Arsenic, iron and sulfur co-diagenesis in lake sediments

Profiles of porewater pH and dissolved As, Fe, Mn, sulfate, total sulfide (ΣS^−II), total zero-valent sulfur (ΣS⁰), organic carbon and major ion concentrations, as well as those of solid As, acid-volatile sulfide (AVS), total S, Fe, Mn, Al, organic C, ²¹⁰Pb and ¹³⁷Cs were determined in the sediment of four lakes spanning a range of redox and geochemical conditions. An inverse modeling approach, based on a one-dimensional transport-reaction equation assuming steady-state, was applied to the porewater As profiles and used to constrain the net rates of reactions involving As (). The model defines depth intervals where As is either released to (positive ) or removed from (negative ) the porewaters.At two of the sites, whose bottom water were oxygenated at sampling time, a production zone ( = 12 × 10⁻¹⁸ mol cm⁻³ s⁻¹-71 × 10⁻¹⁸ mol cm⁻³ s⁻¹) is inferred a few cm below the sediment-water interface, coincident with sharp porewater As and Fe peaks that indicate an intense coupled recycling of As and Fe. This process is confirmed by solid As and Fe maxima just below the sediment surface. In these two lakes a zone of As consumption ( = −5 × 10⁻¹⁸ mol cm⁻³ s⁻¹ to −53 × 10⁻¹⁸ mol cm⁻³ s⁻¹), attributed to the slow adsorption of As to authigenic Fe oxyhydroxides, occurs just above the production zone. A second-order rate constant of 0.12 ± 0.03 cm³ mol⁻¹ s⁻¹ is estimated for this adsorption reaction.Such features in the porewater and solid profiles were absent from the two other lakes that develop a seasonally anoxic hypolimnion. Thermodynamic calculations indicate that the porewaters of the four lakes, when sulfidic (i.e., ΣS^−II ? 0.1 μM), were undersaturated with respect to all known solid As sulfides; the calculation also predicts the presence of As^V oxythioanions in the sulfidic waters, as suggested by a recent study. In the sulfidic waters, the removal of As ( = −1 × 10⁻¹⁸ mol cm⁻³ s⁻¹ to −23 × 10⁻¹⁸ mol cm⁻³ s⁻¹) consistently occurred when saturation, with respect to FeS_(s), was reached and when As^V oxythioanions were predicted to be significant components of total dissolved As. This finding has potential implications for As transport in other anoxic waters and should be tested in a wider variety of natural environments.     

Phosphorus speciation in surface sediments of a hypertrophic lake,Southwestern China: insights from fractionation and 31P NMR

Acta Geochimica - Phosphorus (P) species in surface sediments from a shallow, hypertrophic lake, Lake Dianchi, China, were investigated by P fractionation and 31P nuclear magnetic resonance (NMR)...     

Distribution patterns and potential ecological risk evaluation of heavy metals in the surface sediments of Beibu Gulf

The contents and distribution patterns of the heavy metals including Cu, Pb, Zn, Cd, As and Hg in the surface sediments of Beibu Gulf have been analyzed to understand the current pollution situation and the eclogical risk in Beibu Gulf. Hakanson's Potential Ecological Risk factors and indices were used to assess the potential ecological risk of heavy metals to marine ecosystem in Beibu gulf. The results showed that the contents of Cu,Pb,Zn,As and Cd were low, but in some sites Hg was higher than National Marine Sediments of I Quality Standard. The distribution trend of all the six heavy metals was similar in Leizhou Peninsula, Northwest and South Hainan Island, and the high value zone appeared in the vicinity of Dongfang City. The results of principal component analysis showed that the three major sources of heavy metals contamination were industrial wastewater, agricultural wastewater and degradation of organic matter, with the first three principal components contribution rates of 47.13%, 18.44% and 18.35%. The potential ecological risk of heavy metals for the single element shows that the potential ecological risk order of these heavy metals is Hg＞Cd＞As＞Pb＞Cu＞Zn.And the potential ecological risk of As, Pb, Cu, Zn and Pb is minor, and the potential ecological risk of Hg is great. The comprehensive analysis of potential ecological risk of heavy metals show that Beibu gulf is of intermediate level, while some areas have reached strong level. The estuary of Changhua River has the lowest sediment environmental quality, and more attention must be paid to these areas.     

