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Applied Geochemistry (v.24, #11)

IAGC Membership Application Form (pp. i).

Nitrogen isotopic patterns of vegetation as affected by breeding activity of Black-tailed Gull ( Larus crassiostris): A coupled analysis of feces, inorganic soil nitrogen and flora by C. Mizota (pp. 2027-2033).

Two currently breeding colonies (Matsushima Bay and Rishiri island; northern Japan) of predominant Black-tailed Gull ( Larus crassiostris) were studied for N isotopic patterns of flora, which is affected by increased supply of inorganic soil N derived from the microbial transformation of feces. Coupled samples of feces, topsoil and flora were collected in early to mid July (2008), when input of fecal N onto soils was at its maximum. As bird migration and breeding continued, native Japanese red-pine ( Pinus densiflora), junipers ( Juniperus chinensis and Juniperus rigita; Matsushima Bay colony) and Sasa senanensis (Rishiri colony) declined, while ornithocoprophilus exotic plants succeeded. Among tree species on the islands, P. densiflora with ectomycorrizal colonization appears highly susceptible to elevated concentrations of NH₄–N in the topsoil. A mechanism for best explaining the plant succession associated with the breeding activity of Black-tailed Gull was evidenced by two parameters: first, concomitant elevation of N content in the flora and second, inorganic soil N content, along with changes in N isotopic composition (δ¹⁵N). Earlier isotopic data on the foliar N affected by breeding activity were compiled and reviewed. Emphasis was put on isotopic information for inorganic N in soils that controls plant succession.

Using sulfur and oxygen isotope data for sulfide oxidation assessment in the Freiberg polymetallic sulfide mine by Manuela Junghans; Marion Tichomirowa (pp. 2034-2050).

The isotopic and chemical composition and dissolvedSO42- of mine water from a mined and backfilled ore vein at the polymetallic sulfide deposit in Freiberg was used to study theSO42- sources and mixing processes. The mainSO42- sources in mine water areSO42- in soil seepage water and groundwater, and sulfide oxidation. Using O- and S-isotope analysis, it has been calculated that about 50% (±10%) ofSO42- in the mine water at the deepest accessible level of the ore vein originates from sulfide oxidation. A decrease in δ³⁴S_SO4 and δ¹⁸O_SO4 values from 1997 to 2000/2002, in combination with lowerSO42- concentrations, is attributed to a lowerSO42- input from soil seepage water and ground water. Anthropogenic sources may be responsible for mine water with anomalous stable isotope compositions and concentrations of anions, and metals. Hydrochemical and stable isotope compositions of waters in the central Freiberg and Morgenstern mines were determined to evaluate whether the same trends as those described for the backfilled ore vein are observed in the mines, and what additional processes may operate on a larger geological scale. The δ³⁴S_SO4 and δ¹⁸O_SO4 values of most flowing mine waters follow the mixing trend found for the backfilled ore vein. In addition to theseSO42- sources, anthropogenic sources, such as sewage water and industrial wastewater, were observed to be of importance. Judging from isotope values and element concentrations, no obvious decrease in the intensity of sulfide oxidation in the non-flooded part of the Freiberg mine has occurred during the last 10a. The dual isotope approach to determine both sulfate O- and S-isotopic compositions is useful to better constrain the sources ofSO42- in mine waters and can also be used for pollution assessment (portion ofSO42- formed by sulfide oxidation) in long-term observation studies.

Scaling of adsorption reactions: U(VI) experiments and modeling by Vijay A. Loganathan; Mark O. Barnett; T. Prabhakar Clement; Sushil R. Kanel (pp. 2051-2060).

Iron-coated sands were prepared via two common protocols, a precipitation method, where Fe was precipitated directly onto the sand in a single step, and an adsorption method, where pure goethite was prepared in the first step and then adsorbed onto the sand in a second step. The coated sands from both the systems were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and selective Fe extraction. Although neither of the methods produced a completely crystalline Fe coating, the precipitation method produced sands with larger portions of amorphous Fe than the adsorption method, with the fraction of amorphous Fe decreasing with increasing Fe content. Uranium(VI) adsorption isotherms and pH adsorption edges were measured on three coated sands with Fe contents ranging from 0.04% to 0.3%. Experimentally, the adsorption of U(VI) onto the three sands was more comparable when normalized to surface area than when normalized to Fe content. A surface complexation model, although originally developed for U(VI) adsorption onto amorphous Fe oxide, captured the differences in adsorption when adjusted for the surface area of the coated sand. The findings indicate that surface area is a better scaling parameter than Fe content in predicting U(VI) adsorption to Fe-dominated media. These findings are significant because many common surface complexation models are parameterized on the basis of Fe content rather than specific surface area. Although the interactions of U(VI) and Fe-coated sands were used as representative adsorbate and adsorbent, the general principles may be applicable to other adsorbate–adsorbent systems as well.

