IMPACTS OF BENEFICIAL USE OF SEDIMENT PLACEMENTS ON WATER BIOGEOCHEMISTRY IN A BACK-BARRIER NEW JERSEY SALT MARSH

Salt marshes are one of Earth’s most valuable ecosystems because of the variety of services they provide. Climate change and resulting sea level rise have jeopardized these wetlands, as elevated water levels outpace their natural mechanisms for growth and flood resilience. One high-priority area for restoration efforts is coastal New Jersey due to its rapid rate of relative sea-level rise (~ 4 mm/yr) and large marsh area. A current leading solution for restoring ecological function to submerging salt marshes is the beneficial use of dredged sediment to enhance wetland habitats and protect the marsh from edge effects. In our study, sediment was placed from the New Jersey Intercoastal Waterway onto a subtidal marsh to build an edge protection feature. We investigate the extent to which this dredge placement impacted marine biogeochemical fluxes and function in the marsh. We will use continuous measurements of pH, temperature, salinity, turbidity, and dissolved oxygen (DO) via three In-Situ AquaTroll 600 sondes deployed near the active project and a control platform to quantify biogeochemical disturbance. Data were collected before, during, and after placement from August 2022 to December 2022 within the Seven Mile Island Innovation Laboratory (SMIIL) in collaboration with the US Army Corps of Engineers (USACE) and The Wetlands Institute (TWI). These data will create a mass-balance analysis of metabolic fluxes to enhance understanding of carbon and oxygen dynamics related to anthropogenic disturbance and climate change mitigation techniques. Specifically, we will derive fluxes of gross and net primary productivity, and ecosystem respiration throughout the entire deployment using the diel oxygen technique, supplemented by discrete measurements of oxygen, and dissolved inorganic carbon (DIC) and total alkalinity (TA) to close the carbonate chemistry system. Preliminary results show an increase in ecosystem respiration during sediment placement activity, though long-term effects require further analysis.