Water Quality Concerns After Wildfire

Author - Gene Surber, Extension Service, Montana State University,

Editor - James E. Knight, Extension Service, Montana State University

General Impact of Wildfires

Loss of vegetation canopies

Increase in erosion

General Impacts, cont.

Increase water temperature

Lower water levels Soil and ash pollution Red Slurry

General Impacts – cont.

Nutrient movement Nitrate, organic

nitrogen, potassium, calcium, magnesium

Returns to pre-burn levels within 1 to 2 years

Soil and Water Quality

Changes in soil pore space

Changes to infiltration rates

Run off rates

Physical Water Quality

Temperature More sunlight reaches

streams and soil Aquatic life Livestock

Sediment and Turbidity

Suspended sediment Bedload Turbidity

Algae

Nearly all water have some form

Increased temperatures, increases growth

Blue-green alage

Chemical conditions - pH

Neutral = 7

Over 7 = alkaline

Under 7 = acidic

Chemical conditions - Alkalinity

Ash in stream Above 8.5 – livestock

problems

Chemical Conditions - Salinity

NOT same as alkaline TSD (total dissolved solids) Abrupt changes, problems w/ livestock Expressed as ppm or mg/l

Nutrients - Nitrogen

Nitrates – convert to nitrites

Nitrites decrease oxygen carrying capacity of blood

Nutrients - Phosphorus

Binds to soil Following storms – can wash into surface

waters Eutrophication – aquatic plants

Nutrients – Dissolved Oxygen

Cold water fisheries - between 8 and 13 mg/l

Cold water holds more oxygen

Soil temperatures increase after fire

Cyanide

Red fire retardant slurry

Acutely toxic to salmonids

Other Chemicals

See table 3 - handout