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