Applied Geochemistry (v.26, #3)
An integrated modelling approach to reconstruct complex solute transport mechanisms – Cl and δ37Cl in pore water of sediments from a former brackish lagoon in The Netherlands by H.E. Beekman; H.G.M. Eggenkamp; C.A.J. Appelo (257-268).
► Conservative solute transport studied in sediments under fresh and saline conditions. ► A numerical model was constructed to simulate Cl and δ37Cl in pore water of a boring. ► Erosion, pore water mixing, sedimentation and diffusion were included in the model. ► Cl and δ37Cl could only be explained by taking into account all above processes. ► Cl and δ37Cl proved to be invaluable in explaining this complex transport mechanism.A one-dimensional transport model was developed to reconstruct historical conservative transport of chloride and δ37Cl in pore water of sediments from a former brackish lagoon in The Netherlands, an area now covered by the freshwater Lakes IJssel and Marken. Knowledge of the mechanism of historical solute transport in the sediments and environmental conditions during transport is critical in understanding observed pore water chemistry and will form a basis for simulating effects of changing environmental (climate change) conditions. The model synthesizes present knowledge of geology and historical information on storm surges in the area and takes into account processes such as erosion of sediments, mixing of pore water, sedimentation, and diffusion (EMSD). The chemistry of pore water from one particular boring in the area was found to be mainly controlled by alternating seawater and freshwater diffusion. Models with a constant (averaged) porosity (ϕ = 0.55) and tortuosity factor (τ = 0.3) showed similar results as models incorporating the measured bulk porosity variations (ϕ = 0.4–0.8) and variable tortuosity factors calculated with Archie’s law, τ = ϕ. The relatively small tortuosity factor either results from anion exclusion or from the heterogeneous build-up of the profile in which a peaty layer in the middle part may obstruct diffusion. Diffusion of 35Cl− was found to be 1.0017 times faster than of 37Cl−. Seawater diffusion into the sediments started at least 400 years ago and refreshening took place since the lagoon was isolated from the sea by a dam in 1932.
Precipitation of arsenic under sulfate reducing conditions and subsequent leaching under aerobic conditions by T.C. Onstott; E. Chan; M.L. Polizzotto; J. Lanzon; M.F. DeFlaun (269-285).
► We induced sulfate reduction in As-bearing groundwater and decreased As content. ► We produced microcrystalline overgrowths of FeAsS, AsS, sulfur and phosphates. ► Aerobic leaching of the sediment for 4 months removed only 2% of the As. ► Scaling indicates that the microcrystalline FeAsS would be stable over decades.The stability of As precipitates formed by microbial SO4 reduction was examined via leaching of precipitate-laden sediments with aerobic groundwater. Sediment and groundwater collected from an As-contaminated aquifer were used to construct the flow-through columns utilized to demonstrate precipitate formation and stability. For 4 months, indigenous SO4-reducing bacteria in these columns were stimulated with injections of lactate, ethanol, FeCl2, (NH4)3PO4 and SO 4 2 - . Analyses, including 35S autoradiography, sequential extraction, SEM and XANES, of one of the columns revealed elevated As and 35S sulfide concentrations, and microcrystalline overgrowths comprised of FeAsS, AsS, S and phosphates restricted to “black” zones that had formed within the sediment. Two columns were then treated with a H2O2/K2HPO4 solution in order to produce Fe phosphate coatings that would theoretically protect sulfides from subsequent oxidation. Sediment from an untreated and a treated column were also packed into smaller syringe columns to record As depletion during aerobic leaching. Aerobic, As-bearing natural groundwater and artificial, As-free groundwater were passed through both untreated and treated columns and syringe columns for 4 months during which the As release rate from the columns and the removal of As from the syringe columns was observed. The As release rate from the untreated column and the rate of As removal from the syringe columns of untreated sediment correlated well and both indicated overall leaching of ∼2% of the microbially precipitated As-bearing sulfide. The As release rate from the treated sediments was 3–4 times greater than that of the untreated sediments, contrary to expectations that treatment would minimize As release. Sequential extraction, SEM and XANES analyses of the untreated column after aerobic leaching revealed that a significant portion of the remaining As was arsenate associated with Fe3+ hydroxides. A reactive transport model, which incorporated the oxidative dissolution of Fe and As sulfides and the adsorption of arsenate to Fe3+ hydroxides, reproduced the timing of As and sulfate release from this column and indicated that the release rate was limited by the O2 flux and Fe sulfide abundance. Scaling down the laboratory flow rate to that of the groundwater at a local field site suggests that microbially precipitated FeAsS produced in this manner should be stable over a decadal time scale.
