Geologists Show How Wetlands Can Clean Up Acid Mine Drainage

Geology Professor Barry Maynard and graduate student Adam Flege reported their findings during the recent joint meeting of the North-Central and Southeastern Sections of the Geological Society of America meeting in Lexington, Kentucky.

Acid mine drainage is a global problem that results when chemical reactions involving key elements (sulfur and iron) react with water in the environment, ultimately producing sulfuric acid. This process occurs naturally, but is accelerated when rocks are left exposed to open air.

The three primary problems associated with acid mine drainage are damage to wildlife and cultural resources, the release of toxic chemicals and heavy metals, and the unsightly mess left behind by mine waste pits or open dumps. Maynard and Flege studied the effectiveness of constructed and natural wetlands in six sites affected by acid mine drainage in Indiana (Pike, Warrick, and Greene counties) and Ohio (Coshocton and Muskingum counties).

Wetlands are a possible tool in the remediation of sites affected by acid mine drainage, because they can harbor microbes that have the ability to convert sulfates into sulfides. That transition is a key buffering process, making the water significantly less acidic.

To help in the process, constructed wetlands include a system known as an Anoxic Limestone Drain. The limestone functions in a similar way to the microbes, raising the pH and decreasing the acidity of the water flowing through the wetlands. Maynard and Flege found that some of the wetlands worked quite efficiently to reduce the impact of acid mine drainage. Others were less effective at cleanup. The analysis revealed three critical factors that determine whether the wetlands would work: the acidity of the water entering the wetlands, the destruction of native plants by muskrats and beavers, and the clogging of the limestone drains after one or two years of use.

Even though not all wetlands were successful, Maynard emphasized that the research helps points the way toward designing better bioremediation systems in the future. "There are several implications," said Maynard. "First of all, constructed wetlands need regular maintenance. Second, they should be larger. Third, and most important, the problem of clogging of the limestone drains needs to be solved." Maynard added that the wildlife problem can be handled through routine trapping. "It's not hard. It just requires a continuing expense."

The Indiana Division of Reclamation funded the research. Assistance was provided by UC faculty members David Nash in geology and Jodi Shann in biological sciences, Erika Elswick and Steve Studley from Indiana University and Ron Smith from the Indiana Geological Survey.