Тезисы докладов

Водные экосистемы

Even though the freshwater environments comprise less than 0.01 % of the earth's water, the rivers, lakes and the wetlands exhibit some cases of high biodiversity. Nevertheless, the extent of impoverishment globally of the aquatic environments and great decreases in biodiversity in the recent decades have received much less attention than those in the terrestrial environments, particularly in the tropics. The models of planktonic biodiversity may be broadly applicable to the biodiversity of many aquatic ecosystems. An understanding of species richness and productivity is crucial to understanding of biodiversity in lakes. Also, biodiversity is a key measure of environmental quality in lake ecosystems. It is an indicator of both ecosystems structure (species richness, heterogeneity) and of exergy, i.e. the extent of energy dissipation through the processes of respiration, excretion and egestion. Exergy is a system-oriented characteristic, which is a holistic indicator of both the ecosystem integrity and ecosystem functioning. Both the ecosystem structure and exergy are likely to decrease as eutrophication accelerates.

Biodiversity measurements appear to enhance predictability, which is inversely related to temporal and spatial variations in ecosystem properties. Recent studies show that the consequences of biodiversity tend to persist for longer durations: up to 40-80 generations of dominant organisms. Biodiversity appears to be linked through complex, causal relationships with physical stresses and habitat heterogeneity. Both, immigration and extinction of species, as well as sampling inadequacies, as indicated in the short-term studies on zooplankton, will lead to underestimates of biodiversity.

The use of palaeo-ecological and radioisotope dating techniques, for analysing the core samples from the lake sediments, allows to identify and make an inventory of historical changes in biodiversity over longer time periods. An inherent problem, however, is that only a select set of organisms leave a trace in the sediment records. Such studies on the past history can refine the model predictions for future trends. However, caution needs to be exercised to ensure that the sampling of the sediments is representative of the both 'localised deposition' and that reaching from the lake's bays.

The case studies of lakes in the United States and Europe indicate that factors which adversely affect biodiversity are invariably related to: 1). the lake eutrophication, i.e. nutrient-related increases of production; 2). overstocking of lakes with fish; 3). overfishing; 4). biological invasions; and 5). the anthropogenic influences (climate, UV-B radiation, acidification). Lake restoration studies testify that an increase in planktivorous fish can cause significant top-down effects, leading to drastic changes in diversity of zooplankton. Also, eutrophication related alteration in the macrophytic vegetation have been demonstrated to cause changes in biodiversity. Environmental extremes (e.g. Antarctica), isolation and floods can influence the species richness, and thus also their biodiversity.

Примечание. Тезисы докладов публикуются в авторской редакции

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