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《Applied Geochemistry》2006,21(4):632-642
Acid volatile sulfide (AVS) is an operationally defined sulfide fraction, which is considered important for trace metal fate in reduced sediments. Understanding AVS formation rates is important for the management of metal polluted sediment. However, little is known about the fate and dynamics of AVS in spatially and seasonally variable freshwater environments. The authors monitored in situ AVS formation and degradation and simultaneously extracted metals (SEM) in two floodplain lakes and compared this to AVS formation rates in laboratory experiments with the same sediment. In the laboratory experiments, the formation rates of AVS were studied at 20 °C for initially oxidized sediments that were: (a) untreated; (b) enriched with extra ; and (c) treated with sodium-azide (biocide). In the field, AVS concentrations were highly variable and were significantly correlated to surface water temperature and O2 concentrations as well as to sediment composition. Between February and August, AVS formation was approximately linear at a rate of 0.07 μmol g−1 d−1. Degradation rates differed drastically between the lakes due to different degradation mechanisms. In one lake AVS removal was caused by reworking and oxygenation of the sediments by bream (Abrami brama), at a rate of 0.25 μmol g−1 d−1. In the other lake AVS removal was caused by desiccation, at a rate of ±2.6 μmol g−1 d−1. This illustrates the large differences that can be found between similar lakes, and the importance of biological processes. In the laboratory, concentrations of AVS with and without addition were similar during the first weeks, and increased at a rate of 0.15 μmol g−1 d−1. However, addition increased the AVS concentration at the end of the experiment, whereas sodium-azide eliminated AVS formation, as expected. This suggests that AVS formation was -limited in the laboratory as well as in these shallow freshwater lakes. 相似文献
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Fabrice Fraysse Oleg S. Pokrovsky Jacques Schott Jean-Dominique Meunier 《Chemical Geology》2009,258(3-4):197-206
In order to better understand the reactivity of plant phytoliths in soil solutions, we determined the solubility, surface properties (electrophoretic mobilities and surface charge) and dissolution kinetics of phytoliths extracted from fresh biomass of representative plant species (larch tree and elm, horsetail, fern, and four grasses) containing significant amount of biogenic silica. The solubility product of larch, horsetail, elm and fern phytoliths is close to that of amorphous silica and soil bamboo phytoliths. Electrophoretic measurements yield isoelectric point pHIEP = 0.9, 1.1, 2.0 and 2.2 for four grasses, elm, larch and horsetail phytoliths respectively, which is very close to that of quartz or amorphous silica. Surface acid–base titrations allowed generation of a 2-pK surface complexation model (SCM) for larch, elm and horsetail phytoliths. Phytoliths dissolution rates, measured in mixed-flow reactors at far from equilibrium conditions at 1 ≤ pH ≤ 8, were found to be very similar among the species, and close to those of soil bamboo phytoliths. Mechanistic treatment of all plant phytoliths dissolution rates provided three-parameters equation sufficient to describe phytoliths reactivity in aqueous solutions:Alternatively, the dissolution rate dependence on pH can be modeled within the concept of surface coordination theory assuming the rate proportional to concentration of > SiOH2+, > SiOH0 and > SiO? species. In the range of Al concentration from 20 to 5000 ppm in the phytoliths, we have not observed any correlation between their Al content and solubility, surface acid–base properties and dissolution kinetics.It follows from the results of this study that phytoliths dissolution rates exhibit a minimum at pH ～ 3. Mass-normalized dissolution rates are similar among all four types of plant species studied and these rates are an order of magnitude higher than those of typical soil clay minerals. The minimal half life time of larch and horsetail phytoliths in the interstitial soil solution ranges from 10–12 years at pH = 2–3 to < 1 year at pH above 6, comparable with mean residence time of phytoliths in soil from natural observations. 相似文献
