Published: Jan 1988
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Ecosystems can be regarded as complex biogeochemical systems maintained in a state of thermodynamic nonequilibrium by the flow of materials and energy. The state of such a system at any given time is generally assumed to be characterized by a finite set of measurable quantities. If these variables are taken to be the components of a vector, the instantaneous state of an ecosystem can be represented by a single point in an abstract multidimensional space. As an ecosystem undergoes changes in state, changes in the position of the corresponding vector will result, tracing out a state trajectory over time.
Within a state space representation, the response of an ecosystem to a perturbing influence, such as a toxicant, can be viewed as a displacement of the state vector away from its unperturbed trajectory. Such an approach was used to analyze data from a study of the response of experimental ponds and microcosms to chronic additions of a coal-derived synthetic oil. Ecosystem-level response surfaces and dose-response curves were derived based upon the average separation (distance of displacement) of exposed ecosystems relative to controls. The results exhibited patterns analogous to those observed in classical toxicology based on organismal response and could be used to define acceptable exposure conditions. The state space approach described here provides a coherent and objective framework for summarizing a large multivariate data set, and it should be of general use in providing both qualitative and quantitative descriptions of the behavior of perturbed ecosystems.
state space analysis, ecotoxicology, microcosms, ponds, synthetic oil
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN