What is the impact of urban development and thermokarsting on arctic tundra pond zooplankton communities?

Abstract

Human development and warming in the Arctic are increasingly putting new pressures on the abundant freshwater ecosystems in the region. In particular, recent and rapid expansion of thermokarst ponds in permafrost regions has been associated with these stresses. Our goal was to examine the relative impacts of pond enrichment by urban encroachment and thermokarsting, compared to relatively unimpacted regions, on the environmental conditions and zooplankton communities of tundra ponds near Utqiaġvik, AK, USA. Both urban ponds and thermokarst ponds were found to have substantially different environmental conditions, as well as distinctive zooplankton communities relative to reference sites. Thermokarst ponds presented an environment rich in DOC and nutrients (N, P, and Si) and phytoplankton biomass. Enrichment by nutrients and DOC in thermokarst ponds led to significantly greater zooplankton abundance composed largely of Daphnia middendorffiana (66 individuals L−1) and cyclopoid copepods (65 individuals L−1). Urban ponds had moderate nutrient levels, with elevated benthic algal biomass. These ponds had intermediate numbers of D. middendorffianna (14 individuals L−1), as well as significantly higher numbers of diaptomid copepods (8 individuals L−1) and chydorids (11 individuals L−1), as compared to one or both reference regions. The two reference regions [Barrow Environmental Observatory (BEO) and International Biological Program (IBP)] had consistently lower nutrient concentrations, algal levels, and zooplankton abundances (less than 3 individuals L−1). Finally, harpacticoid copepods and Bosmina longirostris were new records for the zooplankton in the region. Further collections are required to determine the drivers for these new observations. These results identify the large potential relative contributions of urban inputs and thermokarsting to enrichment of Arctic aquatic ecosystems and point to thermokarsting, which will likely increase with warming, as a major contributor to change in these systems.