Changes in Concentrations and Pollution Levels of Trace Elements of Floodplain Sediments of Poyang Lake Basin in Recent Twenty Years

Abstract

Investigating the pollution conditions of trace elements in the Poyang Lake basin, identifying the pollution sources, evaluating the ecological risks play an important part in formulating the effective strategies for protecting the basin ecosystem. To understand the concentration characteristics, pollution levels, and ecological risks of twelve trace elements (Cd, Hg, Pb, As, Cu, Zn, Cr, Ni, Mn, Sb, W, and Sn) in the floodplain sediments of the five main tributaries in Poyang Lake basin in the past twenty years, we used the enrichment factor (EF) and modified pollution index (MPI) to quantify the pollution levels of the trace elements, and analyzed and discussed the pollution sources in the areas with significant pollution level changes. The results indicated that the concentrations of cadmium, zinc, manganese, tungsten and lead in the floodplain sediments of the Poyang Lake basin during the past twenty years have increased by 134%, 26%, 41%, 25%, and 8%, respectively, and mercury, arsenic, chromium, nickel, antimony, and tin have decreased by 35%, 15%, 22%, 10%, 14%, and 13%, respectively, while copper has not changed significantly. The concentrations of cadmium in the Raohe River, Ganjiang River, and Xinjiang River basins have increased by 331%, 151%, and 107%, while mercury decreased in the Fuhe River, Ganjiang River, and Xiushui River basins by 87%, 41%, and 40%, respectively. The classification results based on the EF indicated that the changes in the pollution levels of trace elements in the Poyang Lake basin were characterized by the aggravation of cadmium pollution and the degradation of mercury pollution, the pollution level of cadmium in the Ganjiang River basin was upgraded to moderate and significant, the pollution level of cadmium in the Le'an River was upgraded to very high, and the pollution level of mercury in the Fuhe River basin was reduced to unpolluted or minimal. The MPI classification results established that the increase in the cadmium pollution had intensified the comprehensive pollution in the Poyang Lake basin, causing the proportion of severely and heavily polluted sites to be raised from 17% to 33%. The MRI classification results also demonstrated that the proportion of very high ecological risk sites have increased from 11% to 22%. The element with the highest MRI contribution rate changed from mercury to cadmium, which was caused by the reduction of the ecological risk level from very high to moderate. The results demonstrated that the significant pollution changes in the trace elements in the floodplain sediments of the Poyang Lake basin were primarily caused by human activities, such as mineral exploitation, smelting, and industrial and agricultural production. Our findings can provide scientific evidence for the prevention and control of river pollution and the optimal management of a watershed ecosystem.