Mangroves dramatically increase carbon storage after 3 years of encroachment
In North America, the dynamic ecotonal boundary between mangrove and salt marsh is currently fluctuating in response to freeze-free winters, which can cause rapid alterations in a number of wetland processes and attributes. Permanent plots were established in pure salt marsh habitat along the Atlantic coast of Florida in 2015, and by 2018, mangrove saplings had encroached into plots. In this study, above- and belowground biomass measurements and soil C in the top 10-cm soil profile were quantified in 2018 and compared to 2015 data to better understand the effects of mangrove encroachment on C storage in salt marsh habitat. Plant and soil fractions were tested for δ13C stable isotopic signatures to elucidate soil C sources. In 3 years, mangrove biomass increased dramatically and soil C doubled in pure salt marsh plots, consequently increasing total C in the system. Soil organic matter increased, while there was no change in soil C:N. δ13C values suggest that soil C was derived mainly from salt marsh soil organic matter, especially that of belowground, rather than aboveground biomass. These results provide real-time, quantitative data on the encroachment of mangroves into salt marshes over a relatively short period of time.
KeywordsClimate change Ecotonal boundary Blue carbon Vegetation shift Stable isotopes Salt marsh
This research was funded by the National Aeronautics and Space Administration (NASA) Climate and Biological Response program (NNX11AO94G) and the National Science Foundation (NSF) MacroSystems Biology program (EF1065821). The authors would like to thank Florida State Parks, the Merritt Island National Wildlife Refuge, Guana-Tolmato-Matanzas National Estuarine Research Reserve, and Canaveral National Seashore for permits and unabridged access to their parks. We also thank L.J. Duckett, M.L. Lehmann, K.V. Curtis, and Z.R. Foltz for field and lab assistance. We sincerely thank the two anonymous reviewers for their edits and suggestions, which significantly improved this manuscript.
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