Periphyton Response to a Gasoline Spill in Wolf Lodge Creek, Idaho

A post-impact study on a 94438-L unleaded gasoline spill into Wolf Lodge Creek in northern Idaho was undertaken to determine the temporal and spatial response of periphyton following the spill. Periphytic biomass and chlorophyll a concentrations were determined above and below the spill. Downstream areas were mechanically agitated to release substrate-trapped hydrocarbons 35 d after the spill. Periphyton samples taken 26 d after the spill indicated that periphytic biomass, especially of the heterotrophs, was greater in the impacted than unimpacted areas; the Autorophic Index was up to 30 times greater in the impacted reach. Two months after the spill and 1 mo after stream cleaning, the Autotrophic Index was approximately the same in reference and impacted areas.