Applied Geochemistry (v.63, #C)

Uranium fate in Hanford sediment altered by simulated acid waste solutions by Brandy N. Gartman; Nikolla P. Qafoku; James E. Szecsody; Ravi K. Kukkadapu; Zheming Wang; Dawn M. Wellman; Michael J. Truex (1-9).
Infiltration of aqueous acidic waste to the subsurface may induce conditions that alter contaminant transport. Experiments were conducted to examine the effects of low pore water pH and associated changes to sediment properties on U(VI) behavior in sediments. Macroscopic batch experiments were combined with a variety of bulk characterization studies (Mössbauer and laser spectroscopy), micron-scale inspections (μ-XRF), and molecular scale interrogations (XANES) with the objectives to: 1) determine the extent of U(VI) partitioning to Hanford sediments exposed to acidic waste simulants and held at pH = 2, pH = 5, or under neutral conditions (pH = 8) at varying ionic strength, and in the presence of air [bench-top (BT) experiments] or in the absence of air [glove-box (GB) experiments]; and 2) determine the uranium micron-scale solid phase and associated valence state resulting from the experimental conditions. The investigation showed minimal overall changes in Fe mineralogy as a result of sediment exposure to acid solutions, but an increase in the highly reactive nano Fe fraction of the sediment. Greater uranium partitioning was observed at pH = 5 than at pH = 2 and 8. The μ-XRF inspections and XANES analyses confirmed that high concentration areas on sediment surfaces were rich in U(VI) in the BT experiments, and both U(IV) and U(VI) in the GB experiments. The laser spectroscopy data showed that uranyl phosphates {e.g., metaautunite [Ca(UO2)2(PO4)2·10–12H2O] and phosphuranylite [KCa(H3O)3(UO2)7(PO4)4O4·8H2O]} may have formed in the BT experiments. In the GB experiments, in addition to U(IV) phases, U(VI) phases may have also formed similar to those that are naturally present in the sediment, but at higher concentrations. The results provide insights about U(VI) mobility beneath acidic waste disposal sites.
Keywords: Uranium; Uranium contamination; Uranium sorption; Acid conditions; Hanford sediments;

Identification of spatio-seasonal hydrogeochemical characteristics of the unconfined groundwater in the Red River Delta, Vietnam by Thuy Thanh Nguyen; Akira Kawamura; Thanh Ngoc Tong; Hideo Amaguchi; Naoko Nakagawa; Romeo Gilbuena; Duong Du Bui (10-21).
Groundwater has been the primary source of daily water supplies for people living in the Red River Delta, the second largest delta in Vietnam. For this reason, identification of hydrogeochemical properties of the groundwater is indispensable for sustainable utilization of groundwater sources. In this study, the spatio-seasonal hydrogeochemical characteristics of groundwater in the unconfined aquifer of the Red River Delta have been investigated by systematically applying self-organizing maps (SOM) and Gibbs diagrams. The groundwater chemistry dataset used in the analysis is composed of eight major dissolved ions (i.e., Ca2+, Mg2+, Na+, K+, HCO 3 − , Cl, SO 4 2 − , and CO 3 2 − ) and total dissolved solids that are collected from 47 groundwater monitoring wells within the study area during the dry and rainy seasons. The SOM application classified the hydrogeochemical data into five clusters, which revealed three basic representative water types: high salinity (one cluster), low salinity (two clusters), and freshwater (two clusters). The spatial distribution of clusters and water types were identified. In particular, the low-salinity type was found not only in the downstream area but also in the northeastern parts of the upstream and middle-stream areas, where the groundwater was mainly classified into one specific cluster, in which agricultural activities were considered to influence groundwater chemistry. Cluster changes from the dry to rainy seasons were detected in approximately one-fifth of the observations wells. Dilution by surface water may significantly affect the chemical characteristics of the unconfined aquifer during the rainy season. Based on Gibbs diagrams, rock weathering was found to be the main process in the evolution of chemical composition of freshwater type, whereas the chemical structure of the low- and high-salinity types was primarily controlled by saltwater intrusion or anthropogenic activities.
Keywords: Hydrogeochemistry; Groundwater; Self-organizing maps; Unconfined aquifer; The Red River Delta;

REE concentrations in agricultural soil in Sweden and Italy: Comparison of weak MMI® extraction with near total extraction data by M. Sadeghi; S. Albanese; G. Morris; A. Ladenberger; M. Andersson; C. Cannatelli; A. Lima; B. De Vivo (22-36).
Rare Earth Element (REE) concentrations in agricultural soil obtained from the Mobile Metal Ion (MMI®) weak extraction technique are compared with soil total concentrations (sodium peroxide fusion followed by acid dissolution) for 118 and 174 agricultural soil samples from Italy and Sweden, respectively. Spatial distribution maps and statistics for both analytical techniques are compared between the two national datasets. In spite of similarity of REE concentration in two countries, the median values of REE is higher than Italy but extreme concentration of REE in Italy is due to young volcanic activities. Extractability of REEs is significantly higher in Swedish soils than in Italian soils. Heavy Rare Earth Element (HREE) in Sweden show higher concentrations compared to Italy in MMI® extraction data where correlate with REE mineralisation. Principal Component Analysis (PCA) is used to elucidate correlations and anomalies in the REE distribution. Results show that there is a clear correlation between REE anomalies and natural factors such as lithology of the underlying bedrock, the presence of mineralisations, pH of soils, climate and precipitation. According to the PCA results, anomalous behaviour of Eu, Ce, Tb and Gd can be explained by the dominant mineralogy of the parent material and the variable affinity of REEs to bind to clay minerals and clay-size particles.
Keywords: REE; Italy; Sweden; Weak MMI® extraction; Near total concentration;

Unconventional natural gas production in the Marcellus and Utica formations of the Northeastern United States raises concerns about potential impacts to shallow groundwater. We examined and interpreted 13,040 analyses from pre-drilling groundwater samples from domestic water wells in northeastern (NE) Pennsylvania and 8004 samples from water wells in the “Western Area” which includes southwest Pennsylvania, eastern Ohio, and north-central West Virginia. These samples were acquired on behalf of Chesapeake Energy Corporation as part of its local pre-drilling water supply monitoring program. We evaluated concentrations of major ions and metals relative to federal drinking-water-quality standards upon which regulatory decisions are often based. Chesapeake’s dataset, the most comprehensive for these areas, shows that exceedance of at least one water-quality standard occurs in 63% of water well samples in NE Pennsylvania and 87% in the Western Area. In NE Pennsylvania, 10% of the samples exceeded one or more of the United States Environmental Protection Agency’s (USEPA) primary maximum contaminant levels (MCLs) for drinking-water supplies, 46.1% of the samples exceeded one or more of USEPA secondary maximum contaminant levels (SMCLs), and another 7% exceeded one or more of USEPA health advisory or regional screening levels for tap water.In the Western Area 8% of samples exceeded one or more MCLs, 65% exceeded one or more SMCLs, and 15% exceeded one or more health advisory or regional screening levels for tap water. Chesapeake’s dataset, orders of magnitude larger than any in previously published literature, shows that water-quality exceedances relate to factors such: as where the sample occurs within the groundwater flow system, the natural groundwater chemical type (hydrochemical facies), the geologic unit producing the water, and/or the topographic position (valley versus upland). Our comparison of these results to historical groundwater data from NE Pennsylvania, which pre-dates most unconventional shale gas development, shows that the recent pre-drilling geochemical data is similar to historical data. We see no broad changes in variability of chemical quality in this large dataset to suggest any unusual salinization caused by possible release of produced waters from oil and gas operations, even after thousands of gas wells have been drilled among tens of thousands of domestic wells within the two areas studied. Our evaluation also agrees with early researchers such as Piper (1933) and Lohman (1939, 1937) who found that the saline waters in both areas underlie fresher groundwater. The saline water is naturally-occurring connate brine or salt water which has not been flushed by circulating meteoric water; rather than vertical migration of salt water from deep strata such as the Marcellus shale as suggested by Warner et al. (2012). Elevated metals concentrations, particularly iron and manganese, partly relate to sample turbidity; dissolved metals would provide a more accurate measurement of metals in shallow groundwater than does the total metals analysis typically required by regulations.

Topographic controls on the depth distribution of soil CO2 in a small temperate watershed by Elizabeth A. Hasenmueller; Lixin Jin; Gary E. Stinchcomb; Henry Lin; Susan L. Brantley; Jason P. Kaye (58-69).
Accurate measurements of soil CO2 concentrations (pCO2) are important for understanding carbonic acid reaction pathways for continental weathering and the global carbon (C) cycle. While there have been many studies of soil pCO2, most sample or model only one, or at most a few, landscape positions and therefore do not account for complex topography. Here, we test the hypothesis that soil pCO2 distribution can predictably vary with topographic position. We measured soil pCO2 at the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO), Pennsylvania, where controls on soil pCO2 (e.g., depth, texture, porosity, and moisture) vary from ridge tops down to the valley floor, between planar slopes and slopes with convergent flow (i.e., swales), and between north and south-facing aspects. We quantified pCO2 generally at 0.1–0.2 m depth intervals down to bedrock from 2008 to 2010 and in 2013. Of the variables tested, topographic position along catenas was the best predictor of soil pCO2 because it controls soil depth, texture, porosity, and moisture, which govern soil CO2 diffusive fluxes. The highest pCO2 values were observed in the valley floor and swales where soils are deep (≥0.7 m) and wet, resulting in low CO2 diffusion through soil profiles. In contrast, the ridge top and planar slope soils have lower pCO2 because they are shallower (≤0.6 m) and drier, resulting in high CO2 diffusion through soil profiles. Aspect was a minor predictor of soil pCO2: the north (i.e., south-facing) swale generally had lower soil moisture content and pCO2 than its south (i.e., north-facing) counterpart. Seasonally, we observed that while the timing of peak soil pCO2 was similar across the watershed, the amplitude of the pCO2 peak was higher in the deep soils due to more variable moisture content. The high pCO2 observed in the deeper, wetter topographic positions could lower soil porewater pH by up to 1 pH unit compared to porewaters equilibrated with atmospheric CO2 alone. CO2 is generally the dominant acid driving weathering in soils: based on our observations, models of chemical weathering and CO2 dynamics would be improved by including landscape controls on soil pCO2.Display Omitted
Keywords: Carbon dioxide; Soil atmosphere; Topographic position; Chemical weathering; Carbon cycle;

Field experiments were conducted over a 460-day period to assess the efficiency of different mixtures of organic substrates to remediate coalmine-generated acid mine drainage (AMD). Five pilot-scale, flow-through bioreactors containing mixtures of herbaceous and woody organic substrates along with one control reactor containing only limestone were constructed at the Tab-Simco site and exposed to AMD in situ . Tab-Simco is an abandoned coal mine near Carbondale, Illinois that produces AMD with pH ∼2.5 and notably high average concentrations of SO4 (5050 mg/L), Fe (950 mg/L), Al (200 mg/L), and Mn (44 mg/L). Results showed that the sequestration of SO4 and metals was achieved in all reactors; however, the presence and type of organic carbon matrix impacted the overall system dynamics and the AMD remediation efficiency. All organic substrate-based reactors established communities of sulfate reducing microorganisms that contributed to enhanced removal of SO4, Fe, and trace metals (i.e., Cu, Cd, Zn, Ni) via microbially-mediated reduction followed by precipitation of insoluble sulfides. Additional mechanisms of contaminant removal were active in all reactors and included Al- and Fe-rich phase precipitation and contaminant surface sorption on available organic and inorganic substrates. The organic substrate-based reactors removed more SO4, Fe, and Al than the limestone-only control reactor, which achieved an average removal of ∼19 mol% SO4, ∼49 mol% Fe, 36 mol% Al, and 2 mol% Mn. In the organic substrate-based reactors, increasing herbaceous content correlated with increased removal efficiency of SO4 (26–35 mol%), Fe (36–62 mol%), Al (78–83 mol%), Mn (2–6 mol%), Ni (64–81 mol%), Zn (88–95 mol%), Cu (72–85 mol%), and Cd (90–92 mol%), while the diversity of the intrinsic microbial community remained relatively unchanged. The extrapolation of these results to the full-scale Tab-Simco treatment system indicated that, over the course of a 460-day period, the predominantly herbaceous bioreactors could remove up to 92,500 kg SO4, 30,000 kg Fe, 8,950 kg Al, and 167 kg Mn, which represents a 18.3 wt%, 36.8 wt%, 4.1 wt% and 82.3 wt% increase in SO4, Fe, Al, and Mn, respectively, removal efficiency compared to the predominantly ligneous bioreactors.The results imply that anaerobic organic substrate bioreactors are promising technologies for remediation of coal-generated AMD and that increasing herbaceous content in the organic substrate matrix can enhance contaminant sequestration. However, in order to improve the remediation capacity, future designs must optimize not only the organic carbon substrate but also include a pretreatment phase in which the bulk of dissolved Fe/Al-species are removed from the influent AMD prior to entering the bioreactor because of 1) seasonal variations in temperature and redox gradients could induce dissolution of the previously formed redox sensitive compounds, and 2) microbially-mediated sulfate reduction activity may be inhibited by the excessive precipitation of Al- and Fe-rich phases.Display Omitted
Keywords: Acid mine drainage; Passive treatment bioreactor; Bioremediation; Bacterial sulfate reduction; Abandoned coal mine;