Potential ecological risk assessment,enrichment, geoaccumulation,and source identification of metals in the surface sediments of Choghakhor Wetland,Iran

This study reported the first comprehensive research on identification of metal concentrations (Fe, Mg, Mn, Pb, Cd, Cr) in order to provide baseline data for future studies, identify possible sources, determine degree of pollution, and identify potential ecological risks of metals in surface sediments from Iran’s Choghakhor Wetland. The order of metal concentration was as follows: Fe > Mg > Mn > Pb > Cd > Cr, with mean concentrations of 6140.35, 1647.32, 289.03, 1.10, and 0.45 µg/g of dry weight, respectively. These results reveal that Choghakhor Wetland is not heavily polluted compared to other regions. The results of enrichment factor (EF) and geoaccumulation index (I _geo) showed that Fe, Pb, Mg, Cr, and Mn presented low levels of contamination and probably originated from natural sources. On the other hand, the results of EF and I _geo indices suggested that Cd concentrations in sediments of Choghakhor Wetland originated from anthropogenic sources. Based on the results of three sets of sediment quality guidelines, only Cd concentration in sediments of Choghakhor Wetland is a threat for aquatic organisms of Choghakhor Wetland. The results of multivariate analysis such as principal component analysis and cluster analysis showed that Fe–Mn, Cr–Mg, and Pb groups originated from natural sources, while Cd concentrations in sediments of Choghakhor Wetland originated from both natural and anthropogenic sources (mainly chemical fertilizers). To our knowledge, this is the first study about metal concentrations in sediments of Choghakhor Wetland, and because of low levels of these metals, these concentrations can be considered background levels for future investigation.     

北部湾海域表层沉积物中重金属元素分布特征及潜在生态危害评价

为深入了解北部湾海域沉积物污染现状及生态风险,分析了Cu、Pb、Zn、Cd、As、Hg 6种重金属元素在北部湾海域表层沉积物中的含量及分布特征,并运用潜在生态危害指数法评价了这些重金属元素对研究区生态系统的潜在危害。结果表明: Cu、Pb、Zn、As、Cd元素含量不高,仅部分站位Hg元素含量高于国家Ⅰ类海洋沉积物标准值; 6种重金属元素在雷州半岛、海南岛西北部以及海南岛南部分布趋势相似,高值区均出现在东方市附近。主成分分析结果表明,重金属来源主要有3个途径,分别是工业及生活排污、农业(农药、化肥等)残留和有机物降解,前3个主成分贡献率分别为47.13%、18.44%和18.35%。单项重金属元素潜在生态风险等级评价结果显示,研究区重金属元素潜在生态风险强弱次序为Hg＞Cd＞As＞Pb＞Cu＞Zn,As、Pb、Cu、Zn和Cd重金属元素潜在生态风险等级为轻微,而Hg潜在生态风险等级达到了强级。多项重金属元素潜在生态危害评价综合分析结果显示,北部湾海域生态风险等级为中等,部分区域生态风险等级达到了强级,特别是昌化江入海口附近地质环境较差,相关部门应予以足够重视。     

