Changes to Soil Properties in a Forested Wetland Following 8 Years of Restoration

Abstract

Mitigation credits are awarded to land developers who successfully create or restore a wetland to conditions found in a natural wetland. Because restored wetland vegetation adapts slowly to changes in hydrology, some restoration projects require a minimum of 15 to 20 years before they can be judged as a success or failure based on vegetation. We hypothesized that restoration success can be evaluated in shorter periods of time if soil properties are used to gauge restoration success. The objectives of this study were to: 1) compare soil morphological, physical, and chemical properties in a restored wetland for two time periods – before restoration and 8 years after restoration, and 2) to compare these properties between the restored site and a natural wetland. The study sites occurred in the lower Coastal Plain of North Carolina near Aurora. Soils in the restored site were described in 1995, prior to restoration, and all classified as a Roanoke sandy loam (clayey, mixed, thermic Typic Endoaquults). The natural wetland was adjacent to the restoration site and was classified as a non-riverine wet hardwood forest (NRWHF). In 2003, 30 soil pedons were sampled, 26 in the restored site and four in the reference, to evaluate changes in soil properties. All sampling occurred in the same sample plots sampled in 1995. It was found that redoximorphic (redox) concentrations increased significantly (p<0.05) in the upper 45 cm after 8 years of restoration. The reference site had less redox concentrations than the restored site in the upper 45 cm. Plant available P, Ca, CEC, and BS% had decreased significantly (p<0.05) in the restored site since 1995, but each of these properties was still higher than in the natural wetland. Total organic Carbon (TOC) had not increased in the restoration site and was approximately 20% of the amount of TOC found in the reference. Both sites met the hydric soil technical standard, which indicated that the soils in the restored site functioned as hydric soils. The mature trees in the NRWHF shaded the soil surface and cool the temperature enough to prevent TOC from oxidizing during the summer months. The water table in the reference site was 50 cm lower during the growing season than in the restored site. This caused redox concentrations to form 45 cm below the soil surface in the reference wetland, but they accumulated within 45 cm of the soil surface in the restored site. Evaluation of hydric soil restoration success could be done through use of the hydric soil technical standard, and possibly through changes in redoximorphic features. Most other soil physical and chemical properties changed to slowly to be of value in evaluating restoration success within an 8 year period.