Among the biological methods of analyzing surface waters, saprobiological analysis occupies one of the main places. Progressive pollution of the aquatic environment prompted scientists in the last century to compare the flora and fauna of polluted and uncontaminated water bodies, and to identify the role of hydrobionts in the transformation of a variety of substances entering into internal and external water bodies with human waste. The deterioration of water quality in many water bodies and streams has put researchers in the task of developing systems for assessing the degree of pollution by biological indicators.
The boundary between two groups of waters: the last zone of limnosaprobic waters (polysaprobic) - and the first zone of eusaprobic, from the point of view of the oxygen regime, is the boundary between aerobic and anaerobic conditions.
These are drains or natural waters, to which the notion of saprobity is not applicable
In accordance with the division of all waters into saprobity zones among the population of water bodies, there are indicator or demonstration species that characterize certain zones of saprobity:
In the system of saprobiological analysis there are specially developed lists of indicator organisms with indication of their belonging to a certain zone of saprobity.
To apply this method, the results of qualitative and quantitative treatment of various communities of hydrobionts are needed. Fill the list of species with an indication of their abundance on a seven-point scale.
Then, the scores of the oligosaprobic and ß-mesosaprobic zones and the scores of the a-mesosaprobic and polysaprobic zones are summarized, and a graph is constructed that reflects the ratio of the sums of scores of all saprobity zones along the river cross-section.
As a result of the connection of the corresponding points by straight lines, a figure consisting of 4 parts is obtained, which shows the ratio of the saprobity indicator types at each station.
In addition to visual assessment with assignment of abundance scores, specific values of abundance and biomass of indicator species in the sample are used as values. The index of saprobity in the xenosaprobic zone is 0-0.5; In the oligosaprobic zone 0.5-1.5 (pure water); In the in-mesosaprobic - 1.51-2.50 (water of moderate pollution), a-mesosaprobic - 2.51-3.50 (heavily polluted), polysaprobic zone 3.51-4.50 (very heavily polluted). The conclusion about the level of water pollution at the alignment is made on a six-point scale.
From biological methods, the most widely used system for assessing the state of water according to the index of capacity (trophy-saprobity). The capacity indicates the adaptability of hydrobionts to various influences, thanks to the existence of physiological and biological mechanisms developed in phylogeny.
The degree of water pollution, adequate to the availability of correspondingly existing hydrobionts-indicators, is determined on the basis of experimental and field studies.
A promising system for monitoring the state of aquatic ecosystems is the assessment of the level of accumulation of various substances in organisms of hydrobionts.
The most promising objects for assessing the state of water and ecosystems, in our opinion, are algae - the primary and very informative link of the trophic chain. In addition, unlike other groups of hydrobionts, algae occur almost everywhere, where there is water.
When the content of organic substances in the water changes, the species composition of the algae changes and, as a rule, their abundance, that is, the species that definitely react to changes in environmental conditions are indicator species.