Elevated naturally occurring arsenic in a semiarid oxidizing system, Southern High Plains aquifer, Texas, USA by B.R. Scanlon; J.P. Nicot; R.C. Reedy; D. Kurtzman; A. Mukherjee; D.K. Nordstrom (pp. 2061-2071).

High groundwater As concentrations in oxidizing systems are generally associated with As adsorption onto hydrous metal (Al, Fe or Mn) oxides and mobilization with increased pH. The objective of this study was to evaluate the distribution, sources and mobilization mechanisms of As in the Southern High Plains (SHP) aquifer, Texas, relative to those in other semiarid, oxidizing systems. Elevated groundwater As levels are widespread in the southern part of the SHP (SHP-S) aquifer, with 47% of wells exceeding the current EPA maximum contaminant level (MCL) of 10μg/L (range 0.3–164μg/L), whereas As levels are much lower in the north (SHP-N: 9%⩾As MCL of 10μg/L; range 0.2–43μg/L). The sharp contrast in As levels between the north and south coincides with a change in total dissolved solids (TDS) from 395mg/L (median north) to 885mg/L (median south). Arsenic is present as arsenate (As V) in this oxidizing system and is correlated with groundwater TDS (Spearman’s ρ=0.57). The most likely current source of As is sorbed As onto hydrous metal oxides based on correlations between As and other oxyanion-forming elements (V, ρ=0.88; Se, ρ=0.54; B, ρ=0.51 and Mo, ρ=0.46). This source is similar to that in other oxidizing systems and constitutes a secondary source; the most likely primary source being volcanic ashes in the SHP aquifer or original source rocks in the Rockies, based on co-occurrence of As and F ( ρ=0.56), oxyanion-forming elements and SiO₂ ( ρ=0.41), which are found in volcanic ashes. High groundwater As concentrations in some semiarid oxidizing systems are related to high evaporation. Although correlation of As with TDS in the SHP aquifer may suggest evaporative concentration, unenriched stable isotopes (δ²H: −65 to −27; δ¹⁸O: −9.1 to −4.2) in the SHP aquifer do not support evaporation. High TDS in the SHP aquifer is most likely related to upward movement of saline water from the underlying Triassic Dockum aquifer. Mobilization of As in other semiarid oxidizing systems is caused by increased pH; however, pH in the SHP aquifer is near neutral (10–90 percentiles, 7.0–7.6). Although many processes, such as competitive desorption with SiO₂, VO₄, or PO₄, could be responsible for local mobilization of As in the SHP aquifer, the most plausible explanation for the regional As distribution and correlation with TDS is the counterion effect caused by a change from Ca- to Na-rich, water as shown by the high correlation between As and Na/(Ca)^0.5 ratios ( ρ=0.57). This change in chemistry is related to mixing with saline water that moves upward from the underlying Dockum aquifer. This counterion effect may mobilize other anions and oxyanion-forming elements that are correlated with As (F, V, Se, B, Mo and SiO₂). Competition among the oxyanions for sorption sites may enhance As mobilization. The SHP case study has similar As sources to those of other semiarid, oxidizing systems (original volcanic ash source followed by sorption onto hydrous metal oxides) but contrasts with these systems by showing lack of evaporative concentration and pH mobilization of As but counterion mobilization of As instead in the SHP-S aquifer.

Oxygen isotope evidence for sorption of molecular oxygen to pyrite surface sites and incorporation into sulfate in oxidation experiments by Marion Tichomirowa; Manuela Junghans (pp. 2072-2092).