Tellurium is usually present at very low concentrations in environmental samples, which makes it a challenging element to measure in complex matrices. It exists mainly as Te(IV) and Te(VI) in natural waters and geological samples and its geochemistry is often compared to that of selenium, its upper neighbor in the periodic table of the elements. More than 145 papers that are related to tellurium in freshwaters, marine and estuarine systems, soils and sediments and air particulate maters, as well as various analytical techniques associated to this element, have been reviewed. Concentrations of total dissolved tellurium in open oceans are usually less than 2 ng/L (∼16 pM) and can increase by approximately one order of magnitude in non polluted freshwaters. Most tellurium compounds are considered toxic. Except from samples collected close to sources of contamination, tellurium concentrations in soils and sediments are normally at the low ppb (μg/g) level. In tellurium speciation studies, pre-concentration steps are often required in the analytical protocols. In fact very few studies have reported tellurium speciation in solid samples. Total tellurium reported in studies on aerosols and air particulates is usually below the ng/m3.
Keywords: Tellurium; Natural waters; Soils; Sediments; Air particulates; Speciation;

Modeling past and present activity of a subarctic hydrothermal system using O, H, C, U and Th isotopes by A.I. Malov; I.N. Bolotov; O.S. Pokrovsky; S.B. Zykov; I.V. Tokarev; Kh.A. Arslanov; S.V. Druzhinin; A.A. Lyubas; M.Y. Gofarov; I.A. Kostikova; V.V. Kriauciunas; S.B. Chernov; F.E. Maksimov; Yu.V. Bespalaya; O.V. Aksenova (93-104).
The hot springs of the Pymvashor subarctic hydrothermal system are of considerable interest because the area is devoid of recent volcanism and is located in the permafrost region. We attempted to evaluate the activity of thermal waters with respect to host rocks to quantify the water residence time in this system and date the associated travertine. Therefore, we used the chemical composition of the thermal waters, thermodynamic modeling, δ18O and δ2H labels and isotopes, such as 14C–δ13C, 234U–238U, and 230Th–232Th. The δ18O and δ2H values indicated the infiltration of atmospheric water in the recharge area of the hydrothermal system and suggested a stable paleoclimate in the area over the last 5–7.9 thousand years. The fresh water flows through deep parts of the aquifer system where it mixes with brine followed by discharge. The hot springs geothermal water total dissolved solid (TDS) ranged from 1.8 to 2 g/L, and in the deep wells, the TDS ranged from 7.1 to 198 g/L. The ratios of Na/Cl (mol), Br/10−3Cl (ppm), and Ca/Cl (ppm) in the thermal springs ranged from 0.89 to 0.90, 1.8 to 1.9, and close to 0.12, respectively, reflecting participation of deep brines in their formation. The composition of the thermal water can be formed via a mixture of one part of the brines with 130 parts of the cold water end member with a TDS of 291 mg/L. The results of thermodynamic modeling and mixing diagram analysis indicate that during water–rock interaction in the aquifer, the precipitation of calcite and the dissolution of gypsum and magnesite were accompanied by hydrolysis of the sodium aluminosilicates with precipitating clay secondary minerals. The low uranium concentration in the Pymvashor groundwater (0.24–0.34 ppb) and the sufficiently long water residence time combined with the relatively high 234U/238U activity ratios (3–5) suggest a high α recoil loss and low dissolution rates of the host rocks or a high precipitation rate and adsorption of uranium. The elevated values of the α recoil loss may be due to radioactive decay of the precipitated and adsorbed 238U because in this case, the probability of 234Th release and 234U appearance in water increases ∼4-fold compared to the probability of emission directly from the rock. The 14C age of the water was estimated to be between 4960 and 7870 years, and the 230Th/U age of the travertine ranged from 1970 to 7650 years. Overall, these results allow for a better understanding of the nature and evolution of the thermal waters in this unique subarctic hydrothermal system.Display Omitted
Keywords: Groundwater dating; Radiocarbon; Travertine; Uranium and thorium isotopes;

The major ionic and dissolved inorganic carbon (DIC) concentrations and the stable carbon isotope composition of DIC (δ13CDIC) were measured in a freshwater aquifer contaminated by produced water brine with petroleum hydrocarbons. Our aim was to determine the effects of produced water brine contamination on the carbonate evolution of groundwater. The groundwater was characterized by three distinct anion facies: HCO3 -rich, SO4 2−-rich and Cl-rich. The HCO3 -rich groundwater is undergoing closed system carbonate evolution from soil CO2(g) and weathering of aquifer carbonates. The SO4 2−-rich groundwater evolves from gypsum induced dedolomitization and pyrite oxidation. The Cl-rich groundwater is contaminated by produced water brine and undergoes common ion induced carbonate precipitation. The δ13CDIC of the HCO3 -rich groundwater was controlled by nearly equal contribution of carbon from soil CO2(g) and the aquifer carbonates, such that the δ13C of carbon added to the groundwater was −11.6‰. In the SO4 2−-rich groundwater, gypsum induced dedolomitization increased the 13C such that the δ13C of carbon added to the groundwater was −9.4‰. In the produced water brine contaminated Cl-rich groundwater, common ion induced precipitation of calcite depleted the 13C such that the δ13C of carbon added to the groundwater was −12.7‰. The results of this study demonstrate that produced water brine contamination of fresh groundwater in carbonate aquifers alters the carbonate and carbon isotopic evolution.
Keywords: Produced water brine; Dissolved inorganic carbon; Stable carbon isotopes; Carbonate evolution;

Crystallization behavior of NaNO3–Na2SO4 salt mixtures in sandstone and comparison to single salt behavior by Nadine Lindström; Nicole Heitmann; Kirsten Linnow; Michael Steiger (116-132).
We report on the crystallization behavior and the salt weathering potential in natural rock and porous stone of single salts (NaNO3, Na2SO4) and salt mixtures in the ternary NaNO3–Na2SO4–H2O system. Geochemical modeling of the phase diagram of the ternary NaNO3–Na2SO4–H2O system was used to determine the equilibrium pathways during wetting (or deliquescence) of incongruently soluble minerals and evaporation of mixed electrolyte solutions. Experiments were carried out in order to study the phase changes during dissolution either induced by deliquescence or by the addition of liquid water. In situ Raman spectroscopy was used to study the phase transformations during wetting of pure Na2SO4 (thenardite) and of Na3NO3SO4·H2O (darapskite). In both experiments crystallization of Na2SO4·10H2O (mirabilite) from highly supersaturated solutions is demonstrated confirming the high salt weathering potential of thenardite and darapskite wetting. In order to study the damage potential of darapskite experimentally, wetting–drying experiments with porous sandstone with the two single salts (Na2SO4, NaNO3) and two NaNO3–Na2SO4 salt mixtures were carried out. Different destructive and non-destructive techniques were tested for damage monitoring. NaNO3 was found to be the least damaging salt and Na2SO4 is the most damaging one. The classification of the two salt mixtures was less obvious.
Keywords: Salt weathering; Incongruently soluble double salts; Darapskite; Geochemical modeling; Raman microscopy; Salt crystallization; Crystallization pressure;

Flood zone biogeochemistry of the Ob River middle course by S.N. Vorobyev; O.S. Pokrovsky; S.N. Kirpotin; L.G. Kolesnichenko; L.S. Shirokova; R.M. Manasypov (133-145).
The flood zone of the Ob River, the largest (in watershed area) river of the Arctic Ocean basin, is tens of km wide and, after the Amazon's Varzea, is the world's second largest flooding territory. To better understand the biogeochemistry of the Ob River and adjacent surface waters, we studied, in May and July 2014, the dissolved and colloidal organic carbon and trace metals in small rivers, lakes, and flooded water bodies connected and disconnected with the mainstream as well as the Ob River itself. All major and trace elements were distributed among two major categories depending on their pattern of dependence on the dissolved organic carbon (DOC) concentration. Dissolved inorganic carbon (DIC), Na, Mg, Ca, sulfate, Sr, Mo, Sb and U exhibited a general decrease in concentration with the increase of the [DOC]. The lowest concentration of these elements was observed in DOC-rich humic, acidic (4.9 ≤ pH ≤ 6.1) upland lakes fed by surrounding bogs. These elements marked the influence of underground feeding in July during summer baseflow, which was most visible in flood lakes in the Ob riparian zone and the Ob River itself. In May, the flood lakes were statistically similar to the Ob River. The elevated concentration of DOC (up to 60 mg/L) in the upland lakes was not correlated with groundwater-related elements, suggesting a lack of significant groundwater feeding in these lakes. In contrast, insoluble, usually low mobile elements (Al, Fe, other trivalent hydrolysates, Ti, Zr, Hf) and some metals (Cr, Zn, Ni, Pb) demonstrated a steady increase in concentration with increasing DOC, with the lowest values observed in the Ob River and the highest values observed in small tributaries and organic-rich upland lakes in July. It follows that these elements are limited by their main carriers – organic and organo-ferric colloids, rather than by the availability of the source, peat and mineral soil or plant litter. While for the majority of non-colloidal, groundwater-fed elements with high mobility (DIC, Na, Mg, Ca, K, Sr…) the small tributaries can be used as representatives of the Ob main stream, this is not the case for low mobility “insoluble” elements, such as Fe, Al, trivalent and tetravalent hydrolysates, and metal micronutrients (Cu, Zn, and Mn). The low soluble elements and divalent metals exhibited a much lower concentration in the river mainstream compared to that in the flood lakes, upland lakes and small rivers. This difference is significantly more pronounced in the baseflow in July compared to the spring flood in May. Presumably, autochthonous processes, such as the photo-oxidation and bio-oxidation of organo-ferric colloids and phytoplankton uptake are capable decreasing the concentration of these elements in the river mainstream.Display Omitted
Keywords: Siberia; Flood; Lakes; Rivers; Organic carbon; Metals; Colloids;

Geochemical and isotopic evidences for a severe anthropogenic boron contamination: A case study from Castelluccio (Arezzo, central Italy) by Stefania Venturi; Orlando Vaselli; Franco Tassi; Barbara Nisi; Maddalena Pennisi; Jacopo Cabassi; Gabriele Bicocchi; Luca Rossato (146-157).
In 2009 a deterioration of garden plants watered with domestic wells was related to high boron concentrations (up to 57 mg/L) measured in the shallow aquifer from the industrial area of Castelluccio (Tuscany, Italy), where several factories are or were using boron compounds for their industrial processes. Since 2012 a geochemical and isotopic survey of stream, ground and waste waters, and sediment samples was performed. In addition, monthly geochemical surveys were carried out from January to September 2013, during which concentrations of boron up to 139 mg/L were measured. The geochemical dataset also included raw (borax and sodium boron-hydride) and anthropogenic materials (B-rich slags and muds stored in one of the local factories), the latter being, to the best of our knowledge, analyzed for the first time in this work for bulk and leachate boron concentration and isotopic ratios. The results highlighted that the high concentrations of boron found in the local shallow aquifer had unequivocally an anthropogenic source. It was suggested that prolonged interaction between industrial (presently stored at ground level or buried) by-products and waste and meteoric waters was likely the main process responsible of the groundwater contamination as supported by the analysis of the major solutes. The dispersion of the contaminant could not clearly be observed downward the shallow hydrogeological circuit. Consequently, the presence of other sources of boron in the industrial area of Castelluccio cannot be excluded. This would also explain the reason why no univocal results were obtained by the 11B/10B isotopic ratios measured in water, sediment and (bulk and leachate) anthropogenic samples.To minimize the boron contamination a hydraulic barrier should be constructed where the highest concentrations of boron were measured.
Keywords: Boron; Anthropogenic contamination; Boron isotopes; Arezzo; Water chemistry;

