阳宗海外源氮磷负荷入湖量分析

An Analysis on External Loading of Nitrogen and Phosphorus in Lake Yangzonghai

湖泊的氮、磷入湖负荷解析是湖泊富营养化防治的前提，为有针对性地采取治理措施提供依据。在对阳宗海流域的工业废水、城镇和农村生活污水、外流域引水，化肥施用量、畜禽养殖、农业固废和生活垃圾等进行全面调查的基础上，测算了2010年流域内各污染源的总氮（TN）和总磷（TP）入湖负荷。结果显示：阳宗海流域2010年TN入湖量为293.30t，TP为40.11t；污染源以面源为主，面源TN和TP分别占其总入湖量的78.9％和95.5％；最大污染源为化肥，肥料氮和磷入湖负荷分别为133.66、26.10t，分别占其总入湖量的45.6％和65.1％，减少化肥的使用是湖泊富营养化防治的关键；以磷负荷所占比例排序，畜禽粪便为其次，再次是农村生活污水，二者贡献的磷负荷分别占总入湖量的16.1％和12.5％，所贡献的氮负荷分别占总入湖量的8.1％和23.6％；外流域引水贡献的TN和TP分别占其总入湖量的19.8％和3.5％；阳宗海为磷限制湖泊（N：P为20.4：1），但输入负荷中N：P为7.3：1，磷的占比较高，因此富营养化风险高。

Analysing the constitution of external nitrogen and phosphorus loads entering a lake is a prerequisite for its eutrophication control so as to provide the basis for taking targeted control measures. According to an investigation on industrial wastewater, sewage from towns and villages, water diversion from outside basins, chemical fertiliser application, livestock raising, agricultural solid wastes and domestic refuse, and etc. in Lake Yangzonghai watershed, annual loads of total nitrogen and total phosphorus entering the lake in 2010 have been estimated to be 293.30 and 40.11 tonnes, respectively. Non-point sources contributed most of the loads accounting for 78.9% of total nitrogen and 95.5% of total phosphorus. As chemical fertilisers were the top pollution source to contribute 133.66 tonnes nitrogen and 26.10 tonnes phosphorus a year accounting for 45.6% and 65.1% of the total input loads, respectively, cut-down of the chemical fertiliser use would be of the key measures to prevent the lake from eutrophication. Domestic animal manure ranked second and rural sewage did third in phosphorus loading accounting for 16.1% and 12.5%, and in nitrogen loading accounting for 8.1% and 23.6%, respectively. Total nitrogen and total phosphorus loads from external water diversion made up 19.8% and 3.5%, respectively. As Lake Yangzonghai was restricted by phosphorus that should be kept in a ratio of NIP at 20.4：1, but the real Ioadings were 7.3：1 into the lake so that too high proportion input of phosphorus implied a high risk of eutrophication.