Streamwater pCO2in an Alpine Headwater Catchment

Boreal and alpine streams are highly sensitive to climate change. Previous studies have shown the relevance of streams for carbon cycling in boreal landscapes. Less work has been done on alpine streams, and we do not understand the contributions from these ecosystems to the regional and global carbon cycles. The objective of this study is to assess critical carbon fluxes in an Alpine stream network, by quantifying the partial pressure of carbon dioxide, pCO2, and potential sources. We sampled every 50 meter along the stream network in a small Swiss Alpine catchment, during the four different seasons of the year (winter, spring, summer and autumn of 2016). By doing this, we identify high resolution spatial patterns along the stream network, together with seasonal patterns to capture different hydrological signatures (snowmelt, glacier melt and groundwater). We found that the streamwater was supersaturated in CO2 and the δ13C of dissolved inorganic carbon (DIC) indicated weathered bedrock materials as a major source of CO2, where groundwater transfers carbon to the stream. Moreover, the pCO2 increased with enriched stable isotopes of water, indicating a shift in CO2 sources from upstream to downstream, where the more snowmelt dominated upstream tributaries were diluted with groundwater inflow downstream. These results are yet preliminary. However, the supersaturation of CO2 shows that the contributions of CO2 from Alpine streams may be significant when assessing CO2 outgassing from inland waters. Further analysis of current results is needed, including quantifying the in-stream respiratory contribution to the stream pCO2.