洞庭湖及其入湖口表层沉积物氮、磷、有机质的分布及污染评价

Distribution Characteristics and Pollution Assessment of Nitrogen,Phosphorus and Organic Matter in the Surface Sediments of Dongting Lake and Its Lake Inlets

洞庭湖是中国第二大淡水湖,近年来富营养化日趋严重,氮、磷、有机质是湖泊富营养化程度加剧的重要因子,而沉积物是湖泊氮、磷、有机质的主要蓄积库。因此,了解洞庭湖沉积物中氮、磷、有机质的含量及分布特征,对探究洞庭湖沉积物营养物质的污染状况及其富营养化控制与治理具有重要参考意义。在洞庭湖及其入湖口布设了19个样点,对表层沉积物进行采样,分别采用凯氏定氮法(HJ717—2014)、氢氧化钠碱熔-钼锑抗比色法和重铬酸钾法测定沉积物总氮(TN)、总磷(TP)及有机质(OM)的含量,分析了TN、TP及OM含量的空间分布特征及相关性,并运用综合污染指数法和有机污染指数法对洞庭湖及其入湖口沉积物的污染程度进行评价。结果表明,表层沉积物TN的质量分数变化在402～2 410 mg·kg^(-1)之间,平均值为1 054 mg·kg^(-1);TP的质量分数变化在457～935 mg·kg^(-1)之间,平均值为624 mg·kg^(-1);OM的质量分数变化在1.02%～7.23%之间,平均值为2.24%,空间分布上均表现为南洞庭湖>西洞庭湖>东洞庭湖。Pearson相关性分析表明,OM与TN呈显著正相关(r=0.574,P<0.05),TN与TP(r=0.433,P>0.05)和OM与TP(r=0.073,P>0.05)相关性均不显著。综合污染指数范围为1.00～2.23,全湖及其入湖口平均值为1.42,有机污染指数范围为0.04～0.84,全湖及其入湖口平均值为0.13,两种指数法均显示洞庭湖及其入湖口表层沉积物整体上处于轻度污染,且南洞庭湖污染比东、西洞庭湖及入湖口严重,各个入湖口中以湘江入湖口污染程度最高。

Dongting Lake,the second largest freshwater lake in China,has been undergoing serious eutrophication in recent years.As well known,nitrogen,phosphorus and organic matter in sediments are important sources of lake eutrophication.Hence,characterizing the contents and distribution of nitrogen,phosphorus and organic matter in sediments in Dongting Lake is of great significance for understanding the pollution status and remediation of eutrophication.In this paper,the surface sediments were sampled at 19 sampling sites over the whole lake and its inlets.The contents of total nitrogen(TN),total phosphorus(TP)and organic matter(OM)were analyzed by Kjeldahl method(HJ717-2014),sodium hydroxide alkali fusion-molybdenum antimony colorimetric method and potassium dichromate method,respectively.Spatial patterns of TN,TP and OM and their correlations were examined,meanwhile,comprehensive pollution index and organic pollution index were employed to evaluate pollution status.The results showed that the content of TN ranged from 402 to 2 410 mg·kg^-1 with an average of 1054 mg·kg^-1,the content of TP ranged from 457 to 935 mg·kg^-1 with the average of 624 mg·kg^-1 and OM content ranged from 1.02%to 7.23%with an average of 2.24%.The spatial distributions of TN,TP and OM presented similar spatial patterns in the order of South Dongting Lake >West Dongting Lake >East Dongting Lake.Pearson correlation analysis indicated that TN was significantly correlated with OM(r=0.574,P<0.05),and TP was not strongly correlated with TN(r=0.433,P >0.05),and OM(r=0.073,P >0.05).Ranges of comprehensive pollution index and organic pollution index were 1.00-2.23 and 0.04-0.84,with the average values of 1.42 and 0.13,respectively.The two indices indicated light pollution of TN,TP and OM in the sediment of Dongting lake and its inlets,the pollution level of the South Dongting Lake was more serious than that of the East Dongting Lake,the West Dongting Lake and Dongting Lake inlets,and the pollution level of the Xiangjiang River inlet was the highest among the seven Dongting Lake inlets.