Oak Flat Restoration on Phosphate-Mine Spoils


Address correspondence to R. L. Andrews, email rosslandrews@yahoo.com


Phosphate mining in Beaufort County, North Carolina, impacts a rare plant community type, oak flats (nonriverine wet hardwood forests [NRWHF]). Reclamation of land after mining utilizes three by-products of mining and manufacturing: clay tailings containing dolomite, low-pH phosphogypsum, and bucket-wheel spoil from the surface 10 m. The open mine is backfilled with a blend of phosphogypsum and clay tailings, which may be left as the surface or capped with bucket-wheel spoil. The objective of this study was to determine the feasibility of using these by-products as substrates for restoring NRWHF. A field study measured survival of 11 tree and four shrub species planted in replicated plots of blend or bucket-wheel spoil. Survival at the end of the second growing season was 59% on the blend and 52% on the bucket-wheel spoil. A greenhouse experiment compared growth of four species of NRWHF oaks on bucket-wheel spoil, blend, local topsoil (sterilized and unsterilized), and a commercial potting mix. Germination rates of acorns of all four species planted in topsoil were almost double those in bucket-wheel spoil and 1.5 times greater than those in the blend. Height and stem volume of trees were significantly greater when grown in topsoil than in bucket-wheel spoil and blend. There was no difference in tree growth on bucket-wheel spoil and blend. In field and greenhouse soil tests, the blend had cadmium levels over 100 times that of local topsoil and the bucket-wheel spoil had levels 40 times greater. Leaf chemical analysis in the field and greenhouse found higher cadmium levels in plants grown on the blend than on the bucket-wheel spoil. These results indicate that the use of topsoil from the advancing mine front may lead to successful restoration of NRWHF.