Eroding Wetland Soils in Coastal Louisiana's Barataria Bay Could Impact Future Climate and Sea Level Rise.

Wetlands act as net carbon sinks due primarily to the coupled high levels of primary production and anaerobic conditions in the soils which preserve the organic matter. However, as coastal wetlands erode, organic matter (OM) that was once stored is now exposed to an aerobic water column where further decomposition can occur rapidly. This research project sought to quantify how much faster soil OM decomposition could occur in these aerobic conditions of the coastal bays and whether this increased decomposition rate is dependent upon depth in the soil profile. Soil cores collected from salt marsh sites in Barataria Bay, LA were analyzed for soil physicochemical and microbial characteristics, including total carbon, microbial biomass carbon, and percent organic matter. Carbon mineralization studies were also performed under anaerobic and aerobic conditions for comparison of OM decomposition rates. Aerobic OM decomposition rates for subsurface soils were >10x faster than the corresponding anaerobic rates, and aerobic decomposition was independent of depth. Therefore, the previously stored OM has the potential to decompose rapidly once eroded and deposited into the aerobic water column of the adjacent bay. Consequently, these eroding wetlands can become a substantial source of CO₂ to the atmosphere. This influx of CO₂ would act as a positive feedback loop to the atmosphere under influence of an ever increasing sea level rise. Research along the subsiding coastline of Louisiana also provides an opportunity to better predict and model future global changes to the coastal carbon cycle. And, since Barataria Bay is experiencing relative sea level rise rates that are predicted for world’s stable coastlines in the next 50-100 years, this system provides a valuable opportunity to test wetland restoration and coastal erosion mitigation strategies.