Induced mobility of inorganic and organic solutes from black shales using water extraction: Implications for shale gas exploitation by Franziska D.H. Wilke; Andrea Vieth-Hillebrand; Rudolf Naumann; Jörg Erzinger; Brian Horsfield (158-168).
The study reported here evaluates the degree to which metals, salt anions and organic compounds are released from shales by exposure to water, either in its pure form or mixed with additives commonly employed during shale gas exploitation. The experimental conditions used here were not intended to simulate the exploitation process itself, but nevertheless provided important insights into the effects additives have on solute partition behaviour under oxic to sub-oxic redox conditions.In order to investigate the mobility of major (e.g. Ca, Fe) and trace (e.g. As, Cd, Co, Mo, Pb, U) elements and selected organic compounds, we performed leaching tests with black shale samples from Bornholm, Denmark and Lower Saxony, Germany. Short-term experiments (24 h) were carried out at ambient pressure and temperatures of 100 °C using five different lab-made stimulation fluids. Two long-term experiments under elevated pressure and temperature conditions at 100 °C/100 bar were performed lasting 6 and 2 months, respectively, using a stimulation fluid containing commercially–available biocide, surfactant, friction reducer and clay stabilizer.Our results show that the amount of dissolved constituents at the end of the experiment is independent of the pH of the stimulation fluid but highly dependent on the composition of the black shale and the buffering capacity of specific components, namely pyrite and carbonates. Shales containing carbonates buffer the solution at pH 7–8. Sulphide minerals (e.g. pyrite) become oxidized and generate sulphuric acid leading to a pH of 2–3. This low pH is responsible for the overall much larger amount of cations dissolved from shales containing pyrite but little to no carbonate. The amount of elements released into the fluid is also dependent on the residence time, since as much as half of the measured 23 elements show highest concentrations within four days. Afterwards, the concentration of most of the elemental species decreased pointing to secondary precipitations. Generally, in our experiments less than 15% of each analysed element contained in the black shale was mobilised into the fluid.
Keywords: Unconventional gas; Black shales; Stimulation fluids; Element mobility; Batch experiments;

Partitioning of organic matter in Boom Clay: Leachable vs mobile organic matter by D. Durce; C. Bruggeman; N. Maes; L. Van Ravestyn; G. Brabants (169-181).
Boom Clay (BC) is considered in Belgium as a potential host rock for nuclear waste disposal. The formation contains up to 5 wt% of natural organic matter and the presence of dissolved organic matter (DOM) may have a strong impact on radionuclide mobility. However, due to physical constraints, only a fraction of DOM is mobile through the BC layer and the extent of DOM-facilitated radionuclide transport is controlled by the distribution of OM over the mobile and immobile pools. In this work, we investigate 1/the concentration and the size distribution of leachable organic matter in BC, 2/the variability along the BC layer of the concentration and the size distribution of mobile DOM, 3/the parameters controlling the concentration and the size distribution of the leachable OM pool and of the mobile OM pool. Size exclusion chromatography with UV detection at 280 nm is chosen as the reference technique. The UV response of BC DOM is investigated as a function of MW. In pore waters, i.e for mobile DOM, the SUVA280 is dependent on the OM size/MW with the lowest value measured for low MW species (<1 kDa). The use of dynamic light scattering permits to also estimate the hydrodynamic radius (RH) distribution of BC DOM. In the investigated part of BC, the concentration of mobile DOM represents only 0.15 ± 0.8% of the total organic matter content (TOC) and is mostly <20 kDa (RH < 2.8 nm). In contrast, the OM leached from solid samples is dominated by species with MW > 50 kDa and RH > 5.3 nm and accounts for about 12 TOC%. While the concentration of the leachable OM pool is mostly controlled by the TOC content of the rock and to a lower extent by the hydrogen index of the kerogen, the mineralogy plays a significant role in the concentration and the size distribution of the mobile DOM. Filtration and sorption are promoted by clay minerals that preferentially preserves large organic species and leave only small species mobile in pore waters. Inversely, coarser minerals like silt and/or sand facilitate the transport of DOM and increase both the concentration and the MW/RH of the mobile species. The threshold of 20 kDa (RH = 2.8 nm) is considered as a cut-off over which DOM species are hardly mobile in BC. A large part of OM is showed insoluble or immobile but the distribution of OM over the mobile and immobile/insoluble pools, characterised by an average K d ¯ of 140 L kg−1 is found to rather favour the transport of radionuclides than to act as an additive sorbent phase.
Keywords: Size exclusion chromatography; Nuclear waste; Humic substances; Groundwater;

Dissolved helium concentrations and 3He/4He ratios were measured for 18 groundwater samples collected from the Quaternary confined aquifers in the North China Plain (NCP). The dissolved helium concentrations ranged from 1 × 10−7 to 1 × 10−6 cm3STP·g−1 in the 14 samples from the central plain, but was approximately two orders of magnitude higher, between 6 × 10−6 and 9 × 10−5 cm3STP·g−1, in 4 samples from the coastal plain. Based on these concentrations and the corresponding 3He/4He ratios varying from 0.09 to 0.55 Ra (where Ra is the 3He/4He ratio of air), the dissolved helium in groundwater in the central plain was identified to be primarily a mixture of atmospheric helium with radiogenic helium and a representative radiogenic helium ratio was estimated to be 0.035 Ra. Despite the high fraction of terrigenic 4He in the samples from the coastal plain, their 3He/4He ratios were found to be significantly above this radiogenic value, ranging between 0.20 and 0.37 Ra, indicating the presence of a mantle-derived He component in this area. About 2–4% mantle helium was estimated to be present in the groundwater of the coastal plain, which probably is associated with the regional Cangdong fault and tectonic activities. Based on the radiogenic He component, 4He ages of the groundwater in the central plain were calculated by assuming either pure in situ production or an external helium flux J0 of 4.7 × 10−8 cm3STPcm−2a−1. The estimated 4He ages fall between 9.5 and 51.4 ka and are comparable to the 14C ages, suggesting that the results of 4He dating are reasonable and can be an effective tool to estimate groundwater residence times under suitable conditions.
Keywords: Groundwater dating; Helium; Mantle helium; Confined aquifer; Noble gases;

Use of lithium tracers to quantify drilling fluid contamination for groundwater monitoring in Southeast Asia by Laura A. Richards; Daniel Magnone; Bart E. van Dongen; Christopher J. Ballentine; David A. Polya (190-202).
Drilling is widely used in groundwater monitoring and many other applications but has the inherent problem of introducing some degree of external contamination into the natural systems being monitored. Contamination from drilling fluid is particularly problematic for (i) wells with relatively low water flow rates which are difficult to flush; and for (ii) hydrogeochemical research studies of groundwaters hosted by incompletely consolidated shallow sediments, which are widely utilized as sources of drinking water and irrigation water across many parts of Asia. Here, we develop and evaluate a method that can be simply used to quantify the extent of drilling fluid contribution to a water sample either to optimize sample collection for reduced contamination, or to allow a correction for contamination to be made. We report the utility of lithium chloride tracers using both field and laboratory analytical techniques to quantitatively evaluate and correct for drilling fluid contamination of casing waters through an investigation of 15 sites in Kandal Province, Cambodia. High analytical errors limit the practicality and resolution of field-based lithium ion selective electrode measurements for purposes other than broad estimates of gross contamination. However, when laboratory analysis is integrated with the method (e.g. via inductively coupled plasma atomic emission spectrometry analysis), lithium tracers can provide a robust and accurate method for evaluating drilling-related contamination if appropriate samples are collected. Casing water is susceptible to contamination from drilling fluid which was shown to be significantly reduced within two to three well volumes of flushing but can still persist above background for greater than seven well volumes of flushing. A waiting period after drilling and prior to water sampling was shown to further decrease contamination due to dilution from the surrounding aquifer, particularly in more permeable wells. Contamination values were generally <3% for 34 monitoring wells across 15 sites after flushing a mean of 4.6 ± 3.8 well volumes, even when lithium-spiked water was directly injected during flushing to remove settled mud/debris. Operational issues can be encountered which can (i) lead to contamination being much higher than the mean if wells are highly unproductive and clay-dominated or (ii) lead to higher flushing volumes than the mean particularly in sandy areas where fine sand may enter the well screening. General correction factors have been provided for typical monitoring wells in poorly consolidated shallow aquifers in Southeast Asia, and examples provided for how to correct other groundwater data for contamination. For most analytes such as sodium or dissolved organic carbon (DOC), specific corrections may not be necessary for the typical magnitude of contamination encountered, particularly when the differences in concentrations between the drilling fluid and groundwater are relatively small. In the particular circumstance where drilling fluid may have much higher DOC than groundwaters, or vice versa with drilling fluid having much lower DOC than groundwaters in organic-rich alluvial sediments, corrections may still be necessary and significant. Similarly, for highly sensitive parameters such as 14C model age or other age-related parameters (such as tritium, chlorofluorocarbons (CFCs) or sulfur hexafluoride (SF6)), corrections can be significant in typical field scenarios particularly when contamination values are high and/or there is a large difference in age between groundwater and drilling fluid. The lithium method was verified with comparison to changes in concentration of a suite of representative and naturally occurring groundwater constituents as a function of well flushing from relatively low and high permeability groundwater monitoring wells to further illustrate the technique.
Keywords: Chemical tracers; Lithium; Drilling fluid; Groundwater; Monitoring well contamination;

Cr(VI) occurrence and geochemistry in water from public-supply wells in California by John A. Izbicki; Michael T. Wright; Whitney A. Seymour; R. Blaine McCleskey; Miranda S. Fram; Kenneth Belitz; Bradley K. Esser (203-217).
Hexavalent chromium, Cr(VI), in 918 wells sampled throughout California between 2004 and 2012 by the Groundwater Ambient Monitoring and Assessment-Priority Basin Project (GAMA-PBP) ranged from less than the study reporting limit of 1 microgram per liter (μg/L) to 32 μg/L. Statewide, Cr(VI) was reported in 31 percent of wells and equaled or exceeded the recently established (2014) California Maximum Contaminant Level (MCL) for Cr(VI) of 10 μg/L in 4 percent of wells. Cr(VI) data collected for regulatory purposes overestimated Cr(VI) occurrence compared to spatially-distributed GAMA-PBP data. Ninety percent of chromium was present as Cr(VI), which was detected more frequently and at higher concentrations in alkaline (pH ≥ 8), oxic water; and more frequently in agricultural and urban land uses compared to native land uses. Chemical, isotopic (tritium and carbon-14), and noble-gas data show high Cr(VI) in water from wells in alluvial aquifers in the southern California deserts result from long groundwater-residence times and geochemical reactions such as silicate weathering that increase pH, while oxic conditions persist. High Cr(VI) in water from wells in alluvial aquifers along the west-side of the Central Valley results from high-chromium in source rock eroded to form those aquifers, and areal recharge processes (including irrigation return) that can mobilize chromium from the unsaturated zone. Cr(VI) co-occurred with oxyanions having similar chemistry, including vanadium, selenium, and uranium. Cr(VI) was positively correlated with nitrate, consistent with increased concentrations in areas of agricultural land use and mobilization of chromium from the unsaturated zone by irrigation return.
Keywords: Groundwater; Chromium; Trace elements; Drinking water; California;

Persistent U(IV) and U(VI) following in-situ recovery (ISR) mining of a sandstone uranium deposit, Wyoming, USA by T.J. Gallegos; K.M. Campbell; R.A. Zielinski; P.W. Reimus; J.T. Clay; N. Janot; John R. Bargar; William M. Benzel (222-234).
Drill-core samples from a sandstone-hosted uranium (U) deposit in Wyoming were characterized to determine the abundance and distribution of uranium following in-situ recovery (ISR) mining with oxygen- and carbon dioxide-enriched water. Concentrations of uranium, collected from ten depth intervals, ranged from 5 to 1920 ppm. A composite sample contained 750 ppm uranium with an average oxidation state of 54% U(VI) and 46% U(IV). Scanning electron microscopy (SEM) indicated rare high uranium (∼1000 ppm U) in spatial association with P/Ca and Si/O attributed to relict uranium minerals, possibly coffinite, uraninite, and autunite, trapped within low permeability layers bypassed during ISR mining. Fission track analysis revealed lower but still elevated concentrations of U in the clay/silica matrix and organic matter (several 10 s ppm) and yet higher concentrations associated with Fe-rich/S-poor sites, likely iron oxides, on altered chlorite or euhedral pyrite surfaces (but not on framboidal pyrite). Organic C (<1.62%), total S (<0.31%), and P (<0.03%) were in low abundance relative to the overall bulk composition. Microbial community analysis showed a diverse group of bacteria present with a wide range of putative metabolisms, and provides evidence for a variety of redox microenvironments co-existing in core samples. Although the uranium minerals persisting in low permeability areas in association with organic carbon were less affected by oxidizing solutions during mining, the likely sequestration of uranium within labile iron oxides following mining and sensitivity to changes in redox conditions requires careful attention during groundwater restoration.Display Omitted
Keywords: Uranium; In-situ recovery; ISR; Uranium mining; Sandstone-hosted uranium deposit; Groundwater restoration;