Effects of light fraction organic matter removal on phosphate adsorption by lake sediments by Shengrui Wang; Wenli Yi; Suwen Yang; Xiangcan Jin; Guodong Wang; Fengchang Wu (286-292).
► The LFOM removal decreased the PO 4 3 - adsorbed, especially in the first thirty minutes. ► The replacing ion and destroying colloid were the reasons of decrease PO 4 3 - adsorbed. ► The use of heavy liquid NaI isolated LFOM was the physical protection of organic matter. ► The LFOM removal demolished the colloid material, and exposure mineral and oxide surfaces.The adsorption of PO 4 3 - on lake sediments has an important influence on the transport, degradation, and ultimate fate of P in lake ecosystems. Organic matter in sediment strongly affects PO 4 3 - adsorption, with light fraction organic matter (LFOM), the labile fractions representing only a small proportion of the total organic matter, playing a key role in nutrient cycling in lakes. However, little is known about the effect of LFOM on PO 4 3 - adsorption by sediments. This study examined the effects of LFOM removal on PO 4 3 - adsorption by lake sediments with different trophic status. Results showed that the removal of LFOM did not significantly affect PO 4 3 - adsorption kinetics, which was greatest during the first 0.5 h and reached an equilibrium state thereafter. The amount of PO 4 3 - adsorbed decreased due to LFOM removal from the sediments, especially in the first 0.5 h. The PO 4 3 - adsorption rates for the sediments from Gonghu Lake, Wuli Lake and Yuehu lake decreased from 302.44 mg (kg h)−1 to 138.93 mg (kg h)−1, 322.88 mg (kg h)−1 to 149.21 mg (kg h)−1 and 415.36 mg (kg h)−1 to 46.77 mg (kg h)−1, respectively. The removal of LFOM accelerated PO 4 3 - release from sediments to the overlying water, and PO 4 3 - adsorption efficiency decreased by 83.75%, 70.90% and 66.75% for Gonghu Lake, Wuli Lake and Yuehu Lake, respectively. Two plausible explanations contributed to the decrease, one was the replacement of PO 4 3 - which was in the form of Fe/Al-bound P in the sediment by OH― due to the increased pH, and the other is the destruction of LFOM colloids by the carboxyl group (―COOH) and hydroxyl (–OH).
Major element chemistry of the Huai River basin, China by Liang Zhang; Xianfang Song; Jun Xia; Ruiqiang Yuan; Yongyong Zhang; Xin Liu; Dongmei Han (293-300).
► Major elements compositions in the water of the Huai River basin, China. ► Obvious high ions concentrations in Northern area and low values in Southern area. ► The Huai River main channel is the geographic division between southern and northern China. ► Northern water systems of this basin are not suitable for use as drinking water sources.The chemistry of major ions (Ca, Mg, Na, K, HCO3, SO4, Cl and Si) in the water of the Huai River basin was studied, based on samples from 52 sites from nine different water bodies in July 2008. Ions and total dissolved solids (TDS) displayed clear spatial patterns with lower concentrations in the south and higher in the north of the basin; the same conditions were also found in the East Line of South–North Water Transfer Project (SNWTP) in this region. The Huai River main channel and Hongze Lake have moderate ion concentrations relative to the whole basin. TDS concentrations versus the weight ratios of Na/(Na + Ca) and ternary ions demonstrate that the southern rivers (Shi R. and Pi R.) are mainly controlled by the weathering of carbonates, whereas the northern water systems (Guo R., Shaying R., Nansi Lake and its tributaries) are dominated by the weathering of evaporites. The Huai River main channel, Hongze Lake and the East Line of SNWTP are synergistically influenced by weathering of evaporites and carbonates, yet Hongze Lake and the East Line of SNWTP are mainly controlled by evaporation and crystallization processes. This study also confirmed that the Huai River is the geographic division between southern and northern China. Most rivers of this basin have very high ionic composition relative to the global median and other world rivers. The spatial patterns and ionic composition also suggest that intensive anthropogenic activities in northern areas of this basin are well characterized. A comparison with WHO and Chinese standards for drinking water indicates that the northern water systems of this basin are not suitable for use as drinking water sources, and pollution control should be improved and enhanced in northern areas of the basin.
