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 o f Transport. The lake's physical, chemical and biological characteristics w ere studied between 1968 and 1972 as part of the Char Lake Project, which w as a component of the International Biological Programme (IBP). This was th e first detailed study of high arctic lake eutrophication. However, since t he time of the IBP, use of the North Base has declined markedly. Between 19 92 and 1999, we re-sampled Meretta Lake for a suite of limnological variabl es, and compared our findings to those gathered during IBP. Our data indica te that, although Meretta Lake was still more eutrophic in the 1990s than n ear-by, undisturbed high arctic lakes, it presently has much lower nutrient concentrations and other trophic state variables than it did during IBP. T hese concentrations continued to decline in the 1990s, coincident with furt her decreases in usage of the base. Our most recent data indicate that Mere tta Lake nutrient levels are now near `natural' background levels. Furtherm ore, phytoplankton are characterised by higher abundances of cryptophytes t han those recorded in the early 1970s, again indicating less eutrophic cond itions. Diatom-based, paleolimnological techniques recorded marked species assemblage shifts coincident with the eutrophication from the North Base. H owever, similar to the phytoplankton data, species assemblage changes were different from those recorded following eutrophication in more temperate re gions, with periphytic diatoms overwhelmingly dominating the assemblages.