Systems analysis is the quantitative study of empirical and functional relations of a complex of interacting entities that comprise a specified system. Complex ecosystems can be properly understood only by utilizing the techniques and rationale of systems analysis. The multidisciplinary study of the Lake George, New York, ecosystem is given as an example of a comprehensive study in which geology is an integral part. Systems analysis involves the formulations of models, which are simplifications of the “real world” ; the Lake George study has used a progression of such models, representing different levels of abstraction.
Conceptual models have been used to represent the more important components of the ecosystem and the principal transfer paths among these components; a comprehensive conceptual model has proved useful as a graphical representation of the interrelations among individual research projects. Data from the Lake George sampling program and from concomitant laboratory studies have led to the development of mathematical models of biologic, physical, and chemical processes. These have been expressed in computer logic and used in simulation studies; they have been evaluated by comparing predicted values with data collected in the field. Those models, such as the phytoplankton and hydrologic models, that yield realistic results and seem to be valid representations of actual processes are being analyzed in detail to determine how sensitive they are to various ecosystem changes, including man-induced effects. By combining functional models into a comprehensive ecosystem model, we can begin to forecast future consequences of management decisions and can apply the knowledge gained from all the associated studies in developing guidelines for environmental quality.