Sources of sulfur in Deccan Trap rivers: A reconnaissance isotope study by Anirban Das; N.J. Pawar; Jan Veizer (301-307).
► Origin of sulfate in rivers draining Deccan Traps was studied by using S isotopes. ► Highly enriched 34S was found in most of the rivers, especially the Bhima River system ► Attest to the role of H2CO3 as major proton supplying agent for weathering in Deccan Trap region. ► Minimal role of basalt-sulfides in contributing to sulphate in Deccan Rivers.Sulfur isotopic composition (δ 34S) of dissolved SO 4 2 - was measured in waters of rivers draining the Deccan Trap basalts in order to elucidate the source(s) of elevated SO 4 2 - content in some of these rivers, observed in an earlier study. The δ 34S values range from 8.7‰ to 19.5‰, with an average of 14.5 ± 2.8‰, values generally enriched in 34S compared to data available from other Indian rivers. The Bhima River (a tributary of the Krishna) and most of its tributaries have δ 34S within the 14 ± 2‰ range and high dissolved SO 4 2 - concentrations (256–1556 μM). Measured δ 34S of 7 of the saline/alkaline soils suggest that the high dissolved SO 4 2 - in the Bhima river system is likely derived from this source and/or gypsum concretions in the soils. The δ 34S–SO4 relationship for the Krishna River and its smaller tributaries follows a mixing pattern of two end-members, rainwater with low SO 4 2 - and low δ 34S and an unknown, likely a pollution, source with intermediate SO 4 2 - content and heavy δ 34S. The most important finding that this study brings out is the minimal role that the weathering of basalt-sulfides play in contributing to the dissolved SO 4 2 - in the rivers. This rules out the role of H2SO4-, and supports H2CO3-mediated weathering as the dominant process in the Deccan settings.
Mobilization of actinides by dissolved organic compounds at the Nevada Test Site by Pihong Zhao; Mavrik Zavarin; Roald N. Leif; Brian A. Powell; Michael J. Singleton; Rachel E. Lindvall; Annie B. Kersting (308-318).
► We studied the effect of dissolved organic matter (DOM) on actinide retardation. ► Am/Pu Kds were ∼100 times lower in DOM-rich Nevada Test Site (NTS) waters. ► U Kds decreased due to high dissolved inorganic carbon (DIC). ► Thermodynamic model predictions generally agreed with DIC and DOM effects. ► Reduced Am/Pu retardation in DOM-rich NTS waters may affect contaminant distribution.The effect of dissolved organic matter (DOM) on Am(III), Pu(IV), Np(V), and U(VI) sorption was investigated with natural water (pH ∼8) and zeolitized tuff samples collected from the Rainier Mesa tunnel system, Nevada Test Site, where the USA detonated underground nuclear tests prior to 1992. Perched vadose zone water at Rainier Mesa has high levels of DOM as a result of microbial degradation of mining debris (diesel, wood, etc.). The Am and Pu sorption Kds were up to two orders of magnitude lower in water with high DOM (15–19 mg C/L) compared to the same water with DOM removed (<0.4 mg C/L) or in naturally low DOM (0.2 mg C/L) groundwater. In contrast, Kds of Np and U were less affected by DOM at these solution conditions. Uranium sorption decreased as a result of high dissolved inorganic C (DIC) resulting from microbial degradation of DOM. Thermodynamic model predictions, based on actinide–humic acid stability constants available in the literature, are in general agreement with measured K d data, correctly predicting the effects of DIC and DOM on actinide retardation. This agreement is encouraging to future modeling efforts and suggests that effects of DOM and DIC can be incorporated into reactive transport modeling predictions. The Am and Pu transport rates in Rainier Mesa tunnel waters will be substantially faster as a result of the elevated DOM levels. Low diffusion rates of actinide–DOM macromolecular complexes may focus Pu and Am transport into fractures and minimize retardation via matrix diffusion. The resulting transport behavior will affect actinide distribution patterns and associated risk estimates.
