基于人为氮净输入及入河系数的流域河流氮输出负荷估算

构建基于流域人为氮净输入及其入河系数的河流总氮(TN)负荷模型,以探索解决由于面源污染传输空间异质性、传统入河系数核算不确定性较大等问题所导致的典型流域基本测算单元精细化模拟结果难以向大尺度扩展的问题。以面源污染转化较复杂的亚热带南方丘陵区源头流域为研究区,通过建立流域人为氮净输入模型(NANI)和TN入河系数关键影响因子(水文、地形地貌、土地利用等)回归模型,对河流TN负荷通量进行估算。同时将基于小尺度流域(金井河)构建的相关模型向下游大尺度流域(捞刀河)进行应用。结果表明:金井河流域8个集水区(面积2.6~204.1 km^2)NANI从2012年到2017年呈现显著降低趋势,变化范围为(81.7±7.0)~(198.2±32.5)kg·hm^-2·a^-1,其中氮沉降、化肥净输入为主要输入源;构建了基于径流系数和高程为变量的NANI入河系数回归模型,并结合NANI模型对河流TN负荷进行模拟,模型决定系数(R2)、纳什效率系数(NSE)分别为0.729、0.714;将基于金井河流域构建的河流氮负荷模型应用于捞刀河流域(2543 km^2),4个监测断面模拟值与实测值误差范围为10.3%~17.2%。研究表明,基于流域人为氮净输入及其入河系数的河流TN负荷模型在一定程度上满足科学、便捷、适用性,可用于南方丘陵区农业面源污染负荷的估算。

Estimation of nitrogen output load of a river watershed based on net anthropogenic nitrogen input and river inflow coefficient

We constructed a model for calculating total nitrogen(TN)load in a river, based on the net input of man-made nitrogen to the river basin and its inflow coefficient. In order to explore and solve problems such as the spatial heterogeneity of non-point source pollution transmission and the large uncertainty of traditional river inflow coefficient accounting, the simulation results of typical watersheds must be expanded from basic measurement units to a larger scale. As an example, we used the source watershed of a subtropical southern hilly region where the transformation of non-point source pollution is complicated. The riverine TN exports were estimated by establishing a net anthropogenic nitrogen input(NANI)model for the river watershed, and a regression model of the key factors(hydrology, landform, land use, etc.)affecting the river inflow coefficient of TN. At the same time, a relevant model based on a small-scale watershed(Jinjing River) was applied to the downstream large-scale watershed(Laodao River). The results showed that the NANI of 8 catchments(area 2.6~204.1 km²)in the Jinjing River watershed decreased significantly between 2012 and 2017, and varied from(81.7±7.0)kg·hm^-2·a^-1 to(198.2±32.5)kg·hm^-2·a^-1, in which nitrogen deposition and net input of chemical fertilizer were the main input sources. A NANI river inflow coefficient regression model, based on runoff coefficient and elevation, was constructed, and riverine TN exports were simulated with the NANI model. The model determination coefficient(R²)and Nash efficiency coefficient(NSE)were 0.729 and 0.714, respectively. The river nitrogen load model based on the Jinjing River watershed was applied to the Laodao River Watershed(2 543 km²). The error between the simulated and measured values of the four sections ranged from 10.3% to 17.2%. This shows that the river TN load model based on NANI and its inflow coefficient is scientific, convenient and applicable to a certain extent, and can be used to estimate the load of agricultural non-point source pollution in the hilly region of South China.