Glacier loss and vegetation expansion alter organic and inorganic carbon dynamics in high-mountain streams

High-mountain ecosystems are experiencing the acute effects of climate change, most visibly through glacier recession and the greening of theterrestrial environment. The streams draining these landscapes are affected by these shifts, integrating hydrologic, geologic, and biologicalsignals across the catchment. We examined the organic and inorganic carbon dynamics of streams in four Alpine catchments in Switzerland to assesshow glacier loss and vegetation expansion are affecting the carbon cycle of these high-mountain ecosystems. We find that the organic carbonconcentration and fluorescence properties associated with humic-like compounds increase with vegetation cover within a catchment, demonstrating theincreasing importance of allochthonous dissolved organic carbon sources following glacier retreat. Meanwhile, streams transitioned from carbondioxide sinks to sources with decreasing glacier coverage and increased vegetation coverage, with chemical weathering and soil respiration likelydetermining the balance. Periods of sink behavior were also observed in non-glaciated streams, possibly indicating that the chemical consumption ofcarbon dioxide could be more common in high-mountain, minimally vegetated catchments than previously known. Together, these results demonstrate thedramatic shifts in carbon dynamics of high-mountain streams following glacier recession, with significant changes to both the organic and inorganiccarbon cycles. The clear link between the terrestrial and aquatic zones further emphasizes the coupled dynamics with which all hydrologic andbiogeochemical changes in these ecosystems should be considered, including the carbon sink or source potential of montane ecosystems.