Carbon mineralization and pyrite oxidation in groundwater: Importance for silicate weathering in boreal forest soils and stream base-flow chemistry by J. Klaminder; H. Grip; C.-M. Mörth; H. Laudon (319-325).
► Organic compounds is mineralized during later transport in deep groundwater aquifers. ► Carbonic acid generated by this process stimulates dissolution of silicate minerals. ► Protons derived from pyrite oxidation also affects weathering in deep groundwater. ► The identified weathering mechanisms affect base-flow chemistry in boreal streams.What role does mineralized organic C and sulfide oxidation play in weathering of silicate minerals in deep groundwater aquifers? In this study, how H2CO3, produced as a result of mineralization of organic matter during groundwater transport, affects silicate weathering in the saturated zone of the mineral soil along a 70 m-long boreal hillslope is demonstrated. Stream water measurements of base cations and δ18O are included to determine the importance of the deep groundwater system for downstream surface water. The results suggest that H2CO3 generated from organic compounds being mineralized during the lateral transport stimulates weathering at depths between 0.5 and 3 m in the soil. This finding is indicated by progressively increasing concentrations of base cations-, silica- and inorganic C (IC) in the groundwater along the hillslope that co-occur with decreasing organic C (OC) concentrations. Protons derived from sulfide oxidation appear to be an additional driver of the weathering process as indicated by a build-up of SO 4 2 - in the groundwater during lateral transport and a δ34S‰ value of +0.26–3.76‰ in the deep groundwater indicating S inputs from pyrite. The two identified active acids in the deep groundwater are likely to control the base-flow chemistry of streams draining larger catchments (>1 km2) as evident by δ18O signatures and base cation concentrations that overlap with that of the groundwater.
The geographic distribution of strontium isotopes in Danish surface waters – A base for provenance studies in archaeology, hydrology and agriculture by Karin M. Frei; Robert Frei (326-340).
► Strontium isotope data of 192 surface waters from Denmark. ► Geographic baseline distribution of bio-available fractions. ► Applicable for provenance studies within archaeology, geology, agriculture and hydrology. ► Proposal of a band of strontium isotope values to characterize “local” Danish signatures.In this paper Sr isotope signatures are reported for 192 surface water (lakes/ponds and rivers/creeks) samples from within Denmark and an isotope distribution map is presented that may serve as a base for provenance applications, including archaeological migration studies, ground water – surface water – seawater interaction/contamination monitoring, and potentially for agricultural applications, including cases of authenticity proof for particular food products. The Sr isotopic compositions of surface waters range from 87Sr/86Sr = 0.7078 to 0.7125 (average 0.7096 ± 0.0016; 2σ). This average value lies above the range of 87Sr/86Sr values between 0.7078 and 0.7082 expected from Late Cretaceous to Early Tertiary (Oligocene) limestones which form the dominant bedrock type in a NW–SE trending belt in Denmark. The elevated 87Sr/86Sr signatures >∼0.7095 are explained by additions to the surface waters of radiogenic Sr predominantly derived from the near-surface weathering and wash-out of Quarternary glaciogenic tills and soils deposited and formed during and after the last two ice age stages (Saale and Weichsel). The Sr isotopic compositions and concentrations of the surface waters can, therefore, best be modeled by a two-component mixing involving carbonaceous bedrock and glaciogenic cover sediments as the two predominant Sr sources. A feasibility study for using Sr isotopic compositions of surface waters as a proxy for bio-available Sr signatures was conducted in a representative test area on Zealand (Land