Thermal Effects of Fire on Streams

Stream water temperature is a critical characteristic of water quality. Temperature regulates biological activity and ultimately can limit where an organism lives. The influence of water temperature on the development of aquatic macroinvertebrates is particularly important (Hynes 1970). Not only is macroinvertebrate development in general sensitive to water temperature, macroinvertebrates serve as a food resource to higher trophic levels (Hynes 1970, Vannote and Sweeney 1980). Increases in temperature also generally lead to increased metabolic activity by stream organisms, thus leading to a greater demand on the dissolved oxygen in a stream. Table: Dissolved oxygen and water temperature illustrates the relationship between stream temperature and the solubility of O₂. Thus, with increasing temperature, the supply of oxygen declines while the demand from organisms increases.

Besides the potential for short-term direct heating of streamwater by fires, the removal of overstory vegetation following fires can cause increased temperature in streams due to increased exposure from direct sunlight. In severe cases, when riparian zone vegetation is lost, stream temperatures have been shown to rise by more than 10^oC. Studies in the northeastern and northwestern United States have reported increases of 4^oC and 15^oC when riparian vegetation was removed from small streams (Brooks et al. 1997).