How Does the Burial Rate of Soil Organic Matter Relate to Salinity and Productivity in the Coastal Everglades?

Joshua L Breithaupt, University of South Florida, College of Marine Science, St. Petersburg, FL, United States, Joseph M Smoak, University of South Florida, Environmental Science, St. Petersburg, FL, United States, Christian J Sanders, Southern Cross Univerisity, Centre for Coastal Biogeochemistry, Lismore, Australia and Tiffany Troxler, Florida International University, SE Environmental Research Ctr. & Department of Biological Sciences, Miami, FL, United States
Sea level rise (SLR) produces different types and magnitudes of change spatially within a coastal wetland. Differences in the coastal Everglades include inundation (frequency, duration & depth), salinity and phosphorous availability. Each of these affect mangrove productivity and biogeochemical cycling. To address how accelerated SLR will change the organic carbon (OC) burial rate of a wetland ecosystem it is first necessary to understand the changes at the site level throughout the ecosystem. The objective of this research is to compare site level burial rates in relation to ecosystem gradients in salinity, nutrient availability, and plant productivity in the coastal Everglades. We examined the 210Pb record of soil accumulation rates of OC, total nitrogen (TN), total phosphorous (TP), and calcium carbonate. Organic C and TN burial rates exhibit relatively small spatial variability over the 100-year timespan. The exception to this is evident in three cores near the oligohaline ecotone where both OC and TN rates decrease sharply compared to the rest of the region. These locations have seen increasing surface and groundwater salinities in the past decade, and our findings suggest an early form of “peat collapse” may be discernible in the soil core record. In contrast to OC and TN, there is substantial spatial variability in the burial rates of TP, with downstream rates that are 11 times higher than those at the oligohaline ecotone. These burial rates are highly correlated with those of CaCO3 whose provision via storm surge has been well documented, and is a driver of the ecosystem gradient in mangrove productivity. When stated as a fraction of net primary production, there are significant differences in OC burial efficiency throughout the ecosystem. The least efficient sites are at the oligohaline ecotone followed by the downstream sites. Mid-stream sites, that have theoretically experienced the least amount of SLR change in the past century, are the most efficient.