Boreal Subarctic Lake Water Quality, Zooplankton Communities, and Benthic Macroinvertebrate Communities in Areas Impacted by Wildfire

Wildfires are a natural phenomenon in the boreal forest, but recent studies suggest that there will be increases in the frequency and severity of fires in this region over the next century. When wildfires occur in lake catchments, they may affect water quality and invertebrate communities living in associated lakes. Invertebrates, including zooplankton and benthic invertebrates, play important roles in aquatic food webs, acting as conduits of energy from primary producers to larger organisms such as fish and water birds. Therefore, it is important to understand how these groups will respond to changes caused by fires. Unfortunately, few studies have been conducted in the northern boreal forest to examine how wildfires might impact lakes in this region. For my thesis, I collected data on water quality, macrophytes, zooplankton, and benthic invertebrates from 20 lakes in the Sahtú Settlement Area of the Northwest Territories, which has been impacted by recent fires. Nine of these lakes were affected by fires in their catchments 4-5 years prior to data collection, while eleven were not. My results showed that surprisingly few water quality variables were related to burn history, but lake colour and phenols were higher in lakes affected by burns, and pH and dissolved oxygen were lower in those lakes. Remote sensing data suggest that macrophyte biomass could have increased in lakes affected by burns following the 2014 fires, and macrophyte biomass was an important predictor of community composition for both zooplankton and benthic macroinvertebrates. In addition, burn history was an important predictor of zooplankton richness, and benthic macroinvertebrate richness and abundance. However, my analyses also revealed that natural variability in catchment and lake properties was more important for explaining differences in invertebrate communities among lakes than the effects of wildfires. Overall, my results suggest that shifts in the lake water quality and biology are still detectable 4-5 years after burns in their catchments, suggesting that increased frequency and severity of burns in the north could have long-term impacts on boreal lakes