The Effect of Open Marsh Water Management Practices on the Carbon Balance of Tidal Marshes in Barnegat Bay, New Jerse

Salt marshes have been modified for mosquito control since the early 1900s. Open marsh water management (OMWM) is a mosquito control technique first applied in New Jersey in the 1950s. It has been extensively used in the mid-Atlantic and also in Massachusetts, New York, Connecticut, Florida, and Louisiana. This practice involves excavation of areas of marsh, constructing shallow ponds to provide habitat for mosquito larvae-eating fish with the goal of reducing mosquito populations. Nearly half of Barnegat Bay, New Jersey's coastal marshes have been subject to OMWM since 1976, and its effects on ecosystem function are not well understood. Here, we assess the impacts of OMWM on the carbon balance of salt marshes associated with the conversion of intact vegetation to open water ponds. Using a precise object-based image analysis classification technique, we found that over 7,000 ponds, approximately 3% of Barnegat Bay's coastal marshes, have been constructed for mosquito control. Using state of the art IR technology to examine in-situ greenhouse gas fluxes in Barnegat Bay, we found evidence to suggest that the conversion from intact plants to open water ponds negatively shifted the carbon balance of the salt marsh, both within the footprint of the constructed pond as well as within the area where deposition of sediment has prevented the recolonization of marsh vegetation. We conclude that this management technique has significantly reduced the carbon sequestration capacity of Barnegat Bay's tidal wetlands.