光度法对不同土地利用类型河流在不同水期氮磷分布特性及定量源解析研究

氮和磷是水环境生物生长和繁殖必须的营养成分，影响水体初级生产力的水平，且水体富营养化水平与氮磷形态密切相关，随着水体环境的改变，沉积物会向水体释放氮磷，造成二次污染。同时，对外源氮磷污染来源的贡献进行定量识别，可有效管理和控制水体氮磷污染负荷。毗河和石亭江是沱江的重要支流，影响着长江母亲河的水质。采用钼锑抗分光光度法和连续提取法研究在枯水期和丰水期毗河和石亭江水体和表层沉积物中总氮(TN)、总磷(TP)及各形态氮磷的分布特性，对比不同土地利用类型河流氮磷行为特性及释放风险，并采用Multiple Linear Regression of the Absolute Principal Component Scores(APCS-MLR)受体模型进行氮磷污染源的识别和量化。研究结果表明：① 研究区水体和表层沉积物中氮磷均处于不同程度的污染水平，水体枯水期TP的主要贡献者是颗粒态无机磷(PIP)和颗粒态有机磷(POP)，而丰水期却是颗粒态无机磷(PIP)和溶解态无机磷(DIP)，两水期水体中TN的主要贡献者是硝态氮(NO-₃-N)和有机氮(ON)。而在表层沉积物中，TP的主要贡献者是钙结合态磷(HCl-P)，TN的主要贡献者是酸解态氮(HN)。在枯水期和丰水期，毗河表层沉积物生物有效磷(BAP)占TP的平均值(19.7%和23.0%)比石亭江的平均值(11.0%和12.5%)占比更高，具有较高的磷释放风险。研究发现，枯水期氮磷污染程度高于丰水期，而且石亭江的氮磷污染程度高于毗河。②APCS-MLR模型在毗河提取了城镇生活污水、生活垃圾堆积产生的渗滤液、动植物残体分解和养殖业废水4个污染源因子，其中城镇生活污水对毗河氮磷污染的贡献最大(枯水期50.9%，丰水期54.8%)，而在石亭江提取了工业生产中产生的废水等、动植物残体的降解、农业废弃物的风化、农田排水渠的农业废水和农药化肥的不合理施用5个污染源因子，其中工业生产中产生的废水等对石亭江氮磷污染的贡献最大(枯水期58.7%，丰水期55.8%)。因此，当地相关部门应加强对高贡献污染源的管控，从而降低流域氮磷污染负荷。

Study on Nitrogen and Phosphorus Distribution Characteristics by Spectrophotometry and Quantitative Source Analysis of Rivers With Different Land Use Types in Different Water Periods

Nitrogen and phosphorus are essential nutrients for the growth and reproduction of aquatic organisms and affect the primary productivity of the water body. The eutrophication level of the water body is closely related to the fractions of nitrogen and phosphorus. With the change in the water environment, the sediments will release nitrogen and phosphorus into the water body, causing secondary pollution. At the same time, quantitative identification of the contribution of external nitrogen and phosphorus pollution sources can effectively manage and control the nitrogen and phosphorus pollution load in the water body. Pihe River and Shiting River are important tributaries of Tuojiang River and affect the water quality of the Mother River of the Yangtze River. In this paper, the distribution characteristics of total nitrogen (TN), total phosphorus (TP) and various fractions of nitrogen and phosphorus in the water body and surface sediments of Pihe River and Shiting River in the upper reaches of Tuojiang River in the dry season and wet season were studied by molybdenum blue/ascorbic acid spectrophotometry and continuous extraction method.The behavior characteristics and release risk of nitrogen and phosphorus in rivers with different land-use types were compared. The APCS-MLR receptor model was used to identify and quantify the sources of nitrogen and phosphorus pollution. The results showed that: ① nitrogen and phosphorus in the water and surface sediments in the study area were at different pollution levels. The main contributors of TP in the dry season were particulate inorganic phosphorus (PIP) and particulate organic phosphorus (POP), while in the wet season, it was particulate inorganic phosphorus (PIP) and dissolved inorganic phosphorus (DIP). The main contributors of TN in the two water periods were nitrate-nitrogen (NO-₃-N) and organic nitrogen (ON). In surface sediments, the main contributor of TP was calcium-bound phosphorus (HCl-P), and the main contributor of TN was acidolysis nitrogen (HN). In dry season and wet season, the average ratio of bioavailable phosphorus (BAP) in TP of surface sediments of Pihe River (19.7% and 23.0%) was higher than that of Shiting River (11.0% and 12.5%), indicatinga a higher risk of phosphorus release. It was found that the nitrogen and phosphorus pollution degree in the dry season was higher than that in the wet season, and the nitrogen and phosphorus pollution degree in Shiting river was higher than that in Pihe River. ② APCS-MLR model extracted four pollution source factors in the Pihe River, including urban domestic sewage, leachate generated by domestic garbage accumulation, decomposition of animal and plant residues and aquaculture wastewater. Among them, urban domestic sewage contributed the most to nitrogen and phosphorus pollution in the Pihe River (50.9% in dry season and 54.8% in wet season). At the same time, wastewater generated in industrial production, degradation of animal and plant residues and the weathering of agricultural waste, agricultural wastewater from farmland drainage channels and an unreasonable application of pesticides and fertilizers were five pollution source factors, among them, the wastewater produced in industrial production contributed the most to the nitrogen and phosphorus pollution of Shiting river (58.7% in dry season and 55.8% in wet season). Therefore, the relevant local departments should strengthen the management and control of high contribution pollution sources to reduce the basin’s nitrogen and phosphorus pollution load.