Glacier retreat and increasing vegetation cover alter the sources and sinks of organic and inorganic carbon in alpine streams

High-mountain ecosystems are experiencing acute effects of climate change, most visibly through glacier recession and the greening of the terrestrial environment. The streams draining these landscapes are affected by these shifts, integrating hydrologic, geologic, and biological signals across the catchment. We examined the organic and inorganic carbon dynamics of streams in four Alpine catchments in Switzerland to assess how glacier loss and vegetation expansion are affecting the carbon cycle of these high mountain ecosystems. We find that organic carbon concentration and humic-like fluorescence properties increase with vegetation cover, implying an increasing importance of allochthonous carbon sources following glacier retreat. Meanwhile, streams transitioned from carbon dioxide sinks to sources with decreasing glacier coverage and increased vegetation coverage, with chemical weathering and soil respiration likely determining the balance. Carbon dioxide undersaturation was observed in glaciated and non-glaciated streams, indicating geochemical consumption could be more widespread in high-mountain, minimally vegetated catchments than previously described. Our results demonstrate significant shifts in organic and inorganic carbon dynamics of alpine streams following glacier recession. The clear link between the terrestrial and aquatic zones further emphasizes the coupled dynamics with which all hydrologic and biogeochemical changes in these ecosystems should be considered, including the carbon sink or source potential of montane ecosystems.