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Biogeochemistry

, Volume 140, Issue 2, pp 217–232 | Cite as

Salinity effects on greenhouse gas emissions from wetland soils are contingent upon hydrologic setting: a microcosm experiment

  • Marcelo ArdónEmail author
  • Ashley M. Helton
  • Emily S. Bernhardt
Article

Abstract

Coastal forested wetlands provide important ecosystem services such as carbon sequestration, nutrient retention, and flood protection, but they are also important sources of greenhouse gas emissions. Human appropriation of surface water and extensive ditching and draining of coastal plain landscapes are interacting with rising sea levels to increase the frequency and magnitude of saltwater incursion into formerly freshwater coastal wetlands. Both hydrologic change and saltwater incursion are expected to alter carbon and nutrient cycling in coastal forested wetlands. We performed a full factorial experiment in which we exposed intact soil cores from a coastal forested wetland to experimental marine salt treatments and two hydrologic treatments. We measured the resulting treatment effects on the emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) over 112 days. Salinity effects were compared across four treatments to isolate the effects of increases in ionic strength from the impact of adding a terminal electron acceptor (SO42−). We compared control treatments (DI addition), to artificial saltwater (ASW, target salinity of 5 parts per thousand) and to two treatments that added sulfate alone (SO42−, at the concentration found in 5 ppt saltwater) and saltwater with the sulfate removed (ASW-SO42−, with the 5 ppt target salinity maintained by adding additional NaCl). We found that all salt treatments suppressed CO2 production, in both drought and flooded treatments. Contrary to our expectations, CH4 fluxes from our flooded cores increased between 300 and 1200% relative to controls in the ASW and ASW-SO42− treatments respectively. In the drought treatments, we saw virtually no CH4 release from any core, while artificial seawater with sulfate increased N2O fluxes by 160% above DI control. In contrast, salt and sulfate decreased N2O fluxes by 72% in our flooded treatments. Our results indicate that salinization of forested wetlands of the coastal plain may have important climate feedbacks resulting from enhanced greenhouse gas emissions and that the magnitude and direction of these emissions are contingent upon wetland hydrology.

Keywords

Greenhouse gases Saltwater intrusion Drought Sea level rise 

Notes

Acknowledgements

We thank Dr. Ben Colman, Medora Burke-Scoll, and Anna Fedders for help with the microcosm experiments. We thank the staff at the Phytotron at Duke University for their help with this experiment. We thank Dr. E. Matzner and three anonymous reviewers for their helpful comments and suggestions which helped improve the manuscript. This work was supported NSF DBI-0805576, DEB-1713592, and EF-1713435 to M. Ardón.

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Copyright information

© Springer Nature Switzerland AG 2018

Authors and Affiliations

  1. 1.Department of Forestry and Environmental ResourcesNorth Carolina State UniversityRaleighUSA
  2. 2.Department of Natural Resources and the Environment, Center for Environmental Sciences and EngineeringUniversity of ConnecticutStorrsUSA
  3. 3.Department of BiologyDuke UniversityDurhamUSA

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