Background/Question/Methods The Florida Everglades is a delicate ecosystem that was a carbon sink, but recent hydrologic changes associated with climate change and anthropogenic pressures have led to uncertainties about the system's source/sink capacity. Hydroperiod, the frequency and duration of inundation, is a critical driving factor of wetland biogeochemical cycles and productivity. Anthropogenic influence (i.e., urbanization, agricultural expansion, and water controlling structures) has altered water delivery to the Everglades, which in turn has a large impact on the carbon dynamics of these wetlands. To investigate the effect of hydrology on carbon exchange, we used eddy covariance measurements to estimate rates of net ecosystem exchange (NEE) for two years in long and short hydroperiod freshwater marshes located in Everglades National Park. In this study, we addressed the following hypothesis: NEE rates will be greater in our short hydroperiod marsh due to the reduced length of anoxic soil conditions when compared to our long hydroperiod marsh. We also asked: Do these exchange rates differ between the wet and dry seasons?

Results/Conclusions We found significant seasonal differences in CO₂ exchange rates in our short hydroperiod marsh. Specifically in 2008, maximum rates of CO₂ uptake are much higher in the dry season (maximum net ecosystem exchange, NEE_max, = -5.9 µmol CO₂ m^-2 s^-1) than the wet season (NEE_max = -1.6 µmol CO₂ m^-2 s^-1). Contrary to previous research showing high productivity, we determined that our short hydroperiod site was a small carbon sink (net ecosystem production = -19.55 g C m^-2 yr^-1). At our long hydroperiod site, we found no significant difference between dry season and wet season NEE. This was due to the short period of soil aeration during the dry season. These preliminary findings have led to additional monitoring at both sites to quantify and assess the long-term impacts of hydrologic regime on carbon exchange. This project is a foundational study for these ecosystems prior to the initiation of the Comprehensive Everglades Restoration Plan (CERP). The CERP will attempt to restore natural sheet flow to the Everglades, which may have a significant impact in altering the system's carbon dynamics. Further investigation is needed to determine the long-term effects of restored sheet flow to this ecosystem.