Water loss from a natural pond through transpiration by hydrophytes

The water loss to the air from a natural pond in which hydrophytes are growing consists of two parts, evaporation and transpiration. As both parts vary directly with the same meteorologic factors, the total loss, evapotranspiration, can be computed by means of a simplified mass transfer equation in which the only coefficient has been evaluated for that pond by means of a water budget. In addition to the variation with meteorologie factors, transpiration occurs at different rates throughout the growing season, depending on the stage of growth. Evaporation is affected by the amount of vegetation present. The mass transfer coefficient varies in accordance with these conditions. By assuming that the coefficient during the dormant season represents losses by evaporation alone, a basis is obtained for estimating the coefficient representing evaporation during the growing season. The computed evapotranspiration minus the computed evaporation gives the water loss attributed to transpiration alone. (Key words: Hydrophytes; evapotranspiration; lakes; North Dakota)