2017 Nickerson Fellow Dr. Faming Wang
The Herring River Basin in Wellfleet, MA is an altered salt marsh site, with large areas that are drained as well as areas that are flooded with fresh water. There may be significant potential to reduce greenhouse gas emissions by restoring saltwater tidal flows to the system. The objectives of this study are to quantify the greenhouse gas emissions and net carbon balance of the five dominant vegetation types at the Herring River basin, with the comparison to a natural salt marsh reference site, to evaluate the potential for blue carbon credits from the tidal restoration. After one growing season fieldwork, combined our previous data, we found that Phragmites brackish and Cattail freshwater marsh had higher GPP, NEP and biomass than salt marsh during growing season. However, the C burial rate in the two vegetation types was much lower than the salt marsh, indicating higher C decomposition rates in them. Soil respiration in dry forest, wet forest, and wet shrubland was also measured, we still need more litter fall data to estimate the annual C balance in these vegetation types. The methane emission in Phragmites brackish was over 100 times higher than the rate in Cattail freshwater marsh and 200 times higher than that in the salt marsh. The dry forest and wet shrub do not have much methane emission, while wet forest had similar methane flux rate as Cattail freshwater marsh. The result indicated that restoring Herring river basin to brackish and salt marsh should not only consider the CO2 balance, but also CH4. Although the increased area of salt marsh could greatly improve C sequestration in this region, the invasion of Phragmites to freshwater wetland and brackish would significantly increase CH4 emission, which could offset the C gains by increased salt marsh area. Regarding their high methane emission, Phragmites invasion to brackish and freshwater marsh should be avoided during salt marsh restoration. The total methane C credit in restoration project was calculated based on two scenarios：with freshwater marsh and brackish occupied by Phragmites or by Cattail.
Last updated: June 21, 2018