Experiments were conducted to investigate (i) the rate of O-isotope exchange between SO₄ and water molecules at low pH and surface temperatures typical for conditions of acid mine drainage (AMD) and (ii) the O- and S-isotope composition of sulfates produced by pyrite oxidation under closed and open conditions (limited and free access of atmospheric O₂) to identify the O source/s in sulfide oxidation (water or atmospheric molecular O₂) and to better understand the pyrite oxidation pathway. An O-isotope exchange between SO₄ and water was observed over a pH range of 0–2 only at 50°C, whereas no exchange occurred at lower temperatures over a period of 8a. The calculated half-time of the exchange rate for 50°C (pH=0 and 1) is in good agreement with former experimental data for higher and lower temperatures and excludes the possibility of isotope exchange for typical AMD conditions ( T⩽25°C, pH⩾3) for decades.Pyrite oxidation experiments revealed two dependencies of the O-isotope composition of dissolved sulfates: O-isotope values decreased with longer duration of experiments and increasing grain size of pyrite. Both changes are interpreted as evidence for chemisorption of molecular O₂ to pyrite surface sites. The sorption of molecular O₂ is important at initial oxidation stages and more abundant in finer grained pyrite fractions and leads to its incorporation in the produced SO₄. The calculated bulk contribution of atmospheric O₂ in the dissolved SO₄ reached up to 50% during initial oxidation stages (first 5days, pH 2, fine-grained pyrite fraction) and decreased to less than 20% after about 100days. Based on the direct incorporation of molecular O₂ in the early-formed sulfates, chemisorption and electron transfer of molecular O₂ on S sites of the pyrite surface are proposed, in addition to chemisorption on Fe sites. After about 10days, the O of all newly-formed sulfates originates only from water, indicating direct interaction of hydroxyls from water with S at the anodic S pyrite surface site. Then, the role of molecular O₂ is as proposed in previous studies: acting as electron acceptor only at the cathodic Fe pyrite surface site for oxidation of Fe(II) to Fe(III).

Archaeological reconstruction of medieval lead production: Implications for ancient metal provenance studies and paleopollution tracing by Pb isotopes by Sandrine Baron; Cécile Le-Carlier; Jean Carignan; Alain Ploquin (pp. 2093-2101).

The identification of metal provenance is often based on chemical and Pb isotope analyses of materials from the operating chain, mainly ores and metallic artefacts. Such analyses, however, have their limits. Some studies are unable to trace metallic artefacts or ingots to their ore sources, even in well-constrained archaeological contexts. Possible reasons for this difficulty are to be found among a variety of limiting factors: (i) problems of ore signatures, (ii) mixing of different ores (alloys), (iii) the use of additives during the metallurgical process, (iv) metal recycling and (v) possible Pb isotopic fractionation during metal production. This paper focuses on the issue of Pb isotope fractionation during smelting to address the issue of metal provenance. Through an experimental reconstruction of argentiferous Pb production in the medieval period, an attempt was made to better understand and interpret the Pb isotopic composition of ore smelting products. It is shown that the measured differences (outside the total external uncertainties of 0.005 (2∗sd) for²⁰⁶Pb/²⁰⁴Pb ratios) in Pb signatures measured between ores, slag and smoke are not due to Pb mass fractionation processes, but to (1) ore heterogeneity (Δ²⁰⁶Pb/²⁰⁴Pb_slag-ores=0.066) and (2) the use of additives during the metallurgical process (Δ²⁰⁶Pb/²⁰⁴Pb_slag-ores=0.083). Even if these differences are due to causes (1) and/or (2), smoke from the ore reduction appears to reflect the ore mining area without a significant disturbance of its Pb signature for all the isotopic ratios (Δ²⁰⁶Pb/²⁰⁴Pb_smokes-ores=0.026). Thus, because the isotopic heterogeneity of the mining district and additives is averaged in slags, slag appears as the most relevant product to identify ancient metal provenance. Whereas aiming at identifying a given mine seems beyond the possibilities provided by the method, searching for the mining district through analysis of the smelting workshop materials should provide a more appropriate approach in cases where no archaeological evidence of ancient mining is available. Furthermore, smoke Pb isotopic composition does not seem to be significantly affected by the metallurgical process. Paleopollution recorded in peat deposits could help to detect ancient mining production and workshops. Integrated collaboration between mining archaeologists and geochemists appears crucial to achieve this goal.

Source and flux of POC in two subtropical karstic tributaries with contrasting land use practice in the Yangtze River Basin by F.-X. Tao; C.-Q. Liu; S.-L. Li (pp. 2102-2112).

