Chironomid assemblages from seabird-affected High Arctic ponds

摘要

Seabirds can shunt nutrients and contaminants from marine to terrestrial ecosystems by forming dense breeding colonies and releasing wastes to these sites. A large colony of seabirds at Cape Vera (Devon Island, High Arctic Canada) has resulted in eutrophic conditions and potentially toxic concentrations of sedimentary metals in several freshwater ponds that drain their nesting sites. Here, we investigated the effects of elevated nutrient and sedimentary metal concentrations on the distribution of subfossil chironomids in surface sediments from 21 ponds that span a gradient of seabird influence. Although many ponds registered high nutrient concentrations (e.g., mean TP = 45μg 1~(-1)), eutrophic taxa typical of temperate waters were not common, with most assemblages being dominated by morphotypes of Psectrocladius and Tanytarsina, as well as Corynoneura arctica-type, and Metriocnemus hygropetricus-type. Although the ponds within and outside the area influenced by seabirds contained largely similar taxa, variations did exist in the relative abundances of the different species. Lakewater pH was the only measured environmental variable that explained statistically significant amounts of variation in the chironomid assemblages. Although direct effects of pH on chironomids cannot be ruled out, pH is likely tracking production-related changes driven by limnetic dissolved inorganic carbon dynamics. Sediment cores collected from seabird-affected and seabird-free ponds showed a greater number of chironomid taxa and higher head capsule abundances in the pond receiving seabird inputs. Chironomid assemblages in both cores recorded increased abundances in recent decades, likely in response to warmer conditions and lengthened growing seasons.