Accumulation of Carbon in Created Wetland Soils and the Potential to Mitigate Loss of Natural Wetland Carbon-Mediated Functions
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The current U.S. wetland mitigation policy of “no-net-loss” requires that a new wetland be created to replace any natural wetland destroyed under development pressures. The purpose of this study was to evaluate the ability of created wetlands to accumulate carbon and to mitigate the carbon-mediated functions occurring in natural wetlands. Soil physical properties were analyzed as potential inhibitors of carbon accumulation in the created wetlands. An exponential model was then used to estimate the time for created wetlands to accumulate that carbon found in natural wetlands.
Five created (ages 3-8 years) and four natural freshwater marsh wetlands in central Ohio, USA were selected for this study. Nine to fifteen soil cores were collected at each site and analyzed for soil organic carbon (SOC), mineralizable soil carbon, water-stable aggregates (WSA), particle-size fractions and bulk density. Peak-standing aboveground plant biomass was harvested.
Created wetlands contained less plant biomass, less SOC and less mineralizable carbon than natural wetlands (MRPP, T=-11.6, p< 0.007). For the soil physical properties, created wetlands contained less macroaggregates, more microaggregates, more silt-clay, and had higher bulk density than natural wetlands (MRPP, T=-4.16, p=0.007). The carbon parameters and soil physical properties were found to be correlated by RDA, carbon content was positively correlated with macroaggregate content and negatively correlated with microaggregate content, silt-clay fraction, and bulk density. A fit of the SOC data to an exponential model indicated that a newly created wetland would require 300 years to sequester the amount of SOC contained in a natural wetland. At this rate of carbon accumulation, a mitigation ratio of 2.6:1 (area) would be necessary for successful mitigation over a fifty-year time period. Other models were found to fit the data equally well, however, but provided different estimates to equilibrium (range of 70 to 12,000 years). Lack of older created wetland data (>12 years) prevented selection of a single model and estimate. Until the gaps in the data are filled and a model verified, the best mitigation policy will be a conservative one, with a restrictive permitting process and high mitigation ratios (2.6:1 minimum).
Document number: osu1239285185
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=osu1239285185
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