Hotspots are not targets: scale-matched source-control screening for rural black and odorous waters

Managing water quality in dispersed rural small water bodies requires source-control prioritisation under sparse monitoring and overlapping domestic, agricultural, and livestock pressures. Using reported rural black and odorous waters in China, this study integrates gridded population, cropland, and livestock data with official inventories to compare screening information across provincial macro-scale units, 1-km grids, and 25-km windows. Provincial hotspot rankings were reordered under population-, livestock-, and cropland-normalised frameworks, showing that regional clustering alone cannot identify a source-control target. At the 1-km scale, population pressure showed a near-continuous background-gradient response, whereas livestock pressure showed more concentrated local risk-rise positions in higher-pressure intervals, providing a screening reference for prioritising field checks within otherwise similar backgrounds. Cropland proportion exhibited a robust non-monotonic response that varied with population and livestock backgrounds. At the 25-km scale, local responses formed contiguous mesoscale structures, while population-leaning and livestock-leaning patches remained spatially differentiated. These results support a hierarchical framework in which provincial analyses guide resource allocation, 1-km analyses prioritise local screening, 25-km structures organise dispersed survey tasks, and field investigations confirm water-body status, pollution sources and pathways, and appropriate management measures. The framework converts reported inventories and spatial pressure data into operational screening priorities where exhaustive monitoring is impractical.