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Carme Huguet Jung-Hyun Kim Gert J. de Lange Jaap S. Sinninghe Damsté Stefan Schouten 《Organic Geochemistry》2009,40(12):1188-1194
One of the primary prerequisites for the application of organic proxies is that they should not be substantially affected by diagenesis. However, studies have shown that oxic degradation of biomarker lipids can affect their relative distribution. We tested the diagenetic stability of the and TEX86 palaeothermometers upon long term oxygen exposure. For this purpose, we studied the distributions of alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) in different sections of turbidites at the Madeira Abyssal Plain (MAP) that experienced different degrees of oxygen exposure. Sediments were deposited anoxically on the shelf and then transported by turbidity currents to the MAP, which has oxic bottom water. This resulted in partial degradation of the turbidite organic matter as a result of long term exposure to oxic bottom water. Concentrations of GDGTs and alkenones were reduced by one to two orders of magnitude in the oxidized parts of the turbidites compared to the unoxidized parts, indicating substantial degradation. High-resolution analysis of the Pleistocene F-turbidite showed that the index of long chain alkenones increased only slightly (0.01, corresponding to <0.5 °C) in the oxidized part of the turbidite, suggesting minor preferential degradation of the C37:3 alkenone, in agreement with previous studies. TEX86 values showed a small increase (0.02, corresponding to ～2 °C) in the F-turbidite, like , while for other Pliocene/Miocene turbidites it either remained unchanged or decreased substantially (up to 0.06, corresponding to ～6 °C). Previous observations showed that the BIT index, a proxy for the contribution of soil organic matter to total organic carbon, was always substantially higher in the oxidized part in all the turbidites, as a result of preferential degradation of marine-derived GDGTs. This relative increase in soil-derived GDGTs affects TEX86, as the isoprenoid GDGT distribution on the continent can be quite different from that in the marine environment. Our results indicate that the organic proxies are affected by long term oxic degradation to different extents; this should be taken into account when applying these proxies in palaeoceanographic studies of sediments which have been exposed to prolonged oxic degradation. 相似文献
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Paul T. Behum Liliana Lefticariu Kelly S. Bender Yosief T. Segid Andrew S. Burns Charles W. Pugh 《Applied Geochemistry》2011
This study reports changes in coal-mine drainage constituent concentrations through an anaerobic SO4-reducing bioreactor monitored over a 3-a period. The purpose of the study was to identify and monitor over time the biogeochemical mechanisms that control the attenuation of toxic compounds in the mine drainage. This information is needed to investigate bioreactor performance and longevity. The water treated at the case example site, the Tab-Simco Mine, was highly acidic with an average pH of 2.9, a net acidity of 1674 mg/L CaCO3 equivalent-CCE, and high levels of dissolved , Al, Fe and Mn. The results of this study indicated that the treatment system increased the pH of the acid mine drainage (AMD) to 6.2 and decreased the median acidity to 22.7 mg/L CCE, from 2981 to 1750 mg/L, Fe from 450.6 to 1.76 mg/L, Al from 113 to 0.42 mg/L, and Mn from 36.4 to 23.3 mg/L. Geochemical modeling indicates that the bioreactor discharge is saturated with respect to the minerals alunite, gibbsite, siderite, rhodochrosite, jarosite, and Fe hydroxide precipitates. The observed trends also include seasonal variations in reduction and a general decline in the amount of alkalinity produced. The average δ34S value of the in the untreated AMD was +7.3‰. In the bioreactor, δ34S value of increased from an average of +6.9‰ to +9.2‰, suggesting the presence of bacterial SO4 reduction processes. Preliminary results of a bacterial community analysis show that DNA sequences corresponding to bacteria capable of SO4 reduction were present in the bioreactor outflow sample. However, these sequences were outnumbered by sequences similar to bacteria capable of reoxdizing reduced sulfur species. This study illustrates the dynamic nature of metal removal in SO4-reducing bioreactor-based treatment systems. 相似文献
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