Title:

Spatial variability of carbon fluxes in a subarctic catchment

As the climate continues to warm, permafrost thaw is increasing lateral fluxes of carbon (C) into aquatic systems. However, most studies characterize these fluxes from only one point in a catchment thus the spatial variability of lateral C fluxes from river networks in heterogenous landscapes is not well quantified. The transformation of this C as it flows throughout the catchment is also not well understood. To investigate how C quality and quantity vary across the terrestrial-aquatic interface, we sampled riparian porewater and surface water across a subcatchment that included different land-cover types. Our study subcatchment is 15 km2 and includes the permafrost peatland Stordalen Mire in Sweden (68°21′ N 18°49′ E). The catchment has four stream branches and the landscape transitions from alpine tundra at the upper elevations, then transitions to birch forest before draining into a discontinuous permafrost peatland. We sampled the catchment at high spatial frequency in July 2023 and determined the relative contribution of the varying landcovers to watershed C cycling. We characterized dissolved inorganic carbon, dissolved methane, dissolved organic carbon concentrations and composition (i.e., quality), ions, and nutrients along each stream branch across varying slopes within each land-cover type. To partition sources of carbon from landcover sources, we performed isotopic analyses (δ13C-CO2, δ13C-CH4) of dissolved gases. This spatially resolute sampling will allow us to identify lateral flux patterns across the terrestrial-aquatic interface within river networks and determine the relative contribution of different land-cover types to watershed-scale fluxes. Understanding how different land-cover types affect the spatial variability of C cycling across a watershed will be crucial for understanding watershed-scale lateral C flux as well as C transformation.

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