Spatio-temporal distribution, ecological risks and possible sources of heavy metals in Lake Gahai on northeastern Qinghai-Tibet Plateau: Response to anthropogenic activities and environmental changes

The closed lakes are sensitive to environmental changes and human activities on Qinghai-Tibet Plateau, however, the mechanism of centennial heavy metals (HMs) pollution is still controversial. The sedimentary evolution of Lake Gahai was reconstructed based on the HMs (e.g., Pb, Zn, Cu, Cd, Cr, Hg, As, Mn) concentration, Pb isotope fingerprints (e.g., 206 Pb/ 207 Pb, 208 Pb/ 206 Pb), grain sizes and other proxy indicators during 1852–2023 AD. The earthquake triggered the release of Pb, Cu, Cr and Mn from bedrock in 1937 AD, industrialization led to Hg and Cd deposition flux multiplication during 1975–2006 AD, environmental policies reduced anthropogenic Hg input by 45 % after 2006 AD, which confirmed by Pb isotope ratio ( 206 Pb/ 207 Pb=1.1848–1.1920). The pollution load index (PLI) value was 1.776, suggesting the entire lake was moderately polluted, with Cd and As surface enrichment reaching 2.2–2.6 times higher than the background values. The highest risks of potential ecological risk index (PERI >200) were found near transportation, lake entrance and central sampling sites. Pb isotope ratios showed that the sources in low Pb concentration sites were controlled by natural weathering (66 %) and anthropogenic activities (34 %), which was significantly different from the results of anthropogenic sources calculated by absolute principal component score–multiple linear regression (PCA-APCS-MLR) and positive matrix factorisation (PMF) models. This study had established a driving chain linking geological events, industrialization and policy regulation, and provided a theoretical framework for controlling multi-source pollution in high-altitude lakes.