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

Abstract

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 mg 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.

Impacts of seabird-derived nutrients on water quality and diatom assemblages from Cape Vera, Devon Island, Canadian High Arctic

“…This study further confirms previous diatom work, conducted on Arctic lakes receiving extremely high nutrient additions from sewage (e.g., Michelutti et al, 2007b), that diatom assemblages show much more muted responses to nutrient additions than in temperate regions. The influence of other variables, such as climate (Smol & Douglas, 2007) or interspecific competition, may override the influence of nutrients on diatoms in Arctic ecosystems.…”

“…That the relationships between the dominant diatom taxa at Cape Vera are not easily explained by nutrients across such an extreme nutrient gradient further supports studies suggesting that Arctic diatoms do not respond in a simple fashion to nutrient enrichment (e.g., , unlike diatoms from temperate regions (Hall & Smol, 1999). While paleolimnological studies of Arctic lakes receiving large quantities of human sewage have shown distinct diatom responses, these changes have been markedly different from those recorded in temperate regions and generally are indicative of species associated with periphytic habitats rather than high nutrient concentrations Michelutti et al, 2002aMichelutti et al, , 2007b. These subtle, and sometimes delayed, diatom responses to eutrophication have been attributed to the overriding influence of climate Michelutti et al, 2007b).…”

“…While paleolimnological studies of Arctic lakes receiving large quantities of human sewage have shown distinct diatom responses, these changes have been markedly different from those recorded in temperate regions and generally are indicative of species associated with periphytic habitats rather than high nutrient concentrations Michelutti et al, 2002aMichelutti et al, , 2007b. These subtle, and sometimes delayed, diatom responses to eutrophication have been attributed to the overriding influence of climate Michelutti et al, 2007b). In the ponds closest to the northern fulmar colony, harsh climatic conditions have not prevented the development of obvious standing stocks of mosses, large masses of filamentous algae (qualitatively identified as Cosmarium sp., Zygnema spp., Ulothrix sp., and Tetraspora sp.)…”

“…For example, Bonilla et al (2005) found that nutrient additions stimulated phytoplanktonic, but not benthic, communities in a High Arctic lake. Diatoms (unicellular algae of the class Bacillariophyceae) have been used to track nutrient additions in a wide range of freshwater habitats (reviewed by Hall & Smol, 1999), and previous work in Arctic regions has shown that diatoms have responded to nutrient enrichment from sewage Michelutti et al, 2002aMichelutti et al, , 2007b, the decay of whale carcasses (Douglas et al, 2004a), and anadromous salmon (Gregory-Eaves et al, 2003), albeit in a manner different from responses found in temperate regions. Stable isotopes of N (d 15 N) are commonly employed to track marine-derived eutrophication, as upper trophic level consumers in marine food webs are enriched in d 15 N compared to their terrestrial counterparts (Finney et al, 2000;Robinson, 2001;Douglas et al, 2004a).…”

Trophic position influences the efficacy of seabirds as metal biovectors

“…In fact, TP concentrations in the study ponds are severalfold greater than values typically recorded in High Arctic lakes and ponds ( Table 2). The only TP concentrations recorded in the Arctic that are comparable to the Tern Island sites are from ponds that are similarly affected by ornithogenic inputs (11,12), and sewage oxidation ponds used for facultative treatment of domestic human wastes (13,14).…”