Metabolic power of aquatic ecosystems as a measure of their stability to external effects

Abstract

117 The problem of stability of aquatic ecosystems has become urgent due to intensification of human eco� nomic activity. The limits of stability of aquatic eco� systems determine the highest possible anthropogenic loads, an excess of which can lead to irreversible deg� radation of ecosystems. Thereupon stability is consid� ered as one of the main characteristics of aquatic eco� systems. The notion of stability in scientific literature is diverse and vague to a certain degree. In one review [1] 163 notions of ecological stability based on 70 differ� ent concepts of stability were analyzed. In our work we do not consider the problem of stability in detail but touch upon the assessment of stability in different regimes of functioning of aquatic ecosystems. As was published earlier [2, 3], the ratio of destruc� tion to primary production can be considered as a measure of thermodynamic order of the ecosystem and the rate of changes of the ratio of destruction to primary production can be considered as a thermody� namic criterion of evolution of the ecosystem state. Numerous experiments which have been conducted over 20 years in field models (mesocosms) have dem� onstrated that the known principles of functioning of dissipative systems can be applied for description of the evolution of the state of aquatic ecosystems sub� jected to the impact of hazardous pollutants [4–9]. Analysis of the dynamics of production and destruc� tion processes in the phase space { R/P; Δ(R/Р) ⋅ Δt –1 }, where R is destruction and P is the gross primary pro� duction, made it possible to determine the following main patterns of the ecosystem functioning on the basis of these criteria: undisturbed ecosystems have the minimum density of the phase space; the density of the phase space increases in response to the external effect; the transition of the ecosystem from one state to another occurs after bifurcation not gradually but spasmodically; the presence of attractors has been revealed in the phase space; and a shift of the impact stationary region in the phase space along the R/P axis is observed [10, 11].