Carbon dioxide fluxes of temperate urban wetlands with different restoration history

Carbon dioxide (CO2) exchange of tidal brackish wetlands and how they may be affected by restoration methods are largely unknown. The New Jersey Meadowlands, a tidal brackish estuary system, have had a long history of pollution, hydrological alterations, multiple restoration and mitigation treatments since the early 1970ies. To understand the effects of restoration, net ecosystem exchange (NEE) was measured with the eddy covariance technique in three urban tidal brackish wetland sites over three years: an organic matter amended restored site, a non-amended restored site and a natural (non-restored) wetland site. Our results showed all three sites to be a CO2 source in the wintertime reverting to a weak sink of CO2 in the summer and annually to be sources of CO2 for some of the sites for some of the time. However, the amended restored wetland was found to have the highest release of CO2. Annual destructive harvest of the major species at these wetlands (Spartina ssp and Phragmites australis) did not show significant differences in the aboveground net primary productivity and leaf area over the course of this study. Overall, aboveground biomass production of the three wetlands sites was within the expected range of tidal brackish marshes, but the sites differed in their NEE, ecosystem respiration, and gross ecosystem production. This investigation suggests that CO2 uptake and potential subsequent carbon sequestration may be strongly affected by the management and restoration history of the wetlands, and in our case these wetlands are often acting as a source of CO2, and not as a sink, as may have been expected.