WHAT DO YOU GET WHEN YOU CROSS A HYDROGEOLOGIST, GEOCHEMIST, PHYSICIST, PLANT PHYSIOLOGIST, AND A GRASSLAND ECOLOGIST: AN INTERDISCIPLINARY PROJECT IN THE NEBRASKA SAND HILLS
Groundwater measurements in the wet valley support previous work that indicate significant upward, but variable, vertical gradients ranging from 0.023 to 0.073. Evapotranspiration (ET) rates were initially about 3.5 mm/day and decreased almost linearly to about 0.5 mm/day by the end of the first experiment. At the beginning of the second experiment ET was nearly 1.0 mm/day and increased linearly to about 5.0 mm/day. The dry valley site is characterized by variable downward vertical gradients ranging from 0.004 to 0.014. ET rates in the dry valley in mid-September were 0.5 mm/ day and were zero about 10/17/02. During the spring, ET was variable, but had a mean of 0.5 mm/day and a generally progressive increase after 4/20/02. Individual daily values were as high as 4.0 mm/day.
Our preliminary results indicate that the biosphere and groundwater are strongly coupled in the wet valley, but less so in the dry valley. Our measured peak ET rates of about 3.5 mm/day from the wet valley are similar to calculated potential evapo-transpiration (PET) rates of between 3.4 and 4.2 mm/day for the same time of year. This suggests that calculated PET may be representative of wet valleys. However, the PET values are not representative of the more extensive dry valleys and related uplands in the Sand Hills.