Natural and anthropogenic influences on the arsenic geochemistry of lacustrine sediment from a typical fault-controlled highland lake: Yangzonghai Lake, Yunnan, China

摘要

Located in Yunnan province, China, Yangzonghai Lake is a fault-controlled highland lake where arsenic concentration suddenly increased 20-fold in 2008, which raised great environmental concerns. It is therefore a nice prototype to study the natural and/or anthropogenic influences on the arsenic geochemistry of the sediment in highland lakes. In this study, lacustrine sediments were recovered from the lake and the differences in the occurrence of arsenic between the surface (0-10 cm depth) and sub-surface sediments (>20 cm) were investigated. The arsenic distribution in the sub-surface sediment was in accordance with the locations of springs, suggesting that arsenic therein was affected by groundwater. The surface sediment, however, was affected by human contamination carried by Yangzong River. In the sub-surface sediment, arsenic concentrations increased with pH values but decreased with redox potentials. Higher grain sizes corresponded to lower arsenic contents. Arsenic was strongly positively correlated with Sb and Bi due to their similar geochemical behaviors. In the surface sediment, however, the human activities increased the arsenic concentration in the sediment and weakened the correlations between arsenic occurrence, pH/Eh values, grain size, and trace metals. Although the average differences in the trace element concentrations between surface and sub-surface sediments over the entire Yangzonghai Lake were less than 15 %, the pairwise differences were statistically significant, and the southern portion of the lake showed the greatest anthropogenic influence. This research will provide important information on the geochemistry and environmental science of arsenic in fault-controlled highland lakes.