Biomass and nutrient dynamics in restored wetlands on the outer coastal plain of Maryland, USA

Abstract

A three-year study of aboveground biomass and nutrient dynamics in twelve restored depressional wetlands of different ages demonstrated significant annual variability among sites. Annual variations appeared to be primarily due to differences in hydrologic conditions over the three years of the study. Differences among wetlands were not related to time since restoration. When data for all sites were combined, annual differences in biomass and most measurements of nutrients (concentrations and standing stocks) did not, however, differ significantly. These results suggest that differences that are measured at individual wetland sites may be less important at the landscape level. Biomass decreased from the outer temporary to inner submersed zone, and there were few differences among wetlands when the temporary, seasonal, and submersed zones were compared. Nutrient concentrations in the plant biomass increased from the temporary zone to the submersed zone, resulting in few differences in nutrient standing crops across zones. Results from this study demonstrate that some measurements of restoration success (i.e., biomass production) should be used cautiously because they are likely to be highly variable among sites and across years and thus may be of limited use in post-restoration monitoring. Other ecosystem parameters (e.g., nutrient concentrations of biomass) are much more constant spatially and temporally, indicating that nutrient cycling processes in vegetation were established quickly following restoration. Nutrient characteristics of wetland vegetation thus may be a useful metric for evaluating restoration success or failure.