Elemental (C/N ratio) and C isotope composition ( δ¹³C) of particulate organic C (POC) and organic C content (OC) of total suspended solids (TSS) were determined for two subtropical karstic tributaries of the Yangtze River, the Wujiang (the eighth largest tributary) and Yuanjiang (the third largest tributary). For the latter, two headwaters, the karstic Wuyanghe and non-karstic Qingshuijiang were studied. The Wujiang catchment is subject to intensive land use, has low forest coverage and high soil erosion rate. The δ¹³C of POC covered a range from −30.6‰ to −24.9‰, from −27.6‰ to −24.7‰, and from −26.2‰ to −23.3‰ at the low-water stage, while at the high-water stage varied in a span between −28.6‰ and −24.4‰, between −27.7‰ and −24.5‰, and between −27.6‰ and −24.2‰ for the Wujiang, Wuyanghe, and Qingshuijiang, respectively. The combined application of C isotopes, C/N ratio, OC, and TSS analyses indicated that catchment soil was the predominant source of POC for the Wujiang while for the Wuyanghe and Qingshuijiang, in-stream processes supplied the main part of POC in winter and summer. A significant increase in δ¹³C value (1.4‰) of POC was found in the Wujiang during summer, and was attributed to the enhanced soil erosion of the dry arable uplands close to the riverbanks of the main channel. Based on a conservative estimate, POC fluxes were 3.123×10¹⁰, 0.084×10¹⁰, and 0.372×10¹⁰ga⁻¹ while export rates of POC were 466, 129, and 218mgm⁻²a⁻¹ for the Wujiang, Wuyanghe, and Qingshuijiang, respectively. The POC export rate for the karstic Wujiang, with intensive land use, was 2–3 higher than that of the karstic Wuyanghe or of the non-karstic Qingshuijiang where soil erosion was minor. Such high values imply rapid degradation of related karstic ecosystems impacted by intensive land use activities, and pose a potential threat to the health of the Three Gorges Reservoir.

Evaluation of amendments used to prevent sodification of irrigated fields by Elizabeth Brinck; Carol Frost (pp. 2113-2122).

Gypsum and S are applied to soils being irrigated with Na–HCO₃ dominated coalbed natural gas (CBNG) produced water to protect soil structure and fertility. Wyoming law requires beneficial use of produced water and irrigation with CBNG produced water in the semi-arid Powder River Basin is becoming more common. Strontium isotopes were used to evaluate the effectiveness of the gypsum and S applications in preventing sodification of these irrigated soils. The isotope ratio of Sr on the cation exchange complex of irrigated soil falls between that of the gypsum amendment (0.7074) and that of local soil (0.712–0.713). Strontium isotopes indicate that, to a depth of 30cm, as much as 50% of the Sr on the irrigated soil cation exchange sites originated from the applied gypsum amendment on a field irrigated for 3a. This was also true to a depth of 5cm on a field irrigated less than 1a. Strontium isotope ratio measurements of vegetation illustrate plant utilization of Sr from gypsum amendments, thereby reinforcing the conclusions about the presence of Sr from gypsum on the soil’s exchange sites. This Sr tracing technique may be useful in a wide variety of settings where monitoring soil health is necessary, especially in settings where poor quality water is used for irrigation: a more common occurrence as demand for fresh water increases.

Stable carbon isotopic fractionation of individual n-alkanes accompanying primary migration: Evidence from hydrocarbon generation–expulsion simulations of selected terrestrial source rocks by Yuhong Liao; Ansong Geng (pp. 2123-2132).

The effect of isotopic fractionation during primary migration of hydrocarbons from coals is rarely noticed because it overlaps with the isotopic effects of maturation. In this research, geological chromatography-like effects and possible physical isotopic fractionation effects on n-alkanes during primary migration from four coals and one mudstone were studied through two types of generation–expulsion simulations (generation–expulsion simulations I and II). In order to monitor the kinetic isotopic fractionation effect during primary migration and to differentiate the isotopic effects of primary migration from the isotopic effects of maturation, generation–expulsion simulation was upgraded in two aspects, source rock was separated into at least five layers, and deuterated n-C₁₅D₃₂ was added to the initial layer of the source rock (simulation II). The experimental results suggested that all terrestrial source rocks exhibit significant geological chromatography-like effects in generation–expulsion simulation. Expulsion efficiencies shown by vitrinite-rich coals are much lower than algal cannel, fusinite-rich coal and mudstone. There also exist significant physical isotopic fractionation effects in hydrocarbon primary migration processes from vitrinite-rich coals, but there is no significant isotopic fractionation effect from fusinite-rich brown coal and mudstone. Pore structure and specific surface area of source rock samples were measured by gas adsorption of both N₂ and CO₂. This indicated that vitrinite-rich coals have a higher proportion of microporosity. The differences in pore structure and adsorptive capacity of source rocks may be responsible for differences in expulsion efficiencies and isotopic fractionation effects in generation–expulsion simulations. The isotopic fractionation effect due to primary migration should be considered in making oil-source correlation when vitrinite-rich coals are concerned.

