Abstracts

Water Ecosystems

One of the salient features of open biological systems is to maintain their structure and basic functioning parameters under external impact. In this manner the natural biota with utmost precision sustains environment in the state adequate for life. Yet in the global ecology there is increasing evidence (climate change and ozone layer change, growing concentration of atmospheric СО2, dynamics of the vegetation cover and of the biosphere on the whole) that the biota and its environment lose stability and this can cause catastrophic consequences. This poses a very relevant question of investigating ecosystem response to anthropogenic impact. The work quantitatively analyzes responses of ecosystems with different structural organization to external impact. Under analysis are mathematical models of four closedness types: unclosed, partially closed in terms of dying off, partially predator-closed and fully closed. The system sensitivity coefficient (the ratio of system response to factor variation in the inflow) and primary production were used as impact compensation. This made possible to derive a recurrent formula to calculate the sensitivity coefficient for ecosystems with different length of the trophic chain. Zero and close-to-zero values of the sensitivity coefficient are indicative of high impact compensation. The sensitivity coefficient value equal to one suggests inability of the system to compensate the external impact. Analysis of mathematical models showed that the degree of compensation of external impact by the system depends on the closedness of ecosystem, length of trophic chain and regulation type of the system. E.g. for the systems with "bottom up" regulation the sensitivity coefficient is zero for all closedness types. I.e. the steady-state concentration of the limiting substrate does not depend on its input concentration and the system fully compensates the external impact. For the systems with «top-down» regulation the lower component is not limiting already, and such systems cannot fully compensate the impact. In addition, the fully open systems have been found to better compensate the external impact than the closed ecosystems and the degree of compensation of external impact increases with the length of trophic chain. The work has been done with support of grant KFN-RFFI № 99-04-96017.

Note. Abstracts are published in author's edition

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