Applied Geochemistry (v.24, #9)
Removal of uranium(VI) from the aqueous phase by iron(II) minerals in presence of bicarbonate by Simona Regenspurg; Dieter Schild; Thorsten Schäfer; Florian Huber; Maria E. Malmström (1617-1625).
Uranium(VI) mobility in groundwater is strongly affected by sorption of mobile U(VI) species (e.g. uranyl, UO 2 2 + ) to mineral surfaces, precipitation of U(VI) compounds, such as schoepite (UO2)4O(OH)6·6H2O), and by reduction to U(IV), forming sparingly soluble phases (uraninite; UO2). The latter pathway, in particular, would be very efficient for long-term immobilization of U. In nature, Fe(II) is an important reducing agent for U(VI) because it frequently occurs either dissolved in natural waters, sorbed to matrix minerals, or structurally bound in many minerals. Redox reactions between U(VI) and Fe(II) depend not only on the availability of Fe(II) in the environment, but also on the chemical conditions in the aqueous solution. Under natural groundwater condition U(VI) forms complexes with many anionic ligands, which strongly affect its speciation. Carbonate, in particular, is known to form stable complexes with U, raising the question, if U(VI), when complexed by carbonate, can be reduced to UO2. The goal of this study was to find out if Fe(II) when structurally bound in a mineral (as magnetite, Fe3O4) or sorbed to a mineral surface (as corundum, Al2O3) can reduce U(VI) to U(IV) in the presence of HCO 3 - . Batch experiments were conducted under anaerobic conditions to observe U removal from the aqueous phase by the two minerals depending on HCO 3 - addition (1 mM), U concentration (0.01–30 μM) and pH value (6–10). Immediately after the experiments, the mineral surfaces were analyzed by X-ray photoelectron spectroscopy (XPS) to obtain information on the redox state of U bound to the solid surfaces. XPS results gave evidence that U(VI) can be reduced both by magnetite and by corundum amended with Fe(II). In the presence of HCO 3 - the amount of reduced U on the mineral surfaces increased compared to carbonate-free solutions. This can be explained by the formation of Fe(II) carbonates on the mineral surfaces which represent an easily available Fe(II) pool for the U(VI) reduction. A facilitated U(VI) reduction is also considered possible when U is present as a carbonate complex compared to non-complexed U (e.g. uranyl).
Iron oxyhydroxide coating of pyrite for acid mine drainage control by Danielle M.C. Huminicki; J. Donald Rimstidt (1626-1634).
When pyrite oxidizes at near neutral pH in the presence of sufficient alkalinity, Fe oxyhydroxide coatings develop on the surface. As these coatings grow thicker and denser they block oxidant transport from the solution to the pyrite surface and reduce the rate of pyrite oxidation. The authors’ measurements of pyrite oxidation rates in a NaHCO3 solution show that the coating grows in two stages. In the first stage Fe oxyhydroxide colloids form and then attach to the pyrite surface to produce a slight reduction in oxidant transport. In the second stage interstitial precipitation of Fe oxyhydroxide material between the colloidal particles reduces the oxidant’s diffusion coefficient by more than five orders of magnitude. This causes the pyrite oxidation rate to decline as the square root of time. The kinetic predominance diagram, which compares the rates of Fe transformation reactions, shows that when pyrite oxidation releases Fe quickly enough for the total Fe concentration to rise to about 10−8 m, ferrihydrite forms but lower rates of Fe release will not produce coatings. Extrapolation of the results to longer times predicts that pyrite-bearing materials need to be treated with an extra source of alkalinity for several decades to produce coatings that are thick enough to be sustained by alkalinity levels typical of groundwater. However, once the coatings develop no additional treatment is needed and further pyrite oxidation simply causes the coating to grow thicker and denser until the entire pyrite grain is pseudomorphically replaced by goethite.
In situ laboratory X-ray powder diffraction study of wollastonite carbonation using a high-pressure stage by Pamela S. Whitfield; Lyndon D. Mitchell (1635-1639).