Feldspar dissolution rates in the Topopah Spring Tuff, Yucca Mountain, Nevada by Charles R. Bryan; Katheryn B. Helean; Brian D. Marshall; Patrick V. Brady (pp. 2133-2143).

Two different field-based methods are used here to calculate feldspar dissolution rates in the Topopah Spring Tuff, the host rock for the proposed nuclear waste repository at Yucca Mountain, Nevada. The center of the tuff is a high silica rhyolite, consisting largely of alkali feldspar (∼60wt%) and quartz polymorphs (∼35wt%) that formed by devitrification of rhyolitic glass as the tuff cooled. First, the abundance of secondary aluminosilicates is used to estimate the cumulative amount of feldspar dissolution over the history of the tuff, and an ambient dissolution rate is calculated by using the estimated thermal history. Second, the feldspar dissolution rate is calculated by using measured Sr isotope compositions for the pore water and rock. Pore waters display systematic changes in Sr isotopic composition with depth that are caused by feldspar dissolution. The range in dissolution rates determined from secondary mineral abundances varies from 10⁻¹⁶ to 10⁻¹⁷mols⁻¹kgtuff⁻¹ with the largest uncertainty being the effect of the early thermal history of the tuff. Dissolution rates based on pore water Sr isotopic data were calculated by treating percolation flux parametrically, and vary from 10⁻¹⁵ to 10⁻¹⁶mols⁻¹kgtuff⁻¹ for percolation fluxes of 15mma⁻¹ and 1mma⁻¹, respectively. Reconciling the rates from the two methods requires that percolation fluxes at the sampled locations be a few mma⁻¹ or less. The calculated feldspar dissolution rates are low relative to other measured field-based feldspar dissolution rates, possibly due to the age (12.8Ma) of the unsaturated system at Yucca Mountain; because oxidizing and organic-poor conditions limit biological activity; and/or because elevated silica concentrations in the pore waters (∼50mgL⁻¹) may inhibit feldspar dissolution.

Influence of HCl/HF treatment on organic matter in aquifer sediments: A Rock-Eval pyrolysis study by Tim J. Tambach; Harry Veld; Jasper Griffioen (pp. 2144-2151).

Rock–Eval pyrolysis is increasingly used for the routine characterization of natural organic matter in soils and sediments. In this work the bulk composition of sedimentary organic matter (SOM) in sandy aquifer sediments is studied, as well as purified samples (isolation of SOM) by HCl/HF treatment. This treatment is necessary to avoid detection limit problems for samples with low SOM contents, but the results presented here indicate that this treatment influences the organic geochemistry of the aquifer sediment samples. The FID and CO₂/CO pyrograms show a shift of 10–40°C of the major peak to a lower temperature. Organic matter alteration or removal of components containing O-bearing groups may explain this. It is also suggested that destruction of the mineral matrix may lead to the reduced retention of the material. For the change of the CO₂/CO pyrograms of the RC fraction only organic matter alteration seems to be likely. Concentrated organic matter samples may also accelerate the release of exothermic energy and influence the pyrograms. Results indicate that the organic matter concentration in the sample influences the measured total organic matter (TOM) content and theT _max of the FID pyrogram, while the sample loading (absolute organic matter amount) up to 80mg in the Rock–Eval apparatus does not. The FID pyrograms can be deconvoluted into four subpeaks, which allows comparison of samples at various depths. Rock–Eval pyrolysis may only be routinely applied to characterize SOM in aquifer sediments when such systematic and analytical phenomena are taken into account.