雄安新区白洋淀表层沉积物重金属地球化学特征及生态风险评价

【研究目的】白洋淀为雄安新区核心生态功能区,为支撑白洋淀湿地生态修复与保护,系统开展了全淀区表层沉积物环境质量调查。【研究方法】在白洋淀湿地采集表层沉积物样品484组,查明了白洋淀表层沉积物重金属地球化学特征,并采用地累积指数法、潜在生态风险指数法等多种方法开展了重金属生态风险评价。【研究结果】白洋淀表层沉积物重金属含量普遍偏高于河北省表层土壤重金属含量背景值,府河入淀口及白沟引河入淀口为重金属元素主要富集区,入淀河流输入为白洋淀重金属主要来源;环境地球化学综合评价结果为清洁无污染等级分布面积144.54 km²,占表层沉积物分布总面积的96.68%;各重金属污染程度由重到轻排序为Cd＞Cu＞Hg＞Pb＞Zn＞Ni＞Cr＞As,Cd元素污染程度等级以中度和偏中度为主,Cu元素以轻度和清洁为主,其他元素以清洁无污染为主;重金属潜在生态风险以轻度和中度为主,河流入淀口所在淀区重金属潜在生态风险高于其他淀区,潜在生态风险由高到低排序为南刘庄＞烧车淀＞小白洋淀＞王家寨＞藻苲淀＞捞王淀＞池鱼淀＞泛鱼淀。【结论】白洋淀表层沉积物环境质量总体较好,南刘庄等局部淀区存在重金属污染潜在生态风险,以Cd元素污染最为突出。创新点：采用地累积指数法、潜在生态风险指数法等多种方法,系统评价白洋淀湿地表层沉积物重金属污染程度和生态风险;重金属地球化学特征分析与主成分分析法相结合,揭示表层沉积物重金属污染主要来源为河流输入。     

Mobility and ecological risk assessment of heavy metals in surface sediments of Xiamen Bay and its adjacent areas,China

Xiamen Bay (XMB) has received substantial loadings of pollutants from industrial and municipal wastewater discharged since the 1980s. To assess ecological risks and the current spatial changes of metal contaminants in bottom surface sediments, 12 samples were collected. Samples were subjected to a total digestion technique and analyzed by ICP–OES for Cu, Pb, Zn, Cr, and Cd, and by AFS for Hg and As. Among these metals, Zn had the highest values (68–268 mg kg⁻¹), followed by Pb (27–71 mg kg⁻¹), and lower concentrations were found for Cd (42–1,913 μg kg⁻¹) and Hg (0–442 μg kg⁻¹). In comparison with the average crustal abundance values, the results indicated that nearly half of the sediment samples of XMB and its adjacent areas were contaminated by Cd, Pb, Zn, and As. Furthermore, based on the modified BCR sequential extraction procedure, the chemical speciation of heavy metals (Cd, Cr, Cu, Pb, Zn, Hg, and As) in selected sediment samples were evaluated in this study. Data from BCR sequential extractions indicated that Cd posed a medium ecological risk, whereas, Cr posed low risk since its exchangeable and carbonate fractions were below 4%, and the mobility of heavy metals in XMB decreased in the order Cd > Pb > Cu > Zn > Hg > As > Cr. By applying mean effects range median quotients (mERMQ), the results showed that Yuandang Lagoon with mERMQ value >0.5 would be expected to have the greatest potential toxic risk in amphipod within XMB and its adjacent areas.     

南通近海潮滩表层沉积物重金属含量特征与生态风险评价

基于南通近海(洋口港—吕四)潮滩特点布设潮滩断面并采集表层沉积物,根据样品汞、镉、铅、砷、铬等7种重金属元素含量测试结果,分析研究区沿海潮滩表层沉积物主要重金属元素含量特征,并与江苏其他滨岸地区潮滩沉积物的重金属含量进行对比,初步探讨2009—2012年南通沿海滩涂表层沉积物重金属含量变化与元素的相关性。采用潜在生态危害指数法评价南通近海潮滩表层沉积物中7种重金属元素的潜在生态危害系数及潜在生态风险。南通潮滩表层沉积物重金属含量分布均匀,且低于江苏省苏北其他地区沿海潮滩的沉积物含量。7种重金属元素的相关分析表明,Cu与Pb、Zn具有较好的相关性,Pb与Cd、Hg的相关性最差。潜在生态危害指数法评价表明,南通近岸潮滩表层沉积物7种重金属潜在生态危害系数均属低生态危害范畴,近岸海域(洋口港—吕四段)潮滩表层沉积物环境质量总体较好。     

