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Environmental drivers of evapotranspiration in a shrub wetland and an upland forest in northern Wisconsin
Author(s) -
Mackay D. Scott,
Ewers Brent E.,
Cook Bruce D.,
Davis Kenneth J.
Publication year - 2007
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2006wr005149
Subject(s) - wetland , evapotranspiration , eddy covariance , environmental science , shrub , hydrology (agriculture) , canopy , phenology , ecosystem , latent heat , atmospheric sciences , canopy conductance , growing season , vapour pressure deficit , ecology , geography , transpiration , meteorology , photosynthesis , geotechnical engineering , geology , engineering , biology , botany
To improve our predictive understanding of daily total evapotranspiration ( E T ), we quantified the differential impact of environmental drivers, radiation ( Q ), and vapor pressure deficit ( D ) in a wetland and upland forest. Latent heat fluxes were measured using eddy covariance techniques, and data from four growing seasons were used to test for (1) environmental drivers of E T between the sites, (2) interannual differences in E T responses to environmental drivers, and (3) changes in E T responses to environmental drivers between the leaf expansion period and midsummer. Two simple E T models derived from coupling theory, one radiation‐based model, and another using mass transfer were used to examine the mechanisms underlying the drivers of E T . During summer months, E T from the wetland was driven primarily by Q , whereas it was driven by D in the upland. During the leaf expansion period in the upland forest the dominant driver was Q . E T from the wetland was linearly related to net radiation using coupling coefficients ranging from a low of 0.3–0.6 to a high of 1.0 between early May and midsummer. Interannually, E T from the upland forest exhibited near linear responses to D , with an effective reference canopy stomatal conductance varying from 1 to 5 mm s −1 . The results show that E T predictions in northern Wisconsin and other mixed wetland‐upland forests need to consider both wetland and upland forest processes. Furthermore, leaf phenology effects on E T represent a knowledge gap in our understanding of seasonal environmental drivers.