Abstract
Inland waters, including streams and rivers, are active components of the global carbon cycle. Despite the large areal extent of the world’s mountains, the role of mountain streams for global carbon fluxes remains elusive. Using recent insights from gas exchange in turbulent streams, we found that areal CO2 evasion fluxes from mountain streams equal or exceed those reported from tropical and boreal streams, typically regarded as hotspots of aquatic carbon fluxes. At the regional scale of the Swiss Alps, we present evidence that emitted CO2 derives from lithogenic and biogenic sources within the catchment and delivered by the groundwater to the streams. At a global scale, we estimate the CO2 evasion from mountain streams to 167 ± 1.5 Tg C yr−1, which is high given their relatively low areal contribution to the global stream and river networks. Our findings shed new light on mountain streams for global carbon fluxes.
Highlights
Inland waters, including streams and rivers, are active components of the global carbon cycle
Current estimates of annual CO2 evasion fluxes from inland waters are within the same range as ocean uptake fluxes of CO23, the fluxes are in the opposite direction
The lack of appropriate scaling relationships to predict the gas exchange velocity across the highly turbulent water surface of mountain streams has impeded the appreciation of their CO2 evasion fluxes[13]
Summary
Inland waters, including streams and rivers, are active components of the global carbon cycle. We combine recent insights[13] into the gas exchange through the turbulent water surface of mountain streams with novel streamwater CO2 concentration data to estimate CO2 evasion fluxes from Swiss mountain streams, as well as from the mountain streams worldwide. We estimated streamwater CO2 concentration from a linear regression model (R2 = 0.39, P < 0.001) based on observations from 323 streams from the world’s major mountain ranges (Methods; Supplementary Fig. 2).
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