Geochemical and hydrologic controls on the mobilization of arsenic derived from herbicide application by Arthur G. Fitzmaurice; A. Azra Bilgin; Peggy A. O’Day; Virginia Illera; David R. Burris; H. James Reisinger; Janet G. Hering (pp. 2152-2162).

The fate and transport of As was examined at an industrial site where soil- and groundwater contamination are derived from the application of As₂O₃ as a herbicide. Application of arsenical herbicides was discontinued in the 1970s and soils in the source area were partially excavated in 2003. Arsenic contamination (up to 280mg/kg) remains in the source area soils and a plume of As-contaminated groundwater persists in the surficial aquifer downgradient of the source area with maximum observed As concentrations of 1200μg/L near the source area. The spatial extent of As contamination as defined by the 10μg/L contour appears to have remained relatively stable over the period 1996–2006; the boundary of the 1000μg/L contour has retreated over the same time period indicating a decrease in total As mass in the surficial groundwater.In column experiments conducted with source area soil, the As concentrations in the column effluent were comparable to those observed in groundwater near the source area. A substantial fraction of the As could be leached from the source area soil with ammonium sulfate and ammonium phosphate. Exhaustive extraction with background groundwater removed most of the total As. These results indicate that As in the source area soils is geochemically labile. Source area soils are low in extractable Fe, Mn and Al, and characterization by X-ray absorption spectroscopy and electron microscopy indicated that As is present primarily as arsenate sorbed to (alumino)silicate minerals. Batch sorption experiments showed much less sorption on surficial aquifer sediments than on sediments from the Jackson Bluff Formation (JBF), a presumed confining layer. This limited capacity of the surficial aquifer sediments for As sorption is consistent with the similar As contents observed for these sediments within and upgradient of the As plume. The apparent stability of the As plume cannot be explained by sequestration of As within the surficial aquifer. Sorption to JBF sediments may contribute to As sequestration, but As enrichment in JBF sediments within the plume (i.e., as compared with JBF sediments upgradient) was not observed. These results indicate that neither the persistence of As in the source area soils or the apparent stability of the plume of As-contaminated groundwater at this site can be explained by geochemical controls on As mobility. The absence of demonstrable geochemical bases for such observations suggests that possible hydrologic controls should be further investigated at this site.

Soil pH controls the environmental availability of phosphorus: Experimental and mechanistic modelling approaches by Nicolas Devau; Edith Le Cadre; Philippe Hinsinger; Benoît Jaillard; Frédéric Gérard (pp. 2163-2174).

Inorganic P is the least mobile major nutrient in most soils and is frequently the prime limiting factor for plant growth in terrestrial ecosystems. In this study, the extraction of soil inorganic P with CaCl₂ (P–CaCl₂) and geochemical modelling were combined in order to unravel the processes controlling the environmentally available P (EAP) of a soil over a range of pH values (pH∼4–10). Mechanistic descriptions of the adsorption of cations and anions by the soil constituents were used (1-pK Triple Plane, ion-exchange and NICA-Donnan models). These models are implemented into the geochemical code Visual MINTEQ. An additive approach was used for their application to the surface horizon of a Cambisol. The geochemical code accurately reproduced the concentration of extracted P at the different soil pH values ( R²=0.9, RMSE=0.03mgkg⁻¹). Model parameters were either directly found in the literature or estimated by fitting published experimental results in single mineral systems. The strong agreement between measurements and modelling results demonstrated that adsorption processes exerted a major control on the EAP of the soil over a large range of pH values. An influence of the precipitation of P-containing mineral is discounted based on thermodynamic calculations. Modelling results indicated that the variations in P–CaCl₂ with soil pH were controlled by the deprotonation/protonation of the surface hydroxyl groups, the distribution of P surface complexes, and the adsorption of Ca and Cl from the electrolyte background. Iron-oxides and gibbsite were found to be the major P-adsorbing soil constituents at acidic and alkaline pHs, whereas P was mainly adsorbed by clay minerals at intermediate pH values. This study demonstrates the efficacy of geochemical modelling to understand soil processes, and the applicability of mechanistic adsorption models to a ‘real’ soil, with its mineralogical complexity and the additional contribution of soil organic matter.

Arsenic mobility from anthropogenic impoundment sediments – Consequences of contamination to biota, water and sediments, Poša, Eastern Slovakia by Edgar Hiller; L’ubomír Jurkovič; Jozef Kordík; Igor Slaninka; Michal Jankulár; Juraj Majzlan; Jörg Göttlicher; Ralph Steininger (pp. 2175-2185).

