WATER QUALITY AND CLIMATE CHANGE: EXAMPLE WITH ACID ROCK DRAINAGE

Documentation of actual or potential effects of climate change on water quality has been sparse. The anticipated consequences are expected to be detrimental for human and environmental health. The IPCC report, a Great Lakes report, Environment Canada, and others have begun to report on a series of water-quality issues that are expected from climate change including acidification, increased concentrations of contaminant metals, arsenic, fluoride, pathogens, and organics. Rainfall events cause both increases and decreases in acid and metals concentrations and their loadings from mine wastes, and unmined mineralized areas, into receiving streams based on data from 3 mines sites in the United States and other sites outside the US. Gradual increases in concentrations occur during long dry spells and sudden large increases are observed during the rising limb of the discharge following dry spells (first flush). By the time the discharge peak has occurred, concentrations are usually decreased, often to levels below those of pre-storm conditions and then they slowly rise again during the next dry spell. These dynamic changes in concentrations and loadings are related to the dissolution of soluble salts and the flushing out of waters that were concentrated by evaporation. The underlying processes, pyrite oxidation and host rock dissolution, do not end until the pyrite is fully weathered, which can take hundreds to thousands of years. These observations can be generalized to predict future conditions caused by droughts related to El Niño and climate change associated with global warming. Already, the time period for dry summers is lengthening in the western U.S. and rainstorms are further apart and more intense when they happen. Consequently, flushing of inactive or active mine sites and mineralized but unmined sites will cause larger sudden increases in concentrations that will be an ever-increasing danger to aquatic life with climate change. Higher average metal concentrations will be observed during longer low-flow periods of droughts. Remediation efforts will have to increase the capacity of engineered designs to deal with more extreme conditions, not average conditions of previous years.