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1.
Disposal of saline subsurface drainage waters from croplands into evaporation basins (or ponds) in the San Joaquin Valley of California causes excessive accumulation of salts and elevated concentrations of arsenic (As), a potentially high risk element with little information about its fate, in the agricultural evaporation ponds. We examined dissolved As concentration, speciation, and distribution in waters as well as As fractionation in sediments in the 10-cell South Evaporation Basin for better understanding of processes and conditions affecting As transformations and fate in a specific drainage disposal facility. The increase of total dissolved As concentrations were observed with higher Cl− and electric conductivity along flow path indicating that evaporation was an important factor regulating total dissolved As concentration. The increases of reduced As species such as arsenite [As(III)] and organic As (monomethylarsonic acid and dimethylarsinic acid) were found towards the terminal flow pathway. However, arsenate [As(V)], the oxidized species remained greater than 67% of total dissolved As in all cell waters. Sequential extractions of sediments indicated that reducing conditions may influence As behavior in sediments to be more soluble and exchangeable. Arsenic association with oxides was appreciable only under oxidizing condition. Carbonate minerals played an important role in immobilizing As into the sediments under alkaline condition and a broad range of redox conditions. However, these sink mechanisms did not significantly reduce As concentrations in the cell waters. The reducing condition facilitated by high concentration of organic matter might be a major factor for the increase in As mobility.  相似文献   

2.
The vertical distributions of dissolved Se species [Se(IV), Se(VI) and organic Se] and diagenetic constituents [Fe(II) and Mn(II)] were obtained in porewater samples of two Sudbury area lakes (Clearwater and McFarlane). The sedimentary concentration profiles of total Se, Se species bound to Fe–Mn oxyhydroxides and to organic matter, and of elemental Se were also determined along with the concentrations of Fe, Mn and S in different extractable fractions. Results indicated that the concentrations of total dissolved Se in porewater samples were very low, varying from around 2.0 nM to a maximum level of 6.5 nM, while the concentrations of total Se species in the solid phase varied between 2 and 150 nmol/g on a dry weight basis. The two lakes showed striking differences in the presence of Se(IV) and Se(VI) at the sediment–water interface (SWI). In Clearwater Lake, Se(VI) was present at this interface and Se(IV) was not detectable, whereas the opposite was found in McFarlane Lake. This suggests that reducing conditions might have existed near the SWI of McFarlane Lake at the sampling time; this hypothesis was confirmed by several other measured chemical parameters. The profiles of total dissolved Se of both lakes suggest upward and downward diffusion of dissolved Se species along the concentration gradients. Assuming that no precipitation occurred at the SWI, the fluxes of dissolved Se species across the SWI in Clearwater and McFarlane lakes were estimated to be 0.108 and 0.034 nmol cm−2 a−1, respectively. These values do not include the possible losses of volatile Se species due to microbial methylation. In the reducing sediments of both lakes, the formation of elemental Se and pyritic Se were found to be important mechanisms for controlling the solubility of Se in this environment. The main geochemical processes involving Se identified in this study are: the adsorption of Se onto Fe–Mn oxyhydroxides at or near the SWI, the release of adsorbed Se by the reduction of the same oxyhydroxides and the mineralization of organic matter, and the removal of Se from porewaters to form elemental Se and a S mineral phase such as Se–pyrite or pure ferroselite.  相似文献   

3.
Sediment and porewater samples (1997–1999) were collected in the Northern Reach of the San Francisco Bay and Sacramento–San Joaquin Delta for determinations of sedimentary selenium and its chemical speciation. Total sedimentary selenium increased with depth, with approximately 50% of the sedimentary selenium as elemental selenium and 35% as organic selenide. Porewater total dissolved selenium increased with depth in the estuary and Delta, and fluxes out of the sediments were calculated at 0.01 and 0.06 nmol cm−2 year−1 for the estuary and Delta, respectively. Present-day sediment–water exchange of dissolved selenium and internal transformations cannot explain the observed increase in total sedimentary selenium with depth. However, mass balance calculations demonstrate that the increase in total selenium with depth may be linked to higher dissolved selenium concentrations in the water column in the 1980s, suggesting that the sediments could be used as historical recorders of selenium in the estuary.  相似文献   

