Towards integrated pollution control in inland watersheds: addressing multiple challenges through watershed-scale technological systems and targeted control strategies

Water quality deterioration remains a critical global environmental challenge, with inland watersheds across most regions worldwide affected by varying pollution levels. However, a systematic and in-depth review of the key issues, treatment technologies, and strategic approaches for watershed pollution control is still lacking. The health of watershed ecosystems is shaped by multiple interrelated factors, including external and internal pollution sources, in-stream contamination, and limited self-purification capacity, which interact to determine pollution severity and remediation complexity. Although a wide array of technologies is available to address different types of pollution, traditional classification systems based on physical, chemical, or biological approaches do not adequately correspond to specific pollution scenarios. Unlike conventional process-based classifications, this study proposes a problem-oriented, function-based classification system encompassing five major categories of technology: non-point source control, point source control, internal source remediation, in-stream treatment, and enhancement of self-purification. This technology system offers more targeted solutions for watershed pollution control. Technological choices and implementation strategies vary significantly across countries at different development stages, highlighting the importance of context-specific and scientifically informed decision-making. It further discusses the role of integrated, multi-objective strategies and examines the evolution of decision-making methods in watershed management. Future efforts should focus on building multi-objective, multi-criteria, and multi-stakeholder decision support systems, such as those integrating participatory modeling with scenario simulation and multi-criteria decision-making, to advance more scientific, precise, and systematic watershed governance.