A high-pressure gas stage, recently developed for in-situ X-ray powder diffraction studies of polymer crystallization under CO2, has been used to observe the carbonation of wollastonite under various temperature/pressure conditions despite the fact that the stage was not designed for use with moisture-containing samples. The rate of carbonation of wollastonite at 60 °C was found to be pressure-independent. Additional experiments at 34.5 bar between 43 and 73 °C enabled an activation energy of 53 kJ mol−1 to be determined for the rate-limiting step. This value agrees very well with a published value for the leaching of Ca from wollastonite in acidic conditions and suggests that Ca leaching is the rate-limiting step in wollastonite carbonation at these temperatures.
Trace metals in recharge and discharge ground waters at two sites at the Baltic coast of Sweden by A. Augustsson; B. Bergbäck; M. Åström (1640-1652).
The distribution and controls of trace elements (Cd, Cr, Cu, Ni, Pb, Zn and U) in shallow groundwater in discharge and recharge zones were analysed at two sites on the Baltic coast of Sweden; one granite-dominated and one with a significant addition of calcite. Although the study sites differ in overburden geochemistry and groundwater trace metal concentrations, which were well reflected in the general groundwater composition, the relative hydrochemical differences between recharge and discharge ground waters were similar at both sites, and temporally stable. The concentrations of Cd, Cu, Ni and U were higher in soil tubes in recharge areas, but Cr was higher in discharge zones. Also concentrations of HS, Fe, Mn and NH4 were higher in discharge samples, which in combination with increased 34S values provide strong evidence of a transition from oxidizing to more reducing conditions along the groundwater flow gradient. In terms of trace metals, this might mean either mobilisation due to dissolution of trace-metal carrying Fe(III) and Mn(IV) phases, or immobilisation caused by precipitation of discrete trace-metal sulfides or co-precipitation with Fe sulfides. The results from this study show that the latter is dominant in both the carbonate and granite environments for the metals Cd, Cu and Ni. Chromium concentrations were likely coupled to organic complexation and were higher in discharge groundwater, where DOC was also more abundant. As the concentration of several potentially toxic trace metals were found to differ between recharge and discharge areas, a climate driven change in hydrology might have a substantial impact on the distribution of these metals.
Size and elemental distributions of nano- to micro-particulates in the geochemically-stratified Great Salt Lake by Ximena Diaz; William P. Johnson; Diego Fernandez; David L. Naftz (1653-1665).
The characterization of trace elements in terms of their apportionment among dissolved, macromolecular, nano- and micro-particulate phases in the water column of the Great Salt Lake carries implications for the potential entry of toxins into the food web of the lake. Samples from the anoxic deep and oxic shallow brine layers of the lake were fractionated using asymmetric flow field-flow fractionation (AF4). The associated trace elements were measured via online collision cell inductively-coupled plasma mass spectrometry (CC-ICP-MS). Results showed that of the total (dissolved + particulate) trace element mass, the percent associated with particulates varied from negligible (e.g. Sb), to greater than 50% (e.g. Al, Fe, Pb). Elements such as Cu, Zn, Mn, Co, Au, Hg, and U were associated with nanoparticles, as well as being present as dissolved species. Particulate-associated trace elements were predominantly associated with particulates larger than 450 nm in size. Among the smaller nanoparticulates (<450 nm), some trace elements (Ni, Zn, Au and Pb) showed higher percent mass (associated with nanoparticles) in the 0.9–7.5 nm size range relative to the 10–250 nm size range. The apparent nanoparticle size distributions were similar between the two brine layers; whereas, important differences in elemental associations to nanoparticles were discerned between the two layers. Elements such as Zn, Cu, Pb and Mo showed increasing signal intensities from oxic shallow to anoxic deep brine, suggesting the formation of sulfide nanoparticles, although this may also reflect association with dissolved organic matter. Aluminum and Fe showed greatly increased concentration with depth and equivalent size distributions that differed from those of Zn, Cu, Pb and Mo. Other elements (e.g. Mn, Ni, and Co) showed no significant change in signal intensity with depth. Arsenic was associated with <2 nm nanoparticles, and showed no increase in concentration with depth, possibly indicating dissolved arsenite. Mercury was associated with <2 nm nanoparticles, and showed greatly increased concentration with depth, possibly indicating association with dissolved organic matter.
Molecular biomarker evidence of origins and transport of organic matter in sediments of the Pearl River estuary and adjacent South China Sea by Jianfang Hu; Ping’an Peng; Allan R. Chivas (1666-1676).
