流域氮磷输出、河流输送与库区富营养化关联分析——以福建山仔水库为例

Linking Watershed Nutrient Loads and Riverine Export to Reservoir Eutrophication:The Case of Shanzai Reservoir, Fujian Province

建立流域氮磷输出、河流输送与入库通量的分析方法，以福建省山仔水库为例，基于GIS技术分析乡镇、子流域的氮磷污染分布和来源构成，识别关键源区并探讨库区水质与流域污染输出和河流输送之间的关联性。结果表明，2009年山仔流域单位面积总氮输出负荷为13．4kgN·hm-2·a-1（生活污水和化肥流失占64％），总磷输出负荷为0．82kgP·hm-2·a-1（畜禽养殖和生活污水占90％），入库氮、磷负荷分别为3248tN·a。和192tP-1，其中河流输入占62％和89％，环库区面源污染贡献小于2％；不同乡镇单位面积氮输出负荷为3．54—20．0kgN·hm。，磷输出负荷为0．38—2．50kgP·hm。，其中日溪乡和霍口乡临近库区，化肥流失与畜禽养殖污染最重。上游乡镇污染较轻，但生活污水比重大（42％～84％）。皇帝洞溪子流域污染最重（19．4kgN·hm。；1．95kgP·hm。），其次是霍口溪中下游和日溪子流域。库区总氮高值出现在坝区和日溪湾汉，总磷高值在小沧至霍口溪七里入口之间，水质有明显分区，与流域污染分布、河流输送和库区沉积物的释放相关联，河流输入对库区富营养化起决定性作用。流域氮磷输出负荷比值平均为16。库区水中氮磷比值在15～20之间，意味着该生态系统处于磷的弱限制，水华爆发风险较大，建议采取“分区整治流域污染、氮磷联合削减、畜禽养殖和磷肥流失优先控制”的富营养化防控策略。

A quantitative analysis of watershed nitrogen （N） and phosphorus （P） loads, riverine export and other inputs to reservoir was con- ducted for Shanzai reservoir in Fujian Province. Spatial variation of N and P pollution and major components were interpreted at town and sub-watershed scale using GIS techniques, and the critical source area（CSA） was indentified. The linkage between reservoir water quality and watershed nutrients loading and riverine export fluxes was examined. Results revealed that total N and P loads per unit area of the Shan- zai watershed were 13.4 kg N＂ hm~＂ a-1 and 0.82 kg P＂ hm-2＂ a-~, respectively. Domestic sewage and fertilizer runoff accounted for 64% of total N load, and livestock waste and domestic sewage shared 90% of total P load. Total N and P loads to the Shanzai reservoir were 3248 t N＂ a-t and 192 t P＂ a t 62% and 89% of which were through riverine transport and the remainder mostly from sediment release. Less than 2% of in- puts were from non-point sources in the surrounding area. Town-level N and P loads per unit area ranged from 3.54-20.0 kg N ＂hm~ and 0.38-2.50 kg P＂ hm 2 respectively. Two towns （Rixi and Huokou ） adjacent to the reservoir were identified as CSA of fertilizer runoff and livestock waste, while human sewage dominated the nutrient load（42%-84% of total） in other towns in the upstream area. Huangdidong subwatershed was the most polluted catchment（ 19.4 kg N -hm-2; 1.95 kg P＇hm-2）, followed by the lower reaches of Huokou River and Rixi subwatershed. The high value of total N concentration was observed near the dam head and Rixi inlet, whereas high total P concentration was found in channel from Huokuo inlet to Xiaocang. The spatial variation of the nutrients level in the reservoir was highly associated with water- shed nutrient loads, riverine export and sediment-water exchange, indicating that riverine input is the decisive factor contributing to eutroph- ication of the reservoir. The average N：P ratio of the nutrient load was calculated as 16 for the whole watershed, which combined with the TN： TP ratio of 15-20 observed in reservoir surface water suggested that the reservoir ecosystem was weakly limited by P and tended to stimulate algal bloom. To mitigate eutrophication, reduction of both N and P pollution should be considered in those CSAs, with a priority given to P pollution from livestock and phosphate fertilizer loss.