An impoundment located near the village of Poša, Slovakia, is a significant source of contamination with As originating from the deposited coal fly-ashe. Waters penetrating the impoundment are enriched in As and other potentially toxic elements. As a consequence of the contamination, the Kyjov Brook and the Ondava River have been extensively polluted. The mobility and solid-state partitioning of As in the impoundment material and stream sediments were investigated using column leaching and batch extraction tests, and a five-step sequential extraction procedure. Moreover, to investigate the bioavailability of As, two native plant species ( Typha latifolia, or cattail, and Phragmites australis, or common reed) growing at the site were collected and analyzed. The As concentrations in representative sediment and water samples ranged from 36.3 to 3210mg/kg and from 4.05 to 613μg/L, respectively, both being many times above the background levels. Although a part of As was present in a readily soluble form (6.6%), the majority of As was mainly associated with Fe and Mn oxides (37%) and residual phases (51%). Combined results of the column leaching, batch extraction, and sequential extraction tests, as well as mineralogical analysis, indicated that As mobilisation potential from the sediments is likely controlled by Fe, Al and Mn oxides, and by pH. There was no influence of various anions (PO43-,SO42-,NO3-,Cl-andHCO3-) on As mobility when present in aqueous solution at concentrations analogous to those in the water of the Kyjov Brook. Plants growing in the impoundment had As concentrations 10–100 times greater than did the same plants growing in a relatively non-polluted area.

Phosphorus transport and speciation in the Changjiang (Yangtze River) system by Qing-Zheng Yao; Zhi-Gang Yu; Hong-Tao Chen; Peng-Xia Liu; Tie-Zhu Mi (pp. 2186-2194).

Dissolved and particulate samples were collected from the Changjiang (Yangtze River) in April and September 2006 to determine the sources and distribution of P species in the river system. Concentrations of DIP, DOP and TP varied obviously throughout the basin, and displayed short-term variability and seasonal change. The predominant species of DTP wasPO43-. The concentrations of P are related to water discharge, suspended particulate matter and anthropogenic influences. Based on the study data, the nutrient and the sediment retention capacity of the Three Gorges Reservoir (TGR) were quantified. The P species structure has a significant change throughout the TGR. A mass balance analysis revealed that the reservoir was temporarily acting as a DOP source. Some long-term data forPO43- concentration at the Datong station are presented. ThePO43- level has increased in the last three decades because of the increased use of chemical fertilizer.

Chemical weathering in Luzon, Philippines from clay mineralogy and major-element geochemistry of river sediments by Zhifei Liu; Yulong Zhao; Christophe Colin; Fernando P. Siringan; Qiong Wu (pp. 2195-2205).

Clay mineralogy and major-element geochemistry of 35 surface sediment samples collected in 21 major to moderate rivers of Luzon, Philippines are used to evaluate the present chemical weathering process. The clay mineral assemblage consists mainly of smectite (average 86%) with minor kaolinite (9%) and chlorite (5%) and very scarce illite (1%), and does not show strong island-wide differences. The major element results of both bulk and clay-fraction sediments indicate that the formation of clay minerals is accompanied by leaching of Ca and Na first and of Fe and Mn thereafter during the chemical weathering process. A low-moderate chemical weathering degree of bulk sediments and a moderate-intensive degree of clay-fraction sediments are obtained in Luzon rivers based on proxies of chemical index of alteration (CIA) and smectite crystallinity. It is suggested that the majority of andesitic–basaltic volcanic and sedimentary rocks along with the tectonically active geological setting and sub-tropical East Asian monsoon climate are responsible for the predominance of smectite in the clay mineral assemblage.

Comment on “Reduction of chromate by granular iron in the presence of dissolved CaCO₃”, by L. Gui, Y.Q. Yang, S.-W. Jeen, R.W. Gillham, D.W. Blowes by C. Noubactep (pp. 2206-2207).

Reply to the Comment on “Reduction of chromate by granular iron in the presence of dissolved CaCO₃” by C. Noubactep by Lai Gui; Sung-Wook Jeen; David W. Blowes; Robert W. Gillham; YanQi Yang (pp. 2208-2210).

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Applied Geochemistry (v.24, #11)