Fertilization Changes Seagrass Community Structure but not Blue Carbon Storage: Results from a 30-Year Field Experiment
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Seagrass ecosystems are attracting attention as potentially important tools for carbon (C) sequestration, comparable to those terrestrial and aquatic ecosystems already incorporated into climate change mitigation frameworks. Despite the relatively low C stocks in living biomass, the soil organic carbon pools beneath seagrass meadows can be substantial. We tested the relationship between soil C storage and seagrass community biomass, productivity, and species composition by revisiting meadows experimentally altered by 30 years of consistent nutrient fertilization provided by roosting birds. While the benthos beneath experimental perches has maintained dense, Halodule wrightii-dominated communities compared to the sparse Thalassia testudinum-dominated communities at control sites, there were no significant differences in soil organic carbon stocks in the top 15 cm. Although there were differences in δ13C of the dominant seagrass species at control and treatment sites, there was no difference in soil δ13C between treatments. Averages for soil organic carbon content (2.57 ± 0.08 %) and δ13C (−12.0 ± 0.3 ‰) were comparable to global averages for seagrass ecosystems; however, our findings question the relevance of local-scale seagrass species composition or density to soil organic carbon pools in some environmental contexts.
KeywordsSeagrass Organic matter Sediment Blue carbon
This research was funded by the US Environmental Protection Agency as part of the Florida Keys National Marine Sanctuary Water Quality Protection Program (Contract No. X7 95469210) and by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Grant No. DEB-1237517. Philip Matich provided invaluable lab assistance. Along with Philip, this project was enriched by Jean Alcazar and three anonymous reviewers who offered support and valuable comments. This is contribution number 759 of the Southeast Environmental Research Center at FIU.
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