Spatio-temporal dynamics of nitrogen and phosphorus input budgets in a global hotspot of anthropogenic inputs

The increased input of anthropogenic nitrogen (N) and phosphorus (P) to watershed ecosystems has been cited as among the most important reasons for widespread water pollution. Revealing spatio-temporal patterns of N and P input budgets in regions with intensified human activity can facilitate a better understanding of human-induced N and P cycles. Here, we present budget inventories including both anthropogenic non-point and point N and P inputs into the Huai River Basin, which has been identified as one of the hotspots of anthropogenic inputs across the world. On average, total anthropogenic N and P inputs in the year 2010 reached 28,000 kg N km^-2 yr^-1 and 2800 kg P km^-2 yr^-1, showing a 50% and 42% increases in comparison with 1990, respectively. Both non-point-source and point-source N & P inputs have exhibited a rapid increase from 1990 to 2010, which has been related to the increasing human population and socio-economic development. The intensive farming implemented to meet the growing food demand was responsible for continuous growth in non-point-source inputs. Meanwhile, rapid urbanization with lagged environmental management was the major reason for the increased point-source inputs. Spatial patterns of N & P inputs were similar across different periods, showing that the hotspots generally centralized in a few northern counties. By further interpreting the critical sources and their drivers of inputs to each region through time, our work provides insights for targeted management. Future mitigation strategies such as optimizing the farming methods, improving manure management and enhancing sewage treatment are necessary to address the environmental concerns of excessive inputs.