The impact of climate-driven increases in wildfire intensity on metal deposition to lakes and peatlands in the North Slave Region, NWT, Canada.

Abstract:

Wildfires release large amounts of metals into the air and can remobilize metal pollution previously deposited to terrestrial environments from long-range atmospheric transport. These fires can be a substantial source of metals to aquatic habitats through the deposition of ash and fine particles, and may also be regionally important for mercury, which volatilizes and can travel long distances through the air. Wildfires can also impact lakes through drainage of metals from burned catchments.

The North Slave Region of Canada has recently been subjected to intense wildfires, and the impact of these fires on metal accumulation in lakes remains unknown. It is thought that the intensity (both the frequency and size) of these wildfires has increased in recent decades due to more frequent, prolonged, drought conditions in the spring and summer, although no long-term (multi-decadal) records of wildfire intensity exist for this region. The goals of this study are to reconstruct historical fire intensity over the last few centuries in the North Slave Region to test if wildfire intensity has increased as a result of more extreme drought conditions and to examine if a more intense wildfire regime is related to greater metal loading to aquatic ecosystems. In order to meet these goals sediment and peat cores have been collected from 10 lakes and 6 peatlands to provide a regional perspective on historical wildfire intensity and metal loading to aquatic ecosystems. Preliminary charcoal analysis results suggest that wildfire intensity has increased in recent decades and that this increase in wildfire intensity is related greater mercury concentrations in the sediment record. This study will provide important long-term data on the link between extreme droughts/wildfire intensity/and metal loading to Northwestern Canadian lakes. This information is vital as climate models predict more extreme droughts and wildfires conditions for this region, which may result in greater metal loading to these northern lakes. This is particularly troubling as fish harvesting remains culturally and economically important to Northerners, particularly First Nations, and greater wildfire driven metal loading to lakes may lead to increased metal consumption in their diets.