Surface sediments from the subtropical Pearl River estuary and adjacent South China Sea were investigated by molecular organic geochemical methods to determine the composition, distribution and origin of extractable lipids (n-alkanes, n-alkanols and sterols). The absolute and organic C normalized concentrations of total alkane, n-alkanol, and sterol ranged from 0.16 to 2.67 μg g−1 and 0.9 to 12.3 μg g−1 OC, 24.4 to 427.3 ng g−1 and 63.2 to 1966.7 ng g−1 OC, and 9.0 to 493.5 ng g−1 and 58.4 to 1042.4 ng g−1 OC, respectively. The spatial distributions of these biomarkers indicated that terrestrial-derived molecular biomarkers such as long-chain n-alkanes, n-alkanols and plant-derived sterols were higher at the river mouth and along the coastline, suggesting that a higher proportion of terrestrial particulate organic matter was deposited there. Relatively lower amounts of marine-derived biomarkers such as short-chain n-alkanes, algal sterols at the river mouth reflected the lower primary productivity due to high turbidity. The spatial patterns of these biomarkers were partially related to the estuarine processes and conditions, evidencing an increased terrestrial signal from the Pearl River mouth to the inner estuary, and enhanced marine conditions further offshore.
Particulate aluminium in boreal streams: Towards a better understanding of its sources and influence on dissolved aluminium speciation by Neil Cory; Ishi Buffam; Hjalmar Laudon; Louise Björkvald; Carl-Magnus Mörth; Stephan Köhler; Kevin Bishop (1677-1685).
The adverse impacts of the inorganic labile monomeric Al (Ali) fraction on aquatic organisms have meant that Al (Altot) determination and even speciation has become a routine part of environmental monitoring and assessment. However, if samples are not filtered prior to analysis then particulate Al (Altot(p)) could influence the determination of Altot, and therefore the determination of the more toxicologically important (Ali), both when it is measured analytically or modelled from Altot. This paper shows that the Al/DOC ratio in unfiltered samples can identify the Altot(p) fraction, and thus improve the speciation of Ali. These findings are based on data from a study in a 67 km2 catchment in northern Sweden during the snowmelt-driven spring flood of two consecutive years. Filtered and unfiltered samples were studied to determine the spatial and temporal patterns in Altot(p). The concentrations of Altot(p) were greatest in larger downstream sites where significant silt deposits are located. The sites with no silt in their drainage area showed a mean difference between filtered (Altot(f)) and unfiltered (Altot(uf)) samples of 6%, while sites with silt deposits had a mean difference of 65%. The difference between filtered and unfiltered samples was greatest at peak flow. Spikes in Altot(p) did not behave consistently during fractionation with a cation exchange column, resulting in increases in either measured Ali(f) or non-labile monomeric Al (Alo(f)). Altot(p) spikes were associated with sharp increases in the Al:DOC ratio. The baseflow Al:DOC ratio could be used to model filtered Altot from DOC with a Spearman rho of 0.75.
Production of dissolved organic carbon in forest soils along the north–south European transect by F. Buzek; T. Paces; I. Jackova (1686-1701).
The aim of this study is to estimate the C loss from forest soils due to the production of dissolved organic C (DOC) along a north–south European transect. Dissolved organic matter (DOM) was extracted from the forest soils incubated at a controlled temperature and water content. Soils were sampled from forest plots from Sweden to Italy. The plots represent monocultures of spruce, pine and beech and three selected chronosequences of spruce and beech spanning a range of mean annual temperature from 2 to 14 °C. The DOM was characterized by its DOC/DON ratio and the C isotope composition δ13C. The DOC/DON ratio of DOM varied from 25 to 15 after 16 days of incubation and it decreased to between 16 and 10 after 126 days. At the beginning of incubation the δ13C values of DOC were 1‰ or 2‰ less negative than incubated soils. At the end of the experiment δ13C of DOC were the same as soil values. In addition to DOC production heterotrophic respiration and N mineralization were measured on the incubated soils. The DON production rates decreased from 30 to 5 μgN gC−1 d−1 after 16 days of incubation to constant values from 5 to 2 μgN gC−1 d−1 after 126 days at the end of experiment. The DIN production rates were nearly constant during the experiments with values ranging from 20 to 4 μgN gC−1 d−1. DOC production followed first-order reaction kinetics and heterotrophic respiration followed zero-order reaction kinetics. Kinetic analysis of the experimental data yielded mean annual DOC and respiration productions with respect to sites. Mean annual estimates of DOC flux varied from 3 to 29 g of C m−2 (1–19 mg C g−1 of available C), corresponding to mean DOC concentrations from 2 to 85 mg C L−1.
