Bioremediation

In some situations, artificial wetlands can be engineered to treat acidic waters associated with coal mining or other sources of acidity. Coal mining disturbs soil and fractures rocks exposing large quantities of pyritic sulfur to atmospheric oxygen. Under such conditions, certain species of bacteria oxidize the sulfide of the mineral pyrites to sulfate, generating large quantities of acidity in the process known as acid mine drainage. The resulting acidity is often treated by adding large quantities of acid-neutralizing chemicals such as lime or limestone. However, it has also been recently demonstrated that natural, acid-consuming, ecological processes operate in wetlands. These processes can be taken advantage of in constructed wetlands to decrease much of the initial acidity of acid mine drainages, and thereby reduce the costs of conventional treatments with acid-neutralizing chemicals. The microbial processes that consume acidity are various, but they include: (1) the chemical reduction of sulfate to sulfide at the oxygen-poor interface between the sediment and the water column and around plant roots, (2) the reduction of ferric iron to ferrous in the same anoxic microhabitats, as well as (3) the primary productivity of phytoplankton, which also consumes some acidity.

A less intensive type of bioremediation can be used to mitigate some of the deleterious ecological effects associated with the acidification of surface waters, such as lakes and ponds. In almost any fresh waters, fertilization with phosphate will greatly increase the primary productivity of algae and vascular plants. In acidic waters, this process can be taken advantage of to reduce the acidity somewhat, but the most important ecological benefit occurs through enhancement of the habitat of certain aquatic animals. Ducks and muskrat, for example, can breed very successfully in fertilized acidic lakes, because their habitat is improved through the vigorous growth of vegetation and of aquatic insects and crustaceans. However, the productive but still acidic habitat remains toxic to fish. In this case, manipulation of the ecosystem by fertilization mitigates some but not all of the negative effects of acidification.