Water chemistry and greenhouse gas concentrations in waterbodies of a thawing permafrost peatland complex in northern Norway
Abstract. Thermokarst ponds in thawing permafrost landscapes play a considerable role in greenhouse gas (GHG) emissions despite their small size, yet they remain underrepresented in Earth system models. At the Iškoras site in northern Norway, a peat plateau with decaying permafrost and thermokarst ponds adjacent to a wetland, we studied water chemistry, dissolved organic matter (DOM) processing, and GHG fluxes over two years. Thermokarst ponds exhibited low pH, high organic acidity, and high oversaturation of dissolved carbon dioxide (CO2) and especially high dissolved methane (CH4). Adjacent wetland streams, however, with near-neutral pH, showed lower CH4 and organic acidity but significantly higher CO2 emissions despite moderate saturations driven by turbulence and bicarbonate replenishment. By contrast, CO2 emissions in ponds were primarily linked to DOM mineralization.
DOM mineralization rates were similar between ponds and streams, suggesting that environmental factors like pH and microbial community differences counteract DOM lability variations. As permafrost decays and transitions from peat plateaus to wetlands, ponds as hotspots of CH4 emissions will disappear. However, total GHG fluxes across the peatland-wetland continuum will depend on wetland emissions, where CH4 emissions usually are considerable, and the fate of organic matter within the plateau. Lateral DOC fluxes may represent a significant loss of soil organic carbon, highlighting the importance of hydrological connectivity in linking terrestrial and aquatic systems. This study emphasizes the need to account for the relationship between hydrological and chemical processes when assessing C and GHG fluxes in permafrost-impacted regions.