Model-based analyses of the cesium dynamics in the small mesotrophic reservoir, Pond 4. I. Estimating the inventories of and the fluxes among the pond's major biotic components.

A model of cesium (Cs) dynamics among the principal biotic and abiotic components of an 11.4-ha impoundment is described. The model is derived from analyses of field measurements of Cs-133 concentrations in pond components for 500 days following the addition of 4 kg of stable Cs-133 to the system. This study differs from similar experiments in which radionuclides, or their stable analogs have been added to small ponds in that the biomasses of key pond components were also obtained. The Cs-133 concentrations and biomasses were used to compute the dynamics of Cs-133 inventories and fluxes among the pond components. The model permits interesting comparisons of Cs-133 transport and fate over time among the pond's abiotic components, primary producers, and two-orders of consumers. The importance of the submerged macrophyte and periphyton community in controlling the transport and fate of the added Cs-133 is quantified. Macrophytes intercepted much of the Cs-133 and slowed its ultimate sequestration by the sediments. The macrophytes' rapid absorption and slow release of Cs-133 prolonged the availability of the element to other pond biota. These data are being used within a subsequent paper to further develop the model into one in which the Cs-133 kinetics are described by transfer coefficients so that effects of changing environmental variables and remediation options can be explored.