The impact of land use and socio-economic factors on ammonia nitrogen pollution in Weihe River watershed, China

Rapid socio-economic development has led to a significant deterioration in the water environment, which has limited sustainable regional development. The soil and water assessment tool (SWAT) and statistical regression method were used to model the ammonia nitrogen (NH4+-N) pollution and explore the impacts of land use and socio-economic factors on NH4+-N pollution within the Weihe River watershed in China from 2015 to 2018. The result of SWAT model revealed that the NH4+-N concentrations were usually relatively high under low runoff conditions and relatively low under high runoff conditions. The average NH4+-N concentration in the upper reaches was 0.77 mg/L, whereas it was 0.87 mg/L in the middle and lower reaches of the watershed. Serious NH4+-N pollution mainly occurred in 2015 and 2016, and the V (2.0 mg/L) and V+ (>2.0 mg/L) water quality classes were associated with approximately 6.67% and 28.94% of the total watershed area, respectively. The multiple linear regression indicated that the building land and secondary industry were the significant controlling factors (P < 0.01). According to the scenario analysis, modelled scenarios for interception measures reduced the NH4+-N load to a greater degree than scenarios for source control measures. To improve the surface water quality in the Weihe River, it is recommended to adjust industrial structure, increase sewage treatment, and strengthen the rural management of the watershed.