Effects of shoreline retrogressive thermokarst slumping on the productivity and food web structure of upland Arctic lakes: an experimental approach.




Moquin, Paul

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To assess the affects of permafrost degradation on key components of the aquatic food web, an in situ manipulative mesocosm experiment was performed in an upland, unslumped Arctic lake located near Inuvik, Northwest Territories. In total, twelve replicate mesocosms were established, 3 control and 3 replicates of 3 treatment levels each dosed with differing amounts of sediments sourced from a nearby thermokarst slumped lake. Findings from the experiment showed that pelagic autotrophic processes had the greatest potential to contribute to higher trophic levels regardless of treatment. Even in the high sediment treatment level, which showed the least pelagic autotrophic production, pelagic autotrophic production was two orders of magnitude greater than pelagic heterotrophic production and 5 times greater than benthic autotrophic or heterotrophic production. Sediment treatment had no significant effect on benthic primary productivity; however, a 500% increase in benthic heterotrophic production was observed. This raises the possibility that increased activity in benthic heterotrophic production is the first step in thermokarst-affected lake ecosystem succession leading to the proliferation of benthic primary production observed in many slumped lakes in the western Canadian Arctic. Water column phosphorus concentrations increased with increasing sediment treatment while pelagic primary production decreased and zooplankton biomass increased. These results suggest that the initial effect of thermokarst disturbance is an enrichment of the system and that top-down predation from zooplankton regulate the abundance of phytoplankton in these systems. If incidences of thermokarst disturbance continue to increase as predicted by current climate models/scenarios, results from this study suggest that the structure and function of Arctic aquatic ecosystems will be significantly impacted. This study highlights the need for further research to obtain a better mechanistic and predictive understanding of the potential effects of thermokarst disturbance on the geochemistry and ecology of Arctic lakes at relevant spatial and temporal scales.



Aquatic Ecology, Arctic ecosystems, Climate change, Permafrost degradation