Closing the ecosystem energy balances of everglades fresh water marshes

Background/Question/Methods Anthropogenic forces have caused considerable alterations to Everglades National Park over the past century.  The hydrologic regime has been changed for flood control and water management associated with agriculture and increased urbanization in the south Florida region.  These water management practices may result in rapid alterations of the water level of fresh water marshes (40 cm changes in water table depth over 4 hrs have been reported in these systems).  These rapid changes in hydrology are expected to have a significant effect on marsh ecosystem energy balance.  In the spring of 2008 we established eddy covariance towers in short and long hydroperiod freshwater marshes of the Everglades National Park to test how long and short hydroperiod effect ecosystem energy balances.  We hypothesized that long hydroperiod energy balance would be controlled by latent energy exchange while short hydroperiod energy balance would be controlled by sensible energy exchanges. 

Results/Conclusions Initial results of our study showed poor correlations between net radiation inputs into the systems and energy balance components using standard protocols. Energy balance closure was 19% and 56% for the long and short period marshes respectively.  We determined the poor energy balance closure for these systems was incomplete estimation of the energy holding capacity of water.  To account for this we added an additional variable to the energy balance equation, G_w (heat flux through water).  The incorporation of Gw into the energy balance equations improved the energy budget closure by 47% on average for both systems.  Additional studies have also shown that energy budget closure was improved to over 90% closure rates when nighttime data was removed from the study.  Preliminary evidence shows that systematic errors may occur with standard net radiation sensors in wetland systems. In these systems, condensation is prevalent at night and standing water may limit the measurement of emitted longwave radiation from the surface.  As we develop a more rigorous means of measuring energy dynamics in Everglades freshwater marshes, we are beginning to determine seasonal patterns and drivers that control water and energy fluxes for this rapidly changing ecosystem.  Developing this foundation is imperative due to the pending changes in the hydrological regime that are expected with the reintroduction of historical flow into the Everglades as part of the Comprehensive Everglades Restoration Plan.