Thermodynamic Orientors: A Review of Goal Functions and Ecosystem Indicators

Abstract

This paper reviews a number of goal functions or ecological indicators: emergy, exergy, ascendency, overhead, ratio indirect to direct effect and specific (structural) exergy. The paper illustrates that the various indicators or goal functions to a high extent are related. The paper discusses the difference between the use of maximum exergy storage, maximum exergy destruction and minimum entropy as goal functions. It discusses how maximum exergy destruction for ecosystem under development and minimum entropy for mature ecosystems both are consistent with the principle of maximum exergy storage for ecosystems in all phases of development. It would therefore be advantageous to apply the principle of maximum exergy storage as ecological goal function and indicator and use it in a formulation of a tentative fourth law of thermodynamics (see Jorgensen and Nielsen, Sect. 2.4). As a conclusion of the paper is proposed a number of useful ecological indicators for an intensive and extensive description of an ecosystem under development or a mature ecological system. Most probably it is necessary to apply several ecological indicators simultaneously to get a proper description of the ecosystem.