4.
Since 1982, estimated amounts of 9,400 t, 15,000 kg, 720 kg and 105 kg of Si, Fe, As and Cs respectively have accumulated at the bottom of 18 evaporation ponds as part of the geothermal production cycle at Los Azufres. This accumulation is caused by precipitation of brine solutes during the evaporation of 10% of the total pond water volume before its re-injection into the reservoir. Extraction experiments with pond precipitates and geochemical simulations with the PHREEQC program indicate the high solubility of most precipitates under natural environmental conditions. The comparisons with the primary brine composition indicate that less than 1% of most dissolved brine solutes, except for Co, Cu, Mn, Pb, Ag, Fe and Si, are accumulated at the pond bottom. Arsenic has maximum values of 160 mg/kg in the pond sediments, and Mo, Hg and Tl also exceed international environmental standards for contaminated soils. Elevated concentrations and the mobility potential of several metals and non-metals require the application of remediation techniques for the final disposal of the sediments in the future.  相似文献   

5.
Analytical methods of dissolved Se species in river water and seawater were established and applied to study dissolved Se speciation in the Kaoping and Erhjen rivers and estuaries, southwestern Taiwan. The Kaoping and Erhjen rivers and estuaries were respectively in relatively oxygenated and oxygen-deficient conditions as revealed from the distributions of dissolved oxygen, DOC, nutrients, and dissolved Mn. Concentrations of dissolved total Se increased downstream in the riverine sections, ranging from 0.6 nM to 1.2 nM for the Kaoping River and from 0.8 nM to 1.05 nM for the Erhjen River. The dissolved total Se was only slightly higher in the Erhjen middle estuary than in the Kaoping middle estuary in spite of heavier pollution in the former. The dissolved total Se behaved rather conservatively in the Kaoping estuary but nonconservatively in the Erhjen estuary resulting from anthropogenic inputs, and in this respect showed similarities with the behavior of redox-sensitive Mn. The predominant species of selenium were Se(VI) and organic Se in the Kaoping River and Se(VI) in the Kaoping estuary. The elevated concentration of Se(VI) in the Kaoping estuary may stem from the degradation of organic Se and oxidation of Se(IV). On the other hand, Se(IV) and organic Se were equally dominant in the Erhjen River, and Se(IV) was predominant through most of the Erhjen estuary. The elevated distribution of Se(IV) in the Erhjen middle estuary may result mostly from partial decomposition of organic Se, but further oxidation of Se(IV) was inhibited in reducing waters. However, Se(VI) became dominant at Erhjen outer estuary where water was oxygenated by the replacement of intruded coastal seawater. Apparently, the speciation of dissolved Se was mainly controlled by the biological and redox processes in the Kaoping and Erhjen rivers and estuaries.  相似文献   

6.
Arctic rivers typically transport more than half of their annual amounts of water and suspended sediments during spring floods. In this study, the Sagavanirktok, Kuparuk and Colville rivers in the Alaskan Arctic were sampled during the spring floods of 2001 to determine levels of total suspended solids (TSS) and dissolved and particulate metals and organic carbon. Concentrations of dissolved organic carbon (DOC) increased from 167 to 742 μmol/L during peak discharge in the Sagavanirktok River, at about the same time that river flow increased to maximum levels. Concentrations of dissolved Cu, Pb, Zn and Fe in the Sagavanirktok River followed trends observed for DOC with 3- to 25-fold higher levels at peak flow than during off-peak discharge. Similar patterns were found for the Kuparuk and Colville rivers, where average concentrations of dissolved trace metals and DOC were even higher. These observations are linked to a large pulse of DOC and dissolved metals incorporated into snowmelt from thawing ponds and upper soil layers. In contrast with Cu, Fe, Pb and Zn, concentrations of dissolved Ba did not increase in response to increased discharge of water, TSS and DOC. Concentrations of particulate Cu, Fe, Pb and Zn were more uniform than observed for their respective dissolved species and correlated well with the Al content of the suspended particles. However, concentrations of particulate Al were poorly correlated with particulate organic carbon. Results from this study show that >80% of the suspended sediment and more than one-third of the annual inputs of dissolved Cu, Fe, Pb, Zn and DOC were carried to the coastal Beaufort Sea in 3 and 12 d, respectively, by the Kuparuk and Sagavanirktok rivers.  相似文献   

