THE ENVIRONMENTAL IMPACT OF ACID MINE DRAINAGE

Abstract

This review examine the action of acid mine drainage (AMD), which is a multifactor pollutant, on surface waters. It affects aquatic ecosystems via a number of direct and indirect pathways. Major impact areas are coastal waters, rivers, lakes and estuaries, with AMD affecting ecosystems in different ways. Ground waters can also be severely impacted. Due to its complexity, the impact of AMD is particularly difficult to quantify and predict in lotic systems. Acid mine drainage pollution can be split into a number of impact categories: (i) metal toxicity, (ii) sedimentation processes, (iii) acidity and finally (iv) salinization. The impact of AMD is very difficult to predict due to the variability of the rate of discharge from adits, seasonal variation in adit strength and composition, the effect of surface runoff from exposed mine areas during heavy precipitation, and the effect of catchment discharge characteristics which affects dilution, buffering and both the type and concentration of organic matter in the water. Assessment is difficult due to the complexity of the multiple impacts, although diversity and abundance are key variables for biotic evaluation, both being low in impacted areas. Fish movement and migration are also useful indicators. Acid mine drainage systems may be so complex that no useful information can be obtained by trying to model them. A simpler approach, concentrating on the major interactions (e.g. toxicity of key metals or the degree substrate modification caused by iron precipitation which is directly linked to pH), may prove to be more useful in understanding AMD impacts and predicting effects.