[Spatial-temporal Variations and Pollution Assessment of Heavy Metals in Sediments of Qionghai Lake in Xichang City]

Based on the analysis of the total concentrations of 10 metals in the sediment core and total concentrations and chemical fractions of seven metals in the surface sediments of Qionghai Lake in Xichang City, Sichuan Province, the spatial-temporal characteristics of metal accumulation and pollution over the past century and the potential ecological risk of metals in surface sediments were studied. Before the 1970s, metal concentrations in the sediment core were stable. The total concentrations of Al, Fe, K, and Cr in the sediment core exhibited visible peaks in the 1970s, which were related to the enhanced input of fine-grained topsoil caused by increasing precipitation, lake reclamation, and deforestation. Since the 1990s, the total concentrations of Al, Fe, K, and Cr decreased with the reduced topsoil erosion, whereas the total concentrations of As, Cd, Cu, Pb, and Zn gradually increased or remained stable. The enrichment factor results showed that Cd, Pb, and Zn were the main contaminants, with Cd as the typical contaminant in the sediment core. The Cd contamination started in the 1960s and has remained at a moderate level since the 1990s. In the surface sediments, the total concentrations of Cd were higher in the northwest lake area, and no visible spatial concentration trends of the other metals were displayed. The bioavailable fractions of Cd, Pb, and Zn accounted for 95%, 63%, and 48% of the total metal concentrations on average. Among the bioavailable fractions, Cd was mainly in the acid-soluble fraction, and Pb and Zn were mainly in the reducible and oxidized fractions. The bioavailable fractions of the other metals were less than 27%. The results of total concentrations and bioavailable fractions of metals revealed that Pb and Zn in the surface sediments were slightly or moderately contaminated, and Cd was moderately contaminated on average. Cd contamination was at a severe level in the northwest lake area. The concentrations of anthropogenic Cd, Pb, and Zn in the surface sediments estimated from the total and bioavailable concentrations were comparable (P>0.05), indicating that anthropogenic metals primarily existed in bioavailable fractions in the sediment. Integrating the assessment results from sediment quality guidelines, potential ecological risk index, and chemical forms of metals, Cd in surface sediments may pose a high ecological risk, whereas the other metals has a low ecological risk.

[Historical Trends of Atmospheric Trace Metal Pollution in Northern Guizhou Province as Reconstructed from Alpine Lake Sediments]

Atmospheric trace metal pollution is a striking environmental problem globally. Because of the limitations in monitoring data, our knowledge of the historical processes and sources of atmospheric trace metal pollution in China and its influence on remote terrestrial environmental quality is limited. The historical variations in atmospheric trace metal (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) pollution during the past 400 years in the Fanjing Mountain area, northern Guizhou Province were studied by analyzing the metal concentrations and Pb isotopes in lake sediments. The results showed that concentrations of all metals in the sediments were relatively constant before 1800(A.D.). After 1800, concentrations of Cr, Cu, Ni, and Zn increased at first and then decreased, while concentrations of Hg, Cd, and Pb generally increased gradually over the most recent century and subsequent decades. The enrichment factor and ²⁰⁷Pb/²⁰⁶Pb analysis results indicated that Cd, Pb, and Hg were typical pollutants. Pollution of Hg began at around 1880(A.D.), and pollution of Cd and Pb has occurred since the 1950s; all pollutants exhibited aggravated trends in recent times. Pollution levels of Hg in recent years in the Fanjing Mountain area were comparable to those in other remote areas of East China, but levels were lower than those in Europe, America, and the Tibetan Plateau. In contrast, pollution levels of Cd and Pb in these areas showed large variability. By comparing the historical processes of trace metal pollution in different regions and exploring the potential pollution sources of metals in the study region, it can be deduced that atmospheric Hg pollution in the Fanjing Mountain area was the result of both global and regional emissions, while Cd and Pb pollution largely came from regional sources such as non-ferrous metals smelting and coal combustion emissions.

