莱州湾入海河流总氮来源及季节性变化成因解析:以弥河为例

Analysis of the Sources and Seasonal Variations of Total Nitrogen in the River Entering the Laizhou Bay

入海河流携带的陆源总氮污染是近岸海域无机氮的重要来源,为探究莱州湾入海河流总氮污染内因,本文以弥河为例,分析其2020-2022年生态环境保护部门常规监测及2023年补充调查的加密监测数据,核算各行业总氮污染负荷,系统解析弥河总氮污染来源及季节性变化成因,并提出总氮管控治理措施建议。结果表明:①弥河流域总氮浓度呈现明显的季节性变化规律,即秋冬高、春夏低。②弥河干流总氮浓度呈“上游相对较低、中下游高”的特征,其中,以农业用地(60.6 mg/L)和居民用地(20.4 mg/L)为主的洗耳河、龙岗河和黄龙沟河等支流流域总氮浓度较高,以山地(6.3 mg/L)、荒地(7.6 mg/L)和湿地(6.9 mg/L)为主的五井石河和南阳河等支流流域总氮浓度较低。③弥河流域总氮来源主要为农业面源(49.3%)、工业与城镇生活源(43.3%),其中农田大棚施肥量高、灌溉水量大、氮磷流失系数高等因素,是弥河农业种植源在农业面源中占比较高(45.4%)的主要原因。④弥河流域总氮季节性变化主要与流域内降雨量、农业面源、污水处理厂工艺效率和河道生态系统自净能力相关。研究显示,弥河流域总氮高值区最主要的污染源为农业面源污染,管控重点是洗耳河流域的地下水和农田大棚种植。

The land-based total nitrogen pollution carried by rivers entering the sea is an important source of inorganic nitrogen in coastal waters.In order to explore the internal causes of total nitrogen pollution from rivers entering the Laizhou Bay,this paper takes the Mihe River as an example,and analyzes the routine monitoring data from the environmental protection department in 2020-2022 and the encrypted monitoring data from the supplementary investigations in 2023.The total nitrogen pollution load of various industries is calculated,and the sources and seasonal variations of total nitrogen pollution in the Mihe River are systematically analyzed,and suggestions for control and management measures are proposed.The results show that:(1)The total nitrogen in the Mihe River Basin shows obvious seasonal variations,with high concentration in autumn and winter and low concentration in spring and summer.(2)The total nitrogen concentration in main stream of the Mihe River Basin is relatively low in the upper reaches and high in the middle and lower reaches.Among them,tributaries such as the Xier River,Longgang River and Huanglonggou River mainly held higher concentrations of total nitrogen dominated by agricultural land(60.6 mg/L)and residential land(20.4 mg/L),while tributaries such as the Wujingshi River and Nanyang River mainly held lower concentration dominated by mountainous land(6.3 mg/L),barren land(7.6 mg/L)and wetland(6.9 mg/L).(3)The main sources of total nitrogen in the Mihe River Basin are agricultural non-point sources(49.3%)and industrial and urban living sources(43.3%).The factors such as high fertilizer application to agricultural greenhouses,large irrigation water volume,and high loss coefficients of nitrogen and phosphorus are major reasons for the higher proportion of agricultural cultivation sources(45.4%)in the Mihe River.(4)The seasonal variation of total nitrogen in the Mihe River Basin is mainly related to rainfall,agricultural sources,efficiency of wastewater treatment plants,and self-purification capacity of the river ecosystem.The study has shown that the main source of pollution in the high-value area for total nitrogen in the Mihe River Basin is agricultural non-point source pollution,and the focus for control measures is the groundwater and greenhouse cultivation in the Xier River Basin.