of Legends, Lejre) where there is no use and application of commercial fertilizers. It is demonstrated that the Sr isotopic signatures of lake waters from within this area are slightly higher (but statistically still indistinguishable) from the average value defined by snail shells and soil leachates considered to characterize the true bio-available Sr. In combination with results from other studies, this is interpreted to reflect the wash-out of Sr with a higher 87Sr/86Sr signature released by weathering in the topsoils into the saturated water tables, a component which is consequently not readily transferred into the shallow-rooting plants and into small herbivores feeding on them. Since drinking water is a likely important source of Sr uptake of humans and larger animals, the contention is that a surface water isotopic composition can potentially characterize the bio-available component relevant for human and carnivorous large animals. Spline functions and ordinary linear kriging were used for modeling the geographic distribution of bio-available Sr isotopes over territorial Denmark. As expected, based on the two-source mixing scenario, the water 87Sr/86Sr ratio contour maps (with some notable exceptions) neither mirror the pre-Quarternary bedrock geology nor a (Pleistocene) soil-type distribution map of Denmark.As a conservative suggestion, the use of the average 87Sr/86Sr ratio of 0.7096 ± 0.0015 (2σ) is recommended as an average for bio-available Sr from within Denmark (Bornholm excluded) for human and larger animals and as a confidence band for distinguishing “local” from “non-local” signatures in archaeological provenance studies. The study also reveals that the average 87Sr/86Sr ratio of ∼0.7088 defined from soil extracts and small herbivores lies approximately 0.15% lower than that defined by the surface waters. The authors recommend using this lower value as a “local”–“non-local” discriminator for food and plant authenticity control in agricultural applications.
Seasonal variation of fatty acids from drip water in Heshang Cave, central China by Xiuli Li; Canfa Wang; Junhua Huang; Chaoyong Hu; Shucheng Xie (341-347).
► A 2-year monitoring to investigate the seasonal variation of fatty acids in cave drip water. ► Microbes are the dominant source for fatty acids in drip water. ► The relative abundance of mono-unsaturated responds negatively with external air temperature.In order to investigate how lipids in cave water respond to seasonal climate change, drip water samples were collected from 2006 to 2008 in Heshang Cave, central China for fatty acid analysis. These lipids are abundant in the drip water. Their compositions are dominated by lower-molecular-weight nC16:0, nC18:0 and nC14:0 acids, together with mono-unsaturated nC18:1, nC16:1 and nC14:1. Analysis of one water sample revealed marked differences between the dissolved and particulate fractions. The dissolved fraction contains total fatty acids one order of magnitude higher than that of the particulate fraction. The distributional patterns of the fatty acids suggest that microbes living in the overlying soils and/or groundwater system contribute most fatty acids to the drip water. This 2-a monitoring experiment reveals that the abundance of mono-unsaturated fatty acids relative to the saturated homologues (nC16:1/nC16:0 and nC18:1/nC18:0) relate inversely to the changes of synchronous external air temperature. Higher values occur under cold conditions (winter/spring), while lower values appear in warm intervals (summer). Further studies are needed to elucidate the dynamic processes by which the external temperature affects fatty acids in drip water and to confirm the potential application of fatty acid ratios such as nC16:1/nC16:0 and nC18:1/nC18:0 in paleotemperature reconstructions.
Gas seepage from Tokamachi mud volcanoes, onshore Niigata Basin (Japan): Origin, post-genetic alterations and CH4–CO2 fluxes by G. Etiope; R. Nakada; K. Tanaka; N. Yoshida (348-359).