Unsaturated zone pore water has the potential to record history of recharge, palaeoenvironment, pollution movement and water-rock interaction as it percolates through and moves towards the water table. In this study, two 6-m cores from the Badain Jaran desert (NW China) were collected to explore this potential using directly extracted moisture. Pore waters in these unsaturated zone sediments (1–5% moisture by wet weight) were directly extracted using immiscible liquid displacement and then analysed for major anions, cations and trace elements. Results show enrichment in pore water chemistry in the top 1–2 m where strong temperature and moisture fluxes occur. The enrichment in cations relative to chloride is primarily due to silicate mineral dissolution during infiltration. High nitrate and low iron concentrations indicate the overall oxidizing environment, which allows the mobility of oxyanions, such as uranium, arsenic and chromium. The trace elements show enrichment in the upper zone of fluctuation where chemical gradients are strong, but with lesser reaction lower in the profile. The calculated groundwater recharge rates using the chloride mass balance are negligible in this arid region between 1.5 and 3.0 mm/year. The modern rainfall infiltration signature contrasts with that of the underlying groundwater body, which has a distant, regional recharge signature.This reconnaissance study demonstrates the potential for a new geochemical approach to studying geochemical processes in the unsaturated sediments in semi-arid environments due to both natural and human influences. The use of directly extracted water, rather than extraction by dilution (elutriation), facilitates an improved understanding of hydrological and geochemical processes in the unsaturated zone and into the capillary fringe at the water table, because it avoids potential chemical changes induced during elutriation.
Keywords: Unsaturated zone; Pore waters; Immiscible liquid; Geochemical processes; Chemical tracers;

Whether carbonate weathering could produce a stable carbon sink depends primarily on the utilization of dissolved inorganic carbon (DIC) by aquatic phototrophs (the so-called Biological Carbon Pump-BCP effect). On this basis, water temperature (T), pH, electrical conductivity (EC) and dissolved oxygen (DO) were synchronously monitored at 15-min resolution for one and two days respectively in January and October 2013 in Maolan Spring and the spring-fed midstream and downstream ponds in Maolan Nature Reserve, China. A thermodynamic model was used to link the continuous data to allow calculation of CO2 partial pressures (pCO2) and calcite saturation indexes (SIC). A floating static chamber was placed on the water surface successively at all sites to quantify CO2 exchange flux between atmosphere and water so as to evaluate the BCP effect. Results show that, in both winter and autumn, remarkable diel variations of hydrochemical parameters were present in the midstream pond where DO, pH, and SIC increased in the day and decreased during the night while EC, [ HCO 3 − ] , [Ca2+] and pCO2 showed inverse changes mainly due to the metabolic processes of the flourishing submerged plants, with photosynthesis dominating in the day and respiration dominating at night. However, hydrochemical parameters in the spring and downstream pond show less change since few submerged plants developed there. It was determined that the BCP effect in the midstream pond was 285 ± 193 t C km−2 a−1 in winter and 892 ± 300 t C km−2 a−1 in autumn, indicating a potential significant role of terrestrial aquatic photosynthesis in stabilizing the carbonate weathering-related carbon sink.
Keywords: Karst surface waters; Diel hydrochemical variations; Underwater photosynthesis; Carbon sequestration; CO2 emission; Carbonate weathering;

Oxygen kinetic isotope effects in selenate during microbial reduction by Alexandra E.P. Schellenger; Annalisa Onnis-Hayden; Deb P. Jaisi; Philip Larese-Casanova (261-271).
The redox cycling of selenium oxyanions, elemental selenium, and selenides within water resources has implications for Se bioavailability and ecotoxicity. Dual stable isotope analysis of Se and O may provide important information for interpreting environmental Se transformations. Stable Se isotope systematics within the Se redox cycle has been well characterized within the literature, however concomitant oxygen isotope composition requires additional investigation. This study reports the O isotope fractionation of selenate ( SeO 4 2 − ) during microbial reduction by the dissimilatory Se-reducing bacterium Sulfurospirillum barnesii SES-3. Microbial reduction experiments were conducted under various conditions in order to investigate the range of 18O enrichment factors (εO) in selenate. The reduction of selenate to selenite coupled to the oxidation of lactate to acetate resulted in an 18O kinetic isotope effect with εO values 1.5–5.8‰. Greater 18O enrichment was observed with increasing pH, but no correlation was found between εO and reduction rates, lactate availability, or cell density. εO values from biotic reduction by S. barnesii here are significantly less than those observed for abiotic reduction with Fe(II)-rich minerals reported in the literature, and this difference could be explained by a diffusion limitation during enzymatic reduction. Our results expand the isotope systematics of the selenium redox cycle and suggest εO has potential usefulness as indicators for in situ selenate reduction.
Keywords: Selenium; Reduction; Oxygen isotope ratios; Kinetic isotope effect; Dissimilatory selenium reduction; Sulfurospirillum barnesii SES-3;

To obtain a better understanding of the source compositions of the river sediments around the Yellow Sea and their relationship with source rocks, elements and strontium-neodymium (Sr–Nd) isotopes of different grain-sizes (silt and clay populations) and chemical (labile and residual phases) fractionations in riverine sediments were studied extensively. These results clearly revealed a systematic compositional disparity between Korean river (KR) and Chinese river (CR) sediments, especially in the residual (detrital) fraction. The geochemical dissimilarity between these might reflect inherited signatures of their source rocks but with minor control from chemical weathering. In particular, the remarkable enrichment of some elements (iron (Fe) and magnesium (Mg)) and the behavior of large ion lithophile elements (e.g., barium (Ba), potassium (K) and Sr) during weathering as well as less-radiogenic Sr isotopic compositions implies that CR sediments might be weathering products of relatively more mafic rocks, with abundant ferromagnesian and plagioclase feldspar minerals, compared with KR sediments derived from silicic granites with relatively higher quartz and potassium feldspar contents. This different petrological rationale is clearly evident in an A–CN–K diagram, which estimated the source rock of CR sediments as granodioritic, a composition that reflects accurately the average composition of weathered continental crust in China. The recognition of such geochemical systematics in two river sediments, especially in grain-size and chemically partitioned data, may contribute to the establishment of provenance tracers for the Yellow Sea and East China Sea sediments with multi-sources as well the dust deposition in the western Pacific.
Keywords: Elemental compositions; Sr–Nd isotopes; Sediment origin; Silicate weathering; Yellow Sea;

Iodine is an essential element in the human diet and a deficiency can lead to a number of health outcomes collectively termed iodine deficiency disorders (IDD). The geochemistry of iodine is dominated by its volatility with volatilisation of organo-iodine compounds and elemental iodine from biological and non-biological sources in the oceans being a major component of its global cycle. As a result of the dominant oceanic source, iodine is strongly enriched in near-coastal soils, however, the major zone of marine influence generally stretches to only 50–80 km inland and terrestrial sources of volatilised iodine, from wetlands, soils and plants are also an important aspect of its global geochemical cycle. Iodine in soils is strongly bound with transfer factors from soil to plants being generally small and as a consequence there is only limited uptake of iodine through the plant root system. It is likely that uptake of atmospheric iodine by the aerial parts of plants is an essential process and, along with iodine deposited on plant surfaces, is a major source for grazing animals. Human intake of iodine is mainly from food with some populations also obtaining appreciable quantities of iodine from drinking water. Plant-derived dietary iodine is generally insufficient as evidenced from the low dietary iodine of strict vegan diets. Seafood provides major iodine-rich dietary items but other inputs are mainly from adventitious sources, such as the use of iodised salt and from dairy produce, which is a rich source mainly due to cattle-feed being fortified with iodine, and to the use of iodine-containing sterilants in the dairy industry. While the distribution and geochemistry of iodine are reflected in the global distribution of IDD, the recent upsurge of IDD in developed countries would seem to reflect changes in diet.
Keywords: Iodine; Organo-iodine; Iodine deficiency disorders (IDD); Global cycling; Volatilisation; Dietary iodine;

Neptunium and manganese biocycling in nuclear legacy sediment systems by Clare L. Thorpe; Katherine Morris; Jonathan R. Lloyd; Melissa A. Denecke; Kathleen A. Law; Kathy Dardenne; Christopher Boothman; Pieter Bots; Gareth T.W. Law (303-309).
Understanding the behaviour of the highly radiotoxic, long half-life radionuclide neptunium in the environment is important for the management of radioactively contaminated land and the safe disposal of radioactive wastes. Recent studies have identified that microbial reduction can reduce the mobility of neptunium via reduction of soluble Np(V) to poorly soluble Np(IV), with coupling to both Mn- and Fe(III)- reduction implicated in neptunyl reduction. To further explore these processes Mn(IV) as δMnO2 was added to sediment microcosms to create a sediment microcosm experiment “poised” under Mn-reducing conditions. Enhanced removal of Np(V) from solution occurred during Mn-reduction, and parallel X-ray absorption spectroscopy (XAS) studies confirmed Np(V) reduction to Np(IV) commensurate with microbially-mediated Mn-reduction. Molecular ecology analysis of the XAS systems, which contained up to 0.2 mM Np showed no significant impact of elevated Np concentrations on the microbial population. These results demonstrate the importance of Mn cycling on Np biogeochemistry, and clearly highlight new pathways to reductive immobilisation for this highly radiotoxic actinide.
Keywords: Neptunium; Contaminated land; Biostimulation;

Nitrate contamination of shallow aquifers poses a major challenge in the development of sustainable agriculture, particularly in (semi-)arid regions, where groundwater is also used as potable water. In this study we estimate the relative contribution of the various nitrate sources contaminating the shallow aquifers underlying agricultural fields in the extremely arid region of the Central Arava Valley (CAV), southern Israel. The estimates are based on a chemical and isotopic mixing-reaction model describing the evolution of the δ18ONO3 and δ15NNO3 isotopic compositions from the sources to the aquifer. The model indicates that all fertilizers used in the agricultural fields: synthetic NO 3 − , synthetic NH 4 + and manure, contaminate the CAV groundwater with nitrate. In most of CAV groundwaters, the contribution of each fertilizer to the groundwater contamination is relative to its proportion in the fertilization scheme of the cultivated fields. Two exceptions of this general observation were found: 1. One field showed a direct nitrate contamination from a “leaking” sewage reservoir, as indicated by its exceptionally high δ15NNO3 value that reached 9.2‰; and 2. A very shallow alluvial aquifer, recharged by winter floods and not by the irrigation water, showed no nitrate isotopic “fingerprint” of manure, which is applied to the cultivated fields only during summer. Groundwater nitrate contamination is actuated by infiltration of irrigation water, which in addition underwent salinization as a result of evapo-transpiration in the cultivated fields. Based on the relatively uniform and depleted groundwater δ18OH2O compositions and the depleted δ18ONO3 values, within the possible range of fertilizers-derived nitrate as deduced by the model, the water-loss in the cultivated fields is transpiration-controlled.The isotope mixing-reaction model used here to identify the major nitrate contamination sources maybe used to help design a sustainable cultivation management strategy in similar arid regions. It can also be used to assess the fertilization efficiency and the relative impact of each fertilizer type. Such models may be particularly useful in evaluating highly heterogeneous and complicated aquifer systems, for which the formulation of absolute water and nitrate mass balances are impossible.Display Omitted
Keywords: Groundwater; Nitrate contamination; δ15N; δ18O; Arid regions; Fertilizers;

