Climate-induced changes in nutrient transformations across landscape units in a thermokarst subarctic peatland

Abstract

Across the circumpolar north, the degradation of permafrost has resulted in an increase in the extent of thermokarst landforms. Within thermally disturbed ecosystems, climatically driven changes to hydrology and temperature regimes have the potential to modify nutrient cycling processes. To assess the impacts of changing moisture and thermal conditions on the mineralization of nutrients in the Hudson Bay Lowlands, subarctic Canada, soil cores were extracted along gradients of moisture and topographic position (peat plateaus, sedge lawns, channel fens, and thermokarst collapse scars). Soil subsamples were then subjected to a factorial design of temperature (4°C, 12°C, and 20°C) and moisture treatments (saturated, field moist, and air dried) in oxic conditions for three weeks. Nitrogen transformation rates were highly variable across landscape units (ranging from −1 to 96 μg N-NO3− and from −53 to 73 μg N-NH4+ g−1 dry soil for the incubation period). Shoreline collapse scar material showed the greatest potential for nitrification, with rates two orders of magnitude higher than other landscape positions, under warm (20°C) and saturated conditions. This work shows the potential of increased plant-available nitrate for rapid vegetative colonization of thermokarst collapse scars, and provides novel insight into nutrient cycling processes in permafrost peatland landscapes.

Keywords

• nitrogen
• phosphorus
• nutrient cycling
• peatland
• thermokarst