IMPACTS ON WATER QUALITY AND BIOTA FROM NATURAL ACID ROCK DRAINAGE IN COLORADO’S LAKE CREEK WATERSHED1 David A. Bird2, Matthew A. Sares, Greg A. Policky, Travis S. Schmidt, and Stanley E. Church Abstract. Colorado’s Lake Creek watershed hosts natural acid rock drainage that significantly impacts surface water, streambed sediment, and aquatic life. The source of the ARD is a group of iron-rich springs that emerge from intensely hydrothermally altered, unexploited, low-grade porphyry copper mineralization in the Grizzly Peak Caldera. Source water chemistry includes pH of 2.5 and dissolved metal concentrations of up to 277 mg/L aluminum, 498 mg/L iron, and 10 mg/L copper. From the hydrothermally altered area downstream for 27 kilometers to Twin Lakes Reservoir, metal concentrations in streambed sediment are elevated and the watershed experiences locally severe adverse impacts to aquatic life due to the acidic, metal-laden water. The water and sediment quality of Twin Lakes Reservoir is sufficiently improved that the reservoir supports a trout fishery, and remnants of upstream ARD are negligible. Additional Key Words: Grizzly, Lake, Chaffee, Twin Lakes, Arkansas River, trout, invertebrates ______________________ 1 Paper presented at the 7th International Conference on Acid Rock Drainage (ICARD), March 26-30, 2006, St. Louis MO. R.I. Barnhisel (ed.) Published by the American Society of Mining and Reclamation (ASMR), 3134 Montavesta Road, Lexington, KY 40502 2David A. Bird, Hydrogeochemist, Colorado Geological Survey, 1313 Sherman Street, Denver, CO, 80203,
[email protected]; Matthew A. Sares, Chief – Environmental Section, Colorado Geological Survey, 1313 Sherman Street, Denver, CO, 80203,
[email protected]: Greg A.