7.
以拜泉地区1：5万土地质量地球化学调查数据为基础,开展硒地球化学特征及生态效应研究,探讨硒元素在土壤-植物系统中的迁移富集规律.研究表明：拜泉地区根系土硒含量均值为0.25×10-6,属中等富硒土壤,黄豆和水稻富硒占比相对较高;水溶态硒和离子交换态硒含量之和约为5%,一定程度上制约硒的有效量.土壤理化性质对硒全量、硒形态及其迁移富集具有重要影响：碱性-中性土壤硒含量基本不受pH制约,硒多以亚硒酸盐形式存在,不利于硒元素的转移和植物吸收;硒全量（有效量）与有机质呈显著正相关关系,但有机质含量超过某一界限后,有机质含量的增加虽然可以提高硒含量水平,但也抑制硒元素的迁移富集.  相似文献   

8.
Sediment cores were sampled from Xiamen Western Bay at five sites during the summer and winter of 2006 and Hg–Au microelectrodes were used to make on board measurements of the concentration gradients of dissolved oxygen, Mn2+, and Fe2+ within the sediments. The O2 concentrations decreased sharply from about 200 μmol L−1 in the bottom seawater to zero within a depth of a few millimeters into the sediment. Dissolved Mn2+ was detected below the oxic zones with peak concentrations up to 600 μmol L−1, whereas dissolved Fe2+ had peak concentrations up to 1,000 μmol L−1 in deeper layers. The elemental contents of organic carbon and nitrogen within the sediments were analyzed and their C/N ratios were in the range of 9.0 to 10.1, indicative of heavy terrestrial origin. Sediments from two sites near municipal wastewater discharge outlets had higher organic contents than those from the other sites. These high organic contents corresponded to shallow O2 penetration depths, high dissolved Mn2+ and Fe2+ concentrations, and negative redox potentials within the sediments. This indicated that the high organic matter content had promoted microbial respiration within the sediments. Overall, the organic content did not show any appreciable decrease with increasing sediment depths, so a quadratic polynomial function was used to fit the curve of O2 profiles within the sediments. Based on the O2 profiles, O2 fluxes across the seawater and sediment interface were estimated to be in the range 6.07 to 14.9 mmol m−2 day−1, and organic carbon consumption rates within the surface sediments were estimated to be in the range 3.3 to 20.8 mgC cm−3 a−1. The case demonstrated that biogeochemistry within the sediments of the bay was very sensitive to human activities such as sewage discharge.  相似文献   

9.
 As, Be, Cd, Co, Cr, Cu, Hg, Ni, Pb, V, Se and Zn concentrations were determined and compared in lake and overbank sediments from 33 catchments without local pollution sources in southern Norway. There were no significant differences in concentrations of Be, Co, Cr, Cu, Ni, and V in overbank and pre-industrial lake sediments. In areas with shallow overburden, and significant influence from long-range atmospheric pollution, concentrations of As, Cd, Hg, Pb, Se, and Zn in overbank sediments were probably modified by vertical percolating water. In such areas, we suggest using lake sediments as a better sampling medium for mapping pre-industrial concentrations. Pre-industrial lake sediments yield natural concentrations of Hg and Se, which consist of both geogenic and natural atmospheric deposition. Important covariables like organic carbon content, Fe oxides, and fine mineral fraction were generally higher in pre-industrial lake sediments as compared to overbank sediments. By adjusting for such differences overbank sediments could be used as an alternative in mapping background concentrations of trace metals in regions with few lakes. Received: 19 February 1999 · Accepted: 17 April 1999  相似文献   

