Heavy metal contamination in the lacustrine sediment of a plateau lake: influences of groundwater and anthropogenic pollution

In this study, heavy metal pollution in sediment cores from the Yangzonghai Lake, a fault-controlled highland lake in China, was investigated. All of the sediment samples were unpolluted or slightly polluted with geoaccumulation indexes (I _geo) of <1 and contamination factors (CF) of <2. In the sub-surface sediment (depth >20 cm), all of the heavy metals were controlled by groundwater, and the distributions of the concentrations, enrichments, and pollution indexes were closely associated with springs. The surface sediment at a depth of <10 cm, however, was contaminated by human activities, which significantly increased the I _geo, CF, and enrichment factors covering most of the lake. All elements exhibit accumulations near the mouth of the Yangzong River, suggesting that the pollution predominantly came from the river. In addition, Hg/Cd and As/Pb also exhibit increased enrichments near the thermal plant and the springs, respectively. Combined with multi-statistical analyses, it is suggested that Hg and Cd were mainly polluted by the river and the thermal plant in the surface sediment, while As and Pb were contributed by the river and groundwater. Co, Ni, and Zn were strongly associated with Fe and mainly originated from lithogeochemical processes, although their occurrence was affected by the groundwater in the sub-surface sediment and the river in the surface sediment. This study provided essential information on the heavy metal contamination in both the surface and sub-surface sediments of the Yangzonghai Lake. In addition, it is suggested that groundwater should be taken into consideration to assess the heavy metal contamination in the sediment of fault-controlled plateau lakes.