Carbon export is being measured at 15-year-old 1-ha planted and naturally colonizing created wetlands at the Olentangy River Wetland Research Park (ORWRP) in central Ohio.  Wetlands have been suggested as systems to sequester carbon due to their high productivity and low decomposition rates, but developing systems are inherently open and wetlands are known to export organic carbon to downstream ecosystems.  As part of a larger study determining carbon and nutrient budgets of the developing created wetlands at the ORWRP weekly water samples have been taken from 2005-2009 for dissolved carbon, and more frequent sampling of dissolved carbon plus detrital particulate organic carbon (CPOC) has occurred from July 2008 to December 2009.  The purpose of this study is to determine if these created wetlands are significant sources of organic carbon in the landscape and to investigate long-term trends of that export.  

Results/Conclusions

Over the past 5 years the total dissolved carbon (TC) of inflowing waters (28.4 ± 2.5 mg-C/L) changed little through these wetlands, to 27.5 ± 2.5 mg-C/L and 28.4 ± 2.2 mg-C/L for planted and naturally colonizing wetlands respectively.  Significant decreases (p<0.05) of TC occurred in the planted wetland in 2008 and of total inorganic carbon (TIC) in the planted (2008) and colonized (2006) wetlands.  In 2009 the colonized wetland became a source of TC (28.7 ± 0.5 to 29.7 ± 0.5 mg-C/L, p=0.05).  The planted wetland has a higher rate of CPOC than did the naturally colonizing wetland in 2008-09 (5.3 ± 1.6 mg-C/m²·day v. 3.6 ± 0.8mg-C/ m²·day) during normal flow conditions despite the fact that the naturally colonizing wetland generally has been more productive.  During high flow pulse conditions the naturally colonizing wetland exported more CPOC (18.9 ± 10.4 mg-C/m²·day) than did the planted wetland (8.7 ± 3.6 mg-C/m²·day). The more productive naturally colonized wetland exported less CPOC (2.6 gC/m²) over the study period than did the less productive planted wetland (2.7 gC/m²) in 2008-09.