Ecological restoration guided by hydrological connectivity reduces nitrogen fluxes from river to coast

Greening is the optimal way to mitigate climate change and water quality degradation caused by agricultural expansion and rapid urbanization. However, the ideal sites to plant trees or grass to achieve a win-win solution between the environment and the economy remain unknown. Here, we performed a 12-year comprehensive observation in the Jiulong River watershed (southeastern China) and a nationwide survey on groundwater in China (n = 90), combining them with statistical and AI models to explore the linkages between land use within hydrologically sensitive areas (HSAs) and nitrogen concentrations/fluxes from the perspective of hydrological connectivity. We found that HSAs occupy approximately 20% of the total land area and are hotspots for transferring nitrogen from the land surface to rivers and groundwater. Increasing the proportion of natural lands within HSAs improves river and groundwater quality and reduces the exports of riverine nitrogen to coastal zones. These new findings suggest that prioritizing ecological restoration in HSAs is conducive to achieving harmony between the environment (improving watershed water quality and reducing river nitrogen export flux) and the economy (reducing investment in area management).