Impact of the 1988 Forest Fires on the Chemistry of Ground Water in Yellowstone National Park

Abstract

To determine the character and extent of possible changes in the chemistry of non-thermal ground waters in Yellowstone National Park that may have occurred as a result of the 1988 forest fires, a two-year program of sampling and analysis was begun in August, 1989. Samples from ground-water wells for which pre-fire chemical data could be obtained were selected for this study. The influx of ground water into surface waters (as baseflow) presents a possible pathway for ash­ derived components to impact surface waters in the Park. Data from a recent study of a silicic, non­carbonate aquifer system suggest even small amounts of ground water can significantly affect the chemical balance of dilute lake waters (Kenoyer and Bowser 1992a, 1992b). Because of the dilute nature of non­thermal waters in the Park and the unknown effects that the fire may have had on the solute content of the ground water, this study was commissioned by the National Park Service (NPS) to examine possible fire-induced changes in the chemistry of shallow ground-waters in the Park. Results of this study may allow the NPS to anticipate any future impact upon the chemistry of surface waters in Yellowstone, in addition to identifying any deleterious effects of the fire on quality of non-thermal ground water in the Park. Due to the geochemical, biological and hydrological processes that modify infiltrating precipitation, it was anticipated that the impact of the forest fires on the chemistry of ground-water would be of lesser magnitude than the chemical and physical effects of fire on surface waters in the Park. Samples of soil water and ground water were collected and analyzed to evaluate the impact of the fires on the shallow, non thermal ground waters in the Park. For detailed study sites and methodology see Runnells and Siders (1992).