Regional sustainability outranked damming effects in affecting water quality in the lower reaches of the Jinsha River, China

Besides cascade hydropower development, regional socio-economic activities also significantly affect water quality in the drainage region. However, it remains challenging to ascertain the implications of the damming effects and regional sustainability on water quality. This study examined the variations in water quality indicators, including chemical oxygen demand (CODMn), ammonia nitrogen (NH3-N), and total phosphorus (TP), during the cascade hydropower development (both the construction and impoundment periods from 2006 to 2023) in the lower reaches of the Jinsha River (the upper reaches of the Yangtze River). The relationships between land use changes, point and non-point source nitrogen (N) and phosphorus (P) inputs, and water quality and their interconnections with multiple Sustainable Development Goals (SDGs) were analyzed to assess the impacts of regional sustainability on water quality. The CODMn and NH3-N concentrations did not significantly differ between 1-2 hydrologic years before and after dam construction or reservoir impoundment, while the TP concentrations substantially decreased following reservoir impoundment. Land use changes at the riparian scale and point and non-point source N and P inputs in the sub-watershed effectively accounted for variations in NH3N and TP during cascade hydropower development. Factors influencing water quality were closely linked to regional sustainability, including urbanization progress (SDG 11), urban sewage management (SDG 6), agricultural adjustment (SDG 2), and forest restoration (SDG 15). This study underscores the positive influence of regional sustainability on water quality improvement, which is beneficial for developing sustainable hydropower development strategies.