The Small Spring Method (SSM) for the definition of stable isotope–elevation relationships in Northern Calabria (Southern Italy) by Giovanni Vespasiano; Carmine Apollaro; Rosanna De Rosa; Francesco Muto; Salvatore Larosa; Jens Fiebig; Andreas Mulch; Luigi Marini (333-346).
A total of 141 samples mostly located in the Coastal Chain and the Sila Massif of Northern Calabria have been collected from 125 different springs and analyzed chemically and for the isotopic ratios 2H/1H and 18O/16O of water, with the ultimate aim to investigate isotope–elevation relationships for local meteoric waters. The Small Springs Method (SSM) has been adopted for this purpose. The hydrogeological characteristics of the watersheds of interest indicate that the sampled springs are discharged from water circuits hosted in alluvial and colluvial deposits rather than in the underlying rock substrata. The chemical characteristics of the sampled waters suggest that they are immature and related to shallow and short water circuits, in spite of the variable degree of chemical evolution. The spring waters of relatively high Total Ionic Salinity (TIS >12.5 meq/L) and those from watersheds of comparatively large elevation range (>650 m) and relatively large areas (>17 km2) have been excluded from the analysis of elevation–isotope relationships. An oxygen isotope lapse rate of −0.194 ‰/100 m has been found for the spring water samples of Northern Calabria as a whole, whereas the obtained hydrogen isotope lapse rates are −1.23 ‰/100 m for the Coastal Chain and −1.45 ‰/100 m for the Sila Massif based on measured isotope values and optimized elevation. The following O-isotopes equation is recommended to estimate the average elevation (H i in m) of the recharge areas of Northern Calabria aquifer systems: δ O 18 = − 0.00194 · H i − 5.91 (1)The maximum estimated uncertainty due to variations in the δ 18O value over time is 202 m. Use of H isotopes is not recommended for constraining average recharge elevations due to important local variations, reflecting in different relations for the Coastal Chain and the Sila Massif. Assuming that Equation (1) holds true throughout Northern Calabria, an iso-distribution map of the δ 18O value in rainfall has been drawn for this area.
Keywords: Small Springs Method (SSM); Oxygen isotopes; Hydrogen isotopes; Isotopic lapse rate; Northern Calabria;

Mining and mineral processing operations may generate a wide range of As-rich compounds including scorodite (FeAsO4·2H2O), a common secondary arsenate in near-surface environments and some gold mine tailings. Scorodite has a low solubility in a limited pH range, and it is relatively stable under near-surface conditions, but its behavior under the influence of bacteria is not well understood. Considering that reducing conditions are likely to develop in mine tailings with depth and under prolonged disposal conditions, the present study was undertaken to determine the influence of bacteria on the reductive dissolution of scorodite. Because the systematic studies on the microbial reduction of scorodite are lacking, we used two well characterized dissimilatory iron and arsenic reducing bacteria, i.e., Shewanella sp. ANA-3 and Shewanella putrefaciens CN32 in a chemically defined media, at circumneutral pH, containing various phosphate concentrations (i.e., 15, 40 and 400 μM). The initial rates of reduction and the plateau concentrations of reduced species formed in the aqueous phase were greater in the presence of Shewanella sp. ANA-3 than in the presence of Shewanella putrefaciens CN32. The initial rate of reduction was found to increase with increasing phosphate concentration, however, plateau concentrations of the dissolved reduced species, Fe(II) and As(III), formed in the aqueous phase were highest at the lowest phosphate concentration. The solid products of the post-reduction samples were characterized by synchrotron X-ray absorption spectroscopy (XAS) and powder X-ray diffraction (XRD), scanning, transmission and high resolution electron microscopy (SEM/TEM/HRTEM) and energy dispersive spectrometry (EDS). The results indicate that the post reduction solids contained scorodite, a biogenic ferrous arsenite and parasymplesite (Fe3(AsO4)2·8H2O). Phosphate concentrations had an effect on the concentrations of released Fe(II) and As (III) during the microbial reduction and the formation of secondary phases. The influence of bacteria on the reductive dissolution of scorodite must be taken into consideration during mine waste management and disposal operations because of the potential of arsenic releases to terrestrial and aquatic environments as toxic and soluble As(III) species.
Keywords: Scorodite; Arsenic; Iron; Bacteria; Mining; Reductive dissolution; Shewanella;

A new micro-fluidic method, which is known as the Micro-Reactor Simulated-Channel (MRSC) method, has been employed to rapidly determine the effective diffusion coefficients of lithium in three important representative low permeability lithologies including: Melechov granite (Czech Republic), Borrowdale tuff, and Land's End Cornish granite (both UK). The concept of MRSC is similar to the micro chemical reactor which enables fast measurements to be done on a small intact sample. The effective diffusion coefficients were measured and comparisons between the MRSC results and conventional column methods showed excellent agreement. Our measured effective diffusion coefficient for Melechov granite is 1.7 × 10−12 m2/s, directly comparable to previous conventional measurements. However the measurement time of the MRSC method is at least one order of magnitude faster than the conventional method and only requires small reaction volumes (as small as 10 ml). In addition, by exploiting the advantages of the MRSC method, the effects of velocity and concentration on diffusive transport for the two different UK rock types have also been investigated. Depending on flow rate and inlet tracer concentration, the effective diffusion coefficient for lithium in the Cornish granite ranges between 0.9 and 1.5 × 10−11 m2/s while that measured for the Borrowdale tuff varies between 1.2 and 1.6 × 10−11 m2/s.
Keywords: Diffusion; Granite; Micro-fluidic; Tuff; Permeability;

Rapid ikaite (CaCO3 ·6H2O) crystallization in a man-made river bed: Hydrogeochemical monitoring of a rarely documented mineral formation by Ronny Boch; Martin Dietzel; Peter Reichl; Albrecht Leis; Andre Baldermann; Florian Mittermayr; Peter Pölt (366-379).
During repository building measures a natural river was relocated and the water was directed through a new, artificial river bed lined with a concrete basement and local colluvium. Shortly after, centimetre-thick, beige-colored sinter-crusts were observed in the river bed. An environmental monitoring program launched in order to understand the rapid precipitation process revealed pH values up to 12.9 and high Ca2+ concentrations (196 mg/l) at near-freezing water-temperatures. A first set of crystal aggregates collected was found to disintegrate into a light-colored calcite powder at ambient temperature within few days only. Thus, the metastable precipitates were recovered in original solution and stored in a constantly-cooled refrigerator box. Immediate XRD, FT-IR and ESEM analyses revealed “ikaite” – calcium carbonate hexahydrate – being the rarely documented mineral never reported from such an environmental setting before. Ikaite typically forms in a narrow temperature range (<4–8 °C) from strongly supersaturated solutions, e.g. some specific lake-, sea- and spring-water mixing locations, Arctic- and Antarctic sea-ice. In the present case, enhanced portlandite (Ca[OH]2) dissolution from the concrete river basement by water inflowing during wintertime provided exceptional hydrochemical conditions suitable for rapid ikaite crystallization, e.g. of up to 2 kg d−1 m−2 in a particular stream section. Sampling sites from which ikaite was documented yielded pH > 11 probably reflecting some lower limit of ikaite formation. Our findings do not support nucleation inhibitors (aqueous phosphate, magnesium, organic constituents), strongly elevated ionic strength (brines), or water-mixing as a crucial demand for ikaite precipitation. In this “natural laboratory” distinct ikaite vs. calcite spatial distribution encountered along the stream, and thus the spatiotemporal evolution of fluid–solid interaction could be studied. Finally, the prominent and widespread ikaite precipitates vanished rapidly during pronounced springtime air- and water-temperature rise >6 °C superimposed on more gradual hydrochemical changes, e.g. decrease of pH and Ca2+. The latter development highlights the critical temperature restriction of ikaite occurrence and stability. Anthropogenic combined with natural hydrogeochemical processes observed in this study are of interest for both applied and fundamental environmental research.Display Omitted
Keywords: Ikaite; Hydrous calcium carbonate; Concrete leaching; Environmental monitoring; Portlandite; Rapid precipitation; CO2 absorption;

In CO2 geological storage (CGS) context, the evolution of the caprock sealing capacity has received increasing attention, particularly on a geological time span (thousands of years). At this time scale, geochemical reactions may enhance or weaken the caprock quality. It is widely recognized that, for the reservoir, geological heterogeneities affect the concentration and spatial distribution of CO2, and then affect the extent of gas–water–rock interactions, which in turn alters the hydrogeological properties of the reservoir. However, much less attention of these effects has been paid to the caprock. In this study, we presented and applied a novel approach to evaluate the effects of permeability and porosity heterogeneities on the alteration of minerals, the associated evolution of the caprock sealing efficiency and the containment of supercritical CO2 (scCO2) within the caprock. Even though this is a generic study, several conditions and parameters such as pressure, permeability, and mineral composition, were extracted from a caprock layer of the Shiqianfeng Formation in the Ordos Basin demonstration site in China. For the sake of simplification, a 2-dimensional model was designed to represent the caprock domain. We firstly generated an appropriate heterogeneous random field of permeability with the average permeability taken from the uppermost mudstone layer of the Shiqianfeng Formation, and then the heterogeneity in porosity was incorporated using a joint normal distribution method based on the available data. Homogeneous mineral compositions of the reservoir and caprock were used in all simulations. Simulations of three cases were performed, including a homogeneous case, a case with only permeability heterogeneity and a case with both permeability and porosity heterogeneities. The results demonstrate dramatic influences of permeability and porosity heterogeneities on the migration of scCO2 within the caprock, the alteration of minerals, and therefore the evolution of the caprock sealing quality. Specific to the data used in this study, hydrogeological heterogeneities facilitated the overall penetration of scCO2 within the caprock and promoted the alteration of minerals, thereby weakening the caprock sealing efficiency over the simulation time.
Keywords: CO2 geological storage; Heterogeneity; Caprock sealing efficiency; Mineral alteration; The Ordos Basin; Numerical simulation;

Evaluating natural and anthropogenic trace element inputs along an alpine to urban gradient in the Provo River, Utah, USA by Gregory T. Carling; David G. Tingey; Diego P. Fernandez; Stephen T. Nelson; Zachary T. Aanderud; Timothy H. Goodsell; Tucker R. Chapman (398-412).
Numerous natural and anthropogenic processes in a watershed produce the geochemical composition of a river, which can be altered over time by snowmelt and rainfall events and by built infrastructure (i.e., dams and diversions). Trace element concentrations coupled with isotopic ratios offer valuable insights to disentangle the effects of these processes on water quality. In this study, we measured a suite of 40+ trace and major elements (including As, Cd, Ce, Cr, Cs, Fe, La, Li, Mo, Pb, Rb, Sb, Se, Sr, Ti, Tl, U, and Zn), Sr isotopes (87Sr/86Sr), and stable isotopes of H and O (δD and δ18O) to investigate natural and anthropogenic processes impacting the Provo River in northern Utah, USA. The river starts as a pristine mountain stream and passes through agricultural and urban areas, with two major reservoirs and several major diversions to and from the river. We sampled the entire 120 km length of the Provo River at 13 locations from the Uinta Mountains to Utah Valley, as well as two important tributaries, across the range of hydrologic conditions from low flow to snowmelt runoff during the 2013 water year. We also sampled the furthest downstream site in the Utah Valley urban area during a major flood event. Trace element concentrations indicate that a variety of factors potentially influence Provo River chemistry, including inputs from weathering of carbonate/siliciclastic rocks (Sr) and black shales (Se and U), geothermal groundwater (As, Cs, Li, and Rb), soil erosion during snowmelt runoff (Ce, Cr, Fe, La, Pb, and Ti), legacy mining operations (Mo, Sb, and Tl), and urban runoff (Cr, Pb, and Zn). Although specific elements overlap between different groups, the combination of different elements together with isotopic measurements and streamflow observations may act as diagnostic tools to identify sources. 87Sr/86Sr ratios indicate a strong influence of siliciclastic bedrock in the headwaters with values exceeding 0.714 and carbonate bedrock in the lower reaches of the river with values approaching 0.709. δD and δ18O changed little throughout the year in the Provo River, suggesting that the river is primarily fed by snowmelt during spring runoff and snowmelt-fed groundwater during baseflow. Based on nonmetric multidimensional scaling (NMS) water chemistry was unique across the upper, middle, and lower portions of the river, with high temporal variability above the first reservoir but minimal temporal variability below the reservoir. Thus, the results show that dams alter water chemistry by allowing for settling of particle-associated elements and also by homogenizing inflows throughout the year to minimize dilution during snowmelt runoff. Taken together, trace element concentrations and isotopic measurements can be used to evaluate the complex geochemical patterns of rivers and their variability in space and time. These measurements are critical for identifying natural and anthropogenic impacts on river systems.
Keywords: Trace elements; Strontium isotopes; Urban runoff; Snowmelt; Nonmetric multidimensional scaling;

