Prioritizing riparian scale landscape management is a spatially efficient strategy for controlling river water...

Identifying the optimal spatial scale for landscape management is crucial for effective water quality improvement, specifically regarding whether the watershed scale or the riparian buffer scale is more effective. To address this, we conducted a national-scale analysis of the relationships between water quality and landscape-geoclimatic metrics across 441 watersheds in China, utilizing a multi-scale framework encompassing eight distinct spatial scales. These included four watershed scales (circular areas with radii of 10, 25, 50 km, and the entire watershed) and four riparian buffer scales (1-km wide buffers extending 10, 25, 50 km upstream, and the entire reach). The results indicated that geoclimatic conditions explained 18%-23% of the water quality variation, while landscape metrics explained 17%-32%. Crucially, we found that the riparian buffer scales provided explanatory power (40%-50%) nearly equivalent to that of the watershed scales (40%-49%), despite occupying a significantly smaller area. A distinct scale-dependent trade-off was identified: landscape composition dominated water quality variation within riparian buffer scales, whereas landscape configuration was more influential at the watershed scales. Our findings suggest that prioritizing landscape management within riparian buffers offers an efficient pathway that yields water quality improvements comparable to whole-watershed interventions, providing a precise spatial strategy for environmental planning under resource constraints.