1. Impacts of Forest Fire on Boreal Lakes
Discuss characteristics of boreal zone (aka taiga)
Northern U.S (Minn), Canada (Quebec)
conifer and mixed hardwood forests
thin organic layer
predominant geology- granite
glacial kettle lakes
Source:
Tess Chadil

2. Impacts to Physical Watershed Processes
Devegetation
Hydrophobic Soils
↓interception
↓ transpiration
Hydrophobic soil formation-
waxy organic plant material on forest floor is volatilized into gas
gas penetrates into soil column
gas cools, forms hydrophobic layer beneath the soil surface
prevents infiltration
↑ runoff
↑ erosion
↑ sediment transport
↑ion and nutrient contributions to lakes
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3. Ion and Nutrient Transport
Magnitude of flux into lake depends on
Severity of fire
Depth of organic layer in soil
P and N transport have most significant impacts to lake water quality
Fire leads to increased concentrations of K+, Ca2+, Mg2+, Cl-, SO42-
Local deposition of particulate Hg
Atmospheric Hg deposited in precipitation and carried into lakes via runoff

4. Phosphorous and Nitrogen
Significant increases in total, total dissolved and soluble reactive phosphorous
74% of variance in TP can be explained by percent of basin burned, and time elapsed since fire
Most boreal lakes are naturally P-limited
Significant increases in total and total dissolved nitrogen, nitrates and ammonium
Primary source for nitrates is ash
Persistent nitrate contamination sustained by contaminated groundwater inflows
Boreal Lakes are usually P limited
Quebec study- Soluble reactive phosphorous increased almost 7x pre-burn levels

5. Additional Effects of Fire
Increased concentration of inorganic suspended solids
Mean light extinction nearly doubled in some cases
No significant increases to DOC
Increases in pH varied among studies
some lakes experience permanent increases in pH
Only some lakes reported significant increases in pH
In some cases pH permanently stabilized above pre burn levels

6. Aquatic Ecology Reduced algal species richness
Increased Hg concentrations reported in fish
Hg concentrations limited by “growth-dilution” effect
Source:
Boreal lakes in burned watersheds tend towards eutrophy
Lakes in burned watersheds reported TP:TN ratios between 10 and 20
Cyanobacteria blooms lead to diminished water quality
Reduced clarity helps to limit chlorophyll-a concentrations

7. Recovery Rate Recovery rate dependent on:
Ratio of burned watershed area to lake surface area
Predominant vegetation
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Lakes recover slowly- on the order of decades
Predominant vegetation
conifer
Recovery to pre-burn conditions takes decades
Most studies are short-term (less than 10 years), or
Paleolimnological Investigations (100s or 1000s of years)
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8. Paleolimnology
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9. Management Implications
Climate change
Increased incidence of fire
Increased nutrient transport potential
Fire Management Practices
Fisheries value
Need for further long-term studies
Climate change forecast
increased fires in Canadian boreal zones
Warmer, wetter climate- higher accumulation of organic material
Fire management- suppression vs. let it burn?
thinning/prevention?
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