Results/Conclusions: The porewater chemistry in the brackish sawgrass marsh was very surprising. As expected, Treatment chambers had higher concentrations of salt, chlorides and sulfates, than the Controls. However, they had lower concentrations of total dissolved phosphorus, nitrogen and organic carbon. Concentrations of TDP and TDN averaged around 90 ppb and 5 mg/l respectively, in the Treatment chambers, and 150 ppb and 8 mg/l, respectively, in the Control chambers. The nutrient concentrations in this brackish site were also significantly higher than the freshwater site where, TDP and TDN averaged around 12 ppb and 1.4 mg/l respectively, in the Treatment chambers, and 9 ppb and 0.9 mg/l, respectively, in the Control chambers. The high nutrients in the brackish site suggest high decomposition rates, which agrees with the SET relationships found with hydrology. In continuously flooded mangroves, the annual average elevation change (0.15 cm) was lower than the average annual accretion rate (0.21 cm), indicating that subsidence is so high that these sites cannot keep pace with current sea level rise. On the other hand, frequently flooded mangroves, ones that occasionally have low water and low salinity, had an elevation change of 3.1 mm/yr, but interestingly, only an accretion of 0.11 cm/yr. Since these sites are accreting very little, their ability to keep pace with sea level rise is likely the result of belowground processes; processes that our dosing chambers are illuminating.