Abstract: Saltwater intrusion from human-induced sea level rise is impacting coastal habitats and communities throughout the world. In the Florida Coastal Everglades, controlled mesocosm and insitu experiments studies have shown that saltwater intrusion in the Everglades can alter carbon cycling in peat soils and source-sink dynamics. Specifically, saltwater intrusion can cause variation in ecosystem respiration and soil CO2 efflux, suppress productivity and reduce net ecosystem production. These changing dynamics have contributed to marsh degradation and in some cases collapse of peat soils in these ecosystems. Field observations from these studies also noted increasing surface water and porewater salinity levels with recurring drydown events, suggesting evidence of a positive feedback on marsh degradation and peat collapse. However, whether peat collapse influences rates of potential aquatic organic matter [total dissolved phosphorus (SRP) and nitrogen (TDN)] flux and carbon production, ie, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and methane (CH4) in surface waters and aquatic metabolism of this strongly P-limited coastal environment is a critical knowledge gap. To date, our results show SRP, TDN and DOC porewater concentrations between intact freshwater and collapsing brackish water marshes on the order of 30, 8 and 5 times higher in collapsing peat marshes. We have also observed porewater salinity increase approximately 1.5ppt/yr since 2015. However, the impacts of saltwater intrusion and changing salinity regimes on potential aquatic carbon production rates have not yet been explored. By applying water level manipulations of increasing salinity through a bench-top approach, this work seeks to understand how simulated drydown and rewetting (pulsing) events can impact potential aquatic nutrient and carbon production and aquatic metabolism.
