BIOGEOCHEMISTRY OF ACID ROCK DRAINAGE IN PEEKABOO GULCH, COLORADO

This project examines factors that influence non-anthropogenic acid rock drainage in the Peekaboo Gulch drainage basin, Sawatch Range, Colorado. The goal of this study was to conduct microbial, chemical and geological surveys in an attempt to identify and document those factors that influence the pH changes from the source of Peekaboo Creek to the confluence of Peekaboo Creek with South Fork Lake Creek. Temperature, pH, dissolved oxygen and conductivity measurements were made in several locations in and around Peekaboo Gulch throughout the 2005 field season. Biotraps® were set in June and recovered at periods of 30 days and 60 days after deployment. Biotraps® were shipped to Microbial Insights for analysis using DGGE and PLFA techniques, identifying microbes to species level when possible and describing the microbial communities through quantitative extracellular analysis. Gallionella and unidentified bacteria are present and appear to be heavily involved in sediment accumulation in the valley in biocolloidal processes. The BioTrap® in pH 2.6 water yielded a low-diversity microbial community with a biomass 100 times greater than other sample sites as well as a unique fatty acid profile. Precipitate samples were collected and analyzed using XRD and SEM-EDX. Iron- and aluminum-rich, amorphous colloidal precipitates dominate the system. Smectite, illite, and talc are present exclusively in sediments from the top of Red Mountain and are found to have degraded in the acidic water below. Red Mountain, source of the acidic water, is a down-dropped block of hydrothermally altered, high silica rhyolite. A time series of pH measurements ranging from 5.26 early in the field season to 3.75 at the end indicate that dilution of stream water by seasonal snowmelt is a major factor affecting stream water pH. Toxic levels of metals were found to be present in the drainage and appear to work in conjunction with colloidal precipitates to affect aquatic life. Ponds and iron bogs in the valley control the sedimentation rate and hydrologic processes in the valley. The data collected provide a time series view of the changes of pH, chemistry and microbial populations in an alpine system affected by natural acid rock drainage.