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Along low-elevation coastlines, sea-level rise (SLR) threatens to salinate ecosystems. To understand the effects of SLR and freshwater management on landscape carbon (C) exchange, we measured the net ecosystem exchange (NEE) of CO2 between subtropical wetland ecosystems and the atmosphere along a dynamic salinity gradient. Ecosystems were representative of freshwater marl prairies, brackish ecotones, and saline scrub mangrove forests in the southeastern Everglades. Patterns in NEE explained the landward movement of coastal wetlands, a process observed over the last 70 years. The capacity to capture C was greatest along the coast in the scrub mangrove (−294 ± 0.02 g C m−2 y−1) and declined inland into marl prairies (−47 ± 0.03 g C m−2 y−1). Low resilience to current conditions was evident in marl prairies, a result of the legacy impacts of water diversion throughout the greater Everglades. Although the southeastern Everglades captured approximately 115 metric tons of C in 2021, if the ecotone continues to advance at 25 m y−1 over the next century, we project a 12 % increase (16 mt C y−1) in net CO2 capture. Results emphasize that initial functional responses to changes in conditions may not accurately represent long-term outcomes and highlight the role of brackish ecotone communities as the frontline for climate- and management-induced shifts in coastal ecosystem structure and function. This is the first study to use disequilibrium dynamics to understand landscape-level transitions and their implications for C capture. 

Datasets include hydrology (water level and salinity), net ecosystem exchange of CO2, photosynthetically active radiation (PAR), and air temperature for a freshwater marl prairie, brackish marsh ecotone, and saline scrub mangrove forest. Data were derived from multiple sources, including two sites from the South Florida Water Management District (SFWMD) DBhydro web database, two sites from the Florida Coastal Everglades Long Term Ecological Research (FCE-LTER) program and three AmeriFlux sites in the Southeastern Everglades region. Ameriflux sites were co-located with FCE-LTER sites. To understand the effects of sea level rise and freshwater management on landscape carbon exchange (C), we measured the net ecosystem exchange of CO2 (NEE) between subtropical wetland ecosystems and the atmosphere along a dynamic salinity gradient. Ecosystems were representative of freshwater marl prairies, brackish marsh ecotones, and saline scrub mangrove forests. In the southeastern Everglades, the magnitude of environmental change was greatest along the coast, where mangrove scrub forests exhibited a greater capacity to maintain CO2 uptake with changing conditions.