Wildfire extent and severity influences the streamwater chemistry, sediment and temperature of individual basins during five years following Colorado’s Hayman Fire

The 2002 Hayman Fire was the largest fire in recent Colorado history. The extent of high
severity combustion and its location in watersheds that deliver drinking water to
metropolitan Denver focused public attention on the effects of wildfire on water quality.
This study utilizes a monitoring network begun prior to the fire to characterize patterns in
stream chemistry, temperature and turbidity measured monthly during the five years after
the fire. Concentrations of streamwater acid neutralizing capacity, calcium and electrical
conductivity doubled the first months after the fire and remained evident for two years as
ash was flushed from burned basins. The proportional extent of a basin burned or burned
at high severity was closely related to post-fire streamwater NO3
– and turbidity. Basins
that burned at high severity on > 45% of their area had twice the streamwater NO3
– and
four times the turbidity as basins burned to a lower extent; these analytes remained
elevated through five post-fire years. During recent decades the incidence of large forest
fires has increased in western North America, and there is a growing need for information
about what regulates the magnitude and duration of wildfire effects on the delivery of
clean water from forest watersheds.

LINK: Rhoades Hayman 5June09

Authors: Chuck Rhoades1, Deborah Entwistle2, Dana Butler2
USDA Forest Service, Rocky Mountain Research Station

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