Collection, analysis, and age-dating of sediment cores from mangrove and salt marsh ecosystems in Tampa Bay, Florida, 2015

Coastal wetlands in Tampa Bay, Florida, are important ecosystems that deliver a variety of ecosystem services. Key to ecosystem functioning is wetland response to sea-level rise through accumulation of mineral and organic sediment. The organic sediment within coastal wetlands is composed of carbon sequestered over the time scale of the wetland’s existence. This study was conducted to provide information on soil accretion and carbon storage rates across a variety of coastal ecosystems that was utilized in the Tampa Bay Blue Carbon Assessment (ESA, 2017; linkage below). Ten sediment cores were collected from six Tampa Bay wetland sites in October 2015 (maximum core length 40 centimeters). Three main vegetation types were targeted for core collection: salt marsh, dominated by Juncus and Spartina alternaflora; mangrove, including Rhizophora mangle, Laguncularia racemosa and/or Avicennia germinans; and young mangrove, where wetlands were created within the last three decades. An additional surface sediment sample was collected from a salt barren, as this site was not conducive to coring. Marsh surface elevations were measured at each site (ranging from 0.771 meters to 1.462 meters relative to NAVD88) to determine the marsh boundaries within current tidal conditions. Continuous Rate of Supply age models, based on lead-210 and cesium-137 isotope analysis, were constructed to evaluate how vertical accretion and carbon burial rates have changed during the past century. Over that time, accretion rates were very similar for each ecosystem: restored marsh sites (2.5 mm per year), followed by the salt marshes (2.7 mm per year) and mature mangroves (3.2 mm per year). The resulting carbon burial rates over the past century vary as a function of vegetation type, with mature mangroves burying on average 163 grams carbon per square meter per year, compared to young (restoring) mangroves with an average of 94 grams carbon per square meter per year and the salt marsh with an average of 64 grams carbon per square meter per year . This dataset also includes dry bulk density (0.02 - 1.70 grams per cubic centimeter), percent carbon (0.32 %-39.08 %), and percent loss on ignition (0.66 % – 80.2 %) from a sub-set of core sections in order to assess possible correlative relationships among these parameters. https://estuaries.org/wp-content/uploads/2019/02/FINAL_Tampa-Bay-Blue-Carbon-Assessment-Report-updated-compressed.pdf