Total mercury and monomethylmercury in water, sediments, and hydrophytes from the rivers, estuary, and bay along the Bohai Sea coast, northeastern China by Shaofeng Wang; Yongfeng Jia; Shuying Wang; Xin Wang; He Wang; Zhixi Zhao; Bingzhu Liu (1702-1711).
Mercury contamination in aquatic environments is of worldwide concern because of its high biomagnification factor in food chains and long-range transport. The rivers, estuary and the bay along the northwestern Bohai Sea coast, northeastern China have been heavily contaminated by Hg due to long-term Zn smelting and chlor-alkali production. This work investigated the distributions of total Hg (THg) and monomethylmercury (MMHg) in the water, sediment and hydrophytes from this area. Concentrations of THg in sediment (0.5–64 mg kg−1) and water (39–2700 ng L−1) were elevated by 1–3 orders of magnitude compared to background concentrations, which induced high concentrations of MMHg in these media. The highest concentration of MMHg in sediment reached 35 μg kg−1, which was comparable to that in the Hg mining area, Wanshan, China, and the highest MMHg concentration of 3.0 ng L−1 in the water sample exceeded the MMHg Chinese drinking water guideline of 1.0 ng L−1. Concentrations of THg in a sediment profile from Jinzhou Bay were found to be consistent with annual Hg emission flux from a local Zn smelter (r = 0.74, p < 0.01), indicating that Hg contamination was mainly caused by Zn smelting locally. For some freshwater hydrophytes, concentrations of THg and MMHg ranged from 5.2 to 100 μg kg−1 and 0.15 to 12 μg kg−1, respectively. Compared to sediment, concentrations of THg in hydrophytes were 2–3 orders of magnitude lower but MMHg was comparable or higher, indicating that the bioaccumulation in plants was distinct for the two Hg species studied. The data suggest that a significant load of Hg has been released into the northwestern coastal region of the Bohai Sea.
Attenuation of pyrite oxidation with a fly ash pre-barrier: Reactive transport modelling of column experiments by Rafael Pérez-López; Jordi Cama; José Miguel Nieto; Carles Ayora; Maarten W. Saaltink (1712-1723).
Conventional permeable reactive barriers (PRBs) for passive treatment of groundwater contaminated by acid mine drainage (AMD) use limestone as reactive material that neutralizes water acidity. However, the limestone-alkalinity potential ceases as inevitable precipitation of secondary metal-phases on grain surfaces occurs, limiting its efficiency. In the present study, fly ash derived from coal combustion is investigated as an alternative alkalinity generating material for the passive treatment of AMD using solution-saturated column experiments. Unlike conventional systems, the utilization of fly ash in a pre-barrier to intercept the non-polluted recharge water before this water reacts with pyrite-rich wastes is proposed. Chemical variation in the columns was interpreted with the reactive transport code RETRASO. In parallel, kinetics of fly ash dissolution at alkaline pH were studied using flow-through experiments and incorporated into the model. In a saturated column filled solely with pyritic sludge–quartz sand (1:10), oxidation took place at acidic conditions (pH 3.7). According to SO 4 2 - release and pH, pyrite dissolution occurred favourably in the solution-saturated porous medium until dissolved O2 was totally consumed. In a second saturated column, pyrite oxidation took place at alkaline conditions (pH 10.45) as acidity was neutralized by fly ash dissolution in a previous level. At this pH Fe release from pyrite dissolution was immediately depleted as Fe-oxy(hydroxide) phases that precipitated on the pyrite grains, forming Fe-coatings (microencapsulation). With time, pyrite microencapsulation inhibited oxidation in practically 97% of the pyritic sludge. Rapid pyrite-surface passivation decreased its reactivity, preventing AMD production in the relatively short term.
Petrology and isotopic geochemistry of dawsonite-bearing sandstones in Hailaer basin, northeastern China by Yuqiao Gao; Li Liu; Wenxuan Hu (1724-1738).
