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Ecosystem specific yield for estimating evapotranspiration and groundwater exchange from diel surface water variation
Author(s) -
McLaughlin Daniel L.,
Cohen Matthew J.
Publication year - 2013
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.9672
Subject(s) - evapotranspiration , environmental science , hydrology (agriculture) , diel vertical migration , groundwater , stage (stratigraphy) , wetland , transect , aquifer , soil science , transpiration , ecosystem , atmospheric sciences , ecology , geology , biology , paleontology , geotechnical engineering , photosynthesis , botany
The White method, routinely used to estimate phreatophyte transpiration from diel groundwater variation, also provides measures of total evapotranspiration (ET) and groundwater fluxes in surface waters. Such applications remain rare, however, and critically require accurate representation of stage‐dependent variation in specific yield (S y ). High‐resolution stage data from three Florida swamps were used to evaluate different relationships between S y and stage (ecosystem specific yield, ESY). A discretized form, ESY D , assumes constant S y near unity for inundated conditions, applying soil S y for belowground stage and open water S y (S y,OW ≈ 1.0) for aboveground stage. A mixture approach, ESY M , applies a stage‐dependent interpolation between S y,Soil and S y,OW using stage‐area relationships and assumes rapid lateral equilibration between inundated and non‐inundated wetland areas. Finally, an empirical formulation, ESY RR , uses measured ratios of rain to rise to estimate stage‐specific S y . All formulations yielded reasonable ET rates (ET ≈ PET) at high stage; ESY D markedly overestimated ET (ET/PET > 3) at intermediate stage, whereas ESY M and ESY RR maintained ET/PET near 1.0. Estimated groundwater fluxes using ESY M and ESY RR correlated well with Darcy‐estimated flows, but were larger, likely due to uncertainties in Darcy parameters. Well transects across wetlands documented equal water elevation and diel variation across inundated and non‐inundated areas, verifying rapid equilibration that reduces S y and explaining overestimation by ESY D . However, equilibration area varied within and among wetlands, explaining observed differences between ESY M and ESY RR , and suggesting ESY RR may be preferred. Stage histograms followed the shape of ESY RR , highlighting reciprocal influences of ESY on stage stability. Copyright © 2012 John Wiley & Sons, Ltd.