Researchers tackle land loss-climate change connection

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Credit: John White, LSU

Sea level rise is occurring at a significantly higher rate in coastal Louisiana than at most of the world's coastal communities. The combined effects of global sea level rise and regional subsidence, or sinking, contribute to Louisiana's 13-millimeter-per-year relative sea level rise rate. Despite being higher than average, Louisiana's rate remains within the range of those predicted for the globe in the next 65 to 85 years, which provides a unique opportunity to study the effects of future global sea level rise on wetland-dominated coastlines today.

In addition to the rising sea level, coastal Louisiana also suffers from extensive coastal wetland loss. One to two meters of carbon-rich peat soils are rapidly eroding, submerging and converting to open water at a rate of 65 to 91 square kilometers per year. Despite this influx of carbon-rich organic matter, low amounts of carbon have been detected in sediment. Therefore, scientists believe a majority of this carbon-rich soil is being mineralized and released as carbon dioxide into the atmosphere. This phenomenon is potentially a significant climate change feedback that is currently unaccounted for in climate change models. The mineralization of nitrogen and phosphorus can also affect ocean chemistry and exacerbate hypoxia.

LSU researchers in the Department of Oceanography and Coastal Sciences and the Department of Chemistry with collaborators at the University of Central Florida have been awarded a grant by the National Science Foundation to study the "Fate of Coastal Wetland Carbon Under Increasing Sea Level Rise: Using the Subsiding Louisiana Coast as a Proxy for Future World-Wide Sea Level Projections."

"This study aims to increase our understanding of the magnitude of carbon from soil being returned to the atmosphere relatively quickly. Our results will help build more accurate predictive modeling for future climate change predictions. Policy makers will also be able to plan better for the impacts of sea level rise affecting densely populated coastal communities world-wide," said John White, LSU professor in the Department of Oceanography and Coastal Sciences and one of the co-principle investigators for the project.

LSU Department of Oceanography and Coastal Sciences Assistant Profesor Zuo "George" Xue, LSU Department of Chemistry Professor Robert Cook and University of Central Florida Biology Assistant Professor Lisa Chambers are collaborators on the project.

The research team will test the hypothesis by characterizing surface water, porewater and soil cores along transects from the marsh interior into adjacent Barataria Bay near Grand Isle, La. The elemental and molecular composition of soil organic matter along these transects will be analyzed to determine rates of reburial and transformations of the organic matter. Microcosm experiments will quantify potential soil organic carbon mineralization and nutrient release rates with soil depth, and under varying temperature, salinity and nutrient regimes.

Field and laboratory data will be combined with existing information on wetland loss rates to drive a coupled physical-biogeochemical model of the carbon and nitrogen budget for the Barataria basin.

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