► Tokamachi gas shows signals of subsurface hydrocarbon biodegradation. ► Hydrocarbon molecular fractionation depends on gas flux. ► Substantial gas emission from mud volcanoes is from invisible diffuse seepage. ► Global mud volcano methane emission is likely higher than 10 Mt a−1.Methane and CO2 emissions from the two most active mud volcanoes in central Japan, Murono and Kamou (Tokamachi City, Niigata Basin), were measured in from both craters or vents (macro-seepage) and invisible exhalation from the soil (mini- and microseepage). Molecular and isotopic compositions of the released gases were also determined. Gas is thermogenic (δ 13CCH4 from −32.9‰ to −36.2‰), likely associated with oil, and enrichments of 13C in CO2 (δ 13CCO2 up to +28.3‰) and propane (δ 13CC3H8 up to −8.6‰) suggest subsurface petroleum biodegradation. Gas source and post-genetic alteration processes did not change from 2004 to 2010. Methane flux ranged within the orders of magnitude of 101–104 g m−2 d−1 in macro-seeps, and up to 446 g m−2 d−1 from diffuse seepage. Positive CH4 fluxes from dry soil were widespread throughout the investigated areas. Total CH4 emission from Murono and Kamou were estimated to be at least 20 and 3.7 ton a−1, respectively, of which more than half was from invisible seepage surrounding the mud volcano vents. At the macro-seeps, CO2 fluxes were directly proportional to CH4 fluxes, and the volumetric ratios between CH4 flux and CO2 flux were similar to the compositional CH4/CO2 volume ratio. Macro-seep flux data, in addition to those of other 13 mud volcanoes, supported the hypothesis that molecular fractionation (increase of the “Bernard ratio” C1/(C2 + C3)) is inversely proportional to gas migration fluxes. The CH4 “emission factor” (total measured output divided by investigated seepage area) was similar to that derived in other mud volcanoes of the same size and activity. The updated global “emission-factor” data-set, now including 27 mud volcanoes from different countries, suggests that previous estimates of global CH4 emission from mud volcanoes may be significantly underestimated.
Control of organic and iron colloids on arsenic partition and transport in high arsenic groundwaters in the Hetao basin, Inner Mongolia by Huaming Guo; Bo Zhang; Yang Zhang (360-370).
► Both Fe colloids and organic colloids are present in high As groundwaters. ► Arsenic is more likely to be associated with small-size organic colloids. ► Iron colloids do not significantly affect As distribution and transport.Due to the importance of colloids in regulating element transport and mobility in aquifers, As distribution in the colloidal fraction needs to be identified in high As groundwaters. Groundwater samples were filtered in the field through a progressively decreasing pore size (0.45 μm, 100, 30, 10, 5 kDa) using a filtration technique under a N2 atmosphere. Major and trace elements and organic C (OC) were measured in (ultra)filtrates. The studied groundwater samples have typical physio-chemical characteristics of the basin waters. Declines in concentrations of alkali (Na, K), alkaline-earth (Mg, Ca, Sr, Ba) elements, Mo, Si and Se during ultrafiltration are smaller relative to other elements. Arsenic, Cu, Cr, U and V are generally about 30% lower in 5 kDa ultrafiltrates in comparison with 0.45 μm filtrates. Around 50% of Fe, OC and Al are bound to colloids with grain size between 5 kDa and 0.45 μm. Two types of colloids, including large-size Fe colloids and small-size organic colloids, have been identified. Results indicate that As would be more likely to be associated with small-size organic colloids than Fe colloids. SEM images and EDS analysis and synchrotron XRF analyses confirm the association of As with NOM with molecular weights of 5–10 kDa. The better correlation between As(V) and OC in the 5–10 kDa fraction indicates that the small-size organic colloids have a greater affinity for As(V) than As(III). Arsenic associated with organic complexes may not be immobilized by adsorption, and, therefore, easily transported in the aquifer. Thus, the presence of As-containing colloidal complexes in high As groundwaters must be considered in the modeling of As transport in the aquifers.
Strontium isotope geochemistry of groundwater affected by human activities in Nandong underground river system, China by Yongjun Jiang (371-379).
