Abstract:
Investigating the progress of created mitigation wetlands can provide useful information on current and future wetland design and management efforts, including monitoring activities legally mandated to ensure ecosystem development to properly mitigate the loss of natural wetlands. The study investigated structural vegetative and soil properties along with functional vegetative measures in four non-tidal freshwater wetlands created in the Piedmont region of Virginia. During the 2009 growing season, vegetation and soil samples were collected from wetlands ranging in age from 3 to 10 years. Vegetation attributes included percent cover (i.e., total, seeded, volunteer and non-native), richness (S), diversity (H'), floristic quality assessment index (FQAI), prevalence index(PI) and productivity (i.e., peak above and below-ground biomass). Soil condition attributes included soil organic matter (SOM), total organic carbon (TOC), total nitrogen(TN), C:N ration, gravimetric soil moisture (GSM), pH and bulk density(Db). There were no significant differences in vegetation percent cover, S, H' and FQAI by site. The lack of significant vegetation differences between sites was attributed to the abundance of a few common species. with the common soft rush, Juncus effusus, L., being the most dominant. However, significant site-based differences were detected for soil condition attributes (p<0.001), thus soil attributes were further analyzed using clustering statistics (60% dissimilarity applied), which resulted in four soil condition (SC) groups across the study sites. Vegetation data was then analyzed based on the SC groups. SC groups with greater SOM, lower Db, more circumneutral pH, and higher GSM, all indicative of maturity in wetland ecosystem development. were associated with higher H' and FQAI, and total and volunteer percent cover, and lower AGB, PI and seeded percent cover. A significant predictive relationship was found between peak AGB and other attributes of vegetation and soils (Standardized: AGB = 0.41H'+0.37PI-0.29SOM-0.24pH,R2=0.47, p<0.001), which can be of use in assessment of the functional trajectory of the wetlands. The outcomes of the study suggest that the inclusion of soil attributes can significantly enhance understanding and prediction of plant community development in created mitigation wetlands.
