| Abstract: | The concept of the distribution coefficient is invoked to rationalize the observed dependence of the watershed residence time of a radionuclide on its nature. A mathematical model is presented to show that this residence time is proportional to the dimensionless field distribution coefficient of the radionuclide. The proportionality constant, β, is defined as the ratio of the volume of rain-impacted soil in the watershed and the annual volume of rainfall in the watershed or expressed as the ratio between the water penetration depth in soil and the annual thickness of water above the soil surface. An empirical evaluation of β supports our assumption of its constancy in a given watershed. The described model may be very useful in deciphering the impact of atmospherically delivered pollutants on watershed quality. Expressions are also derived to estimate the value of soil erosion constant using naturally occurring radionuclides. |
