Journal Article

Integrated Modeling of Flow, Soil Erosion, and Nutrient Dynamics in a Regional Watershed: Assessing Natural and Human‐Induced Impacts

Lancia, Michele, Andrews, Charles B., Zheng, Chunmiao, Tian, Yong, Wang, Xiaoli, Sun, Taotao, Yu, Jiang

2024

Overview

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. Plain Language Summary Water nutrient pollution is a global problem caused by both natural and human factors. To better understand nutrient pollution, a new model has been developed that combines water flow, soil erosion, and nutrient transport to simulate water and nutrient cycling on a regional scale. This model can assist in the management of water pollution by providing a better understanding of nutrient sources and quantifying the contribution of climate change and different human activities. Tested in the Pearl River Basin from 2002 to 2020, the model accurately simulated water flow and nutrient patterns. A key finding is that groundwater supplies 18% of water and 14% of nitrogen inputs of the Pearl River. The main sources of pollutants are non‐point agricultural sources, primarily from fertilization. Climate variability leads to more runoff and nutrient input, while improved sewage treatment and afforestation have reduced nutrient pollution. The model allows the exploration of different influencing factors to better control nutrient pollution. Understanding how human activities impact different regions is crucial for effective nutrient pollution management. Key Points A novel system model integrates water, soil, and nutrient dynamics for effective regional watershed management Non‐point source nutrients are the major contributors of nitrogen and phosphorus levels in the Pearl River Basin, accounting for 64%–90% The rise in fertilization poses a growing concern for the Pearl River Basin, underscoring the need for cost‐effective mitigation strategies

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Afforestation / Base flow / Biological fertilization / Budgets / Climate change / Climate variability / Cost analysis / cost effectiveness / Ecosystem disturbance / Erosion processes / Fertilization / Fertilizers / Groundwater / Groundwater discharge / Groundwater treatment / Human factors / Human influences / integrated modeling / Mitigation / Modelling / Natural disturbance / Nitrogen / Nutrient cycles / Nutrient dynamics / Nutrient pollution / Nutrient sources / Nutrient transport / Nutrients / Pearl River basin / Phosphorus / Pollution / Pollution control / Pollution sources / River basins / Rivers / Seasonal variations / Sediment transport / Sewage / Sewage treatment / Simulation models / Soil erosion / Soil pollution / Soil water / South China Sea / Stream discharge / Stream flow / Surface water / surface water‐groundwater interaction / Surface-groundwater relations / Wastewater treatment / Water discharge / Water flow / Water management / Water pollution / Water quality / water quality management / watershed nutrient sources / Watersheds