Acid Precipitation in the Colorado Front Range: An Overview with Time Predictions for Significant Effects

Abstract

Natural features in the Colorado Front Range interact to form a region that is potentially sensitive to acid precipitation. A survey of published work on soil and surface water chemistry establishes a framework from which predictions are made as to when significant ecological effects of acid precipitation on aquatic ecosystems in the Front Range will occur. Regression analysis on 88 lakes and streams showed significant (P < 0.001) decreasing pH and alkalinity trends with increasing elevation. A similar significant (P < 0.008) decreasing trend as elevation increases was found for soil pH and base saturation. Considering both soil and water chemistry, regions above 3300 m (alpine) were most sensitive to continued inputs of acidic materials. If current acid loading rates remain constant, strong potential exists for buffering losses in surface waters, increases in soil acidification and adverse effects on biota. Using reported rates of decline in buffering capacities of Front Range lakes, a model was constructed suggesting these changes are likely to become important in a matter of decades. If acid deposition rates increase, buffering capacity losses in lakes and streams will sooner reach levels where adverse biological changes may become rapid.