ACID MINE RECLAMATION IN SPOTSYLVANIA COUNTY, VIRGINIA, USA: USING WATER CHEMISTRY AND VEGETATION RE-ESTABLISHMENT AS A MEASURE OF SUCCESS

摘要

In watersheds of the mid-Atlantic region of the US where sulfide spoils occur from mining operations, geochemical reactions develop additional acids in the soil and water supply. The resulting condition lowers ambient pH to very low values (2 to 4 SU). The low pH impairs the soil chemistry and water quality to the extent that native flora and fauna can not survive on the site. This work presents the design and evaluation of remedial work implemented to abate acid mine drainage from a sulfide mine (Valzinco Mine) in the Piedmont Provence of Virginia, USA. Water quality conditions were measured before and after the remediation work, and documented the re-establishment and abundance of native wetland and aquatic vegetation within the site. Data showed that average pH increased from 3.4 to 5.1 and a decrease in total dissolved solids (Fe, Al, Zn, Pb, Cu, Cd, and SO_4~(2-)) over the study period. Initial wetland vegetation, both planted and volunteer, quickly colonized the site with an average ground cover of >74 percent after five years. Aquatic vegetation cover averaged >50 percent after 2 years and many plots had coverage >100 percent. Composition, species richness, and abundance of the new vegetation communities was similar to that of near-by reference (un-affected by mine activities) wetland (>75 percent, 6.0 spp. m~(-2) vs. 5.5 spp. m~(-2), average cover 74 percent vs. 67 percent, respectively). Two amphibians (southern leopard frog, pickerel frog) and two aquatic reptiles (brown water snake and northern water snake) were captured on the site during the fifth year, indicating a return of herpatifauna to the wetland and aquatic communities. We conclude that the increase in pH, decline in total dissolved minerals, success of the re-vegetation of the site, and return of the reptiles to the site, is a strong indication that the remedial work successfully restored the soil and water chemistry closer to pre-mining conditions. Therefore, we suggest that the successful restoration of this site was based on sound hydrological and biogeochemical principles that can be applied to restoration efforts in other acid damaged watersheds in the mid-Atlantic region. The reader is also directed to another paper in this volume by Seal et al which presents additional material on this project. The geologic setting, mine location, geochemistry and water quality sampling data are published there.