Seasonal evapotranspiration patterns in mangrove forests

Abstract

Diurnal and seasonal controls on water vapor fluxes were investigated in a subtropical mangrove forest in Everglades National Park, Florida. Energy partitioning between sensible and latent heat fluxes was highly variable during the 2004-2005 study period. During the dry season, the mangrove forest behaved akin to a semiarid ecosystem as most of the available energy was partitioned into sensible heat, which gave Bowen ratio values exceeding 1.0 and minimum latent heat fluxes of 5 MJ d À1. In contrast, during the wet season the mangrove forest acted as a well-watered, broadleaved deciduous forest, with Bowen ratio values of 0.25 and latent heat fluxes reaching 18 MJ d À1. During the dry season, high salinity levels (> 30 parts per thousand, ppt) caused evapotranspiration to decline and correspondingly resulted in reduced canopy conductance. From multiple linear regression, daily average canopy conductance to water vapor declined with increasing salinity, vapor pressure deficit, and daily sums of solar irradiance but increased with air temperature and friction velocity. Using these relationships, appropriately modified Penman-Monteith and Priestley-Taylor models reliably reproduced seasonal trends in daily evapotranspiration. Such numerical models, using site-specific parameters, are crucial for constructing seasonal water budgets, constraining hydrological models, and driving regional climate models over mangrove forests.

Approximations of stand water use versus evapotranspiration from three mangrove forests in southwest Florida, USA

“…Integrating stable isotope studies with sap flux studies are important next steps in understanding how water sources are partitioned seasonally (e.g., Ewe et al, 2007) and water use patterns are altered with salinization. For example, for every 10 PSU increment in salinity, CO 2 uptake from the Shark River mangrove canopy decreased 5% (Barr et al, 2013b) through reductions in light use efficiency (gross ecosystem productivity divided by PAR: Barr et al, 2010); salinity undoubtedly affects stand-level transpiration as well (Barr et al, 2014), but we currently know very little about salinity effects in regulating water uptake by mangroves (Reef and Lovelock, 2014).…”

Spatial and temporal variability in spectral-based surface energy evapotranspiration measured from Landsat 5TM across two mangrove ecotones

“…Satellite images were confined to the dry season (November-May) because of a lack of cloud-free images during the wet season (May-November) when convective clouds begin to form. The distribution of images throughout the dry season provided a detailed inter-seasonal variability and span reported minimum (November-December) and maximum (May-June) surface energy balance fluxes (Barr et al, 2014). Under those circumstances, only cloud-free images from the dry season were used in this study and were not necessarily from the same year or spaced at regular intervals.…”

“…There have been few studies dedicated to modeling ET and surface energy balance in mangrove environments (Monji et al, 2002;Barr et al, 2013Barr et al, , 2014, despite a number of studies that have measured or calculated various biophysical parameters (i.e., leaf area index, water use efficiency, spectral indices) that are useful in estimating ET (see reviews by Green et al, 1998;Kuenzer et al, 2011). Even fewer studies have investigated the role of satellite remote sensing in modeling surface energy balance and ET in mangroves (Jiang et al, 2009).…”

“…Exhaustive research has investigated energy balance and ET in south Florida (German, 2000;Douglas et al, 2009;Schedlbauer et al, 2011;Barr et al, 2013Barr et al, , 2014. Many of the referenced studies utilized expensive meteorological equipment in the form of eddy-covariance towers to measure changes to solar irradiance, temperature, wind velocity, and water vapor.…”

“…Using the sophisticated equipment, surface energy balance models and ET models, the south Florida studies identified site-specific seasonal patterns with the greatest monthly average ET (∼5-6 mm day −1 ) occurring during the early summer (May-July) and the lowest ET (∼2-3 mm day −1 ) in early winter (German, 2000;Barr et al, 2013). Excluding the recent work by Barr et al (2013Barr et al ( , 2014, the majority of the measurements originate from vegetated environments outside the mangrove zone. A regional-scale evaluation of the spatial variability of ET across a coastal mangrove community using satellite remote sensing will provide a better understanding of the variability in energy and water budgets associated with mangrove productivity and their response to damage and recovery from tropical storms.…”