Evapotranspiration Characteristics Distinct to Mangrove Ecosystems Are Revealed by Multiple‐Site Observations and a Modified Two‐Source Model

Abstract

AbstractA quantitative accounting of how mangrove ecosystems respond to tidal perturbations is needed to anticipate changes in these ecosystems when sea level rises. Here we use long‐term field observations and a two‐source ecohydrological model to reveal specialized characteristics of evapotranspiration (ET), soil surface evaporation (E), and canopy transpiration (T) in three subtropical mangrove ecosystems in southeastern China. Average wintertime ET observed in these three mangrove forests (2.6 mm day–1) was consistent with values for semiarid ecosystems, while average summertime ET (6.2 mm day–1) approached that observed in rainforests. By contrast, T fluxes were small year‐round, averaging 1.3 mm day–1 in winter and 2.5 mm day–1 in summer. Combining our results with measurements from three Florida mangroves, observed values of T ranged from 350 to 870 mm year−1, varying primarily with salinity, while T/ET increased exponentially from 30% to 70% with rising leaf area index. Simulations of half‐hourly ET and T using a modified two‐source model were highly correlated with eddy covariance observations of ET (I, index of agreement >0.93 at all three sites) and sap flow gauge‐based estimates of T (I = 0.93 at the Yunxiao site). Variations of T in mangrove ecosystems are distinguished from those in terrestrial forests mainly by the sensitivity of stomatal conductance to leaf temperature, with tidal and salinity effects superimposed. Our modified model accounts for these effects and therefore holds promise for improving our understanding of how mangrove ecosystems may respond to changing stress conditions under global warming and sea level rise.