Vegetation development and succession in mitigation wetlands of Ohio

Background/Question/Methods

Field surveys were conducted in August 2008 through 2010 to observe vegetation development and estimate net primary productivity of seven wetland sites in Ohio.   These sites included five mitigation banks created by the Ohio Wetlands Foundation, one site created at the Olentangy River Wetland Research Park, and a natural reference site.  Wetlands at these sites varied in size, from small pools to larger wetlands with expanses of open water and ranged in age from 3 to 18 years of age.  The objective of this study was to examine vegetation structure and function within created wetlands of less then 20 years of age and to compare these created mitigation bank wetlands to reference wetlands.  Data collected included species richness, above-ground net primary productivity (using both destructive and non-destructive methods), number of dominant plant communities, depth of standing water, and area of the dominant macrophyte communities.  Information gathered was then used to obtain floristic quality assessment index (FQAI) scores for each site.

Results/Conclusions

Net primary productivity (NPP) weighted by community area ranged from 201±94 to 802±115 g DW m^-2 within the mitigation sites, 529±104 to 866±159 g DW m^-2 within the research wetlands and 1093±380 g DW m^-2 within the natural reference wetland.  FQAI scores ranged from 13.5 to 29.5 at the mitigation banks, 19.9 to 23.8 at the research site, and 26.9 at the natural wetland.  Species richness ranged from 41 to 109 within the mitigation sites, while the research/natural wetlands ranged from 87 to 99 species.  There was a significant positive relationship between age of the wetland and NPP (p=0.006), but a significant negative relationship with age and FQAI score (p=0.005) and species richness (p=0.033).  Over the different types of wetlands, the natural/research wetlands tended to have higher NPP, FQAI scores, and species richness than the mitigation sites (p<0.001, p=0.042, and p<0.001, respectively).  Wetlands in northern Ohio were more similar structurally to the natural/research wetlands.  For the most part, the mitigation wetlands do not seem to be functioning on the same level as the reference wetlands but, some of the newer mitigation banks more closely resemble the reference wetlands, possibly due to better initial construction techniques of the newer sites.