WETLAND EVAPORATION AND ENERGY PARTITIONING - INDIANA DUNES NATIONAL LAKESHORE

For most wetlands precipitation and evapotranspiration are the major c omponents of water gain and loss. However, studies of the hydrology of wetlands largely ignore evaporation, or calculate it by difference or some very simple measure. As part of an integrated study of the hydro logy and ecology of wetlands in the Indiana Dunes National Lakeshore, evaporation was measured directly as its energy equivalent, the latent heat flux, using eddy correlation techniques for a 10 day period in J une 1994. In addition, data were collected on the other surface energy balance fluxes (net all-wave radiation and sensible heat flux), and a ncillary meteorological variables (wind speed and direction, temperatu re, pressure, relative humidity, solar radiation and water depth). Ove rall, latent heat flux dissipated 48% of the available radiant energy, storage heat flux 35%, and sensible heat flux 17%. A simple hysteresi s model for the storage heat flux was developed which performed extrem ely well. Proximity to Lake Michigan resulted in evaporation rates clo se to the equilibrium rate (average Priestley-Taylor alpha = 1.035), w hich were affected strongly by net all-wave radiation. Three commonly used models of evaporation, Penman, Priestley-Taylor (alpha = 1.26) an d equilibrium (alpha = 1.0) are evaluated. The relative success of the equilibrium model, with its limited data requirements, offers great p otential for longer-term modeling of water and energy exchanges in thi s type of wetland environment.