Current integrated modeling frameworks for simulating nutrient sources and dynamics are inadequate for large regional watersheds dominated by groundwater-surface water interactions due to their simplistic representations of groundwater. In this study, we develop a coupled model that integrates comprehensive surface water, 3-D groundwater, soil erosion, and nutrient processes. The model is intended to enhance the understanding of nutrient dynamics and sources in the Pearl River Basin (PRB). The model exhibits satisfactory performance in simulating streamflow and sediment transport patterns, capturing essential seasonal variations in water quality indicators. Hydrological budget assessments from 2002 to 2020 in the PRB reveal that 54% of precipitation drains into the South China Sea as surface water, while groundwater discharge as baseflow accounts for 18% of the streamflow. The nutrient budget for the PRB indicates that non-point sources are the dominant contributors to both nitrogen (N) and phosphorus (P), ranging between 64% and 90%. Improved sewage collection and treatment have reduced point source nutrient contributions over the evaluation period. Groundwater remains a significant and consistent source of N, contributing between 11% and 19%. Natural disturbances and fertilization have led to an upward trend in river N inputs, while afforestation and sewage reduction efforts have resulted in a downward trend in river P inputs. Increased fertilization emerges as a central concern for the PRB, suggesting cost-effective mitigation of fertilizer usage a pragmatic solution. The coupled simulation model developed in this study offers a novel systems approach for basin-wide nutrient analysis and pollution control strategies, considering both natural and human-induced disturbances.

中文翻译：

---

区域流域流量、土壤侵蚀和养分动态的综合建模：评估自然和人为影响


目前用于模拟养分源和动态的综合建模框架不足以适应以地下水与地表水相互作用为主的大型区域流域，因为它们对地下水的描述过于简单。在这项研究中，我们开发了一个耦合模型，集成了综合地表水、3D 地下水、土壤侵蚀和养分过程。该模型旨在增强对珠江流域（PRB）养分动态和来源的了解。该模型在模拟水流和泥沙输送模式、捕捉水质指标的基本季节性变化方面表现出令人满意的性能。长江资源委员会2002年至2020年水文收支评估显示，54%的降水以地表水形式排入南海，地下水作为基流排入南海的流量占18%。 PRB 的养分预算表明，非点源是氮 (N) 和磷 (P) 的主要贡献者，范围在 64% 到 90% 之间。改进的污水收集和处理减少了评估期间点源养分的贡献。地下水仍然是氮的重要且稳定的来源，占 11% 至 19%。自然扰动和施肥导致河流氮输入量呈上升趋势，而植树造林和污水减排工作则导致河流磷输入量呈下降趋势。增加施肥成为 PRB 关注的中心问题，这表明以具有成本效益的方式减少化肥使用是一种务实的解决方案。 本研究开发的耦合模拟模型为全流域养分分析和污染控制策略提供了一种新颖的系统方法，同时考虑了自然和人为干扰。