Comparison of bucket-wheel spoil and phosphogypsum/clay blend as substrates for Nonriverine Wet Hardwood Forest restoration.

Abstract

Phosphate mining in Beaufort county, NC impacts a rare plant community type, Nonriverine Wet Hardwood Forest (NRWHF). Reclamation of land after mining utilizes three byproducts of mining and manufacturing: clay tailings containing dolomite, low pH phosphogypsum and bucket-wheel spoil from the surface 10 meters. The 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 byproducts as substrates for restoring NRWHF. A field study measured survival of 11 tree and 4 shrub species planted in replicated plots of blend or bucket-wheel spoil. After the first growing season, survival across all species was 92% on the blend and 81% on the 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. Half of the pots in each treatment were fertilized using a complete nutrient solution with 100 mg L-1 N. Tree height and stem volume were significantly greater on topsoil than on bucket-wheel spoil and blend, but did not differ between bucket-wheel spoil and blend. Leaf chemical analysis found cadmium in both field and greenhouse plants. These results indicate that the use of topsoil from the advancing mine front will lead to successful restoration of NRWHF, thereby meeting the mine's original goal of restoring bottomland hardwoods, improving wildlife habitat, and contributing to the conservation of a rare plant community.