Potential fate of wetland soil carbon in a deltaic coastal wetland subjected to high relative sea level rise

Abstract

The fate of soil carbon in eroding coastal wetlands is of great concern, given the potential for a feedback loop from coastal wetland soil that would dramatically increase atmospheric CO2 concentrations. The biogeochemical transformations and overall fate of this soil carbon upon coastal erosion were investigated through geophysical and spectroscopic analysis of soil and associated dissolved organic matter. Bay water and core sections were collected across transects encompassing both intact and eroded, submerged, sections of a coastal marsh in Barataria Bay, Louisiana. We noted: i) a vertical increase in carbon content, humification of organic matter, and decrease in biotic degradation with depth at all sites; ii) an erosion and ultimate collapse of the top ~ 0–20 cm of the intact marsh’s edge into the bay water due to the undercutting caused by tidal/wave forces; iii) the loss of the stored carbon from the submerged site’s top 10 cm layer; and iv) leaching, dilution, abiotic, and biotic degradation of the marsh carbon due to the exposure to the bay water. This erosion and degradation of wetland soil carbon stores demonstrates the potential impact of rising sea levels on the future fate of coastal wetland carbon and atmospheric CO2 levels.