Modeling Coastal Wetland Responses to Warming and Elevated Carbon Dioxide
Authors
Genevieve Noyce1* (noyceg@si.edu), Teri O’Meara2, Nick Bruns3, Alex Smith1, Roy Rich1, Matt Kirwan3, Pat Megonigal1
Institutions
1Smithsonian Environmental Research Center, Edgewater, MD; 2Oak Ridge National Laboratory, Oak Ridge, TN; 3Virginia Institute of Marine Science, Gloucester Point, VA
Abstract
Coastal ecosystems are important biogeochemical zones but have largely been ignored in Earth Systems Models (ESMs). Plant-microbe interactions drive the redox-active biogeochemical processes that structure ecosystem resilience, especially in wetlands where plant-mediated oxygen transport into the rhizosphere can stimulate aerobic microbial processes, but it can be difficult to isolate the mechanisms needed to model ecosystem responses to warming temperatures and elevated carbon dioxide (eCO2). As a result, SMArtX was established in 2016 to advance model representation of coastal wetland responses to global change.
Researchers have measured continuous soil redox potential in SMArtX since 2020 and found redox is consistently lower with warming and higher with eCO2, which researchers attribute to plant-microbe feedbacks. These effects are most pronounced close to the soil surface, where the bulk of the roots are located, and illustrate the importance of rhizosphere influences on ecosystem biogeochemistry. After initial data showed a nonlinear effect of temperature on belowground root growth, researchers recently developed a simple mechanistic model of how biomass allocation responds to nitrogen supply and demand that successfully explains the field data and also reveals a surprising interaction between warming and eutrophication, predicting that enhanced nitrogen loading to marshes may reduce adverse impacts of warming on root growth.
Using a version of PLFOTRAN updated to include redox reactions relevant to coastal ecosystems, researchers found that including plant and microbial responses to eCO2 and temperature also more accurately represents SMArtX porewater profiles. This indicates the importance of characterizing tightly coupled vegetation-subsurface processes for developing predictive understandings as well as ongoing measurements of plant-microbe feedbacks to global change. Researchers have also recently implemented key biogeomorphic feedbacks into Energy Exascale Earth System Model (E3SM) that simulate the elevation change and productivity responses to flooding in coastal wetlands that were previously neglected. Combined with field elevation and productivity data from SMArtX, researchers will be able to determine projected wetland stability and function in response to global change.