Long-term water quality dynamics and influencing factors under ecological compensation mechanisms: A case study of China's first cross-provincial ecological compensation watershed.

Abstract

Despite the widespread implementation of watershed ecosystem payment schemes globally, their specific impacts on water quality remain inadequately characterized. This study quantifies long-term (1988-2020) nitrogen (N) and phosphorus (P) inputs and riverine N and P dynamics (2000-2020) to discern trends in water quality changes and to comprehensively consider the impacts of ecological compensation (EC) practices, legacy nutrient sources, and climatic conditions on water quality in China's first cross-provincial EC pilot watershed. The results indicate that EC practices are effective in reducing source inputs and improving water quality, as evidenced by significant reductions in net anthropogenic N and P inputs (1.17-fold and 1.42-fold reductions) and ammonia N concentrations and loads during the EC period. However, the limited improvements in riverine N and P levels highlight the potential impact of legacy nutrients and precipitation on water quality. Notably, the observed potential lag times for N (7-12yr) and P (8-12yr) somewhat delayed water quality improvements, while increased precipitation may result in more pollutants being released from soil or groundwater, thus masking water quality improvement signals. Overall, this work demonstrates the critical role of EC in improving water quality, while also emphasizing the need to consider legacy nutrient sources and climate impacts when implementing management measures.