我国渔港沉积物的重金属污染及潜在生态风险评价

分析了青岛、宁波、舟山、厦门、深圳、珠海、澳门、茂名和三亚共9个渔港（包括综合港口区）表层沉积物中的Cd、Cu、Pb、Zn、Co和Ni等典型重金属元素的含量,探讨了其可能的来源。采用沉积物质量基准法和Hakanson潜在生态风险指数法,评价了各渔港重金属的污染状况和潜在生态风险。结果表明：（1）渔港沉积物中重金属Cu、Zn、Pb和Cd的富集较为严重,位于珠江三角洲的渔港重金属含量显著高于其他渔港,尤其是Cu和Zn,最高含量分别达到1249mg／kg和664mg／kg,而Cd和Pb的污染也不容忽视;（2）珠三角渔港具“高”或“中等”潜在重金属生态风险,其中Cu和Cd具有高的潜在生态风险,其他渔港均属低生态风险,渔港总的潜在生态风险由高至低顺序为：澳门〉深圳〉珠海〉茂名〉三亚〉厦门〉青岛〉宁波〉舟山;（3）渔港沉积物中重金属主要来自工业废水、生活污水、污灌土壤以及大气沉降的污染和渔船防护漆的使用。而船体防护漆中Cu／氧化亚铜的大量使用是渔港中Cu污染的主要来源。     

Spatial variations and ecological risk assessment of heavy metals in surface sediments on the upper reaches of Hun River, Northeast China

The distribution, accumulation, and ecological risk of heavy metals (Cu, Cd, Pb, Zn, Ni, Cr, and As) in the surface sediment were investigated in the upper reaches of Hunhe River, Northeast China. Sediment samples from 51 points throughout the upper reaches of Hunhe River were collected and measured for heavy metal concentrations, TN content, and TP content. Results showed that heavy metal concentrations at the vicinity of mines and towns were higher than those at other locations. According to sediment quality guidelines (SQGs), Cd and Zn were enriched in the sediments. The correlation analysis and principal component analysis (PCA) were conducted to assess the heavy metal sources. Close correlations between metal distribution and TP indicated that the sediments may be affected by application of phosphate fertilizer. Elements, Cu, Cd, Pb, Zn, and As, were grouped together, reflecting they were released from the same sources. PCA suggested that their primary sources were anthropogenic, namely mining and extensive use of fertilizers. Therefore, heavy metal pollution due to mining and agricultural intensification in the upper Hunhe River basin should be taken into account during the formation of regional management strategies for the water environment.     

重庆南山老龙洞地下河表层沉积物重金属环境地球化学特征及生态风险评价

2013年12月采集了重庆南山老龙洞地下河表层沉积物样品,利用电感耦合等离子体质谱仪(ICPMS)、电感耦合等离子体发光质谱仪(ICP-OES)分析样品中Mn、Pb、Cu、As和Cr的含量,并用地累积指数法和潜在生态风险指数法对重金属的生态风险进行评估。结果表明:地下河表层沉积物存在重金属富集现象,富集程度依次为CrCuMnPbAs,其中UGR0处重金属污染相对较严重;地下河表层沉积物重金属含量主要受总有机碳(TOC)控制,与沉积物pH、粒径无显著相关性,TOC也控制着重金属稳定度,影响着重金属的迁移性,进而影响上覆水水质;地累积指数法评价显示地下河表层沉积物重金属整体上处于轻度污染状态,潜在生态风险指数法评价表明老龙洞地下河表层沉积物重金属含量水平引发有害生物效应的可能性不大。     

Distribution,fractionation, and contamination assessment of heavy metals in offshore surface sediments from western Xiamen Bay,China