Bromine is a microelement present in waters, both in inorganic and in a wide range of organic compounds, though at lower concentrations. Typically, concentrations of organobromine compounds in waters are several orders of magnitude lower than of bromides. Two issues are addressed in the paper: the influence of bromides on the quality of treated waters and organobromines as contaminants of natural waters. Bromide presence in treated water gives rise to formation of potentially mutagenic disinfection by-products (DBPs). Registered amounts of DBPs in potable waters, exceeding the admissible levels, and the published data on DBPs in waters used for leisure and recreation activities, clearly indicate the health risk. Major sources are identified and registered concentrations of EDB, DBCB, methyl bromide, bromacil and PBDEs in the aquatic environment are summarized. The effects of bromide on DBPs formation and numerous examples of organobromine contamination of the aquatic environment indicate that the presence of bromides and organobromine compounds in the aquatic environment will have to be given more consideration, for several reasons. Firstly, larger amounts of bromide are present in saline and contaminated waters and the proportion of such waters being handled is increasing. Similarly, the processes of water purification, treatment and disinfection are now playing a major role. Secondly, emissions from manufacturing of bromine-containing materials growing, due to, inter alia, intensive development of the electronic industry and the plastic manufacturing sector. Thirdly, bromine compounds are also used as medicine ingredients. There is now a growing awareness of the presence of pharmaceuticals in the aquatic environment. Fourth, low bromide concentrations in hypergene zones may be modified in the future, partly because of the climate changes, which may give rise to difficulties with water treatment systems.Water quality standards having relevance to water used for consumption are based only on the best-known (most widespread) DBPs. However new more restrictive legal regulations relating to the use of bromine compounds have been put in place prohibiting the use of certain bromine-based substances or restricting their amount in finished products. In the light of current legislation, the monitoring of water contamination with potentially toxic, mutagenic and endocrine-disrupting organobromine compounds is still unsatisfactory because newly discovered compounds are not included and certain factors governing the exposure to those substances are still left out.The effects of bromine (bromide and organobromine compounds) on water quality have been investigated by researchers from several fields of expertise. The water management authorities ought to make use of the available research data and identify the problems which need to be addressed directly and those which may emerge in the future.Display Omitted
Keywords: Bromine; Bromide; Organobromine compounds; Occurrence in aquatic environment; Water quality;

Boron geochemistry from some typical Tibetan hydrothermal systems: Origin and isotopic fractionation by Wenjie Zhang; Hongbing Tan; Yanfei Zhang; Haizhen Wei; Tao Dong (436-445).
The Tibetan plateau is characterized by intense hydrothermal activity and abnormal enrichment of trace elements in geothermal waters. Hydrochemistry and B isotope samples from geothermal waters in Tibet were systematically measured to describe the fractionation mechanisms and provide constraints on potential B reservoirs. B concentrations range from 0.35 to 171.90 mg/L, and isotopic values vary between −16.57 ‰ and +0.52 ‰. Geothermal fields along the Indus-Yarlung Zangbo suture zone and N–S rifts are observed with high B concentrations and temperatures. The similar hydrochemical compositions of high-B geothermal waters with magmatic fluid and consistent modeling of B isotopic compositions with present δ11B values imply that the B in high-B geothermal waters is mainly contributed by magmatic sources, probably through magma degassing. In contrast, geothermal fields in other regions of the Lhasa block have relatively low B concentrations and temperatures. After considering the small fractionation factor and representative indicators of Na/Ca, Cl/HCO3, Na + K and Si, the conformity between modeling results and the isotopic compositions of host rocks suggests that the B in low-temperature geothermal fields is mainly sourced from host rocks. According to simulated results, the B in some shallow geothermal waters not only originated from mixing of cold groundwater with deep thermal waters, but it was also contributed by equilibration with marine sedimentary rocks with an estimated proportion of 10%. It was anticipated that this study would provide useful insight into the sources and fractionation of B as well as further understanding of the relationships between B-rich salt lakes and geothermal activities in the Tibetan plateau.
Keywords: The Tibetan plateau; Geothermal fields; Boron isotopes; Isotopic fractionation; Boron source;

Hydrochemistry and biogeochemistry of tropical small mountain rivers by Steven T. Goldsmith; Ryan P. Moyer; Russell J. Harmon (453-455).
Keywords: Small mountainous rivers; Tropics; Hydrochemistry; Biogeochemistry;

River water chemistry of Pambar River Basin (PRB), draining a rain shadow region of the southern Western Ghats, India, with granite gneiss and hornblende-biotite-gneiss lithology, was monitored for three sampling seasons, such as monsoon (MON), post-monsoon (POM) and pre-monsoon (PRM) to ascertain the spatio-temporal trends in hydrochemistry. In PRB, upstream and downstream areas have differing climate (i.e., tropical-wet–dry/humid upstream, while semi-arid downstream) and land use (plantations and farmland dominate the upstream, while pristine forest environment covers the downstream). The hydrochemical attributes, except pH and K+, exhibit distinct temporal variation mainly due to monsoon-driven climatic seasonality. Relative abundance of cations between upstream and downstream samples of PRB shows noticeable differences, in that the upstream samples follow the order of abundance: Ca2+  > Mg2+  > Na+  > K+, while the downstream samples are in the order: Na+  > Mg2+  > Ca2+  > K+. Ca2+  + Mg2+/Na+  + K+, Si/Na+  + K+, Cl/Na+ and HCO3 /Ca2+ ratios suggest multiple sources/processes controlling hydrochemistry, e.g., atmospheric supply, silicate weathering, dissolution of carbonate minerals and soil evaporites as well as anthropogenic inputs (domestic and farm/plantation residues). Even though weathering of silicate and carbonate minerals is the major hydrochemical driver in both upstream and downstream portions of PRB, Gibbs diagram and scatter plot of Mg2+/Na+ vs. Mg2+/Ca2+ imply the importance of evaporation in the downstream hydrochemistry. Piper diagram and partial pressure of CO2 (pCO2) values suggest that a groundwater dominated discharge exerts a significant control on the downstream hydrochemistry, irrespective of sampling season. Although spatial variability of rainfall in PRB shows a linear downstream (decreasing) trend, the best-fit model for the dissolved load suggests that the downstream hydrochemical variability in PRB (i.e., an increasing trend) follows a power function ( f ( x ) = ax k ). This study suggests that climate has a significant role in the spatio-temporal variability of hydrochemistry in PRB.
Keywords: Hydrochemistry; Rain shadow rivers; Weathering; Downstream hydrochemical trend; Southern Western Ghats;

Two sides to every range: Orographic influences on CO2 consumption by silicate weathering by Brandon C. McAdams; Annette M. Trierweiler; Susan A. Welch; Carla Restrepo; Anne E. Carey (472-483).
The effect of an orographic rain shadow on CO2 consumption by silicate weathering (ØCO2, Si ) was examined in the Sierra de Las Minas, a mountain range in eastern Guatemala. This range is tall enough to intercept prevailing winds, leading to greater rainfall on the windward or north compared to the leeward or south side of the range. Water was collected from and discharge was measured for streams draining both the north and south sides of the Sierra de Las Minas. Water samples were analyzed for major ions and silica and this chemistry was used to interpret weathering inputs and calculate ØCO2, Si . The median ØCO2, Si in north side streams (260 × 103  mol CO2  km−2  yr−1) was roughly 3-fold greater than the median ØCO2, Si in south side streams (78 × 103  mol CO2  km−2  yr−1). This difference is similar to the 3-fold greater discharge measured for north side streams compared to south side streams of the same area. A positive linear relationship was observed between volumetric water yield (L s−1  km−2) and ØCO2, Si , supporting transport (i.e. precipitation) as the main factor controlling the differences observed between north and south side ØCO2, Si . Lithology and basin morphology differences had a negligible influence on ØCO2, Si patterns across the aspects of the range. These orographically induced differences in ØCO2, Si may increase with changing precipitation regimes in a warming climate.Display Omitted

Stable-isotope and solute-chemistry approaches to flow characterization in a forested tropical watershed, Luquillo Mountains, Puerto Rico by Martha A. Scholl; James B. Shanley; Sheila F. Murphy; Jane K. Willenbring; Marcie Occhi; Grizelle González (484-497).
The prospect of changing climate has led to uncertainty about the resilience of forested mountain watersheds in the tropics. In watersheds where frequent, high rainfall provides ample runoff, we often lack understanding of how the system will respond under conditions of decreased rainfall or drought. Factors that govern water supply, such as recharge rates and groundwater storage capacity, may be poorly quantified. This paper describes 8-year data sets of water stable isotope composition (δ 2H and δ 18O) of precipitation (4 sites) and a stream (1 site), and four contemporaneous stream sample sets of solute chemistry and isotopes, used to investigate watershed response to precipitation inputs in the 1780-ha Río Mameyes basin in the Luquillo Mountains of northeastern Puerto Rico. Extreme δ 2H and δ 18O values from low-pressure storm systems and the deuterium excess (d-excess) were useful tracers of watershed response in this tropical system. A hydrograph separation experiment performed in June 2011 yielded different but complementary information from stable isotope and solute chemistry data. The hydrograph separation results indicated that 36% of the storm rain that reached the soil surface left the watershed in a very short time as runoff. Weathering-derived solutes indicated near-stream groundwater was displaced into the stream at the beginning of the event, followed by significant dilution. The more biologically active solutes exhibited a net flushing behavior. The d-excess analysis suggested that streamflow typically has a recent rainfall component (∼25%) with transit time less than the sampling resolution of 7 days, and a more well-mixed groundwater component (∼75%). The contemporaneous stream sample sets showed an overall increase in dissolved solute concentrations with decreasing elevation that may be related to groundwater inputs, different geology, and slope position. A considerable amount of water from rain events runs off as quickflow and bypasses subsurface watershed flowpaths, and better understanding of shallow hillslope and deeper groundwater processes in the watershed will require sub-weekly data and detailed transit time modeling. A combined isotopic and solute chemistry approach can guide further studies to a more comprehensive model of the hydrology, and inform decisions for managing water supply with future changes in climate and land use.

Use of Sr isotopes as a tool to decipher the soil weathering processes in a tropical river catchment, southwestern India by G.P. Gurumurthy; K. Balakrishna; M. Tripti; Jean Riotte; Stéphane Audry; Jean-Jacques Braun; H.N. Udaya Shankar (498-506).
River water composition (major ion and 87Sr/86Sr ratio) was monitored on a monthly basis over a period of three years from a mountainous river (Nethravati River) of southwestern India. The total dissolved solid (TDS) concentration is relatively low (46 mg L−1) with silica being the dominant contributor. The basin is characterised by lower dissolved Sr concentration (avg. 150 nmol L−1), with radiogenic 87Sr/86Sr isotopic ratios (avg. 0.72041 at outlet). The composition of Sr and 87Sr/86Sr and their correlation with silicate derived cations in the river basin reveal that their dominant source is from the radiogenic silicate rock minerals. Their composition in the stream is controlled by a combination of physical and chemical weathering occurring in the basin. The molar ratio of SiO2/Ca and 87Sr/86Sr isotopic ratio show strong seasonal variation in the river water, i.e., low SiO2/Ca ratio with radiogenic isotopes during non-monsoon and higher SiO2/Ca with less radiogenic isotopes during monsoon season. Whereas, the seasonal variation of Rb/Sr ratio in the stream water is not significant suggesting that change in the mineral phase being involved in the weathering reaction could be unlikely for the observed molar SiO2/Ca and 87Sr/86Sr isotope variation in river water. Therefore, the shift in the stream water chemical composition could be attributed to contribution of ground water which is in contact with the bedrock (weathering front) during non-monsoon and weathering of secondary soil minerals in the regolith layer during monsoon. The secondary soil mineral weathering leads to limited silicate cation and enhanced silica fluxes in the Nethravati river basin.

