Decade-scale contrasts in sediment metal(loid)s across Qinghai-Xizang Plateau lakes

Lake sediments on the Qinghai-Xizang Plateau capture shifting metal(loid) dynamics within an alpine ecosystem uniquely vulnerable to climate change and anthropogenic pressures. However, plateau-wide ecological risk assessments incorporating quantitative source apportionment remain scarce, leaving a critical gap that hinders targeted ecosystem conservation and precise policy interventions. Here we present a plateau-scale analysis of sediment geochemistry across 110 lakes over two decadal periods (2014 and 2024), utilizing a hybrid positive matrix factorization-random forest framework. Arsenic serves as the primary diagnostic sentinel, persistently exceeding baseline thresholds across both decades. Although mean chromium concentrations declined from 85.7 to 68.0 mg kg^-1, the broader multi-metal pool exhibits remarkable regional stability, with low baseline ecological risks dominated by cadmium toxicity alongside localized high-risk anomalies in Lakes Tosu, Gahai, and Xiligou. Hybrid source apportionment demonstrates that a mixed footprint of transport emissions, transboundary atmospheric influx, and lithogenic weathering increasingly drives geochemical variance, surging from 44% to 66% over ten years, whereas the independent arsenic source remains invariant at approximately 15%. These patterns reveal that while natural weathering constrains the regional background, localized anthropogenic signatures are rapidly intensifying around emerging infrastructure corridors. This predictive framework establishes a transferable template for tracking contaminant dynamics in vulnerable alpine headwaters, providing a vital baseline for targeted, source-specific mitigation globally.