Spatiotemporal characteristics of agricultural nitrogen and phosphorus emissions to water and its source identification: A case in Bamen Bay，China

Abstract

The spatiotemporal characteristics and sources identification of agricultural nitrogen (N) and phosphorus (P) emissions to the gulf are rarely reported in tropical regions of China, mainly due to the lack of local reliable data and quantitative tools for spatiotemporal changes. In this study, we constructed a high-resolution NUFER (NUtrient Flow in food chains, Environment and Resources use) model based on geology, meteorology, land use data, statistical data, and field investigation to quantify the spatiotemporal characteristics and sources of N and P emissions. Bamen Bay (BMB), a bay with a mangrove national wetland Park in the Hainan Island, China, was chosen as a case study. The results showed that agricultural N emission to water in 2018 increased fivefold compared to 1990. Leaching was the main method of agricultural N emission and was mainly distributed in farms in the west and north. The contribution of N emission from crop system to water increased 20.3% in 28 years. Poultry and fruits have contributed the most to N output, and the trend is continuing. P emission to water increased sevenfold compared 1990. The contribution of P emission from animal system to water increased from 86.8% in 1990 to 90.1% in 2018 due to low removal rate of livestock manure. P emission was mainly via direct discharge of manure, mainly distributed in livestock breeding sites near the bay. Poultry has consistently contributed the most to P output in 28 years, accounting for 49.1% in 2018. Fertilizers and fodder were the largest sources of N and P. The average N and P loss rates of BMB were 5.32 t km2 yr−1 and 0.26 t km2 yr−1. The future agricultural transformation is essential, and it is necessary to reduce the application of N fertilizer and increase the removal rate of livestock manure. These results can provide reference for other typical agricultural pollution bays in exploring the spatiotemporal characteristics of N and P emissions to water and the identification of agricultural sources.