Responses of benthic invertebrate communities to shoreline retrogressive thaw slumps in Arctic upland lakes

Abstract

Permafrost disturbance (shoreline retrogressive thaw slumping [SRTS]) causes solute-rich terrestrial inputs to Arctic tundra lakes. Eight upland tundra lakes (3 undisturbed [U], 5 disturbed [D]) in the Inuvik region of the Northwest Territories, Canada, were sampled to assess the effects of SRTS on benthic invertebrate community structure, abundance, and whether localized SRTS effects in D lakes could be discriminated by comparing samples taken adjacent to (Da) or further from (Do) the disturbance. Community composition and abundance differed between U and D lakes. Macroinvertebrates were more abundant in areas adjacent to SRTS (Da) than in areas away from SRTS (Do), but community composition did not differ between Da and Do areas. Abundance was >2× greater in D than in U lakes. Ostracoda abundance was 4× greater in D than U lakes and 2× higher in Da than Do areas. Nematoda abundance was ∼10× higher in D than U lakes, whereas Chironomidae abundance was lower in D than U lakes. Bivalvia and Oligochaeta had similar abundance in D and U lakes, and both groups were more abundant in Da than Do areas. Differences in abundance and community composition were related primarily to higher concentrations of Ca2+ in D than U sediments and to higher organic C and N in U than D sediments. Sediment organic C and Mg concentrations, macrophyte biomass, and dissolved organic C concentrations best explained differences in community composition among lake types and areas. Our study adds to our understanding of cascading changes in the foodweb structure and ecological states of freshwater ecosystems caused by climate change in the Arctic.