[Contamination and Potential Ecological Risk Assessment of Heavy Metals in the Sediments of Yilong Lake, Southwest China]

The concentrations of Al, Ti, As, Cd, Cr, Cu, Ni, Pb, Zn, and Hg and chemical speciation of Cd, Cr, Cu, Ni, Pb, and Zn in four short cores sampled from the Yilong Lake, Yunnan Province were analyzed. The vertical and spatial features in the pollution levels and potential ecological risks of heavy metals in the sediments were studied. Except for the wide concentration ranges of Cd, the metals in the sediments showed narrow variations in their concentrations with coefficients of variation less than 0.3. According to the cluster analysis results, all metals could be classified into two groups:metals in group Ⅰ included As, Cd, Hg, and Pb, while metals in group Ⅱ included Al, Ti, Cr, Cu, Ni, and Zn. The metals in each group exhibited similar vertical variations in each core, but their variations were highly different between the cores. The correlation analysis results demonstrated that the variations in metal concentrations in the sediments were greatly regulated by the sediment texture. Therefore, the enrichment factor (EF) method was used for the differentiation of metals from the natural and anthropogenic sources and for the pollution assessment based on the total metal concentrations. The Cd and Pb in the sediments were mainly presented in the reducible speciation with percentages of 48% and 42%, respectively; Cr, Cu, Zn, and Ni were primarily (68%-82%) associated with the residual speciation. Based on the EF and chemical speciation of metals and their enrichment coefficients of the secondary phase, Cd was the typical pollutant with moderate pollution on average, and the other elements were observed in non-to weak pollution levels. Anthropogenic metals were mainly associated with the extractable speciation in the sediment. Combining the ecological risk index, the sediment quality guidelines, as well as the pollution level and chemical speciation of metals, As, Cu, Hg, Ni, Pb, and Zn in the surface sediments of Yilong Lake should have low potential ecological risk. However, Cd may pose a high potential ecological risk.

[Spatio-temporal Variations, Contamination and Potential Ecological Risk of Heavy Metals in the Sediments of Chenghai Lake]

Heavy metals pollution in the sediments is one of the main factors impacting the water quality and ecosystem health. In this study, concentrations of ten metals in nine sediment cores from the Chenghai Lake were determined. Chronology of a typical core (CH2012) was constructed by the ²¹⁰Pb and ¹³⁷Cs dating method. The spatio-temporal variations in concentrations and contamination characteristics of As, Cd, Cu, Hg, Ni, Pb, and Zn were evaluated. The potential eco-risks of heavy metals in the surface sediments were studied by combining the ecological risk index and sediment quality guidelines (SQGs) assessment as well as their pollution levels (enrichment factors, EF). The metal concentrations in each sediment core showed little vertical change with coefficients of variation of less than 0.20, except for Cd, whose coefficient of variation was 0.59. Spatially, the average concentrations of each metal showed minor difference among the cores, with ratios ranging from 1.2 to 1.8, suggesting similar sedimentary characteristics of metals in the whole lake. Cd and Pb were influenced by anthropogenic contamination that has started in the mid-1980s. The pollution level of Cd decreased in the past decade and still belongs to the moderate pollution degree, whereas the pollution level of Pb increased continually and could be classified as the weak pollution degree. The Hg contamination began in the late 1990s, with EFs ranging from 0.9 to 1.6, belonging to the weak pollution degree. The As, Cu, and Zn pollution occurred mainly near the surface sediments with weak pollution degrees. Spatially, there were no obvious trends in pollution levels of the metals. The heavy metals pollution is mainly influenced by atmospheric deposition that originates from non-ferrous metal smelting emissions, as well as agricultural and domestic discharges. As, Cu, Ni, Pb, and Zn in the surface sediments have low potential ecological risks, whereas Hg and Cd may pose middle-high potential risks.