The CO2 gas reservoir sandstones in the Hailaer Basin contain abundant dawsonite and provide an ideal laboratory to study whether any genetic relationship exists between dawsonite and the modern gas phase of CO2. The origins of dawsonite and CO2 in these sandstones were studied by petrographic and isotopic analysis. According to the paragenetic sequence of the sandstones, dawsonite grew later than CO2 charging at 110–85 Ma. The dawsonite δ18O value is 7.4‰ (SMOW), and the calculated δ18O values of the water present during dawsonite growth are from −11.4‰ to −9.2‰ (SMOW). This, combined with the NaHCO3-dominated water linked to dawsonite growth, suggests meteoric water being responsible for dawsonite growth. The δ13C values of gas phase CO2 and the ratios of 3He/4He of the associated He suggest a mantle magmatic origin of CO2-rich natural gas in Hailaer basin. Dawsonite δ13C values are −5.3‰ to −1.5‰ (average −3.4‰), and the calculated δ13C values of CO2 gas in isotopic equilibrium with dawsonite are −11.4‰ to −7.3‰. These C isotopic values are ambiguous for the dawsonite C source. From the geological context, the timing of events, together with formation water conditions for dawsonite growth, dawsonite possibly grew in meteoric-derived water, atmospherically-derived CO2 maybe, or at least the dominant, C source for dawsonite. It seems that there are few relationships between dawsonite and the modern gas phase of CO2 in the Hailaer basin.
Occurrence of biogenic schwertmannite in sludge bioleaching environments and its adverse effect on solubilization of sludge-borne metals by Yuehua Liao; Lixiang Zhou; Shuangyou Bai; Jianru Liang; Shimei Wang (1739-1746).
Secondary minerals such as Fe(OH)3 and jarosite are often hypothesized to be formed in sludge during bioleaching processes involving Acidithiobacillus ferrooxidans and be responsible for the lower solubilization efficiencies of sludge-borne metals. Schwertmannite is a ubiquitous mineral formed in acid mine drainage (AMD) impacted environments. However, the authors report for the first time the occurrence of schwertmannite as the sole secondary Fe mineral in a dissolved organic matter (DOM)-rich tannery sludge bioleaching system and its scavenging effect on soluble metals in bioleached sludge. The tannery sludge bioleach solution with pH ∼3 was mainly rich in Fe, Cr(III), SO 4 2 - and Acidithiobacillus ferrooxidans, but also contained high concentrations of DOM (300–400 mg C L−1). The ocherous precipitate that formed rapidly within 40 h in the sludge bioleach solution during incubation was identified to be pure schwertmannite by XRD and FTIR. Results of SEM coupled with EDS analyses showed that the schwertmannite was present as spherical particles with a diameter of about 1 μm and its chemical formula could be expressed as Fe8O8(OH)4.6(SO4)1.7. Newly formed schwertmannite contained about 2.43% Cr(III) derived from already solubilized sludge-borne Cr(III) by bioleaching, suggesting a strong adverse influence of schwertmannite formation on solubilization efficiency of metals from sludge. Biogenic Fe mineral synthesis experiments varying the concentrations of DOM and metals indicated that the occurrence of schwertmannite as a monominerallic phase in the sludge bioleaching environment was predominantly attributed to the presence of insufficient concentrations of monovalent cations and the high content of DOM. Moreover, the short reaction time, high SO 4 2 - concentration and low pH value in this system also facilitated the existence of monominerallic schwertmannite.
Behavior of arsenic and antimony in the surface freshwater reaches of a highly turbid estuary, the Gironde Estuary, France by Matthieu Masson; Jörg Schäfer; Gérard Blanc; Aymeric Dabrin; Sabine Castelle; Gilbert Lavaux (1747-1756).
