Multi-scale riparian land use, landscape configuration, and water quality in a tidal urban river: spatial gradients and sensitive bands along the Huangpu River, Shanghai

To characterize the scale-dependent associations between riparian land use, landscape configuration, and water quality in a tidal urban river, this study used water-quality monitoring data from multiple river reaches. Multi-scale cumulative buffers of 0–100 m, 0–200 m, 0–400 m, and 0–800 m were delineated, from which land-use composition and landscape-pattern metrics were derived. Correlation analysis and redundancy analysis (RDA) were employed to identify the land-use and landscape variables most strongly associated with variations in water quality. The results indicate that urban land use is consistently positively correlated with COD Mn , BOD₅, TN, and TP and negatively correlated with DO at three or four of the four buffer scales examined, making it the most consistently associated land-use variable across buffer widths. IL showed significant associations with water-quality indicators at the 0–100 m scale but not at broader scales, while AL–TP and AL–TN associations reached statistical significance at the 0–200 m and 0–400 m scales but were non-significant at the 0–100 m and 0–800 m scales. Forest land, green land, and wetland/water areas are associated with higher dissolved oxygen and lower pollutant concentrations, consistent with the known filtering and oxygen-replenishment functions of riparian ecological land. AL–TP and AL–TN correlations reached significance at the 0–200 m and 0–400 m buffer scales but were non-significant at the narrowest (0–100 m) and broadest (0–800 m) scales; this scale-dependent significance pattern is treated as a hypothesis-generating finding, as formal cross-scale comparisons did not reach statistical significance at the current sample size ( n = 8). At the 0–800 m scale, ED showed significant associations with TN and TP; given limited statistical power and a modest RDA contribution (3%), this is reported as an exploratory finding. Based on these findings, we propose a zoned management framework—“near-bank ecological buffering–intermediate-scale source–pathway management–source-area structural optimization”—to integrate riparian spatial planning with nonpoint-source pollution control. This study provides transferable spatial evidence and an approach for identifying sensitive bands for water-quality management in tidal urban river networks from both multi-scale and landscape-configuration perspectives. • Urban land consistently links to water-quality indicators across all buffer scales. • Across scales, AL–TP and AL–TN are significant at 200–400 m only—an exploratory pattern. • Industrial land links only at 0–100 m; agricultural at 200–400 m only. • At 0–800 m only, edge density links to TN/TP (exploratory: power ∼0.42, R² = 3%). • A three-tier gradient zoning framework is proposed for tidal urban riparian management.