Surface sediment samples were collected at 21 offshore sites in western Xiamen Bay, Southeast China. Total concentrations of Li, V, Cr, Co, Ni, Cu, Zn, Sr, Mn, Pb, Ba, Fe, and Ti were determined by inductively coupled plasma-optical emission spectrometry; Hg was determined by atomic fluorescence spectrometry. A modified BCR sequential extraction procedure was used to extract fractions of the above elements. Concentrations of Pb, Cr, and Hg at most sites met the primary standard criteria of Marine Sediment Quality except site S12 for Pb and S7 for Cr, while concentrations of Zn at 17 sites and Cu at seven sites exceeded the criteria. The mean concentration of Hg was three times higher than the background, with a possible source being the Jiulong River. Fe, Ti, Ba, Co, V, and Li dominated the residual phase, mainly from terrestrial input. Ni, Cr, Pb, and Hg in the non-residual phase varied largely between sites. Sr, Mn, Cu, and Zn were mainly in the non-residual fraction. Most sites showed considerable ecological risk; exceptions were site S7 (very high) and sites S10, S11, and S14 (moderate). Cu showed moderate-to-high pollution and Pb exhibited no-to-low pollution, while other metals had a non-pollution status according to their ratios of secondary phase to primary phase (RSP). Results of two assessment methods showed moderate pollution and a very high ecological risk for Cu, Zn, Ni, and Cr at site S7, which might be due to the local sewage treatment plant.     

Salinity control on long-chain alkenone distributions in lake surface waters and sediments of the northern Qinghai-Tibetan Plateau, China

Long-chain alkenones in lacustrine settings are potentially excellent biomarkers for the reconstruction of past terrestrial environmental conditions, and have been found in many different types of lakes around the globe. A wider range of factors influence the occurrence and distribution of alkenones in lake sediments and waters when compared to marine systems. Lake environmental conditions, such as temperature (in particular) and salinity, are among the key factors controlling alkenone distributions in lacustrine settings. Here we investigated alkenone distribution patterns in lakes of the northern Qinghai-Tibetan Plateau, China, and their possible relationship with environmental conditions, by analyzing paired samples of suspended particulate matter in surface waters and surface sediments. Salinity of investigated lake waters ranges from almost 0 to ∼100 g/L, while temperature variation among the lakes is minimal, effectively eliminating temperature effects on the alkenone distribution patterns observed here. We show that (1) alkenone concentrations vary substantially between the lakes, yet controlling mechanisms remain elusive; (2) C₃₇/C₃₈ ratios are substantially lower in the lakes of the Qaidam Basin than in the Lake Qinghai region, probably indicating different alkenone producers in the two regions; and (3) large variations in %C_37:4 (the percentage of the C_37:4 alkenone), determined from both surface waters and sediments, are negatively correlated with salinity. We suggest that the %C_37:4 index could be used as a salinity indicator at least on a regional scale, with careful considerations of other potentially complicating factors. However, potential reasons for why salinity could significantly affect %C_37:4 values need further investigation.     

Selective extraction of organically bound gold in soils, lake sediments and stream sediments

The extraction of organically bound gold from surficial materials is accomplished by using a solution of 5% sodium hypochlorite. A 10-g sample is digested at least twice with 50 mL of hypochlorite solution. The recovery of gold from the organic phase is nearly quantitative for lake sediments and stream sediments high in organic content. For stream sediments and soils low in organics, the recovery of gold is complicated by the sorption of released gold onto inorganic sample components. For these materials, recoveries as low as 70% of the organically bound gold are possible. For a stream sediment sample containing 53.4 ppb gold, the precision of the method is approximately 6% for a 10-g sample and 14% when a 5-g sample of stream sediment is used. The results obtained for all materials tested indicate that a substantial fraction of the gold found in sediments and soils exists as organically bound gold.     

