When the Source of Flooding Matters: Divergent responses in carbon fluxes in an Alaskan Rich Fen to two types of inundation

The extent of groundwater-influenced rich fens is increasing across northern regions as permafrost thaws. The increase in the extent of these fens, which store large amounts of carbon in deep organic deposits, is coupled to increases in rainfall and runoff. We examine interannual variations in carbon and water fluxes at a rich fen in interior Alaska that included early (May–June) and mid-late (July–September) dry and wet periods, with early season wet periods coincident with runoff from snowmelt and later season wet periods coincident with inundation from rainfall. From May 2011 to December 2018, the fen was estimated as a 170 ± 64 g C m−2 source of CO2. When controlling for soil temperature, net CO2 uptake was greatest during the early season under dry conditions, with the water table position below the surface, and least during the mid-late season when the water table position was above the surface. Methane emissions were lowest during early season wet periods and greatest during late season wet periods. Our results suggest that it is important to consider the seasonality of wet and dry periods, and how these may potentially be related to runoff from snowmelt versus rainfall in boreal rich fens, when considering the annual net C balance and making accurate projections of carbon balance in northern wetlands