Promoting Denitrification in Restored Wetlands with Amendments of Differing Carbon Lability.

Wetlands contribute a wide variety of ecosystem functions, including the improvement of water quality through denitrification. In order to offset the negative environmental impact of destroying wetlands for development, the U.S. has a policy in which destroyed wetland area must be compensated for through the restoration of a wetland elsewhere. However, these restored wetlands are estimated to require decades to achieve equivalent levels of functioning to natural wetlands. This study evaluates the efficacy of using carbon amendments during wetland restoration to promote denitrification potential in four restored wetlands in Ithaca, New York. The amendments used during restoration were straw, topsoil, and biochar, which have differing levels of carbon lability and thus different rates of decomposition by soil microbes. Soil samples analyzed in this study were collected six years after the restoration of the four wetland sites. These samples, in addition to samples from a natural reference wetland, were analyzed for denitrification potential as well as for a suite of associated soil properties, including organic carbon, respiration, microbial biomass, and pH. Denitrification potential was significantly higher in plots with carbon amendments than in plots where no amendment was added, but there were no significant differences between amendment types. Denitrification potential was significantly positively correlated with both soil organic carbon and microbial biomass nitrogen. This demonstrates that the availability of organic carbon in restored wetlands is vital for supporting populations of microbes that carry out ecosystem functions such as denitrification, and that the incorporation of carbon amendments can help provide this important requirement. However, denitrification potential in the natural wetland was at least 50 times higher than in the restored wetlands, highlighting the limitations of using restoration to compensate for the destruction of natural wetlands.