6. Conclusions

[52] On the basis of the results from this study, several conclusions can be drawn regarding wetland surface energy budgets and estimation of changes in heat energy stored in a column of wetland surface water. These conclusions likely are directly transferable to other humid subtropical wetlands dominated by open water, saw grass and rush vegetation communities.

[53] 1. Changes in heat energy stored in wetland surface water were a substantial component of the surface energy budget more frequently in the winter than in the summer. This result is explained by the magnitude of solar radiation during the winter and the control of air temperature on water temperature. Specifically, solar radiation during the winter was relatively low and air temperature changes were more variable, creating water temperature changes that were more variable. Interaction of these two factors resulted in fluxes of stored heat energy in wetland surface water that approached the magnitude of net radiation more frequently during the winter than in the summer.

[54] 2. The magnitude of changes in heat energy stored in wetland surface water generally decreased as surface energy budgets were upscaled temporally. Daily fluxes of stored heat energy accounted for 20% or more of the magnitude of mean daily net radiation for about 40% of the data examined here. Weekly fluxes of stored heat energy were 20% or more of the magnitude of mean weekly net radiation for about 20% of the same data examined here. This result is explained by fluxes of stored heat energy being inversely proportional to time, such that larger lengths of time result in smaller fluxes of stored heat energy.

[55] 3. Air temperature changes can be used to approximate changes in water temperature and, ultimately, fluxes of stored heat energy in wetland surface water through the application of a convolution integral with a regression-defined transfer function. This method was most accurate at sites where surface water temperature changes mostly were controlled by air temperature changes rather than water management activities, evaporative cooling or other heat exchange processes. The accuracy of computed fluxes of stored heat energy also increased when 30 min convolution results were composited to net daily values.

[56] 4. Heat energy exchanges more rapidly at the air-water interface over open water sites than at vegetated sites, as suggested by a statistically significant difference between the values of regression-defined thermal exchange coefficients at open water and vegetated sites. Several mechanisms may explain this difference, including enhanced wind-driven and thermal convective mixing at open water sites due to less vegetational surfaces providing roughness obstacles.

[57] 5. Energy fluxes from rainfall generally were minimal compared to mean daily fluxes of net radiation, indicating that energy fluxes from rainfall probably do not need to be considered within surface energy budgets at daily and larger time scales.

[58] 6. Wetland vegetation was not dense enough to create a large equivalent surface water reservoir for energy. The equivalent surface water depth of the maximum vegetation density was about 4 cm. This depth was minimal considering water depths in the Everglades frequently exceeded 1 m, and suggests changes in heat energy stored in wetland vegetation likely can be ignored with little error in surface energy budgets at daily and larger time scales.