Nitrogen and phosphorus emission to water in agricultural crop - animal systems and driving forces in Hainan Island, China

Identifying the spatial characteristics of nitrogen (N) and phosphorus (P) emission from agriculture to water bodies and quantifying effect factors are critical to explore the mitigation options. A high-resolution NUFER (Nutrient Flow in food chains, Environment and Resources) model based on geology, meteorology, land use data, statistical data, and field investigation was used to quantify the spatial characteristics of N/P emissions in Hainan Island, China, driving forces was analyzed and effective measures to reduce emissions in 2035 was explored with scenario analysis. Overall, 98 Gg N from agriculture entered water bodies in 2018, of which the crop system contributed 70%; 15 Gg P entered water bodies, animal system contributed 78%. Nitrate ( NO -3 ) leaching (65%) and direct discharge of animal manure (69%) accounted for the most to the N and P emissions, respectively. 89% of N and 92% of P emissions occurred in plain areas. Spatial overlay analysis showed that high N and P emissions mainly concentrated in the western and northeastern plain areas. At the sub-basin scale, Nandu River was the largest basin of agricultural N/P emissions, accounting for more than 20% of the total emissions. Our correlation analysis showed that N/P emissions were significantly correlated to natural (such as elevation, slope and soil texture) and anthropogenic (e.g., rural income, population density, planting structure and livestock density) factors. We further analyzed the emissions of N/P can be reduced by 71Gg and 14 Gg by 2035 respectively, via reducing food chain waste and consumption, importing more food and improving production efficiency, especially prohibiting the direct discharge of livestock manure. Our research quantified agricultural N and P emissions to the water bodies in a high-resolution context and explored the most effective options for reduction of agricultural non-point source pollution (ANPS) emissions at the island scale.