EVAPOTRANSPIRATION RATES FROM WETLANDS WITH DIFFERENT DISTURBANCE HISTORIES - INDIANA DUNES NATIONAL LAKESHORE

This study examines the effects of different disturbance histories, sp ecifically patterns of ditching and drainage on wetland evapotranspira tion rates for two sites within the Indiana Dunes National Lakeshore, Indiana, USA. The effect of drainage at the disturbed site is to lower the water table and to reduce the depth and duration of inundation. E vapotranspiration was measured as its energy equivalent, the latent he at flux, within the framework of the surface energy balance using the eddy correlation approach. Results show that when standing water is pr esent at each site, there is very similar flux partitioning; the laten t heat flux accounts for approximately 50% of the net radiation (appro ximately 3.5 mm d(-1)), storage heat Bur 30%, and sensible heat flux 2 0%. When the disturbed site has no standing water, evapotranspiration rates are maintained at, the same level (3.5-3.75 mm d(-1)), but the s torage heat flux drops significantly, and the sensible heat flux is en hanced. Excellent results are obtained with the Penman Monteith evapot ranspiration model using a very small surface resistance (5 s m(-1)) w hen there is no standing water. Although the absolute magnitudes of th e results reported are directly relevant only to similar sites in the Midwest USA in summer, the processes and controls described are repres entative of wetlands located near large water bodies (like Lake Michig an) subjected to diurnal lake (sea) breezes, with vascular vegetation, and a water table at or very close to the surface.