Eutrophication and recovery in the High Arctic: Meretta lake (Cornwallis Island, Nunavut, Canada) revisited

Meretta Lake (Resolute Bay, Cornwallis Island, Nunavut, Canada) is a polar lake that has been receiving sewage since 1949 via a series of watercourses and utilidors from the so-called 'North Base' of the Canadian Department of Transport. The lake's physical, chemical and biological characteristics were studied between 1968 and 1972 as part of the Char Lake Project, which was a component of the International Biological Programme (IBP). This was the first detailed study of high arctic lake eutrophication. However, since the time of the IBP, use of the North Base has declined markedly. Between 1992 and 1999, we re-sampled Meretta Lake for a suite of limnological variables, and compared our findings to those gathered during IBP. Our data indicate that, although Meretta Lake was still more eutrophic in the 1990s than near-by, undisturbed high arctic lakes, it presently has much lower nutrient concentrations and other trophic state variables than it did during IBP. These concentrations continued to decline in the 1990s, coincident with further decreases in usage of the base. Our most recent data indicate that Meretta Lake nutrient levels are now near `natural' background levels. Furthermore, phytoplankton are characterised by higher abundances of cryptophytes than those recorded in the early 1970s, again indicating less eutrophic conditions. Diatom-based, paleolimnological techniques recorded marked species assemblage shifts coincident with the eutrophication from the North Base. However, similar to the phytoplankton data, species assemblage changes were different from those recorded following eutrophication in more temperate regions, with periphytic diatoms overwhelmingly dominating the assemblages.