The development and application of complementary variables (potential and flux) for modeling environmental systems are illustrated for the hydraulic and dissolved oxygen subsystems of laboratory microcosms. These sediment-water, semi-continuous flow microcosms were used to determine nutrient interchange and mercury interactions under lighted (aerobic) and dark (anaerobic) conditions. The approach of using complementary variables to describe such systems forces a more complete conceptual understanding of the system and better attention to those parameters (many of which are unknown) requiring measurement. Complementary variables are incorporated into basic linear component equations which describe basic processes of energy transfer and transformation. The components are interconnected through the use of bond graphs and reduced through topographic and matrix techniques to state space system equations. A transfer function is determined from the state equations and from time domain analysis of the system output. These two expressions of the transfer functions are used to determine component values.
Hill IV, James, "Component Description of Sediment-Water Microcosms" (1974). Reports. Paper 417.