Human influence on heavy metal distribution in the upper Lake Nansi sediments, Shandong Province, China

Core and surface sediment samples were collected from three sub-lakes (Lake Nanyang, Lake Dushan and Lake Zhaoyang) in the Lake Nansi Basin, Shandong Province. In order to reveal the characteristics of spatial and historical distribution of heavy metals in different sub-lakes of the Upper Lake Nansi, heavy metal (As, Cr, Cu, Hg, K, Mn, Ni, Pb, Zn, Al, Fe, Ti and V) concentrations of sediment samples were investigated. Based on the activity of ¹³⁷Cs in the sediments, the modern accumulation rate of Lake Nansi sediments is 3.5 mm/a. Our results show that the whole Upper Lake Nansi has been already polluted by heavy metals, among which Lake Nanyang has been polluted seriously by mercury, as well as by lead and arsenic, while Lake Dushan has been most seriously polluted by lead and arsenic. Historical variation of heavy metal (Cr, Cu, K, Ni, Zn, Al, Fe, Ti and V) concentrations shows an abrupt shift in 1962, resulting in a division of two periods: from 1957 to 1962 when metal enrichment increased with time, and from 1962 to 2000 when it decreased with time, while that of some anthropogenic elements such as Hg, Pb and Mn tend to increase toward the surface. However, the variation trend of As in the sediments is different from that of Hg, Pb and Mn, with its maximum value appearing in 1982. Since 1982 the concentrations of As have decreased due to the forbidden use of arsenite pesticides. This variation trend revealed changes in manner of human activity (coal combustion, waste discharges from both industries and urban sewage) within the catchment during different periods.