Latent and sensible heat fluxes in a short hydroperiod Everglades wetland

Background/Question/Methods

Little is known of energy balance in low latitude wetlands where a year-round growing season and a climate defined by wet and dry seasons are likely to induce dynamics much different from those observed in temperate or high-latitude wetlands.  The Florida Everglades is a highly managed subtropical wetland (>6000 km²) that exerts a substantial influence on the hydrology and climate of the South Florida region.  However, the effects of seasonality and active water management on energy balance in the Everglades ecosystem are poorly understood.  In January 2008, an eddy covariance and micrometeorological tower was established in a short hydroperiod Everglades marsh, and data were collected from this site over a two year period.  Energy balance and micrometeorological data were used to determine the dominant environmental controls on latent energy (LE) and sensible heat (H) fluxes, as well as the effects of seasonality and water management on these turbulent energy balance parameters.

Results/Conclusions

Regression analyses indicated that net radiation was a strong driver of LE and H fluxes across nearly all seasons and years (R²_adj = 0.48-0.79, p<0.001).  The 2009 dry season LE data were inconsistent with this relationship because a soil moisture deficit limited LE fluxes (R²_adj = 0.08, p<0,001), likely by forcing stomatal closure in the sedges and grasses dominant at this site.  Residuals analyses showed that H fluxes were also significantly related to soil volumetric water content (VWC), water depth, and air temperature, while LE fluxes were significantly related to VWC and vapor pressure deficit (p<0.05).  Seasonal variation in turbulent fluxes was observed, such that both fluxes were of similar magnitude during the dry season, but LE was as much as four times higher than H in the wet season.  As such, the Bowen ratio was high for much of the dry season (1.5 to 2.4), but relatively low (<0.7) in the wet season.  These data indicate that seasonality differentially affects LE and H fluxes in this short hydroperiod Everglades marsh.  During periods of adequate moisture availability environmental drivers can predict turbulent fluxes.  However, drought stress, which can be induced by water management, appears to decouple LE fluxes and microclimate.