This study reports on the behavior of two redox-sensitive elements, As and Sb, along the turbidity gradient in the freshwater reaches of the turbid Gironde Estuary. During a 17-month survey, surface water and suspended particulate matter (SPM) were sampled monthly at six sites representing both fluvial branches of the Gironde Estuary. Additionally, two longitudinal high resolution profiles were sampled along the fluvial estuary of the Garonne Branch during two contrasted seasons, i.e. with and without the presence of the maximum turbidity zone (MTZ). Seasonal variability and spatial distribution of dissolved (<0.2 μm; <0.02 μm) and particulate As, Sb and Fe were measured and combined with SPM data to understand metalloid behavior in the estuarine freshwater turbidity gradient.At the two main fluvial entries of the Gironde Estuary, dissolved As and Sb concentrations showed strong (by a factor of 2–4) seasonal variations, that were only partly controlled by discharge-related dilution. Seasonal addition of dissolved As and Sb was attributed to the degradation of particulate As and Sb carrier phases in bottom sediment and/or in the adjacent aquifers, rather than release from SPM. In the surface freshwater reaches of the Gironde Estuary, Sb behaved conservatively under all hydrological conditions. In contrast, As was strongly reactive in the presence of the MTZ, with opposite behaviors in the two fluvial branches of the estuary: in the Garonne Branch As was removed from the dissolved phase, whereas in the Dordogne Branch As was added. Redistribution of As between the dissolved and the particulate phases along the turbidity gradient in estuarine freshwater only affected the <0.02 μm fraction, as the 0.02–0.2 μm fraction remained constant (∼300 ng L−1 in September 2005). Accordingly, As removal seemed to be decoupled from concomitant “colloidal” (0.02–0.2 μm) Fe flocculation in the turbidity gradient. The contrasting behavior of dissolved As in the fluvial estuaries of the Garonne and Dordogne Branches was attributed to sorption processes during equilibration of river-borne dissolved As with estuarine SPM forming the MTZ. This equilibrium, described by a distinct distribution coefficient K d(As) ∼ 11,000 L kg−1 in the MTZ, resulted in either As release (desorption; Dordogne Branch) or removal (adsorption; Garonne Branch) in the respective fluvial estuaries. A mixing experiment under controlled laboratory conditions tended to support that equilibration between the dissolved phase and MTZ particles may induce both As release and removal in the estuarine freshwater reaches, with As distribution evolving towards a distinct K d value for increasing SPM concentrations. The long-term survey allowed estimating annual (2004) dissolved fluxes of As and, for the first time Sb, at the main fluvial entries of the Gironde Estuary at 30.7 t a−1 and 3.2 t a−1 (Garonne River) and at 8.0 t a−1 and 2.3 t a−1 (Dordogne River), respectively.
Carbonate precipitation in artificial soils as a sink for atmospheric carbon dioxide by P. Renforth; D.A.C. Manning; E. Lopez-Capel (1757-1764).
Turnover of C in soils is the dominant flux in the global C cycle and is responsible for transporting 20 times the quantity of anthropogenic emissions each year. This paper investigates the potential for soils to be modified with Ca-rich materials (e.g. demolition waste or basic slag) to capture some of the transferred C as geologically stable CaCO3. To test this principal, artificial soil known to contain Ca-rich minerals (Ca silicates and portlandite) was analysed from two sites across NE England, UK. The results demonstrate an average C content of 30 ± 15.3 Kg C m−2 stored as CaCO3, which is three times the expected organic C content and that it has accumulated at a rate of 25 ± 12.8 t C ha−1 a−1 since 1996. Isotopic analysis of the carbonates gave values between −6.4‰ and −27.5‰ for δ 13C and −3.92‰ and −20.89‰ for δ 18O, respectively (against V-PDB), which suggests that a combination of carbonate formation mechanisms are operating including the hydroxylation of gaseous CO2 in solution, and the sequestration of degraded organic C with minor remobilisation/precipitation of lithogenic carbonates. This study implies that construction/development sites may be designed with a C capture function to sequester atmospheric C into the soil matrix with a maximum global potential of 290 Mt C a−1.
Carbon chemistry and groundwater dynamics at natural analogue site Ruprechtov, Czech Republic: Insights from environmental isotopes by Ulrich Noseck; Kazimierz Rozanski; Marek Dulinski; Václava Havlová; Ondra Sracek; Thomas Brasser; Mirek Hercik; Gunnar Buckau (1765-1776).
