Declines in Plant Productivity Drive Carbon Loss from Brackish Coastal Wetland Mesocosms Exposed to Saltwater Intrusion
Coastal wetlands, among the most productive ecosystems, are important global reservoirs of carbon (C). Accelerated sea level rise (SLR) and saltwater intrusion in coastal wetlands increase salinity and inundation depth, causing uncertain effects on plant and soil processes that drive C storage. We exposed peat-soil monoliths with sawgrass (Cladium jamaicense) plants from a brackish marsh to continuous treatments of salinity (elevated (~ 20 ppt) vs. ambient (~ 10 ppt)) and inundation levels (submerged (water above soil surface) vs. exposed (water level 4 cm below soil surface)) for 18 months. We quantified changes in soil biogeochemistry, plant productivity, and whole-ecosystem C flux (gross ecosystem productivity, GEP; ecosystem respiration, ER). Elevated salinity had no effect on soil CO2 and CH4 efflux, but it reduced ER and GEP by 42 and 72%, respectively. Control monoliths exposed to ambient salinity had greater net ecosystem productivity (NEP), storing up to nine times more C than plants and soils exposed to elevated salinity. Submersion suppressed soil CO2 efflux but had no effect on NEP. Decreased plant productivity and soil organic C inputs with saltwater intrusion are likely mechanisms of net declines in soil C storage, which may affect the ability of coastal peat marshes to adapt to rising seas.
KeywordsCladium jamaicense Florida Everglades Biogeochemistry Salinity Marsh Peat collapse
We thank Shawn Abrahams, Laura Bauman, Kristina Morales, and Ryan Stolee for help in the field. Viviana Mazzei, Steven Oberbauer, and Fred Sklar provided valuable feedback on early drafts of this manuscript. This is contribution number 16 of the Sea Level Solutions Center and 877 of the Southeast Environmental Research Center in the Institute of Water & Environment at Florida International University.
Funding for research was supported by the Florida Sea Grant R/C-S-56, including cooperative agreements with the South Florida Water Management District (SFWMD), the Everglades Foundation, and Everglades National Park (ENP). Additional funding was provided through the National Science Foundation’s Florida Coastal Everglades Long Term Ecological Research Program (DEB-1237517). ENP and the Everglades section of the SFWMD provided in-kind support for the mesocosm facilities. Benjamin Wilson was supported by a Florida International University Teaching Assistantship, Florida Sea Grant, FCE LTER, and FIU Dissertation Year Fellowship
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