Stable Carbon Isotopes Reveal Soil‐Stream DIC Linkages in Contrasting Headwater Catchments.

Abstract: Large CO₂ evasion to the atmosphere occurs as dissolved inorganic carbon (DIC) is transported from soils to streams. While this physical process has been the focus of multiple studies, less is known about the underlying biogeochemical transformations that accompany this transfer of C from soils to streams. Here we used patterns in stream water and groundwater δ¹³C‐DIC values within three headwater catchments with contrasting land cover to identify the sources and processes regulating DIC during its transport. We found that although considerable CO₂ evasion occurs as DIC is transported from soils to streams, there were also other processes affecting the DIC pool. Methane production and mixing of C sources, associated with different types and spatial distribution of peat‐rich areas within each catchment, had a significant influence on the δ¹³C‐DIC values in both soils and streams. These processes represent an additional control on δ¹³C‐DIC values and the catchment‐scale cycling of DIC across different northern landscape types. The results from this study demonstrate that the transport of DIC from soils to streams results in more than just rapid CO₂ evasion to the atmosphere but also represents a channel of C transformation, which questions some of our current conceptualizations of C cycling at the landscape scale. [ABSTRACT FROM AUTHOR]