Wetland water level projected to control 21st century carbon and warming source/sink behavior at a temperate wetland

Abstract:

Wetland water level influences both microbial and plant communities, which can alter the above- and below-ground carbon cycling of a wetland. We used a mechanistic ecosystem model, ecosys, to simulate a range of water level scenarios in a temperate lacustrine wetland, and analyzed simulated carbon dioxide (CO₂) and methane (CH₄) emissions over the 21^st century. We tested our model using eddy covariance measurements of CO₂ and CH₄ emissions collected at the Old Woman Creek National Estuarine Research Reserve during 2015 and 2016. Using empirical models we found that the water level of the wetland is highly dependent on the water level of the nearby Lake Erie and used this relationship to drive the later flows of water, as a modified boundary condition. We used four projections of Lake Erie’s water level to model our site. Two of the four 21^st century projections for Lake Erie water levels used in this study indicated that the water level of the wetland would remain nearly steady; however, the other two indicated decreases in the wetland water level, which would have significantly dampened carbon cycling effects. Empirical relationships suggest that decreased water levels would cause more widespread colonization of the wetland by macrophyte vegetation, suggesting that the four scenarios will result in differing vegetation coverage. The mechanistic model also finds that further drying could result in other, non-wetland vegetation such as broadleaf trees to emerge, dramatically altering soil carbon cycling. In three of our four projections, we found that CO₂ and CH₄ fluxes would remain largely unchanged (i.e., a sink of CO₂ and a source of CH₄). In the driest cases though, we projected that the wetland would shift in behavior, approaching nearly neutral carbon fluxes over a 70-year time horizon due to decreasing CO₂ and CH₄ fluxes.