Hydrological, geochemical and environmental isotope data from groundwater wells at Ruprechtov natural analogue site were evaluated to characterize the flow pattern and C chemistry in the system. The results show that water flow in the Tertiary sediments is restricted to 1–2 m thick zones in the so-called clay/lignite horizon with two different infiltration areas in the outcropping granites in the western and south-western part of the investigated area. Generally the flow system is separated from the underlying granite by a kaolin layer up to several tens of metres thick. Differences in stable isotope signatures in the northern part of the site indicate very local connections of both flow systems via fault zones. The observed increase of δ13C values and decrease of 14C activities in dissolved inorganic C during evolution of the groundwater from the infiltration area to the clay/lignite horizon was modelled using simple open- and closed-system models as well as an inverse geochemical model (NETPATH), which included changes in other geochemical parameters. The results from both types of models provided some insights into timescales of groundwater flow, but mainly revealed that additional sources of C are active in the system. These are very likely biodegradation of dissolved and sedimentary organic C (DOC and SOC) as well as the influx of endogenous CO2. The occurrence of microbial degradation of SOC in the clay/lignite layers is indicated by the increase of biogenic DIC, DOC, and phosphate concentrations. The impact of microbial SO4 reduction on this process is confirmed by an increase of δ34S values in dissolved SO 4 2 - from the infiltration area to the clay/lignite horizon with an enrichment factor of 11‰. The very low DOC concentrations of 1–5 mg C/L in the clay/lignite horizon with an organic matter content up to 50% C is probably caused by very low availability of organic matter to the processes of degradation and DOC release, demonstrated by extraction experiments with SOC.
Vertical distribution and source identification of polycyclic aromatic hydrocarbons in anoxic sediment cores of Chini Lake, Malaysia: Perylene as indicator of land plant-derived hydrocarbons by Alireza Riyahi Bakhtiari; Mohamad Pauzi Zakaria; Mohammad Ismail Yaziz; Mohamad Nordin Hj Lajis; Xinhui Bi; Mohamad Che Abd Rahim (1777-1787).
Four anoxic sediment cores were collected from Chini Lake, Malaysia in order to investigate the variability of polycyclic aromatic hydrocarbon (PAH) and perylene concentrations. The study also determined significant differences of perylene concentrations in different sediment layers. Total PAH concentrations ranged from 248 to 8098 ng g−1 in the samples. Diagnostic PAH ratios such as methylphenanthrenes/phenanthrene (MP/P), phenanthrene/anthracene (P/A) and fluoranthene/(fluoranthene + pyrene) (Fl/(Fl + Py) revealed a dominance of pyrogenic influences and partial petrogenic inputs to the top sediment layers. Perylene concentrations were high in the top layers (<12 cm) and increased with increasing depth. There is a significant positive correlation (r = 0.705, p = 0.01) between perylene concentrations and TOC. Analysis of variance (ANOVA) and LSD revealed significant differences (p < 0.05) in TOC-normalized perylene concentrations between the upper (<12 cm) and bottom layers (>12 cm). The average perylene concentrations accounted for 26–50% (0–12 cm) and 50–77% (12–36 cm) of pentacyclic-aromatic hydrocarbon isomers (PAI) present whereas it made up 10–34% (0–12 cm) and 46–66% (12–36 cm) of the total PAH. The average pyrene concentrations decreased with increasing depth and accounted for 62% (0–3 cm), 20–23% (3–12 cm) and 3–1.4% (12–36 cm) of perylene present. The results of hierarchical cluster analysis based on these ratios suggested different input sources for the top and bottom layers. It is concluded that the activity of termites on woody plants produced perylene which is supplied to the lake by run-off from the heavy and frequent rains in this Asian tropical climate. In addition, there was also in situ formation of perylene in the bottom layers due to diagenetic processes.
Potentially mineralizable nitrogen in sediments of the shallow lakes in the middle and lower reaches of the Yangtze River area in China by Shengrui Wang; Xiangcan Jin; Dalin Niu; Fengchang Wu (1788-1792).
Potentially mineralizable N (PMN) in sediments is an important N source to aquatic ecosystems. However, there are few studies on PMN in lake sediments. The main N fraction in lake sediments is organic, and mineralization is through benthic metabolism in sediments rather than in the water column in most shallow lake systems. It is shown that PMN contents in the studied sediments were higher than the inorganic N in the shallow lakes in the middle and lower reaches of the Yangtze River area, China, and were also higher than those in soils from the same region. PMN constituted 3–26% (14%, on the average) of total N (TN) in sediments. Amino-acid N was the major contributor to the organic N pool in PMN. Potentially mineralizable N, TN, total P, organic matter, cation exchange capacity and fine-grain size were significantly correlated. With TN increasing in the slightly polluted sediments, PMN increased more rapidly in the heavily polluted sediments. The results suggest that more attention should be paid to organic N mineralization both in heavily and in less polluted sediments.
