Impacts of Forest Fire on Boreal Lakes
Tess ChadilSource: http://blog.e-democracy.org/posts/91
Impacts to Physical
Watershed Processes
Source: http://www.wrh.noaa.gov/wrh/02TAs/0212/figure23.gif
http://wwwbrr.cr.usgs.gov/projects/Burned_Watersheds/Rll_IntR.jpg
Devegetation Hydrophobic Soils
↓interception↓ transpiration
↑ runoff
↑ erosion
↑ sediment transport
↑ion and nutrient contributions to lakes
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-, SO4
2-
• Local deposition of particulate Hg
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
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
Aquatic Ecology
• 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
Source: http://biology.mcgill.ca/grad/alison/photos/researchInterest1.jpg
• Reduced algal species richness•Increased Hg concentrations reported in fish
•Hg concentrations limited by “growth-dilution” effect
Recovery Rate• Recovery rate
dependent on:– Ratio of burned
watershed area to lake surface area
– Predominant vegetation
•Recovery to pre-burn conditions takes decades
•Most studies are short-term (less than 10 years), or•Paleolimnological Investigations (100s or 1000s of years)
Source: http://barbagallo.files.wordpress.com/2009/09/img_4721.jpg
Source: http://interwork.sdsu.edu/fire/resources/images/MiddlePeak2.jpg
Paleolimnology
Source: http://www.scielo.br/img/revistas/bn/v6n1/a01f06.gif
Source: http://www.pc.gc.ca/eng/pn-np/bc/kootenay/natcul/natcul23.aspx
Source: http://post.queensu.ca/~low/Research%20Page.html
Source: http://www.biol.canterbury.ac.nz/ferg/Images/Sediment-core-lake-Rotorua-(Kaikoura)-lg.jpg
Management Implications• Climate change – Increased incidence
of fire– Increased nutrient
transport potential
• Fire Management Practices
• Fisheries value• Need for further
long-term studiesSource: http://www.ec.gc.ca/INRE-NWRI/0CD66675-AD25-4B23-892C-5396F7876F65/ch8-forestfire%5B1%5D.jpg
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