Stream hydrograph separation using naturally occurring geochemical tracers holds great potential for elucidating mineral weathering and solute transport. This study addresses a critical need to characterize catchment runoff generation in the humid tropics using multiple natural tracers for hydrograph separation and concentration/discharge (C/Q) hysteresis analysis. We use hydrometric and geochemical data collected at the start of the wet season from three small, steep catchments located in the humid seasonal tropics of central Panama that differ primarily in land cover. We apply a dual source hydrograph separation model between two end-members: new event water precipitation and pre-event water stored in the catchment. We compare the effectiveness of electrical conductivity (EC) and stable water isotopes (δD and δ18O) tracers for identifying precipitation event water in stream runoff using across forested (1.43 km2), mixed land use ‘mosaic’ (1.82 km2) and pasture (0.42 km2) catchments. Hysteretic C/Q loops are analyzed for flowpath interpretation using δD, Ca2+, Mg2+, Na+, K+, Cl, and SO4 2−. During a medium-large magnitude event on May 23, 2013, forest and mosaic stream δD, Ca2+, Mg2+, and Na+ exhibited clockwise hysteresis, SO4 2− exhibited anticlockwise hysteresis, and K+ and Cl each showed no hysteresis. EC as a surrogate for total dissolved solids agrees acceptably with stable water isotope hydrograph separations during small peak runoff events (<3 mm/h). However, isotope and conductivity tracers strongly disagree during a large runoff event (>10 mm/h) in the mosaic catchment. Early wet-season events indicate lower event water fractions than events farther into the wet season. Despite previous work showing land cover strongly controls storm runoff efficiencies, hydrograph separation and hysteresis analyses only indicate weak event water delivery differences between the paired forest and mosaic catchments.
Keywords: Tropical hydrology; Stream chemistry; Runoff mechanisms; Land-use change;

Assessment of stream geochemistry in west central Nicaragua during baseflow conditions by Anne E. Carey; José Alfredo Mendoza; Kathleen A. Welch; Christopher B. Gardner; Steven T. Goldsmith; W. Berry Lyons (519-526).
Water samples were collected from streams in west-central Nicaragua at the end of the dry season as part of a study of riverine solutes in volcanic terrains. Streams in volcanic watersheds had lower mean Ca2+ and Mg2+ concentrations (0.29 mM Ca2+; 0.13 mM Mg2+; 0.96 mM Ca2+ and 0.51 mM Mg2+) and slightly higher Ca:Mg molar ratios (2.1) than streams in marine carbonate rocks (1.89). Dissolved Si concentrations averaged 1.12 mM L−1 in the 15 streams sampled, indicating a very high degree of silicate mineral weathering. Younger rocks yielded higher concentrations. At least a portion of the weathering in some watersheds is by strong acids derived from volcanic input. Mean Si, Ca, and Mg concentrations (0.74, 0.39, and 1.12 mM respectively) in these streams are higher than those measured in volcanic rock dominated watersheds in Panama and in first and second order streams flowing through basalts in Costa Rica. These differences reflect the lithologies and the ages of the rocks. N:P molar ratios vary from 6.4 to <1 in the Nicaraguan stream waters, suggesting these streams may be N-limited. In general, the highest phosphate concentrations were associated with lower Cl values, implying that at least a portion of the P is derived from chemical weathering sources, although anthropogenic sources cannot be ruled out. The information presented herein represents some of the first data on small mountainous river systems in Nicaragua. The data provide information that may prove important for the understanding of the pre-Nicaragua canal conditions.

Impact of trace mineral phases on the total solute flux from andesitic volcanics by Susan A. Welch; Steven T. Goldsmith; Anne E. Carey (527-539).
Recent work on the weathering of high standing islands (HSI’s) of New Zealand (Goldsmith et al., 2008), Dominica (Goldsmith et al., 2010) Martinique and Guadeloupe (Rad et al., 2006) and portions of the Philippines (Schopka et al., 2011) shows weathering rates based on stream water chemistry for areas draining andesitic terrains are comparable to weathering rates determined for basaltic terrains, indicating that andesite weathering might be much more important in drawing down atmospheric CO2 than previously recognized. While an easily erodible parent material has been largely attributed to sustaining rates at these locations, little is known to known regarding its associated reaction kinetics. We conducted a series of batch dissolution experiments on andesitic material collected from ∼10,000 year old tephra deposits from Dominica to determine the dissolution rate of major and trace mineral phases to better understand geochemical processes controlling weathering flux from these areas. Dissolution experiments were conducted over a range of pH (4 and 7) on bulk samples and mineral separates.The dissolution rates based on Si release from the Dominica tephra bulk samples were similar, and ranged from 0.04 to 0.13 μmole Si/g-day in water, and ∼0.14 to 0.27 μmole Si/g-day in dilute acid (initial pH ∼4). Although the bulk of the ash is predominately composed of vesicular felsic (Na–Al–Si) volcanic glass, reaction rates and stoichiometry indicate ash dissolution is dominated by the reactivity of trace Mg or Ca-bearing silicate phases (olivine, pyroxene or amphiboles) and Ca–phosphate phases (apatite), especially under slightly acidic conditions. Analysis of reacted phases by SEM shows little evidence of alteration of glassy material, whereas surfaces of Ca–Mg inosilicates, olivine and apatite show etched features indicative of dissolution. Results of the dissolution experiments suggest that, although these phases are relatively minor components of the ash, they contribute disproportionately to the overall weathering flux, and their reactivity may be particularly important in areas where physical weathering and erosion are constantly exposing new fresh surfaces available for chemical reaction.
Keywords: weathering; volcanic ash; apatite dissolution; ash dissolution;

Organic carbon concentrations and transport in small mountain rivers, Panama by Steven T. Goldsmith; W. Berry Lyons; Russell S. Harmon; Brendan A. Harmon; Anne E. Carey; Gregg T. McElwee (540-549).
Tropical small mountainous rivers (SMRs) are increasingly recognized for their role in the global export of dissolved organic carbon (DOC) to the oceans. Here we utilize the Isthmus of Panama as an ideal place to provide first-order estimates of DOC yields across a wide assemblage of bedrock lithologies and land cover practices. Samples for dissolved organic carbon (DOC) analysis were collected across Panama along an E–W transect from the central Panama area to the Costa Rican border for 24 mainstem rivers, 3 large tributary rivers, and one headwater stream. Sampling occurred during both the wet and the dry seasons. DOC concentrations during the wet season are higher than during the dry season in all but three of the rivers. Concentrations vary greatly from river to river and from season to season, with values as low as 0.64 mg l−1 to greater than >25 mg l−1 with the highest concentrations observed for the rivers draining Tertiary marine sedimentary rocks in the Burica and Azuero peninsulas. DOC yields from Panamanian rivers (2.29–7.97 tons/km2/y) are similar to or slightly lower than those determined for other tropical SMR systems. Areas underlain by Tertiary aged sediments exhibited significantly higher mean DOC yields compared to their igneous counterparts, despite maintaining substantially lower aboveground carbon densities, suggesting the important influence of lithology. Finally, regression analyses between DOC yields and select watershed parameters revealed a negative and statistically significant relationship with maximum and mean gradient suggesting lower soil retention times may be linked to lower DOC yields.
Keywords: Organic carbon; Riverine yields; Watershed; Panama;

Abundance, distribution, and fluxes of dissolved organic carbon (DOC) in four small sub-tropical rivers of the Tampa Bay Estuary (Florida, USA) by Ryan P. Moyer; Christina E. Powell; David J. Gordon; Jacqueline S. Long; Chelsea M. Bliss (550-562).
The delivery of organic carbon (C) from rivers to the coastal ocean via estuaries is recognized as an important component of the global C budget however, smaller river systems are often overlooked and modern flux estimates are not very different from historical estimates. Here, the seasonal (wet vs. dry) concentration and fluxes of dissolved organic C (DOC) were measured in five small sub-tropical rivers that drain into the Tampa Bay (FL, USA) estuary. DOC distributions were highly variable among riverine, mesohaline, and marine end-member samples in all river catchments and no significant differences were observed among or between DOC concentrations with respect to river catchment, season, or year of sampling. In general, DOC mixed non-conservatively during the wet seasons, and conservatively during the dry seasons, with the estuarine reaches of each river serving as a sink of DOC. Fluxes were strongly tied to discharge irrespective of season, and the estuaries removed 15–65% of DOC prior to export to coastal Bay and Gulf of Mexico waters. DOC concentrations were similar to others reported for low-elevation sub-tropical rivers, and a combination of elevation, residence time, and climate appear to control the abundance and variability of DOC in sub-tropical vs. tropical river systems. The characterization of DOC in small, sub-tropical rivers, which share characteristics with both their temperate and tropical counterparts, is critical for quantitatively constraining the importance of these systems in local-to-regional scale ocean C budgets. In addition to geomorphic properties, the role of past, present, and future land cover and other environmental change in small coastal rivers also exerts control on the quantity and flux of DOC in these systems.
Keywords: Small sub-tropical rivers; Dissolved organic carbon; Coastal carbon cycle; Tampa Bay Estuary; Estuarine Carbon Flux;

Carbon transport in rivers of southwest Haiti by W.R. McGillis; D.Y. Hsueh; Y. Zheng; M. Markowitz; R. Gibson; G. Bolduc; F.J. Fevrin; J.E. Thys; W. Noel; J.K. Paine; Z.A. Wang; K. Hoering; R. Hakimdavar; P.J. Culligan (563-572).
Hydrology and carbon speciation have been measured in watersheds of southwest Haiti to quantify the amount of inorganic carbon transport. Surrounded by limestone deposits, the rivers and reservoirs of southwest Haiti have some of the highest dissolved inorganic carbon (DIC) and alkalinity (TA) reported. Precipitation and discharge in these small mountainous rivers (SMRs) are continuously measured with autonomous, real-time hydrometeorological stations. The hydrometeorological studies have been conducted from 2010 to 2015 and carbon speciation measurements have been conducted since 2013. Stage and discharge capabilities were generated in this study as they did not exist for this region of the country. Episodic, event-driven discharge from these rivers drastically varies in time. Annual rainfall varies from 1 to 3 m a−1. In all rivers and reservoirs, measured DIC was always less than, but close to measured TA. The DIC discharge flux for 2014–2015 was 4.24 × 108 mol yr−1. A small percentage of that is exchanged to the atmosphere (>0.3%). Measured suspended solids were extremely low. Coincident water quality measurements were taken during nominal baseline flow.

Elemental signature of terrigenous sediment runoff as recorded in coastal salt ponds: US Virgin Islands by Rebekka A. Larson; Gregg R. Brooks; Barry Devine; Patrick T. Schwing; Charles W. Holmes; Tom Jilbert; Gert-Jan Reichart (573-585).
A high-resolution, multi-proxy approach is utilized on mm- to cm-scale laminated coastal salt pond sediments from St. John, U.S. Virgin Islands, to determine: (1) the sedimentological signature of depositional events/processes, (2) link this sedimentological signature with known depositional events/processes in the historical (past ∼100 years) record; and, (3) project back into the recent geologic past (past ∼1400 years) to investigate the natural variability of depositional events/processes. High-resolution, short-lived radioisotope geochronology (210Pb, 137Cs, 7Be) combined with high-resolution elemental scanning techniques (scanning XRF and scanning LA-ICP-MS) allows for the direct comparison of well-preserved salt pond deposits to historical records of depositional events (e.g., runoff/rainfall, tropical cyclones, tsunamis) to identify the sedimentary signature of each type of event. There is a robust sedimentary record of terrigenous sediment runoff linked to the frequency of rainfall events that exceed a threshold of ∼12 mm/day (minimum to mobilize and transport sediment) for study sites. This is manifested in the sedimentary record as increases in terrigenous indicator elements (%Al, %Fe, %Ti, %Si), which agree well with rainfall records over the past ∼50 years. Variability in the sedimentary record over the past ∼100 years reflects decadal-scale fluctuations between periods of increased frequency of rainfall events, and decreased frequency of rainfall events. Dm-scale variability in terrigenous indicator elements over the past ∼1400 years represents the natural system variability on a decadal–centennial scale, and provides a high-resolution, long-term baseline of natural variability of rainfall/runoff events. A period of increased terrigenous sediment delivery during the 1700s and 1800s likely indicates increased erosion in response to anthropogenic activities associated with the island’s plantation era, and perhaps increased frequency of rainfall events.Conceptual model of sediment sources and their sedimentological signature, as well as depositional processes/events controlling variability in sediments accumulating in salt ponds.Display Omitted

Effects of a tectonically-triggered wave of incision on riverine exports and soil mineralogy in the Luquillo Mountains of Puerto Rico by Gilles Y. Brocard; Jane K. Willenbring; Frederick N. Scatena; Art H. Johnson (586-598).
We document the long-term response of a tropical mountain stream to tectonics and show how this response exerts a first-order spatial control on the delivery of weatherable minerals to forest soils in its catchment. These minerals, in turn, affect nutrient availability and biogeochemical cycles. The Luquillo Mountains is a rainforest-covered isolated massif on Puerto Rico Island. Instead of displaying typical concave-up long profiles of most mountain streams, the rivers draining the southern flank of these mountains display a systematic downstream increase in gradient. Using concentrations of in situ-produced cosmogenic 10Be in quartz from river sediments, we find that the downstream steepening is due to the propagation of an erosion wave along the rivers from the coastal plain upstream, toward the headwaters. Decreased 10Be concentration along the steepened reaches (knickpoint faces or knickzones) results from faster denudation of the valley sides around the steepened reaches. The upper portions of the steepened reaches (knickpoint lips) cluster in elevation around the altitude of a flat-lying, dissected surface traceable around the Luquillo Mountains. Inspection of similar platforms over other parts of Puerto Rico and in the surrounding seas suggests that the dissected surface is an uplifted shore platform formed in the Early Pliocene (∼4 My ago). Upstream of the knickpoints, rivers possess alluvial reaches still graded to this uplifted platform. They represent relict profiles of the rivers that once drained an island that was surrounded by the now-uplifted platform. We conclude that the knickpoints initiated when the platform started to rise above the Caribbean Sea. The knickpoints then started propagating upstream, defining the front of a slow-moving wave of erosion. 10Be-derived catchment-scale denudation rates measured above and below the knickpoints indicate a 30–210% increase in denudation associated to the passage of the knickpoints. Mineralogical analysis of the soils show that soils upstream of the knickpoints overlie deeply depleted saprolite and only contain recalcitrant minerals, whereas soils downstream of the knickpoints experience an input of fresh, weatherable minerals. This influx considerably increases nutrient availability (Porder et al., 2015) in a forest where atmospheric inputs are otherwise the main source of nutrients (McDowell et al., 1990; Zarin and Johnson, 1995; Pett-Ridge, 2009).

