Microbial ecology and acidic pollution of impoundments.

Many impoundments are becoming acidifed by acid precipitation (AP) and acid mine drainage (AMD). Because of its more dilute constitution, AP is not expected to significantly affect microbial processes in mesotrophic or eutrophic impoundments, although some reduction in heterotrophic activity might be expected in oligotrophic situations. AMD can cause extensive alteration of the microbial community and associated functions. The input of sulfate in the pollution tends to enhance bacterial sulfate reduction in the anaerobic waters and sediments of the impoundment. Sulfate reduction generates carbonate alkalinity which can effectively neutralize the acid pollution if the alkalinity is not consumed by CO fixation during reoxidation of the reduced sulfur species. Presence of reduced iron precipitates the sulfides preventing diffusion into the oxic zones. Bacterial sulfate reduction represents an important homeostatic mechanism in acidified impoundments, and should be explored as a possible management tool for impoundments acidified by AP or AMD.-Authors