Glacier Melt Enhances Suspended Sediment and Mercury Export from the Tibetan Plateau

Glacier-fed streams (GFSs) export large amounts of suspended sediment (SS) and associated mercury, with important implications for downstream water quality, yet the controls on Hg export remain poorly constrained. This issue is particularly acute on the Tibetan Plateau, where glacier meltwater sustains major Asian rivers. Here, we quantify seasonal and diurnal variability (n = 350) in SS and Hg across six Tibetan Plateau GFSs and synthesize observations from 36 GFSs worldwide. Tibetan Plateau GFSs exhibit total Hg (THg) concentrations and yields comparable to Alaska, but higher than most GFSs with similar glacier coverage. In GFSs without proglacial lakes, THg export scales with SS and increases with glacier coverage and velocity, indicating mobilization of erosion-derived, particle-associated Hg. THg–SS hysteresis differs among glacier thermal regimes in response to particle sorting and subglacial drainage evolution. Our results suggest that intensifying melt and rainfall on the Tibetan Plateau may increase Hg yields and delay the timing of peak Hg export, whereas expanding proglacial lakes may temporarily buffer further downstream Hg export. This study identifies controls on SS and THg export in Tibetan Plateau GFSs and highlights implications for downstream water quality and ecosystem exposure under glacier retreat.