► Spatio-temporal variations of Sr concentrations and Sr isotopic composition of groundwater were investigated in a karst underground river system. ► Agricultural fertilizers and sewage effluents significantly modified the natural Sr isotopic signature of karst groundwater. ► Sr in the carbonate aquifers was relatively non-radiogenic, with low Sr concentrations, while anthropogenic Sr correlated with agricultural fertilizers and sewage effluents was relatively radiogenic, with higher Sr concentrations. ► 87Sr/86Sr ratios can provide key information for natural and anthropogenic sources in karst groundwater.The Nandong Underground River System (NURS) is located in a typical karst area dominated by agriculture in SE Yunnan Province, China. Groundwater plays an important role in the social and economical development in the area. The effects of human activities (agriculture and sewage effluents) on the Sr isotope geochemistry were investigated in the NURS. Seventy-two representative groundwater samples, which were collected from different aquifers (calcite and dolomite), under varying land-use types, both in summer and winter, showed significant spatial differences and slight seasonal variations in Sr concentrations and 87Sr/86Sr ratios. Agricultural fertilizers and sewage effluents significantly modified the natural 87Sr/86Sr ratios signature of groundwater that was otherwise dominated by water–rock interaction. Three major sources of Sr could be distinguished by 87Sr/86Sr ratios and Sr concentrations in karst groundwater. Two sources of Sr are the Triassic calcite and dolomite aquifers, where waters have low Sr concentrations (0.1–0.2 mg/L) and low 87Sr/86Sr ratios (0.7075–0.7080 and 0.7080–0.7100, respectively); the third source is anthropogenic Sr from agricultural fertilizers and sewage effluents with waters affected having radiogenic 87Sr/86Sr ratios (0.7080–0.8352 for agricultural fertilizers and 0.7080–0.7200 for sewage effluents, respectively), with higher Sr concentrations (0.24–0.51 mg/L). Due to the overlapping 87Sr/86Sr ratios, it is difficult to distinguish the sources of Sr in groundwater samples contaminated by agricultural fertilizers or sewage effluents based only on their 87Sr/86Sr ratios. However, 87Sr/86Sr ratios do provide key information for natural and anthropogenic sources in karst groundwater.
Black colored sandy sediments caused by bacterial action, and the mechanism for arsenic enrichment of groundwater in Inner Mongolia by H. Hagiwara; J. Akai; K. Terasaki; T. Yoshimura; H. Luo (380-393).
► Arsenic enrichment of groundwater in Inner Mongolia is described. ► Characteristic black sands by FeS are always associated with this enrichment. ► Bacterial activity plays a key role in forming highly reducing environments and H2S. ► Arsenic is released from Fe oxyhydroxide and H2S reacts with Fe2+, resulting in formation of black FeS. ► Black sands are indicative of As release in this region.High As concentrations in groundwater were detected in the village of Ershe, Jianshe but were not detected in the village of Qishe, Fengle in Inner Mongolia. In this study, core samples from two comparable regions were mineralogically examined. Results of X-ray diffractometry (XRD) showed that the principal minerals present in the drill core samples are quartz, micas, feldspars, calcite and clay minerals. Variation of these mineral species does not correlate with depth but to lithofacies; minerals were As-rich in muddy sediments and As-poor in sandy sediments. The results of X-ray fluorescence analysis (XRF) are consistent with those of XRD. The As content shows a positive correlation with total Fe2O3, V and loss of ignition (LOI). In order to identify the chemical forms of As present, a selective sequential extraction (SSE) method was carried out. The results of the SSE experiment suggested that in highly reducing environments, As that is adsorbed on Fe oxyhydroxides is released. Extremely black sand was found in deep drill core samples. To investigate the cause of black sands, inorganic and bacterial culture experiments were carried out. The black color in sands is due to the Fe sulfide greigite evolved from the Fe oxyhydroxide film coating the sand grains. This change in color occurred upon reaction with H2S gas most probably associated with bacterial activity. Transmission electron microscope (TEM) observations clarified that the sulfide structure of black sand grains is that of greigite. In summary, based on water chemistry, geology, mineralogical characteristics, and geomicrobiological features, the As release mechanisms in Ershe and Qishe are discussed. Then, a possible model was proposed that includes formation of Fe sulfides around sand grains from SO 4 2 - under strongly reducing conditions.