广西茅尾海入海河口表层沉积物重金属分布及风险评价

为揭示茅尾海入海河口表层沉积物中重金属分布特征及生态风险,在茅岭江、大榄江、钦江入海河口采集13件表层沉积物样品进行重金属分析。研究结果表明,茅尾海沉积物中重金属As、Cd、Cr、Cu、Hg、Pb、Zn含量平均值分别为7.78×10-6、0.14×10-6、37.6×10-6、18.9×10-6、0.004 8×10-6、22.5×10-6、54.7×10-6,均低于GB 18668—2002的一类标准。沉积物中重金属空间分布差异较大,茅尾海东部工业区和西部茅岭江附近具有较高的重金属含量。重金属污染分析表明,大部分重金属元素显示为无污染—轻度污染水平,Cr具有中等污染水平;生态风险分析显示,重金属总体处于较低潜在风险,东部工业区Hg、Cd显示出中等生态风险。通过相关性分析、聚类分析、主成分分析探讨重金属污染物来源,结果显示重金属污染主要受河流控制,Hg、As、Cd还受到临港工业区废水排放的影响。综合研究表明,茅尾海生态环境总体较好,但建议重点关注东部工业区重金属排污状况。     

Evaluating the influence of lake morphology,trophic status and diagenesis on geochemical profiles in lake sediments

Recent geochemical studies provide evidence that changes in vertical distributions of nutrients in lake sediments are driven by anthropogenic activities, based primarily on trends of increasing concentrations in upper sediment layers. However, the present study shows that vertical concentration profiles of C, N and P in lake sediments can be higher in the upper, most recently deposited sediment strata, driven largely by natural diagenetic processes and not eutrophication alone. Sediment cores from 14 different lakes in New Zealand and China were examined ranging from oligotrophic to highly eutrophic and shallow to deep, and it was found that the shape of vertical profiles of total P, a key nutrient for lake productivity, can be similar in sediments across gradients of widely differing trophic status. Empirical and mechanistic diagenesis steady state profile models were derived and applied to describe the vertical distribution of C, N and P in the sediments. These models, which focus on large scale temporal (decades) and spatial (up to 35 cm in the vertical) processes, revealed that density-differentiated burial and biodiffusive mixing, were strongly correlated with vertical concentration gradients of sediment C, N and P content, whereas lake trophic status was not. A sensitivity analysis of parameters included in the diagenetic model further showed that the processes including flux of organic matter to the sediment–water interface, burial (net sedimentation), breakdown of organic matter and biodiffusion all can significantly influence the vertical distribution of sediment P content. It was concluded that geochemical studies attempting to evaluate drivers of the vertical distribution of sediment C, N and P content in lake sediments should also account for the natural diagenetic drivers of vertical concentration gradients, assisted with application of similar models to those presented in this study. This would include quantification of key sediment diagenesis model parameters to separate out the influence of anthropogenic activities.     

福建泉州湾近岸海域沉积物重金属来源分析与生态风险评价

【研究目的】 受重金属含量影响,泉州湾表层沉积物环境质量面临巨大生态风险,然而重金属含量影响因素及潜在来源研究相对薄弱。【研究方法】 通过采集泉州湾近岸海域表层沉积物样品,以元素含量及粒度分析归纳出重金属分布特征、富集程度为基础,使用Hakanson生态风险指数法识别湾内沉积物潜在生态风险程度,并进一步通过正定矩阵因子分解法及主成分分析,定量分析不同重金属主要来源。【研究结果】 在晋江与洛阳江交汇处出现沉积物粒度低值区,易于重金属富集,表层沉积物重金属富集程度为Hg>As>Cd>Pb>Zn>Cu>Cr>Ni。湾内沉积物整体处于中度生态风险状态,Cd对生态风险贡献程度最高（37.90%）,其次为Hg（29.38%）。Cr与Ni主要源于母岩风化,Cu与Zn、Pb受母岩风化影响及矿山冶炼的共同影响,Cd与As分别主要源自近岸污水排放与燃料燃烧,而Hg的来源较为复杂。研究区表层重金属主要来源依次为矿山冶炼、母岩风化、污水排放以及燃料燃烧,贡献率依次为33.95%,31.16%,22.26%与12.21%。【结论】 陆域物质随地表径流的输送对泉州湾表层沉积物生态环境质量造成了巨大风险,未来需要特别加强对不同介质中Hg的归趋及环境行为研究。     

