Systems Analysis of 134Cesium Kinetics in Terrestrial Microcosms

Laboratory experiments were conducted to determine patterns and rates of ¹ 34Cs exchange in microecosystems composed of different combinations of radioactive leaf litter, soil, microflora, millipedes, and aqueous leachate. Rate constants were determined by fitting models to data with an analog computer. Simulations with the models permitted comparisons of different microcosms in terms of time to radiocesium equilibrium, steady state concentrations, concentration factors, input and output fluxes, turnover rates, and stability. Rate constants varied with different compartment combinations, indicating both qualitative and quantitative differences in the cesium exchange patterns within different systems. This result is generalized: transfers of energy and matter in ecosystems are functions of networks which define intercompartmental interactions; internal coupling should be considered a significant variable in investigation of ecosystems processes. Points of particular interest derived from the computer simulations are (i) organism concentration factors for a material may vary in different systems, depending upon how the organism is coupled to other compartments; (ii) total flux of a material in a steady state system may vary considerably from that in another system which receives identical input; (iii) material turnover within compartments and in the system as a whole tends to increase as more compartments are added; and (iv) stability of material concentration does not appear to increase with system complexity.