Abstract: Background, aim, and scope Heavy metals are a serious type of contaminant in lake sediments due to their toxicity, durability, non-degradability and bioaccumulation. Therefore, the study about geochemical characteristics, source analysis and pollution status of heavy metals in lake sediments are of great practical significance. Materials and methodsBosten Lake is the biggest freshwater lake in arid region of northwest China. In June 2016, 22 surface sediment samples (0—5 cm) were collected in the major district of the lake, and a sediment core with 41cm-in-length was drilled near the entrance of Kaidu River. Surface sediment samples from Bosten Lake were analyzed for the 24 elements’ concentration, grain size distribution and organic matter content (TOC). Samples of the sediment core were analyzed for 210Pb chronology and geochemical elements. The PIRLA method was used to the elements’ contents before 1950s for obtaining the background values of geochemical elements. R-cluster analysis combined with Pearson correlation analysis were used to acquire the influencing factors of geochemical elements. Q-cluster analysis was used to partition the samples, and the results was tested by one-way analysis of variance. At last, by the use of the background values of geochemical elements, enrichment factors and geoaccumulation index were calculated to evaluate the pollution degree of heavy metals. Results The concentrations of Ca, Sr, Mg were obviously higher and the concentrations of Al, Fe, Mn, Ti, V and heavy metals were lower than Xinjiang Soil background values. R-cluster analysis indicated that, Al, K, Be, Tl, Pb, Co, Zn, Ni, Fe, Cr, V, Ti, Cd, Sb, As, Mg, Cu, Mn, P, Hg and terrestrial fine particulate matter(<4µm，4—16µm) were divided into one group, Ba, Na and coarse grain size content（>63µm）were divided into the second group, and Ca, Sr, Mo, TOC, medium-sized content (16—63µm) formed the third group. Through Q-cluster analysis, the sampling points can be divided into three regions. RegionⅠwas widely distributed in the lake, including Hekou district, Huxin District and the most area of the Eastern Distirct. The contents of Al and heavy metals were relatively high and stable in the sediments, while the contents of Ca were low. RegionⅡwas located on the west side of the lake, including Huangshuigou District and nearby areas, the contents of fine grains（<4µm，4—16µm）and elements (including Al and heavy metals) were relatively low, and the contents of Ca were relatively high in the sediments. Region Ⅲ was located in southeast corner of the lake, the sediment was mainly influenced by the desert, the contents of Ca and heavy metals contents were relatively low, while contents of coarse particles（＞63µm）were high. The average enrichment factors of Pb, Cr, Tl, Ni, Cu, Co in all the sampling spots were slightly above 1, which indicated the above elements were slightly enriched in the sediments. The sampling spots with postive geo-accumulation index (Igeo)（Cr, Co, Pb, Ni, Tl, Cu, As, Zn）were mainly distributed in the south part of the lake. Discussion The high contents of Ca, Sr, Mg in the sediments were mainly due to the intense evaporation in arid region. Al, K, Be, Tl, Pb, Co, Zn, Ni, Fe, Cr, V, Ti, Cd, Sb, As, Mg, Cu, Mn, P, Hg were mainly influenced by the terrestrial fine particles（<4µm, 4—16µm）, Ba, Na were affected by the contents of coarse particles（>63µm）, Ca, Sr, Mo, TOC were mainly derived from endogenesis, and were related to the 16—63µm particles. The distributions of heavy metals were basically the same with fine particles and Al, and contrary with Ca. Nevertheless, heavy metals in the sediments of some area in RegionⅡ have been influenced by drainage from the basin. Conclusions Grain size compositions had significant influences on the elements composition of Bosten Lake sediment, while TOC had little effect. Some area in Huangshuigou District has been influenced by human inputs. In general, there were no heavy metal pollution in Bosten Lake sediments. Recommendations and perspectives This results can provide some references for the study of geochemical elements of lake sediment, and also have important values for environmental management of Bosten Lake.
Keywords: Bosten Lake; sediment; geochemical elements; heavy metals; cluster analysis; pollution assessment