10.
The Carson River Superfund Site in west-central Nevada is an area of Hg-contaminated soil, sediment, water, air, and biola resulting from the amalgamation milling of Ag-Au ores of the Comstock lode worked approximately a century ago. In order to develop an understanding of the behavior, transport, and fate of Hg at this site, a technique was developed to estimate the proportions of total, elemental, exchangeable, organic, and sulfide Hg in soils, sediments, and tailings.Results of this analysis performed on active Carson River sediments indicate that Hg is selectively dissolved out of Hg-Au amalgam particles and subsequently adsorbed to fine-grained sediments which are then deposited in downstream, low-energy reaches of the Carson River and Labontan Reservoir. In the relatively more-reducing environment of the reservoir Hg appears to be converted, in large part, to relatively-insoluble HgS.The original elemental form of Hg released to the environment is the chemical form which is still dominant in most highly-contaminated soils, sediments, and tailings. Deeper, more-reducing soil horizons, however, appear to fix a significant portion of the Hg as HgS, analogous to the Lahontan Reservoir example described above. This fixation as HgS is documented to be largely limited to higher-sulfur areas where sulfide minerals from the Comstock ores increase the total sulfur concentrations of contaminated soils, sediments, and tailings.  相似文献   

11.
The water, pore water, sediment, and fish samples were collected from the Hongfeng Reservoir in November 2003 and February 2004 in accordance with trace metal protocols. The average concentrations of total mercury （THg）, dissolved mercury （DHg）, reactive mercury, dissolved gaseous mercury, total methylmercury, and dissolved methylmercury in the water columns were 8.00, 5.70, 0.63, 0.05, 0.16, and 0.07 ng/L, respectively. THg and DHg in the water columns, THg in pore water and THg in lake sediments of the Hongfeng Reservoir showed the level of mercury in the Hongfeng Reservoir was higher than in other natural waters in the world due to the loading of a lot of waste water with relatively high concentrations of mercury, whereas methylmercury concentrations in fish （wet weight） varied from 1.73-51.00 ng/g, much lower than in most remote lakes and reservoirs reported in northern Europe and North America. Methylmercury distributions in pore water and sediments showed methylation occurred mainly in the upper several centimeters of sediment cores in the Hongfeng Reservoir. The concentrations of dissolved organic carbon, total suspended particles, total Hg, and methylmercury were higher at Houwu than those at Daba in November 2003. It is suggested that other pollutants such as N and P from fishing farm and other waste water at Houwu, which resulted in deterioration of water quality, affected the concentrations and distributions of mercury species in the reservoir.  相似文献   

12.
The results of a study of the contribution of microbial metabolic products to total dissolved organic carbon (DOC) levels in coastal sediments are presented. The data indicate that acidic volatile compounds make up a substantial fraction of pore water DOC's in both oxic and anoxic pore waters of coastal marine sediments. Formic, acetic and butyric acids are the principal volatile species identified at levels exceeding 10 μM. Acid concentrations are up to five times higher in anoxic pore waters than in oxic waters. Volatile organic acids show promise as indicators of diagenetic processes in marine sediments and of the ecological succession of microorganisms, in particular.  相似文献   

13.
The Casamance estuary, on the coast of Senegal, is an inverse hypersaline estuary: salinity increases landward, and dry season salinity values are up to 172 psu due to the evaporation of seawater. Dissolved inorganic carbon (DIC) concentrations decreased landward as a negative linear function of salinity. Thermodynamic modelling and the absence of CaCO3 in the sediments indicate that this loss of DIC was not due to calcite precipitation in the main water body. The innermost, almost landlocked, waters contained high phytoplankton biomass (50–300 μg chl I?1) and high concentrations of allochthonous dissolved organic carbon. Photosynthetic uptake of DIC and subsequent particulate organic carbon sedimentation is proposed as hypothetical explanation of the relationship between DIC and salinity; localized overheating in shallow waters might also be involved.  相似文献   

14.
西南寒武、二叠系富硒碳质岩中硒结合态的比较研究   总被引：6，自引：0，他引：6  
使用硒的7步连续化学提取技术,对采自贵州寒武纪牛蹄塘组和湖北恩施二叠纪茅口组富硒碳质岩中的水溶态、可交换态、有机态、元素态、酸性提取态、硫化物/硒化物态和残渣态硒进行了比较研究,应用氢化物－原子荧光法测定了岩石总硒和各结合态硒。结果表明,恩施二叠纪沙地新鲜富硒碳质硅质岩和碳质页岩中的硒主要以有机结合态和硫化物/硒化物态硒为主,残渣态硒较低;遵义松林早寒武世碳质硅质岩中的硒主要以有机结合态和硫化物态硒为主,碳质页岩与镍钼矿层中则以有机结合态、残渣态和硫化物态硒为主,斑脱岩中主要以有机结合态、元素态和可交换态硒为主。根据硒结合态的这种分布特征,推测二叠纪、寒武纪富硒碳质岩中硒初始富集的生物地球化学过程略有差异：前者碳质硅质岩中主要以微生物还原为主,碳质页岩中则是微生物还原作用和生物同化吸收或吸附兼而有之;后者主要以生物同化吸收或吸附为主,微生物还原次之。  相似文献   

