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Vegetation loss following vertical drowning of Mississippi River deltaic wetlands leads to faster microbial decomposition and decreases in soil carbon

April 15, 2024

Wetland ecosystems hold nearly a third of the global soil carbon pool, but as wetlands rapidly disappear the fate of this stored soil carbon is unclear. The aim of this study was to quantify and then link potential rates of microbial decomposition after vertical drowning of vegetated tidal marshes in coastal Louisiana to known drivers of anaerobic decomposition altered by vegetation loss. Profiles of potential CH4 and CO2 production (surface to 60 cm deep) were measured during anaerobic incubations, organic matter chemistry was assessed with infrared spectroscopy, and soil porewater nutrients and redox potentials were measured in the field along a chronosequence of wetland loss. After vertical drowning, pond soils had lower redox potentials, higher pH values, lower soil carbon and nitrogen concentrations, lower lignin: polysaccharide ratios, more NH4+ and PO43−, and higher rates of potential CO2 release than vegetated marsh soils. Potential CH4 production was similar in vegetated marshes and open water ponds, with depth-dependent decreases in CH4 production as soil carbon concentrations increased. In these anoxic soils, vegetation loss exerts a primary control on decomposition rates because flooding drives sustained increases in porewater nutrient availability (NH4+ and PO43, dissolved organic carbon) and decreases in redox potential (from −150 to −500 mV) that lead to higher potential CO2 fluxes within a few years. Without new carbon inputs following wetland loss, the sustained decomposition in open water ponds may lead to losses of stored soil carbon and could influence global carbon budgets.

Publication Year 2024
Title Vegetation loss following vertical drowning of Mississippi River deltaic wetlands leads to faster microbial decomposition and decreases in soil carbon
DOI 10.1029/2023JG007832
Authors Courtney Creamer, Mark Waldrop, Camille Stagg, Kristen L. Manies, Melissa Millman Baustian, Claudia Laurenzano, Tiong Gim Aw, Monica Haw, Sergio Merino, Donald R. Schoolmaster, Sabrina N. Sevilgen, Rachel Katherine Villani, Eric Ward
Publication Type Article
Publication Subtype Journal Article
Series Title JGR Biogeosciences
Index ID 70253005
Record Source USGS Publications Warehouse
USGS Organization Geology, Minerals, Energy, and Geophysics Science Center; Wetland and Aquatic Research Center
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