EFFECTS OF THE LAKE-INTERCONNECTED ENGINEERING ON THE DISTRIBUTION OF POLLUTANTS IN THE SEDIMENTS OF EUTROPHIC LAKES

In order to reveal the influence of the Donghu-Shahu lake-interconnected engineering on the pollutants in the sediments, we collected and analyzed samples of 20 cm sediment cores in two sublakes-Shuiguohu (SG) and Guo Zhenghu (GZ)-of the Donghu Lake in July 2013. We evaluated the vertical distribution of the total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), acid volatile sulfides (AVS) and simultaneously extracted metals (SEM), and compared the results to the data in 2004, 2006, 2008 (TOC, TN and TP) and 1999 (AVS, SEM). We also studied the release characteristics of TN and TP at different disturbance intensities. We found that the level of pollutants in SG was generally higher than that in GZ, and the levels of the pollutants in both increased over the past years until the connected project was implemented. Compared to 2008, the average levels of TOC and TN in the sediments were significantly reduced (P0.05) in 2013, and the reduction was 25.1% and 56.3% respectively in SG, and 31.9% and 66.1% in GZ. Although the average level of TP was slightly higher than that in 2008, it was lower than that in 2004 and 2006 in SG, and the level of TP in the surface layer of GZ was lower in 2013 in the past years. The results suggested that the TP pollution had been inhibited, and that the enhanced flow helped improve the oxygen recovery of the Donghu Lake water and hence reduce the level of the pollutants in the sediments. In addition, the level of AVS in the surface layer decreased, and the peak value of AVS dropped from 26.4 to 15.1 mmol/kg in SG, and 26.2 to 18.2 mmol/kg in GZ. Compared to the past years the level of SEM was elevated which resulted in an increase in the SEM/AVS value. However, the toxicity of heavy metals in the sediments was not detected because SEM/AVS 1. The results of the release test suggested that there was a potential risk of the release of TN and TP, and this could be related to the disturbance intensity and the level of the pollutants. Therefore, we concluded that the lake-interconnected engineering facilitated the removal of pollutants in the sediments. Nonetheless effective policies are still needed for the control of the release of pollutants.