连通工程对富营养化湖泊沉积物中污染物的影响

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

为揭示东湖-沙湖连通工程对富营养化湖泊沉积物中污染物的影响,于2013年7月在东湖的水果湖及郭郑湖心采集了20 cm的柱状沉积物,按2 cm分层测定了总有机碳(TOC)、总氮(TN)、总磷(TP)、酸挥发性硫化物(Acid volatile sulfides,AVS)及同步提取金属(Simultaneously extracted metals,SEM),并与2004、2006和2008年(TOC、TN和TP)及1999年(AVS、SEM)数据进行了比较;同时研究了郭郑湖沉积物氮磷的释放特性。结果表明,(1)水果湖沉积物中污染物含量普遍高于郭郑湖,在连通前均呈增加的趋势;连通后,TOC、TN的平均含量显著降低(P<0.05),与2008年比分别降低了25.1%和56.3%(水果湖)及31.9%、66.1%(郭郑湖);TP平均含量虽略高于2008年,但水果湖沉积物低于2004及2006年,郭郑湖表层沉积物也低于历年,表明TP污染的趋势得到了遏制,湖水流动性的增强有利于沉积物中污染物含量的降低;(2)随着沉积物表层氧化还原状况的改善,表层沉积物AVS含量降低,且最高含量分别由26.4(水果湖)和26.2 mmol/kg(郭郑湖)降低到15.1和18.2 mmol/kg;SEM含量则升高,导致SEM/AVS上升,但SEM/AVS值均小于1,沉积物尚未呈现重金属毒性;(3)东湖沉积物中的氮磷存在潜在的释放风险,其释放与扰动强度有关,且污染物含量高的底层沉积物释放更明显。因此,连通工程有利沉积物中污染物含量的降低,但同时需要采取措施控制污染物释放的风险。

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 （P〈0.05） 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-intercormected engineering facilitated the removal of pollutants in the sediments. Nonetheless effective policies are still needed for the control of the release of pollutants.