Landscape legacies and the biogeochemistry of surface waters in permafrost affected terrains

Permafrost thaw is increasingly causing materials locked in frozen soils to enter contemporary biogeochemical cycles, while also fundamentally altering how water flows across landscapes. From a carbon cycle perspective, this means that we expect greater opportunity for both organic matter mineralization and chemical weathering as organic carbon and minerals from permafrost soils are able to enter the aquatic continuum. However, although these changes in biogeochemical function are agreed upon in a general sense, we have a much weaker understanding of how they might vary regionally, particularly in the systematic fashion necessary for large-scale modelling efforts. Ultimately, it is the interaction between local factors such as the chemical composition of permafrost soils, landscape attributes including topography, ground ice content, and surficial geology, and connections between terrestrial and hydrologic systems that will determine region-to-region variation in the biogeochemical effects of thaw.

This talk will use compositional measures of stream and permafrost thaw waters from across the Canadian north to consider landscape drivers of surface water biogeochemistry in permafrost-affected terrains. In the ice-rich, till-dominated western Canadian Arctic, substantial hillslope thermokarst is altering sediment regimes and causing particles to dominate and mediate the biogeochemical response, while also enabling a switch in carbon cycle function towards one that is governed by inorganic processes. Throughout the Canadian north, ecoregion attributes fundamentally regulate the abundance, and relative importance of the species participating in carbon cycle reactions, and this region-to-region variation appears to also control whether various carbon species increase or decrease as permafrost extent declines. Moving towards a systematic understanding of how permafrost thaw will play out across aquatic systems requires research efforts that span scales from pore waters to watersheds, and encompass broad geographic variability. Only with multi-disciplinary collaborative efforts will we begin to be able to bridge this gap.