Trace element of small lake sediments sensitively recorded environmental changes in the watershed: Implications for mining history and urbanization

Lake sediments serve as a sink for trace elements and provide a record of watershed changes resulting from anthropogenic activities and natural processes. In this study, eight trace elements in the sediments of Lake Aha, an urban lake in Guiyang City, Southwest China, were investigated to reveal the effects of historical coal mining and rapid urbanization in the watershed. Results showed that the median contents of measured trace elements in order of Zn (220.00 mg/kg) > Ni (98.16 mg/kg) > Cr (70.26 mg/kg) > Cu (66.20 mg/kg) > As (58.14 mg/kg) > Co (41.66 mg/kg) > Pb (28.33 mg/kg) > Cd (1.39 mg/kg). Except for Cr and Pb, the median concentrations of Cd, As, Zn, Ni, Co, and Cu were 4.64, 2.33, 2.00, 1.92, 1.81, and 1.09 times higher than regional natural background values respectively. Trace element contents in sediments of the center of the lake were significantly higher than in the rest of the sediment cores, resulting from relatively stable hydrodynamic processes in the region. Vertical variation of trace elements indicated that the fluctuations in the intensity of coal mining activities in the tributaries were effectively tracked by variations of trace element levels in the middle layer sediments of the Youyu River and Baiyan River estuaries. The elevated concentrations of Pb in the surface sediments of the Jinzhong River estuary reflected the rapid urbanization in the basin over the past 20 years. PMF analysis demonstrated that As, Cd, and Pb in sediments were from a mixture of natural and urban activities, and Cu, Zn, Ni, and Co originated from coal mining. This study provides important information for comprehending the anthropogenic activities of small-scale lakes and historical environmental changes.