2016~2017年长荡湖流域河湖系统营养盐时空分布机制分析

Spatiotemporal Variations in Nutrient Loads in River-lake System of Changdang Lake Catchment in 2016-2017

以江苏省常州市长荡湖流域河湖系统为研究对象,基于野外监测与室内分析,探讨了水体氮、磷等营养盐的时空分布特征及其影响因素.结果表明,2016~2017年长荡湖流域河湖系统氮、磷污染突出,河流TN、NO-3^-N、NH+4^-N、TP和Chla平均质量浓度和高锰酸盐指数分别为(3.70±0.76)mg·L^-1、(1.81±0.42)mg·L^-1、(1.03±0.61)mg·L^-1、(0.38±0.31)mg·L^-1、(25.74±37.00)μg·L^-1和(6.35±0.81)mg·L^-1.河流总氮污染季节差异明显,表现为冬、春季劣于夏、秋季,河流总磷污染表现为秋、冬季劣于春、夏季,空间差异表现为北>西北>南>东部,河流处于中~高度富营养化状态.湖区TN、NO-3^-N、NH+4^-N、TP和Chla平均质量浓度和高锰酸盐指数分别为(2.25±0.94)mg·L^-1、(0.98±0.47)mg·L^-1、(0.19±0.14)mg·L^-1、(0.11±0.03)mg·L^-1、(18.71±8.76)μg·L^-1和(4.59±1.09)mg·L^-1,氮、磷质量浓度均超过Ⅲ类水标准,在空间上表现为从西部向东、南部降低的趋势,湖区处于轻~中度富营养状态.丹金溧漕河、通济河与薛埠河等河流是长荡湖流域河湖水系的主要污染物输送通道,丹金溧漕河干流输送氮、磷年通量最大,约为通济河和薛埠河年通量总和的10~12倍.长荡湖流域河流氮、磷污染同时受到农业面源污染物流失与城镇污水排放的影响.土地利用方式转变和大气沉降是导致长荡湖流域河湖系统氮、磷污染加剧的重要驱动因素.

Eutrophication of shallow lakes in the middle and lower reaches of the Yangtze River has become an increasingly serious problem.In this study,we investigated the temporal and spatial variations in nutrient loads(nitrogen,N and phosphorus,P)in the Changdang Lake Catchment located to the northwest of Lake Taihu through field sampling and laboratory analysis in 2016-2017.The results show the severity of the N and P pollution in the Changdang Lake catchment.The mean river water concentrations of TN,NO-3^-N,NH+4^-N,TP,Chla,and permanganate index are(3.70±0.76)mg·L^-1,(1.81±0.42)mg·L^-1,(1.03±0.61)mg·L^-1,(0.38±0.31)mg·L^-1,(25.74±37.00)μg·L^-1,and(6.35±0.81)mg·L^-1,respectively.N pollution in the river is more severe in winter and spring than in summer and autumn whereas P pollution in the river is worse in autumn and winter than in spring and summer.Spatially,the magnitude of river N and P pollution follows the order of northern>northwestern>southern>eastern part of the study area.The rivers are in a state of moderate to severe eutrophication.The mean lake water concentrations of TN,NO-3^-N,NH+4^-N,TP,Chla,and permanganate index are(2.25±0.94)mg·L^-1,(0.98±0.47)mg·L^-1,(0.19±0.14)mg·L^-1,(0.11±0.03)mg·L^-1,(18.71±8.76)μg·L^-1,and(4.59±1.09)mg·L^-1,respectively.The water quality in Changdang Lake is categorized as worse than classⅢfor TN and TP concentrations,which show decreasing trends from the west to the east to the south of the lake.The lake is in a status of slight to moderate eutrophication.The lake water quality is affected by the combination of sewage discharge and non-point source pollutant losses.The inflow rivers including the Danjinlicao River,Tongji River,and Xuebu River are the dominant pollution sources for Changdang Lake.The Danjinlicao River transports 10-12 times the total N and P loads transported by Tongji and Xuebu rivers.Changes in land use and atmospheric deposition are the driving factors of the deterioration of water quality and eutrophication in the catchment.