Variability in dissolved organic matter fluorescence and reduced sulfur concentration in coastal marine and estuarine environments by Sarah G.S. DePalma; W. Ray Arnold; James C. McGeer; D. George Dixon; D. Scott Smith (394-404).
► Humic and fulvic fluorophores correlate with dissolved organic carbon (r 2 = 0.7). ► Humic and fulvic components show no statistical differences between sources. ► The amino acid fluorescence quality factors show variation between sources. ► Chromium reducible sulfide concentrations are variable (0.07 ± 0.01 to 7703 ± 98 nM). ► CRS only correlates with DOC for terrigenous source waters (n = 13, r 2 = 0.55).Fluorescence characterization of dissolved organic matter (DOM) and measurements of Cr-reducible sulfide (CRS) are presented for 72 coastal marine and estuarine water samples obtained from the USA and Canada. Each sample is identified according to source: terrigenous, autochthonous, wastewater or mixed. Fluorescence data are resolved into contributions from humic, fulvic, tyrosine and tryptophan-like fluorophores. Humic and fulvic-like fluorophores correlate well with dissolved organic C (DOC) (r 2 = 0.73 and 0.71, respectively) but tyrosine and tryptophan-like fluorophores show no correlation with DOC. Quality factors are identified by normalization of fluorescence contributions to DOC. Humic and fulvic components show no statistical differences between sources but the amino acid-like fluorescence quality factors show significant variations between source, with highest values for autochthonous sources (0.07 ± 0.01 arbitrary fluorescence units per mg of C) versus low values (0.015 ± 0.005) for terrigenous source waters. CRS concentrations are highly variable from 0.07 ± 0.01 to 7703 ± 98 nM and do no correlate with DOC except when terrigenous source waters (n = 13) are separated out from the total sample set (r 2 = 0.55). There is an open question in the literature; does DOC source matter in terms of protective effects towards metal toxicity? Here is shown that DOC molecular-level quality does vary and that this variation is mostly in terms of the contributions of amino acids to total fluorescence.
Enrichment of metals in soils subjected to different land uses in a typical Mediterranean environment (Murcia City, southeast Spain) by J.A. Acosta; A. Faz; S. Martínez-Martínez; J.M. Arocena (405-414).
► All land uses exhibited higher Zn, Mn, Cr, and Ni contents than natural soils. ► Metal enrichment was due to fertilizer, pesticide, industrial activities, and traffic. ► High concentrations of Mn in some samples were attributed to parent materials. ► There is a need to monitor land management practices to reduce human/ecological risks.Industrialization, urbanization, and agricultural practices are 3 of the most important sources of metal accumulations in soils. Concentrations of Cr, Mn, Ni, Cu, Pb, Zn and Cd were determined in surface soils collected under different land uses, including urban (UR), industrial (IN-1 and IN-2), agricultural (AG), abandoned unused (AB), and natural (NA) sites to examine the influence of anthropogenic activities on metals in soils formed in a typical Mediterranean environment. The highest concentrations of Cr, Cd, and Pb observed in the NW industrial area (IN-2) were 63.7, 3.34 and 2330 mg metal kg−1 soil, for each metal, respectively. The SW industrial area (IN-1) contained the highest Zn content at 135 mg kg−1. However, soils with the highest concentrations of Ni and Cu were located in AG sites at 30.9 and 64.9 mg kg−1 soil, respectively. Sampling locations with the highest concentrations of Mn were identified in AB sites. Using the concentrations of metals at the NA sites as the baseline levels, soils collected from all other land uses in the study area exhibited significantly higher total contents of Zn, Mn, Cr and Ni. Metal enrichment was attributed to fertilizer and pesticide applications, industrial activities, and metal deposition from a high volume of vehicular traffic (for Pb and Cd). High concentrations of Mn in some samples were attributed to parent materials. The study demonstrated that anthropogenic activities associated with various land uses contribute to metal accumulation in soils and indicated a need to closely monitor land management practices to reduce human and ecological risks from environmental pollution.