Regeneration of soil microbial, physical, and chemical properties in restored bottomland hardwood forest wetlands
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Wetlands provide a wide range of important ecological services, including flood mitigation, habitat for wildlife, and nutrient retention. The Wetland Reserve Easement (WRE) Program [formerly the Wetland Reserve Program (WRP)] was initiated with the goal of reducing the loss of wetlands and restoring wetlands previously converted to agricultural land use. Despite the importance of preserving and restoring wetlands, the benefits of wetland restoration have not been well documented. Specifically, soil health indicators can be used to determine the extent of soil degradation and monitor recovery in restored wetlands. This research was conducted on 38 WRE sites located in the western areas of Tennessee and Kentucky to gain an understanding of the impact of restoration practices on the functionality and ecology of these soils. The effects of habitat type, season, and time under restoration on soil physical, chemical, and biological indicators were investigated. Habitat types included Forest, Planting, Regeneration, Shallow Water Area (SWA), and Reference. Sampling season was also evaluated which included Winter, Spring, and Fall samplings. It was found that both the Habitat type (p < 0.0001) and Season (p < 0.0001) had a statistically significant effect on all the indicators. While some recovery was seen in the data, the undisturbed habitats (Reference and Forest) had favorable conditions and the restored habitats (Planting, Regeneration, and SWA) were still degraded from the former agricultural practices. SWA had significantly lower values than the other habitat types. Aggregate stability was lowest in the Regeneration (28 percent) and highest in the Reference (46 percent) habitats. The restored habitats had the lowest total carbon (~1.02 percent) and nitrogen (~0.11 percent) and the highest bulk density (1.28g/cm3). The undisturbed habitats had the highest total carbon (1.91 percent) and nitrogen (0.18 percent) and the lowest bulk density (1.10 g/cm3). Habitat also had a similar significant effect (p < 0.0001) on the biomass of the microbial communities, with higher biomass observed in undisturbed habitats relative to restored habitats. Biomarkers for arbuscular mycorrhizal fungi (AMF), gram negative bacteria, gram positive bacteria, and actinomycetes were highly correlated with each other. Based on soil health indicators, the dry conditions of the Fall were more favorable except for total protein and eukaryotic biomass, whereas the flooded Winter conditions appeared to provide less favorable conditions overall; all soil health indicators were negatively correlated with increased water depth. The time under restoration showed no detectable, significant effect on any of the measured soil health indicators. These results highlight the effects of historic soil disturbance from agricultural management, disturbance from restoration activities, and ongoing, seasonal hydrologic disturbances on the potential recovery of degraded wetland soils.
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M.S.