Biogeochemistry and Function in Soils Transitioning from Coastal Forest to Wetland in the Chesapeake Bay


Stephanie J. Wilson1* (, Patrick Megonigal1, Roy Rich1, Alice Stearns1, Evan Phillips1, Erin Fien1, Lani DuFresne1, Peter Regier2, Allison Myers-Pigg2, Stephanie Pennington2, Anya Hopple1, Kendalynn A. Morris3, Jun Yan Ding2, Xingyuan Chen2, Li Bing2, Nate McDowell2, Ben Bond- Lamberty3, Michael N. Weintraub4,2, Nicholas D. Ward2, Kenneth M. Kemner5, and Vanessa Bailey2


1Smithsonian Environmental Research Center, Edgewater, MD; 2Pacific Northwest National Laboratory, Richland, WA; 3Joint Global Change Research Institute, College Park, MD; 4University of Toledo, Toledo, OH; 5Argonne National Laboratory, Lemont, IL



Sea level rise drives spatial migration of coastal ecosystems and can lead to the replacement of coastal forests with tidal wetlands. Stressed or dead trees are well-recognized indicators of this conversion, but carbon (C) cycling, and soil biogeochemistry will also shift during this transition. Changes in soil biogeochemistry and vegetation during marsh migration may occur on different timescales, and this potential asynchrony will influence ecosystem function. Here, as a part of the Coastal Observations, Mechanisms, and Predictions Across Systems and Scales–Field, Measurements, and Experiments (COMPASS-FME) project, researchers determine how biogeochemical cycling of C and nutrients shift as upland coastal forests transition to tidal wetlands. Transects were established at four sites located throughout the Chesapeake Bay that represent spatial variation in elevation, soil types, vegetation, and salinity regimes. At each site, monthly measurements of soil methane (CH4) fluxes, redox profiles, conductivity, and porewater constituents were made in upland forest, forest transitioning to wetland, and herbaceous tidal wetland transect locations. Despite live trees in the transition zone, researchers observed that soil biogeochemistry and function deviate strongly from conditions observed in the upland forest: along the gradient from upland forest to wetland, soils switched from a net sink to a net source of CH4, soil redox potential decreased, and soil conductivity and porewater sulfate concentrations increased. The results indicate that transition zone soils begin to function similarly to tidal wetland soil prior to mass tree mortality, suggesting that by the time ghost forests are identified, soil function and biogeochemistry has already changed drastically. This has important implications for understanding the impacts of sea level rise and marsh migration on ecosystem-scale greenhouse gas emissions and C cycling across the terrestrial-aquatic interface.