With an estimated 8mm/year rate of sea lever rise (SLR) in the New York-Newark bay area in mind and the current Sediment Elevation Table records indicating that New Jersey’s marshes will not keep up with the projected local SLR, the question emerges: what will happen to the Hackensack River Estuary’s marshes and how will the region’s carbon sequestration potential change in the future? In anticipation of the marshes’ future retreat to higher elevation and potential mudflat expansion, the study compares the amounts of carbon fixed via photosynthesis among the three most characteristic wetland surface types in the Meadowlands: mudflat, Spartina alterniflora dominated low marsh and high marsh habitats with S. patens dominance. Utilizing Eddy-covariance method (indirect) and gas chamber measurements (direct approach), marsh canopy net ecosystem exchange (NEE) and annual gross ecosystem production (GEP) were calculated based on two years of data collection.
Results/Conclusions
The study showed that temperate macro-tidal salt marshes are net sinks of carbon with potential for long term carbon storage while the mudflat habitat is a net carbon source. Both low and high marshes turned into a carbon sink at the beginning of May and switched back to being a source in mid-November. The low marsh habitat showed the highest monthly NEE during the growing season (ranging from -28 to -105 gC/m2/s) indicating high sink potential, while the mudflat proving to be a long term source with ranges between +9.3 and +28 gC/m2/s. Tidal fluctuation showed little effect on the low and high marsh carbon flux, while it was a major factor in diurnal CO2 flux patterns in case of the mudflat; as significant as solar radiation for all the habitat types.
According to the current topography and hydrology of the estuary and assuming an 8mm/year SLR and 4mm/year accretion rates, we project that by the year of 2100, the area of mudflats will increase by 7-10%, while low marsh will overtake the current high marsh habitats, and there will be an approximately 30% loss of high marsh habitats due to commercial and industrial development in the region and the lack of supporting elevation in the estuary. This in turn will lead to an overall reduction of marsh surface area, and the current annual net uptake of 213 gC/m2 in the estuary - when all surface types combined - will likely decrease with every meter square lost.