► Colluvial soils with lower denudation rates (above the knick point) are enriched in fine size fractions, Zr, and pedogenic crystalline Fe oxides. ► In the two steep hillslopes below the knickpoint, no systematic topgraphic trends were found for soil geochemistry. ► Soils show increasing Zr enrichment in the downslope direction only in the hillslope above the knickpoint.How and how fast do hillslope soils form as the landscape’s morphology changes over time? Here results are shown from an ongoing study that simultaneously examines the morphologic and geochemical evolution of soil mantled hillslopes that have been exposed to distinctively different denudation history. In Northern Sierra Nevada, California, the authors are investigating a tributary basin to the Middle Fork Feather River. A major incision signal from the river is well marked in a knickpoint within the tributary basin which stretches from its mouth to the Feather River at an elevation of ∼700 m to the plateau at an elevation of ∼1500 m. Hillslopes are significantly steeper below the knickpoint. The area’s total denudation rates are currently being constrained using cosmogenic radio nuclides, but a previous study suggested an order of magnitude difference in total denudation rates below and above the knickpoint. When compared with topographic attributes calculated from LIDAR data, physical erosion rates can be modeled as a linear function of ridge top curvature. Surprisingly, over the wide range of total denudation rates, soil thicknesses do not vary significantly until a threshold point where soil mantled landscapes abruptly shift to bedrock dominated landscapes. Bioturbation by tree falls appear to buffer soil thickness over the wide range of physical soil erosion rates. From three hillslopes with different physical erosion rates, the concentrations of Zr, which were considered conserved during dissolution and leaching, were determined and used as a proxy for the degree of mass losses via chemical denudation. There is a general trend that colluvial soils along the hillslopes with lower physical erosion rates are enriched in fine size fractions, Zr, and pedogenic crystalline Fe oxides. Likewise, the saprolites show greater degrees of chemical denudation at the sites above the knickpoint, presumably because of the saprolites’ longer turnover time in the slowly eroding landscapes. In the two steep hillslopes below the knickpoint, no significant or systematic topgraphic trends were found for soil geochemistry. However, soils show increasing Zr enrichment in the downslope direction in the hillslope above the knickpoint, which suggests a critical denudation rate beyond which soils’ turnover time is too short to develop a geochemical catena. As detailed CRN-based soil production rates and catchment scale denudation rates are acquired, the data will be combined with a mass balance model to calculate the rates of chemical denudation and weathering in soils and saprolites along the denudation gradient.

The subalpine to montane zones within the Critical Zone (CZ) of the Colorado Front Range, USA outside Pleistocene glaciation limits are characterized by the abundance of stratified and multilayered slope deposits exhibiting depths >1 m. Initial luminescence dating for the upper sediment layers in different profiles give last glacial ages ranging between 40 and 12 ka. A periglacial origin by solifluction is hypothesized for these slope deposits, which is corroborated by geomorphic and sedimentologic parameters. The stratified slope sediments have a strong influence on the physical and chemical properties as well as on soil forming processes in the CZ. Examples are provided for the sediment derived contribution of some elements and common clay minerals together and the great importance of slope sediments as barriers and pathways for the interflow that runs in sediment layers are shown.

Food webs and ecosystem services during soil transformations by Jeroen P. van Leeuwen; Lia Hemerik; Jaap Bloem; Peter C. de Ruiter (S142).
► Soil food web development along chronosequences. ► Food web diversity and stability. ► Food web and soil formation.

► Archive Borehole logs describe thickness of soil over sandstone outcrop (750 km2) in UK. ► Median soil depth is approx. 1.7m. ► Chemical weathering profile is similar through soil and saprolite to depths of 3m. ► Carbonate and gypsum cement removed leaving only clay cement. ► Active zone development responsible for breaking clay cement and producing soil thicknessThe work examines the chemical and physical processes that are likely to have contributed to forming the soil thickness across the Sherwood Sandstone outcrop in Nottinghamshire, England, UK. The similarity in the extent of chemical weathering across the interface of the loosely compacted sand that forms the soil and regolith and the non-durable rock underneath suggests that physical weathering processes are required as the final part of the weathering process, essential to breaking the clay cement that maintains the structural integrity of the non-durable rock. With prior knowledge that the outcrop was the input point for water currently in the aquifer with ages between 10 and 35,000 a, periglacial processes such as ‘frost cracking’ and ‘active zone development’ are considered major influences on soil thickness.

Exploring weathering and regolith transport controls on Critical Zone development with models and natural experiments by Suzanne P. Anderson; Robert S. Anderson; Eve-Lyn S. Hinckley; Patrick Kelly; Alex Blum (S3-S5).
► Different slope aspects provide natural experiments to explore controls on weathering. ► N-facing slopes in Gordon Gulch show deeper rock weathering. ► Modeled higher intensity weathering on N-facing slopes explains this pattern.The architecture of the Critical Zone, including mobile regolith thickness and depth to the weathering front, is first order controlled by advance of a weathering front at depth and transport of sediment at the surface. Differences in conditions imposed by slope aspect in the Gordon Gulch catchment of the Boulder Creek Critical Zone Observatory present a natural experiment to explore these interactions. The weathering front is deeper and saprolite more decayed on north-facing than on south-facing slopes. Simple numerical models of weathering front advance, mobile regolith production, and regolith transport are used to test how weathering and erosion rates interact in the evolution of weathered profiles. As the processes which attempt are being made to mimic are directly tied to climate variables such as mean annual temperature, the role of Quaternary climate variation in governing the evolution of Critical Zone architecture can be explored with greater confidence.