Plant biomass and nutrients (C, N and P) in natural, restored and prior converted depressional wetlands in the Mid-Atlantic Coastal Plain, U. S.

Monitoring is an essential component of restoration and measurements of biomass and nutrient concentrations are often used as indicators of ecosystem function. We studied restored depressional wetlands in the U.S. Mid-Atlantic Region. The first study, part of the U. S. Department of Agriculture Conservation Effects Assessment Project (CEAP-Wetlands), compared hydrologically restored wetlands (aged 5-10 years) with natural wetlands and prior converted croplands. We measured aboveground biomass and plant nutrient concentrations at Coastal Plain sites, from Delaware to North Carolina. At the CEAP sites, herbaceous biomass was highest in Restored wetlands, while existing tree biomass was highest in Natural sites. Nutrient concentrations were significantly higher in Prior Converted and Restored sites, relative to Natural sites. In the second study, we compared biomass and nutrient data at a separate set of restored sites, originally sampled by the Smithsonian Environmental Research Center (SERC) in 1994 and resampled in 2011, 15 years later. The primary temporal change was increased tree biomass near the upland-wetland boundary. Both studies indicate that these restored wetlands are in early stages of plant succession, but should develop similarly to natural sites if succession is allowed to progress for decades. This time could be reduced by planting late-successional species characteristic of undisturbed local natural sites. Nutrient data, especially for the SERC wetlands, indicated that these restored wetlands resemble natural sites more in terms of plant nutrient concentrations and that the sites, similar to natural wetlands, will become less nitrogen limited as the impacts of previous agricultural activities decline.