ABSTRACT: Seasonal variation in freshwater geochemistry across the arctic treeline near Churchill, MB.

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Abstract

Lakes and ponds in the Arctic have been identified as potential climate change indicators but there is limited information available on the freshwater chemistry of these water bodies through time or space. Increasing precipitation coupled with thawing of permafrost will mobilize ions stored in their catchments to be released with runoff into water bodies. These increasing ion concentrations will be magnified by lower water levels due to evaporation under warmer conditions. Given the rates of environmental change expected to occur in the Arctic there is a need for monitoring projects to gauge these changes. Arctic ponds are defined as water bodies that freeze to the bottom each winter whereas lakes maintain an unfrozen water column during the winter months. Three lakes and three ponds located across the arctic treeline ecotone near Churchill, MB were selected and have been monitored to detail their geochemical responses to present day conditions. A representative pond and lake were sampled through May 2003-November 2004 in each of three general environments found across the arctic treeline; tundra, tundra/forest transition and open spruce forest. Analysis of water samples taken weekly included pH, conductivity, dissolved organic carbon (DOC) and an ICP-MS scan for 37 major, minor and trace cations. Pond water samples were found to have greater concentrations of DOC and major cations throughout the season than the lakes. The variability of DOC and cations in the pond water columns was attributed to the annual freezing and thawing of the water column and sediments and shorter water residence times. Higher concentrations of Ca, Mg, Na and K in the tundra water bodies are a function of the proximity to the coast and the younger terrain age. Higher concentrations of Al in samples from the open forest upland pond may be indicative of soil development processes occurring in the catchments. Geochemistry of pond water columns varies more significantly throughout the open water season than lakes, often increasing an order of magnitude in concentration throughout the season. Continued long-term monitoring will assist in recording the impacts on northern freshwater ecosystems and assessing trends.

Bibliography of Canadian Geomorphology