西苕溪支流河口水体营养盐的特征及源贡献分析

支流是干流营养物质的重要贡献源,也是流域水污染控制的关键区域.为探明西苕溪营养物质来源,有效控制该流域的水质污染,对西苕溪支流河口水质的时空变化特征及营养盐的输出通量进行了分析,利用PMF源解析模型对西苕溪10条典型支流的污染源贡献进行了定量解析.结果表明,中下游支流的TN、TP浓度高于上游支流,枯水期TN、TP浓度均值是4.25 mg·L~(-1)和0.11 mg·L~(-1),丰水期对应浓度均值为3.15 mg·L~(-1)和0.09 mg·L~(-1),枯水期高于丰水期,其时空变化较显著;支流水体的氮磷形态组成各不相同,反映支流流经区域周围土地利用的差异.污染源解析结果显示,影响西苕溪支流营养盐的污染源有农田径流、养殖废水和生活污水三类,在丰水期和枯水期,上游支流营养盐中农田径流的贡献率是40%和35%,中游养殖废水贡献率是33%和30%,而枯水期的生活污水则比丰水期贡献较多营养盐.因此,在整治改善西苕溪流域水质时,应考虑营养物的时空变化特点和支流周边环境.

Characteristics and Pollution Source Analysis of Nutrients in Tributary Outlets of Xitiaoxi Watershed

The input of tributary is the important source of nutrients to the main stream, and it is the key area for water pollution control of watershed. In order to explore the sources of nutrient and seek the effective measures to control the river pollution, the spatial and temporal variations of aquatic parameters and the output of nutrient flux in the tributary outlets of Xitiaoxi watershed were analyzed. The quantitative analysis concerning the contribution of pollution sources from 10 typical tributaries was carried out, using the PMF analytical model. The results showed that the TN and TP concentrations were higher in the middle and lower reaches. In the temporal scale, the concentrations of nutrients in the dry season were higher than those in the wet season. In the dry season, average concentrations of TN and TP were 4.25 mg·L^-1 and 0.11 mg·L^-1, respectively, compared to the corresponding values of 3.15 mg·L^-1 and 0.09 mg·L^-1 in wet season. Because of the differences of surrounding lands, the sources of nitrogen and phosphorus forms were various. The results of PMF(Positive Matrix Factorization) method identified the three nutrient sources as agricultural source, aquaculture source and municipal source. In different seasons and river reaches, the contribution rates of three sources were different. Agricultural source contributed nutrient largely to the tributaries in the upstream reaches, and the aquaculture source was the main contributor in the middle reaches, while the municipal source contributed more nutrient in the wet season than in the dry season. Therefore, to better improve water quality of Xitiaoxi watershed, the surrounding environment of tributary and the characteristics of nutrients in spatial and temporal variations should be considered.