Arsenic release and attenuation in a multilayer aquifer in the Po Plain (northern Italy): Reactive transport modeling by Marco Rotiroti; Rasmus Jakobsen; Letizia Fumagalli; Tullia Bonomi (599-609).
Groundwater As concentrations >WHO limit (10 μg/L) are frequently found in the Po Plain (N. Italy). Although several hypotheses on As mobilization exist (i.e., reductive dissolution driven by peat degradation), the mechanisms of As release and subsequent attenuation acting in the multilayer aquifer in the Po Plain were poorly understood.The present work aims at implementing a reactive transport modeling of the aquifer system in Cremona, affected by As <183 μg/L, in order to quantify and test the feasibility of As release by the reductive dissolution of Fe-oxides driven by the degradation of peat contained in leaky aquitards and As attenuation downstream by the co-precipitation in iron sulfides.The model, based on a partial equilibrium approach, revealed that the observed As, Fe and Mn chemistry could be mostly explained by the simultaneous equilibrium between Fe-oxide and sulfate reduction and FeS precipitation and by the equilibrium of rhodochrosite precipitation/dissolution. Model results, together with litholog analysis, supported the assumption of peat as the likely source of organic matter driving As release. The model fitted to measured data showed that the peak in the organic carbon degradation rate at 20–40 m below surface (average of 0.67 mM/y), corresponding to the shallow peaty aquitard and the upper portion of the underlying semiconfined aquifer, is associated with the peak of net release of As (average of 0.32 μM/y) that is followed just downstream by a net precipitation in iron sulfides at 40–60 m below surface (average of 0.30 μM/y). These results support the assumptions of peaty aquifers as drivers of As release and iron sulfides as As traps. The model also outlined the following aspects that could have a broad applicability in other alluvial As affected aquifers worldwide: (a) shallow peaty aquitards may have a greater role in driving the As release since they likely have young and more reactive organic matter; (b) the occurrence of Fe-oxide reduction and FeS precipitation, that represent the As source and sink, together with sulfate reduction occurring simultaneously close to equilibrium may restrict the As mobility limiting the extent of contamination just downstream the source of organic matter that drives its release.
Keywords: Reactive transport modeling; Peat; Aquitard; Iron sulfide; As mobility; Cremona;

Kerman Cenozoic Magmatic Arc (KCMA) is located in the southeastern part of the Central Iranian Volcano-Plutonic Copper belt. Arsenic contamination from geo-genic source is one of the most important environmental concerns in this area. The main objective of this study was to determine the role of geothermal related activities in the arsenic contamination. For this purpose, the old and active geological indicators of the geothermal activities were investigated through the quaternary travertine deposits and the present hydrothermal warm springs, respectively. Results showed that arsenic is highly concentrated (ranged mainly from 12,400 to 90,500 mg/kg) in the reddish-brown deposits of the travertine rocks. Arsenic showed geochemical association with Co, Cu, Mo, Sb, Tl, Se, Fe, and Mn in these samples. Yukonite [Ca7Fe3+ 12 (AsO4)10(OH)2015H2O], a rare Ca ferric arsenate hydrous mineral, was the only As-bearing mineral identified in the reddish-brown deposits of the travertine rocks. Arsenic concentration in the hydrothermal warm springs (<38 °C) ranged from 15,900 to 30,500 μg/L (the dominant form was as H 3 ASO 3 0 ). Hydrothermal contaminated waters also were characterized by Na–Cl type and high values of EC (11,400 μs/cm), TDS (8300 mg/L), B (42,700 μg/L), Li (3000 μg/L), Fe (900 μg/L), Sb (82.8 μg/L), and Si (47,000 μg/L) and natural anomalies of Cs, Mn, Mo, Rb, Se, and Tl. The obtained hydro-geochemical results are similar to those reported in the literature for worldwide hydrothermal waters. Although, natural attenuation processes, such as adsorption/co-precipitation or mixing/dilution, reduce most of the arsenic contamination from hydrothermal source, but some urban and rural communities are still depending on the arsenic contaminated waters with arsenic concentrations higher than recommended values for drinking or irrigation, a subject that increases the risk of arsenic-related diseases in some areas of the Kerman province.
Keywords: Arsenic; Kerman Cenozoic Magmatic Arc; Geothermal activities;

To investigate the potential of Mo and As as possible geogenic contaminants, three sediment cores were examined to evaluate their mineralogical association, distribution and mobility. The cores were described and analyzed for total organic carbon (TOC), Ca, Mg, Si, Al, P, Sr, As, Mo, Fe, and S content. Except in the uppermost segment, limestone was the main lithology with the occasional presence of dolomite and clay. That change in lithology was also observed in the bulk chemical composition, where Ca, Mg and Sr concentrations increased with depth, while Si, Al and P concentrations decreased with depth. Minor minerals included pyrite (FeS2), powellite (CaMoO4) and ferrihydrite. The minimum, maximum, median and standard deviations for all analyzed elements, including As and Mo were comparable for all three cores. Molybdenum and As, however, varied significantly with depth and median As and Mo values were above their respective crustal averages of approximately 1.1 mg/kg and 1.5 mg/kg. The median values for As were 1.9 mg/kg in core DEP-1, 3.3 mg/kg in DEP-2 and 1 mg/kg in DEP-5. The median values for Mo were 2.3 mg/kg in core DEP-1, 2.5 mg/kg in DEP-2 and 2.5 mg/kg in DEP-5. Maximum concentrations for As were 101.9 mg/kg, 47.5 mg/kg and 56.2 mg/kg in cores DEP-1, DEP-2 and DEP-5, respectively. Maximum concentrations for Mo were 880 mg/kg, 123 mg/kg and 225 mg/kg in cores DEP-1, DEP-2 and DEP-5, respectively. Electron microprobe analyses of individual minerals revealed variable concentrations of As ranging from approximately 300 to 9000 mg/kg, in pyrite and up to 17,600 mg/kg in powellite (CaMoO4). The Mo concentration in pyrite was consistently below the detection limit of approximately 100 mg/kg. In powellite the Mo concentration was up to 42 wt%.A subset of 10 samples from different stratigraphic sections and with different As and Mo concentrations was further investigated to assess As and Mo mobility under changing physicochemical conditions. Leaching the aquifer matrix with a 1 M NaOAc solution at a pH of 8.1 removed more than 70% Mo in 8 of the 10 samples. The maximum value was 97%. In contrast to Mo, As was mobilized to a lesser degree. In 8 of the samples less than 30% were removed and the maximum was only 50%. Molybdenum, which seemed to be loosely bound to mineral and organic matter surfaces thus could easily be removed from the aquifer matrix, while As on the other hand should be much less mobile, because it occurred either tightly adsorbed by hydrous ferric oxide or as an impurity in pyrite. Thus, it is advisable to include Mo in the analytical program whenever elevated As concentrations are encountered in groundwater.
Keywords: Geogenic; Arsenic; Molybdenum; Aquifer matrix; Limestone; Groundwater;

What is a successful environmental geochemical study? by Jörg Matschullat; Eleonora Deschamps (634-641).
A successful piece of applied research will not only influence the related problem perception within the scientific community, but also lead to much better understanding of a complex challenge, including the delivery of solutions. Ideally it may contribute significantly to reducing possible risk situations for people and/or the natural environment. In short, a successful study will have a broader impact beyond the sphere of science. Planning, timing, funding, networking, communication, and interdisciplinarity are identified as key aspects for a successful project and are being examined in their scope and boundary conditions, while not neglecting the particular role of local and regional people and authorities.Defining what makes a successful environmental geochemical study is clearly based upon experience and evidence found, and not upon any particular theoretical concept. Here, experience is drawn from the outcome of many projects and specifically first-hand from the complex ARSENEX project in Minas Gerais, Brazil. Against the backdrop of both perceived and real arsenic contamination of environmental compartments, including local people, all subsequent project steps and proposals were set up using a three-prong approach that sought to a) understand the processes, b) educate and inform the public and all other stakeholders and c) remediate the situation.
Keywords: Impact; Risk assessment; Project management; Project planning; Project timing; Project funding; Networking; Communication; Interdisciplinarity; Bangladesh; Brazil;

In some groundwaters, arsenic and fluoride can reach concentrations that are hazardous to human health if geological and geochemical conditions favour the release of these contaminants. This can especially pose a problem in developing countries where water service providers already struggle with the provision of clean water. The Geogenic Contamination Handbook, released in January 2015, aims to provide concise guidelines for practitioners faced with the problem of geogenically contaminated drinking water in low- and middle-income countries. The handbook is a digital resource, with the reader benefitting from numerous weblinks and embedded documents giving additional information where relevant. The necessary steps needed for sustainable mitigation of arsenic or fluoride-contaminated drinking water are outlined. This includes information on water quality testing (e.g. how to plan a field survey), different water treatment options as well as practical guidelines on the integration of technical, institutional and sociological aspects of arsenic and fluoride mitigation.
Keywords: Arsenic; Fluoride; Groundwater; Geogenic contamination; Mitigation; Guidelines;

Riverbank sediment cores and pore waters, shallow well waters, seepage waters and river waters were collected along the Meghna Riverbank in Gazaria Upazila, Bangladesh in Jan. 2006 and Oct.–Nov. 2007 to investigate hydrogeochemical processes controlling the fate of groundwater As during discharge. Redox transition zones from suboxic (0–2 m depth) to reducing (2–5 m depth) then suboxic conditions (5–7 m depth) exist at sites with sandy surficial deposits, as evidenced by depth profiles of pore water (n = 7) and sediment (n = 11; diffuse reflectance, Fe(III)/Fe ratios and Fe(III) concentrations). The sediment As enrichment zone (up to ∼700 mg kg−1) is associated with the suboxic zones mostly between 0 and 2 m depth and less frequently between 5 and 7 m depth. The As enriched zones consist of several 5–10 cm-thick dispersed layers and span a length of ∼5–15 m horizontally from the river shore. Depth profiles of riverbank pore water deployed along a 32 m transect perpendicular to the river shore show elevated levels of dissolved Fe (11.6 ± 11.7 mg L−1) and As (118 ± 91 μg L−1, mostly as arsenite) between 2 and 5 m depth, but lower concentrations between 0 and 2 m depth (0.13 ± 0.19 mg L−1 Fe, 1 ± 1 μg L−1 As) and between 5 and 6 m depth (1.14 ± 0.45 mg L−1 Fe, 28 ± 17 μg L−1 As). Because it would take more than a few hundred years of steady groundwater discharge (∼10 m yr−1) to accumulate hundreds of mg kg−1 of As in the riverbank sediment, it is concluded that groundwater As must have been naturally elevated prior to anthropogenic pumping of the aquifer since the 1970s. Not only does this lend unequivocal support to the argument that As occurrence in the Ganges-Brahmaputra-Meghna Delta groundwater is of geogenic origin, it also calls attention to the fate of this As enriched sediment as it may recycle As into the aquifer.
Keywords: Arsenic; Meghna river; Groundwater discharge; Redox transition; Arsenic trapping;