Delayed response of diatom assemblages to sewage inputs in an Arctic lake

Many Arctic communities use lakes as a cost effective method for facultative treatment and disposal of sewage and other liquid wastes. These sites represent ideal locations to study eutrophication processes in Arctic regions, where very little is known about accelerated nutrient fertilization, despite increasing threats from growing populations and long-range transport of eutrophying compounds. Here, we use paleolimnology, historical records, and nutrient modeling to assess the limnological response of Annak Lake (Belcher Islands, Nunavut, Arctic Canada) to a quarter century of persistent and increasing sewage inputs. Our reconstruction data indicate that the lake became hypereutrophic ( > 200 μg L−1 total phosphorus) shortly after sewage additions began in the late 1960s. Water chemistry data dating back to the early 1980s reflect the fertilizing influence of the wastewater discharge. Our fossil diatom assemblages show marked changes in the most recent sediments, changing from predominantly small, benthic Fragilaria sensu lato taxa to a more diverse benthic assemblage dominated by Navicula, Diadesmis, Fistulifera, and Nitzschia taxa. Interestingly, this species level response did not occur until the late 1980s, about two decades after initial sewage inputs. The incredible resilience displayed by the original, pre-impact Fragilaria sensu lato assemblage to 20 years of nutrient enrichment likely reflects the overriding influence of extended snow and ice coverage on diatom assemblages in Arctic regions.