Determination by stable isotopes of underground inflow and outflow and evaporation of young artificial groundwater lakes

The evaporation rate as well as the subsurface inflow and outflow rate of two young artificial groundwater lakes, which did not reach their isotope steady state during the period of investigation, could be determined by using stable isotopes. The main results of the research performed, which are also important for stable isotope studies of natural lakes, can be summarized as follows: (a) deuterium is better suited to determine a component of the water balance of a lake than 18O, because the same error of the kinetic separation induces a much larger error in the case of 18O than in the case of D; (b) stable isotopes are above all suited to determine the inflow and outflow rate of a lake; (c) large errors can arise if the surface lake water temperature, which has to be known for the calculation of the normalized humidity, is not measured directly; (d) as the evaporation rate cannot be determined with an accuracy better than 30% by using stable isotopes in most cases, other methods should be preferred for determining the evaporation rate of a lake. (author)