Distribution and fractionation of heavy metals in the surface sediments of the Ganges- Brahmaputra-Meghna river system in the Bengal basin

 The lower Ganges-Brahmaputra-Meghna (G-B-M) drainage basin occupies the total Bengal Basin, which is one of the unique basins of the world because of its location and size, density of population, and catastrophic deposition of sediments. The increased heavy metal concentration in the 63 m fraction of surface sediments shows similarity among major segments of the G-B-M system in the basin, which reflects the homogenization of lithologic and chemical diversity of the greater denudation regime by the river processes. The differences in heavy metal concentation in the lower G-B-M system with that of its upper and middle counterpart is mainly related to the contrast between Himalayan rivers and the other major South Asian rivers, and may be due to the geological differences of their denudation regime. Heavy metals in the Lower G-B-M system have an affinity towards the clay fraction of the sediments. The correlation matix of heavy metals in the lower Brahmaputra and Meghna suggests the importance of Fe-Mn oxyhydroxides in their accumulations. Iron, Ti and Mn are higher in the Meghna main channel, Zn is higher in the Meghna tributaries, and Cr is higher in both the Brahmaputra and Meghna compared to the value for standard shale. The enrichment factor is ≤1 for most of the metals except Mn which is relatively higher in the Meghna and lower Ganges main channels. The geoaccumulation index (I_geo) for most of the heavy metals lies below grade zero, suggesting unpolluted sediment quality. The lower Ganges system shows relatively higher concentration in the nondetrital fraction of heavy metals, probably due to the presence of petroleum refinery, industrial and mining effluents, and agricultural runoff in the drainage basin. The relative uniformity in concentration of heavy metals in vertical profiles may be due to the uniformity in sediment grain size and catastrophic deposition of sediments, where the time period represented by the vertical sediment column is not enough to reflect the cultural accumulation of heavy metals. The Bengal basin thus represents a relatively unperturbed alluvial basin with regards to heavy metal pollution. Received: 21 July 1997 · Accepted: 13 October 1997     

可可西里盐湖表层沉积物中粘土矿物的环境信息

通过对可可西里盐湖表层沉积物中粘土矿物的研究,以期获得近年来湖区的某些环境信息.研究结果表明:沉积物中的粘土矿物主要为伊利石和绿泥石,非粘土矿物主要为石英、方解石和长石以及少量白云石、文石、闪石和石膏等.样品中＜2μm的粘土矿物以伊利石和绿泥石为主,局部样品含少量有序伊/蒙混层.根据样品分布特点和粘土矿物的组合类型,将样品划分为3个区域:1区和3区的矿物组合为伊利石、绿泥石和有序伊/蒙混层;2区为伊利石和绿泥石,无伊像混层矿物.其中1区和3区样品的结晶度(IC)范围为0.41～0.59,均值为0.51;2区样品的结晶度范围为0.25～0.40,均值为0.34,明显低于1区和3区,说明2区样品中的伊利石具有更高的结晶度.样品的伊利石化学指数(CI)均小于0.5,表明该伊利石为富Fe-Mg伊利石,主要是物理风化作用的结果.伊利石和绿泥石作为主要粘土矿物反映了近年来整个湖区的环境以干冷为主,局部区域(1区和3区)出现的少量有序I/S混层矿物则指示在短期内曾经历过短暂的干湿交替环境.此外,在酸性介质条件下,少量伊利石发生弱水解作用导致晶格中的K+淋失,并转化为伊/蒙混层矿物,同时也降低了伊利石的结晶度.