A Source-pathway-receptor Framework for Quantifying Ecological Risk to Shallow- and Deep-rooted Vegetation under Heavy Metal Contamination.

Heavy metal contamination in river basins poses a global challenge to vegetation health, crop productivity, and long-term ecological security. However, existing ecological risk assessment methods typically assume uniform vegetation exposure, overlooking how contamination sources and hydrological pathways differentiate vegetation vulnerability across varying soil depths. To address this gap, a novel depth-specific vegetation ecological risk assessment framework was developed using a source-pathway-receptor approach. An integrated environmental risk assessment was first performed for the 2023 pre- and post-monsoon seasons to characterize baseline environmental conditions across the basin. Subsequently, contamination source intensity, environmental pathway intensity, and vegetation receptor vulnerability were combined via the entropy weighting method to quantify spatiotemporal risk patterns within shallow-root (S-VER) and deep-root (D-VER) systems. The framework was validated using vegetation response derived from a normalized difference vegetation index (NDVI).The results indicate that moderate S-VER was primarily associated with surface hazards and exhibited seasonal variability under changing hydrological conditions. This behavior was particularly evident within the agricultural production and ecological function zones. In contrast, D-VER remained comparatively stable with low-to-moderate risk, reflecting the influence of subsurface contamination and limited seasonal variability. Crucially, the lower Hindon Basin emerged as a major ecological risk hotspot for both shallow- and deep-root vegetation due to cumulative upstream contaminant loading and reduced vegetation resilience. These patterns were further supported by an inverse relationship between NDVI-derived vegetation response and ecological risk. Collectively, the proposed depth-specific framework provides a targeted diagnostic tool for watershed management and localized ecological remediation in contaminated river basins.