ASSESSMENT OF METAL LOADS IN WATERSHEDS AFFECTED BY ACID MINE DRAINAGE: AN INTEGRATED SCIENCE APPROACH

Instream concentrations of metals and their impacts on a stream ecosystem result from the interaction of geology, hydrology, and mining history within a watershed. The U.S. Geological Survey’s Abandoned Mine Lands Initiative (AMLI) has developed an integrated science approach for assessing impacts of mine drainage in watersheds. Based on the premise that a stream integrates all the factors that influence ecosystem health, an important part of this approach is the use of stream tracer-injection experiments to quantify the hydrologic context of the effects of geology and mining in a watershed. Tracer-injection methods quantify detailed, spatial changes in metal loads along the stream. Results of a tracer injection are used to identify the (1) relative importance of multiple sources of metals in a watershed; (2) locations and approximate amounts of dispersed subsurface inflows of water and metals, which would otherwise not be measurable; (3) extent of biogeochemical processes affecting metal transport; and (4) effect of hydrologic parameters on solute transport. These results provide land management agencies with enhanced levels of detailed spatial information for use in remediation decisions. The AMLI has provided a successful model of integrated science with hydrologists, geologists and geochemists, biologists, and cartographers merging their skills for a better understanding of watershed-scale impacts.