Nitrogen flow characteristics and environmental effects in agricultural systems of Zhuxi basin，Hainan Island

The issue of agricultural non-point source pollution is significant in the small watersheds of Hainan Island. To effectively conduct pollution control and water environment management， this study employs the NUFER （NUtrient flows in Food chains， Environment and Resources use） model to quantify the nitrogen flow characteristics and environmental emission intensity of the agricultural system in the Zhuxi river basin from 1990 to 2020. The results show that， compared to 1990， environmental nitrogen emissions in 2020 increased by 1.9 times， with chemical fertilizers and feed being the main sources of nitrogen. Since 1990， the contribution of aquaculture nitrogen emissions to water pollution increased from 0.84×10^-3 Gg to 0.35 Gg. The crop planting system contributed the most to the total nitrogen in water bodies， primarily through gaseous emissions and leaching， while the livestock and poultry breeding system was the second-largest contributor. Spatially， leaching losses were mainly concentrated in the downstream and western areas of the basin. Therefore， key measures to reduce nitrogen emissions include replacing chemical fertilizers with organic fertilizers， treating livestock and poultry manure， regulating aquaculture practices， and improving tailwater treatment technology. This study quantifies the nitrogen flow characteristics and sources in the agricultural system of small watersheds， providing guidance for agricultural management and water environment governance.