Water level changes in Lake Erie drive 21st century CO2 and CH4 fluxes from a coastal temperate wetland

• Published in: The Science of the total environment 2022-05, Vol.821, p.153087-153087, Article 153087
• Main Authors: Morin, Timothy H., Riley, William J., Grant, Robert F., Mekonnen, Zelalem, Stefanik, Kay C., Sanchez, A. Camilo Rey, Mulhare, Molly A., Villa, Jorge, Wrighton, Kelly, Bohrer, Gil
• Format: Article
• Language: English
• Subjects: Eddy covariance; ENVIRONMENTAL SCIENCES; Lake Erie; Mechanistic model; Projection
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.153087

Wetland water depth influences microbial and plant communities, which can alter the above- and below-ground carbon cycling of a wetland. Wetland water depths are likely to change due to shifting precipitation patterns, which will affect projections of greenhouse gas emissions; however, these effects are rarely incorporated into wetland greenhouse gas models. Seeking to address this gap, we used a mechanistic model, ecosys, to simulate a range of water depth scenarios in a temperate wetland, and analyzed simulated predictions of carbon dioxide (CO2) and methane (CH4) fluxes over the 21st century. We tested our model using eddy covariance measurements of CO2 and CH4 fluxes collected at the Old Woman Creek National Estuarine Research Reserve (OWC) during 2015 and 2016. OWC is a lacustrine, estuarine, freshwater, mineral-soil marsh. An empirical model found that the wetland water depth is highly dependent on the water depth of the nearby Lake Erie. Future wetland surface water depths were modeled based on projection of Lake Erie's water depth using four separate NOAA projections, resulting in four wetland water-depth scenarios. Two of the four 21st century projections for Lake Erie water depths used in this study indicated that the water depth of the wetland would remain nearly steady; however, the other two indicated decreases in the wetland water depth. In our scenario where the wetland dries out, we project the wetland's climatological warming effect will decrease due to smaller CH4 fluxes to the atmosphere and larger CO2 uptake by the wetland. We also found that increased water level can lower emissions by shifting the site towards more open water areas, which have lower CH4 emissions. We found that decreased water depths would cause more widespread colonization of the wetland by macrophyte vegetation. Using an empirical relationship, we also found that further drying could result in other, non-wetland vegetation to emerge, dramatically altering soil carbon cycling. In three of our four projections, we found that in general the magnitude of CO2 and CH4 fluxes steadily increase over the next 100 years in response to higher temperatures. However, in our driest simulations, we projected a different response due to increased oxidation of soil carbon, with CH4 emissions decreasing substantially from an annual cumulative peak of 224.6 to a minimum of 104.7 gC m−2 year−1. In that same simulation, net cumulative flux of CO2 changed from being a sink of 56.5 gC m−2