15.
Using stable isotope tracer techniques in 4-h bottle incubations, the importance of organic matter transfer from phytoplankton to heterotrophic bacteria (bacteria) has been re-evaluated in the Delaware Estuary, considering carbon (C) and nitrogen (N) cycles separately. The hypothesis is that the transfer of C and N from phytoplankton to bacteria varies both temporally and spatially along estuarine gradients in response to variation in factors such as terrestrial organic C supply, inorganic N speciation and concentrations, and extracellular release of dissolved organic matter by phytoplankton. The percentage of autochthonous dissolved organic C being assimilated by bacteria varied between 3% and 10% of primary production and was not related to the rate of primary production. The transfer of N was considerably more variable when compared to C transfer, averaging ca. 20% of phytoplankton N assimilation; individual experiments yielded rates as high as 50%. Unlike C, autochthonous dissolved organic N transfer appears to vary with the magnitude of primary production, and its assimilation by bacteria accounted for 0–56% of the total measured bacterial N uptake. The results highlight the importance of separate consideration of C and N elemental cycles in evaluating sources of organic matter to the estuarine microbial loop.  相似文献   

16.
To understand the impact of Selenium (Se) into the biogeochemical cycle and implications for palaeo-redox environment, a sequential extraction method was utilized for samples including black shales, cherts, a Ni-Mo-Se sulfide layer, K-bentonite and phosphorite from Lower Cambrian Se-enriched strata in southern China. Seven species (water-soluble, phosphate exchangeable, base-soluble, acetic acid-soluble, sulfide/selenide associated, residual Se) and different oxidation states (selenate Se(VI), selenite Se(IV), organic Se, Se (0) and mineral Se(-II)) were determinated in this study. We found that the Ni-Mo-Se sulfide layer contained a significantly greater amount of Se(-II) associated with sulfides/selenides than those in host black shales and cherts. Furthermore, a positive correlation between the degree of sulfidation of iron (DOS) and the percentage of the sulfide/selenide-associated Se(-II) was observed for samples, which suggests the proportion of sulfide/selenide-associated Se(-II) could serve as a proxy for palaeo-redox conditions. In addition, the higher percentage of Se(IV) in K-bentonite and phosphorite was found and possibly attributed to the adsorption of Se by clay minerals, iron hydroxide surfaces and organic particles. Based on the negative correlations between the percentage of Se(IV) and that of Se(-II) in samples, we propose that the K-bentonite has been altered under the acid oxic conditions, and the most of black shale (and cherts) and the Ni-Mo-Se sulfide layer formed under the anoxic and euxinic environments, respectively. Concerning Se accumulation in the Ni-Mo-Se sulfide layer, the major mechanism can be described by (1) biotic and abiotic adsorption and further dissimilatory reduction from oxidized Se(VI) and Se(IV) to Se(-II), through elemental Se, (2) contribution of hydrothermal fluid with mineral Se(-II).  相似文献   

17.
Selenium (Se) concentrations more than 12 times greater than the provincial freshwater quality guideline (2 µg/L) were detected in the Elk River downstream from the five open-pit coal mines in southeastern British Columbia's Elk River Valley. To identify possible sources of Se to the Elk River, samples from the coal-bearing Mist Mountain Formation were studied using X-ray diffraction, elemental and oxide analyses, sequential extractions and heavy liquid separation. Between 2.5 and 21.3% of the total Se in the five types of materials studied is water-soluble and 1.0 to 10.6% is associated with hydrous ferric and manganese oxides. Se associated with sulphides and organic material varies between 60 and 84% of the total Se and Se in the silicate structure varies from 5.9 to 24.7%. The ratio of sulphides to the total of organic carbon is well-correlated with the amount of Se in materials closely associated with coal seams containing less than 6 mg/kg of Se (r=0.916). This may suggest that the amount of organic matter present during deposition affects the amount of Se incorporated into sulphides.  相似文献   

