Abstract
ABSTRACT In Canada, disturbance of boreal forests has increased due to expanding anthropogenic activities, particularly forestry. A first attempt was made to evaluate impacts of forest harvesting and wildfire on changes in water quality and biota of lakes. We present case studies in two major geological and climatic subregions of the boreal ecozone in Canada: the Boreal Plain and the Boreal Shield. Responses of lake ecosystems to wildfire and logging differed. In upland Boreal Plain lakes, total phosphorus (P), inorganic nitrogen (N) and algal biomass were higher in lakes with burned watersheds, whereas, only total P increased in lakes with watershed logging. Logging on the Boreal Shield and wildfire in wetland-and permafrost-dominated watersheds on the northern Boreal Plain were associated with increases in dissolved organic carbon (DOC) and water colour, possibly causing light-limitation of algae in both regions, and a decrease in calanoid biomass in eastern Boreal Shield lakes. The number of water quality indicators affected by watershed disturbances was greater in the oligotrophic ecosystems of the Boreal Shield. The nutrient response of disturbed lakes was strongly related to lake drainage ratios: lakes with high drainage ratios had the strongest response to disturbance. Effects were also dependent on climate, wetland coverage, and regional lake characteristics. Morphometric, chemical, and biological indicators are recommended to monitor natural and anthropogenic watershed disturbances of aquatic ecosystems in Canada's Boreal forest.
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