A multi-spatial scale analysis of anthropogenic nitrogen and phosphorus inputs in a large river basin: environmental effect and policy impact

Intense human activities have increasingly reshaped the global nutrient cycle, causing frequent environmental issues owing to excessive nitrogen (N) and phosphorus (P) inputs. Therefore, it is necessary to explore the component structure, driving factors, and environmental impacts of regional nutrient inputs. Based on net anthropogenic N and P input (NANI and NAPI, respectively) models, combined with data mining and statistical analysis, the spatiotemporal changes of NANI and NAPI in the Yangtze River Basin were studied. Their environmental and scale effects, policy impacts, and classification management were then discussed. The results reveal that NANI and NAPI showed a significant downward trend in the Yangtze River Basin from 2011 to 2019, with an average value of 7968 kg N km⁻² year⁻¹ and 1241 kg P km⁻² year⁻¹, respectively. Moreover, the contribution of varying fertilizer intensity resulted in an approximate change in both NANI and NAPI by 50%. Meanwhile, NANI and NAPI exhibited decreasing spatial trends from east to west and north to south, with developed agricultural plain areas and densely populated urban agglomeration areas being the focal areas of nutrient inputs. Despite the spatiotemporal differences, there was a strong dependence between higher nutrient input and higher nutrient concentration conditions. To relieve the environmental pressure, the fertilizer policy was implemented and had a marked impact on the change in nutrient input trend. Based on the classification of cities through the comparison of major input items, plain regions where fertilizer dominates nutrient input need to be managed by improving the utilization rate of fertilizer.