Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are key radiatively active greenhouse gases (hereafter GHGs) with variable global warming potential. Wetlands plays a vital role in regulating global GHG emission through plant assimilation and soil sequestration of CO2 as well as microbial production of CH4 and N2O. These gas dynamics are greatly affected by seasonal water level fluctuations that modulate plant productivity and dictate the location and extent of oxic and anoxic zones, which regulate soil microbial processes including denitrification and mineralization of organic carbon in detritus. It has been recognized that high water levels may increase CH4 emission while decreasing CO2 emission in wetlands but the interacting roles of plant communities, nutrient flow, and hydroperiod on GHG exchange are poorly understood. Here, we investigate the interactions of 4 variable hydroperiods, 3 residence times, and 3 levels of N-loading on CO2, CH4, and N2O gas exchange over a 40-year period by simulating a Great Lakes coastal wetland using Mondrian, a process-based ecosystem simulation model
Results/Conclusions
Preliminary modeling results suggest that high water level lowers net CO2 emissions by promoting C storage while seasonally fluctuating water level increased N2O production. High N-loading and high residence time of water consistently lowered net CO2 emissions but increased N2O production. Under constant water level (0.2 m, 0.09 m and -0.02 m), we found that CO2 had the lowest emissions with highest N loading (10 g N/m2 y) and longest residence time of water (67 days). Correspondingly, N2O had the lowest production with lowest N loading (5 g N/m2 y) and shortest residence time of water (13 days). Under seasonally fluctuating hydroperiods representative of wetlands found in the Great Lakes region net CO2 emissions was below lowest constant water level only for high N-loading and long residence time. When seasonally fluctuating water levels were combined with low N-loading and low water residence time, CO2 emission was generally higher than all constant water-level conditions. Importantly, due to coupled nitrification-denitrification in the model, N2O production was always greater with fluctuating hydroperiod than at any constant water level scenario we tested.