Spatial-temporal variations of pollutant fluxes of inflow and outflow of Lake Poyang (2008-2012)

Abstract

研究鄱阳湖入、出湖污染物通量是加强鄱阳湖及长江水功能区限制纳污红线管理的前提,是建立鄱阳湖水质预测模型的基础.基于2008 2012年鄱阳湖8条主要入湖河流、出湖口的逐月水量、水质同步监测资料,根据污染源特征优选算法,计算总磷(TP)、氨氮(NH₃-N)、高锰酸盐指数(COD_Mn)的入、出湖污染物通量,并分析时空变化特征及影响因素.结果表明:(1)出湖口和乐安河入湖口断面的NH₃-N、TP及昌江入湖口断面的TP,以点源污染为主,采用每月瞬时通量作为月平均通量的算法更准确;其余以非点源污染为主,采用瞬时污染物浓度与月平均流量之积来计算月平均通量更准确.(2)2008 2012年COD_Mn、NH₃-N和TP年平均入湖通量分别为304398、53063和9175 t,年平均出湖通量分别为367436、45814和8452 t.8条入湖河流每年的入湖水量、COD_Mn通量和个别年份的NH₃-N、TP通量小于出湖,这主要是因为未计算区间产流及相应排污和采砂引起的内源污染.(3)入、出湖污染物通量在年际间主要受水量影响而呈现W型波动变化趋势,COD_Mn、NH₃-N、TP入湖通量及COD_Mn出湖通量均集中在汛期,NH₃-N、TP出湖通量则是冬季较多(低水位下湿地植被净化作用受限).入湖TP、NH₃-N、COD_Mn通量主要来自赣江、信江、乐安河,而NH₃-N、TP浓度最高的是乐安河、信江.;Research on pollutant fluxes of inflow and outflow is an essential prerequisite to establish water quality prediction model of Lake Poyang, and strengthen the management of pollutants receiving capacity threshold in the water function zones of Lake Poyang and Yangtze River. This paper estimated the influxes and outfluxes of total phosphrous(TP), ammonia nitrogen(NH₃-N), permanganate index (COD_Mn) of Lake Poyang, analysed their spatial-temporal variations and main influencing factors, based on appropriate estimation methods, and characteristics of pollution sources for inflow(8 main rivers) and outflow of Lake Poyang, using the synchronous monthly water quality and quantity data during the period of 2008-2012. The results showed:(1) Point source was the main source for TP, NH₃-N of outflow and Le'an River inflow, and for TP of Changjiang River inflow. Therefore, applying monthly instantaneous flux as monthly average flux is more accurate for estimation. For other pollutants at the monitoring sites, applying the product of instantaneous pollutant concentration multiplying monthly average flow as monthly average flux is more appropriate. (2) During 2008-2012, annual average influxes of COD_Mn, NH₃-N and TP were 304398, 53063 and 9175 t, respectively, and annual average outfluxes were 367436, 45814 and 8452 t, respectively. For annual water quantity and COD_Mn flux, and TP flux and NH₃-N flux of some specific years, inflow values of 8 rivers were smaller than those of outflow values due to the fact that flows and pollution fluxes from the intervening basin, and internal pollutants discharges from sediments accelerated by dredging had not been included in this study. (3) During 2008-2012, both annual inflow and outflow pollutant fluxes showed a wavy variation trend, mainly influenced by water quantity. Higher TP, NH₃-N, and COD_Mn influxes of 8 main inflow rivers and COD_Mn outflux mainly occurred in high-water periods, while higher TP, NH₃-N outfluxes mainly occurred in winter (as in lowerwater periods, the biological purification of wetland plants were inhibited). TP, NH₃-N and COD_Mn influxes were mainly from Ganjiang River, Xinjiang River and Le'an River, while the highest concentration of TP, NH₃-N occurred in Le'an River and Xinjiang River.