Temporal and Spatial Distribution, Ecological Risk Assessment, and Source Apportionment of Heavy Metals in Surface Sediments of Ranwu Lake, Xizang

• • During glacial ablation (July 2024), mean concentrations of Cr, Cd, Pb, and As exceeded Xizang soil background values, indicating anthropogenic enrichment; in late ablation (November 2024), only Cd, Pb, and As remained above background, suggesting seasonal dilution or source variation. • • The potential ecological risk index (RI) averaged 81.79 in the ablation period and 98.30 in the late ablation period, both indicating low overall risk, but Cd was identified as the dominant risk factor, contributing disproportionately to the RI. • • Source apportionment via APCS-MLR quantified that natural sources dominated Cr, Ni, and As, while traffic emissions were the primary source for Cd and Pb; Cu and Zn had mixed natural and traffic origins, with traffic being the major ecological risk contributor. • • Spatial analysis using IDW revealed that high heavy metal concentrations shifted from the middle and lower lake reaches during ablation to the lower reaches in the late ablation period, suggesting hydrological control on metal distribution.