Sammendrag
Northern lakes are globally significant sources of atmospheric methane (CH4) and are especially sensitive to environmental changes. Due to ongoing climate change (e.g., increasing mean annual air temperature, changes in precipitation and seasonality), many Arctic and subarctic lakes are at risk of transitioning from a clearwater into a brown-water state. However, little is known about the direct effects of this transition on the CH4 cycle in lake sediments. Here, we seek to improve our understanding of methane related processes in Arctic lake sediments to help to improve the predictions of future CH4 emissions from Arctic lakes.
Through high-resolution sampling of lake sediment cores, we investigate sediment CH4-production responses to various hydrology and landscape variables. We collected short lacustrine surface sediment cores (40-60 cm) using a gravity corer from two sets of lakes with different hydrology. One set is located in northern Norway (4 lakes: Troms area); the other, following a precipitation gradient increasing from the coast towards inland in northern Sweden (3 lakes: Abisko area). We focus on the catchment-to-lake area ratio, which has a potential for organic carbon transport; the steepness of catchment, vegetation cover, elevation, annual precipitation, bathymetry of each lake, groundwater discharge and other possible physical and chemical properties of the lakes. We explore the potential to predict variability in sediment CH4 concentrations from different variables (landscape and hydrology factors, sediment depth, total organic carbon (TOC), δ13C-TOC, dissolved inorganic carbon (DIC), δ13C-DIC). Our preliminary results indicate most variability in sediment CH4 concentration may be related to the groundwater input, however the lowest CH4 concentration was measured from a glacial meltwater-fed lake. Overall, CH4 concentration is stable below the upper 30 cm of sediment, whereas in this upper interval, we observe a decrease in CH4 concentration caused by CH4 consumption
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