Sustained‐Flux Global Warming Potential Driven by Nitrogen Inflow and Hydroperiod in a Model of Great Lakes Coastal Wetlands. Issue 8 (21st August 2021) - Yuan, Y.
Abstract: Wetlands impact global warming by regulating the atmospheric exchange of greenhouse gases (GHGs), including carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O). We investigated GHG emissions in the Great Lakes coastal wetlands across various hydrologic, temperature, and nitrogen (N) inflow regimes using a process‐based simulation model. We found the emission of CH4, N2 O, and sequestration of C (i.e., negative net ecosystem exchange, NEE) in our simulations were all positively related to water residence time and N inflow, primarily due to greater plant productivity and N uptake, which facilitated greater C and N cycling rates in the model. Water level scenarios also had an effect on GHG exchanges by moderating the transitions between aerobic and anaerobic conditions. Temperature effects on GHGs were minimal compared with other factors. The net sustained‐flux global warming potential (SGWP; i.e., sum SGWP of CH4, N2 O, and NEE) of wetlands on 20‐year and 100‐year time horizons were both primarily driven by CH4 emissions and strongly controlled by the tradeoffs between CH4 emission and CO2 sequestration, with a negligible amount of simulated N2 O emissions. Future research could include model enhancements to provide increased process‐level details on the aerobic‐anaerobic transitions or the direct effects of plants on mediating GHG exchanges. Field studies addressing the interaction of N inflows and water residence time at appropriately large scales are needed to test the complex interactions revealed by our modeling study. Our results highlight the previously under‐appreciated role of nitrogen and water residence time in modulating SGWP in coastal wetlands. Plain Language Summary: Wetlands impact global warming by emitting carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O) to the atmosphere, but can absorb these greenhouse gases (GHGs). In our study, we investigated GHG emission in the Great Lakes coastal wetlands under different hydrologic, temperature, and nitrogen (N) inflow regimes using a simulation ecosystem model. We found the emission of CH4 and N2 O increased with longer water residence time and higher N inflow in our modeling results, but at the same time, more carbon was absorbed by wetlands because wetland plants produced more biomass with more nutrients. The summed sustained‐flux global warming potential of wetlands on 20‐year and 100‐year time horizons both depend on if global warming potential caused by CH4 could be offset by the negative global warming potential of CO2 . Key Points: Wetland methane emissions had a far greater effect on net sustained‐flux global warming potential than carbon dioxide or nitrous oxide The positive net sustained‐flux global warming potential was dominated by methane emission in our simulations Our study illustrated the strength of using a process‐based model to reveal the interactions between drivers of greenhouse gas emissions