CHEMICAL STREAM WATER INDICATORS OF FOREST WILD FIRES IN THE INTERIOR WESTERN US

Water quality affected by wild fires in the Interior Western US has been characterized in few studies and is affected my many complex factors. Historic wild fire maps available at the US Forest Service Forest Inventory and Analysis program (FIA) provide new insights into water resources problems of the region. Temporally dense and long-term water chemistry samples analyzed by the Environmental Protection Agency together with collaborating state agencies of environmental quality in respective states and the United States Geological Survey were used in three focus areas in Colorado, Idaho and Nevada and compared to shorter term observations directly following large wild fires in the Lake Tahoe, Nevada, Glacier’s National Park, Montana, and Boulder, Colorado. All study areas are affected by strong seasonal flow fluctuations and intense, short lasting rain precipitations which significantly affect stream temporal chemical concentrations. Because of limited existing water chemical data, chemical fluxes which last at least several days to weeks in the focus study areas are more useful to be linked to wild fires. Short-term changes related to wild fires and described in previous studies include water turbidity, pH, calcium, magnesium, potassium, carbonates and nutrients. Some of these changes have significant effects that only last for hours to days and they are not equally consistent between all study areas, as wildfire ash contribution and resulting soil erosion co-occur with several other factors in the temporarily and spatially diverse watershed stream chemistry. Variable fire severity also complicates temporal and spatial influences on watershed water chemistry. The most useful short term and long term water parameter identified for all focus study areas is total nitrogen load calculated from total discharge and nitrogen concentrations. Presented trends will be tested in additional watersheds and will be used to make recommendations of possible use of forest wild fire disturbance maps coupled with FIA data to predict future effects of forest wild fires on water.