Geochemical characteristics of the fluids and muds from two southern Taiwan mud volcanoes: Implications for water–sediment interaction and groundwater arsenic enrichment by Chia-Chuan Liu; Jiin-Shuh Jean; Bibhash Nath; Ming-Kuo Lee; Lien-I Hor; Kao-Hung Lin; Jyoti Prakash Maity (1793-1802).
Mud volcanoes distributed in the southern part of Taiwan are believed to be sourced from an accretionary prism located along the collision boundary between the Philippine Sea plate and the Asian Continental plate. Fluid and mud samples have been collected from Wushanting and Hsiaokunshui mud volcanoes during October 2004, March and June 2005, and analyzed for major ions, trace elements, and stable isotopes. The results show that the mud volcano fluids are enriched in Na+ and Cl− but are depleted in Ca2+ and Mg2+. The chemical composition and oxidation state of the fluids fluctuate seasonally, with ionic contents being notably higher during the dry pre-monsoon period. The enriched ionic (e.g., Na+, NH 4 + , K+, Mg2+ and Cl−) compositions of the exchangeable fractions indicate that the muds were sourced from a marine depositional environment. δD and δ18O values indicate that the mud volcano fluids may have been modified by chemical exchange with 18O-rich crustal rocks and possibly originated from mixing of deep brines with circulating meteoric water. The spatial and temporal distribution of ions in the muds suggests a varied mixing regime within the mud volcanoes. Incubation study of the muds shows the leaching of soluble salts under aerobic conditions, which is generally consistent with the fluid geochemical characteristics. Moreover, elevated trace element (e.g., As, Zn, Cu and Mn) concentrations are also observed in the fluids and muds. Geochemical correlations between As, Zn and Cu in the muds suggest prevailing SO4-reducing conditions at depth. The relatively low Eh values (range: −50 to −30 mV) of the fluids near the surface would favor bacterial Fe reduction and mobilization of As. The dewatering of mud volcanoes may represent a significant source of groundwater As in the nearby Chianan plain.
Rare earth elements (REE) of dissolved and suspended loads in the Xijiang River, South China by Zhifang Xu; Guilin Han (1803-1816).
The Xijiang River is the main channel of the Zhujiang (Pearl River), the second largest river in China in terms of water discharge, and flows through one of the largest carbonate provinces in the world. The rare earth element (REE) concentrations of the dissolved load and the suspended particulate matter (SPM) load were measured in the Xijiang River system during the high-flow season. The low dissolved REE concentration in the Xijiang River is attributed to the interaction of high pH and low DOC concentration. The PAAS-normalized REE patterns for the dissolved load show some common features: negative Ce anomaly, progressively heavy REE (HREE) enrichment relative to light REE (LREE). Similar to the world’s major rivers the absolute concentration of the dissolved REE in the Xijiang River are mainly pH controlled. The degree of REE partitioning between the dissolved load and SPM load is also strongly pH dependent. The negative Ce anomaly is progressively developed with increasing pH, being consistent with the oxidation of Ce (III) to Ce (IV) in the alkaline river waters, and the lack of Ce anomalies in several DOC-rich waters is presumably due to both Ce (III) and Ce (IV) being strongly bound by organic matter. The PAAS-normalized REE patterns for the dissolved load and the SPM load in rivers draining the carbonate rock area exhibit middle REE (MREE) enrichment and a distinct maximum at Eu, indicating the preferential dissolution of phosphatic minerals during weathering of host lithologies. Compared to the Xijiang River waters, the MREE enrichment with a maximum at Eu disappeared and light REE were more depleted in the South China Sea (SCS) waters, suggesting that the REE sourced from the Xijiang River must be further fractionated and modified on entering the SCS. The river fluxes of individual dissolved REE introduced by the Xijiang River into the SCS vary from 0.04 to 4.36 × 104 mol a−1.