[Enrichment characteristic of phosphorus in surface and core sediments of Chaohu Lake and the pollution quantification]

Content of phosphorus (TP) and three species (NaOH-P, OP and HCl-P) in the sediment core from the central region of west Chaohu Lake and surface sediments of the lake were determined. TP exhibited three stages variation in the sediment core over the last 150 years, which was with relatively constant values in 1850-1950, increased gradually in 1950-1980 and reached the maximum average values of 858.3 mg x kg(-1) after 1980. Content of NaOH-P increased in parallel with that of TP. The percentage of NaOH-P increased gradually in the three stages. Content of OP also varied in parallel with that of TP, however, the percentage of OP was relatively constant in the three stages. HCl-P was with constant content over the last 150 years, but the percentage of which decreased more recently. In the surface sediment, NaOH-P and TP exhibited similar variation trends, which were with higher values in the west region of the lake than those in the east region and with higher values in the north region of the lake than those in the south region. Anthropogenic pollution of phosphorus in the core and surface sediments was quantified after the geochemical normalization for the compensation of "grain size effect". Anthropogenic phosphorus, mainly presented in the specie of NaOH-P, were 59.5 mg x kg(-1), 118.8 mg x kg(-1) and 297.9 mg x kg(-1) averagely during the three periods of 1850-1950, 1950-1980 and after 1980 in the sediment core from the central region of west Chaohu Lake, and was 22.9-2 500.0 mg x kg(-1) in the surface sediment. Content of anthropogenic phosphorus in surface sediment presented similar spatial variations of TP in the water, decreased to the southeast lake part away from the northwest region near Nanfei River mouth. We deduced that the discharge via Nanfei River of sewage from Heifei City should dominantly contribute the enrichment of anthropogenic phosphorus in the sediment of west Chaohu Lake in addition to the non-point agricultural sources.

[Assessment and characterization of heavy metals and nutrients in sediments from Taihu Lake]

The concentrations of Zn, Cu, Mn, Cr, Pb, Al, Fe, iron-bound P (Fe-P) and TP in the sediments from Taihu Lake, a eutrophic shallow lake, China, were determined. The results show that the concentrations of heavy metals are higher than those in the earth crust. Particularly, enrichments of Cr and Pb are more conspicuous than other metals. Moreover, the Pb content in all the sample sites increase markedly from bottom to top, which related to the numerous run-off of Pb-containing wastewater and atmospheric precipitation since 1950. Pollution level in Zhushan Bay of heavy metals and phosphorus is much more serious than other lake regions, and heavy metals and phosphorus contents increase rapidly from about 20 cm of the sediment profile upward, which reveal that the Zhushan Bay is a serious sewage discharging area since 1950. Besides, the significant correlation between Fe-P and TP indicates that Fe-P is an important phosphorus form which can release into the overlying water and be ingested by aquatic organism. That is, Fe-P is responsible for the algae bloom in north and northwest region of Taihu Lake.

[Chemical fractionation and pollution characteristics of heavy metals in the sediment of Nansihu Lake and its main inflow rivers, China]

Chemical forms of Cr, Cu, Mn, Ni, Pb and Zn in the surface sediments of Nansihu Lake and its main inflow rivers are determined by the BCR sequential extraction method. The chemical fractionation composition characteristics, pollution state and potential ecological effects of the heavy metals are discussed. Cr, Cu, Ni and Zn in the sediments of Sihe River, Jinghang Canal, Zhuzhaoxin River, Guangfu River, south area of the Upper Lakes, and Down Lakes mainly exist in residual fraction, which account for 80% - 90% of their content, mainly reflecting the natural characteristics of the heavy metals; but for the sediment of Old Canal, Guangfu River estuary, Baima River, nearly 80% of Cr, Cu, Ni and Zn exist in extractable fractions due to human pollution, especially with high oxidizable and acid extractable fractions content. Pb and Mn mainly exist in residual fraction and oxidizable fraction in the sediment of Nansihu Lake and its main inflow rivers, which account for 95% and 70% of the content of Pb and Mn, similar to other unpolluted sediments. With the mineralization and decomposition of organic matter and change of environment condition of the surface sediment, the extractable fractions of Cr, Cu, Ni, Zn in the polluted sediment can be reactivated, bringing on ecological harm to the water ecological system.