18.
Organic matter was isolated from the water columns and sediments of two pond systems in the south-eastern United States. Water column material was ultrafiltered to provide three fractions, i.e. <0.45 μm, but > 50,000 daltons; <50,000 daltons, but > 5000 daltons; and <5000 daltons. Sedimentary organic matter was separated into humic acid and fulvic acid fractions based on solubility criteria and the humic acid fraction was ultrafiltered to provide the same fractions as the water column isolates. All fractions were analysed for organic carbon, Al, Ca, Cu, Fe, Mg and Mn. Infra-red spectra were also measured for the sedimentary organic fractions. Organic matter isolated from the water column of the two ponds had similar organic carbon and elemental distributions, as did the organic matter isolated from the two sediments. However, significant differences in the organic carbon and elemental distributions were observed for water column and sedimentary organic matter isolated from the same pond. These studies have relevance to diagenetic alterations of organic matter and geochemical cycles of elements within lakes.  相似文献   

19.
Rates of sulfate reduction, oxygen uptake and carbon dioxide production in sediments from a short Spartina alterniflora zone of Great Sippewissett Marsh were measured simultaneously during late summer. Surface sediments (0–2 cm) were dominated by aerobic metabolism which accounted for about 45% of the total carbon dioxide production over 0–15 cm. Rates of sulfate reduction agreed well with rates of total carbon dioxide production below 2 cm depth indicating that sulfate reduction was the primary pathway for sub-surface carbon metabolism. Sulfate reduction rates were determined using a radiotracer technique coupled with a chromous chloride digestion and carbon disulfide extraction of the sediment to determine the extent of formation of radiolabelled elemental sulfur and pyrite during shortterm (48 hr) incubations. In the surface 10 cm of the marsh sediments investigated, about 50% of the reduced radiosulfur was recovered as dissolved or acid volatile sulfides, 37% as carbon disulfide extractable sulfur, and only about 13% was recovered in a fraction operationally defined as pyrite. Correlations between the extent of sulfate depletion in the marsh sediments and the concentrations of dissolved and acid volatile sulfides supported the results of the radiotracer work. Our data suggest that sulfides and elemental sulfur may be major short-term end-products of sulfate reduction in salt marshes.  相似文献   

20.
Extracellular enzymatic hydrolysis of high-molecular weight organic matter is the initial step in sedimentary organic carbon degradation and is often regarded as the rate-limiting step. Temperature effects on enzyme activities may therefore exert an indirect control on carbon mineralization. We explored the temperature sensitivity of enzymatic hydrolysis and its connection to subsequent steps in anoxic organic carbon degradation in long-term incubations of sediments from the Arctic and the North Sea. These sediments were incubated under anaerobic conditions for 24 months at temperatures of 0, 10, and 20 °C. The short-term temperature response of the active microbial community was tested in temperature gradient block incubations. The temperature optimum of extracellular enzymatic hydrolysis, as measured with a polysaccharide (chondroitin sulfate), differed between Arctic and temperate habitats by about 8-13 °C in fresh sediments and in sediments incubated for 24 months. In both Arctic and temperate sediments, the temperature response of chondroitin sulfate hydrolysis was initially similar to that of sulfate reduction. After 24 months, however, hydrolysis outpaced sulfate reduction rates, as demonstrated by increased concentrations of dissolved organic carbon (DOC) and total dissolved carbohydrates. This effect was stronger at higher incubation temperatures, particularly in the Arctic sediments. In all experiments, concentrations of volatile fatty acids (VFA) were low, indicating tight coupling between VFA production and consumption. Together, these data indicate that long-term incubation at elevated temperatures led to increased decoupling of hydrolytic DOC production relative to fermentation. Temperature increases in marine sedimentary environments may thus significantly affect the downstream carbon mineralization and lead to the increased formation of refractory DOC.  相似文献   

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