Organic substances in waters of sapropelic lakes(Tomsk Region)

Organic substance samplesfrom the waters of 20 sapropelic lakes, located in Asino, Zyriansk, Tomsk, Kozhevnikovo, Shegarka and Krivosheino regions of Tomskoblast in the floodplains of the Ob, the Tom, the Chulym, the Kiya, the Shegarka and the Chet Rivers were studied. Lake waters primarily havealkalescent, alkaline and even neutral geochemical environments (pH=6.88-8.46), however, an oxidizing environment with Eh value rangingfrom +32 to 237 microvolt can also be observed. Only in tuff-like sapropelic overgrown lakes there is a reducing environment (Eh ranging from-43 to -82 mV). High organic substance concentration was determined in sapropelic lake waters, which in its turn, colours the water into theyellow-brownish. The correlation between the organic substance and biogenic elements content and lake water mineralization was determined.The maximum concentration in waters with mineralization ranges from 100 mg/l to 400mg/l, while the minimum one - with mineralization upto 100 mg/l and over 400 mg/l. The following results were established: in waters with mineralization up to 100 mg/l the atmogenic source ofchemical elements prevails; when mineralization is of 100-400 mg/l the biogenic source prevails; with mineralization of more than 400mg/l thelithogenic source is prevalent. Water enrichment by organic compounds is the result of high biological lake productivity. Besides aquatic vegetation,another characteristic feature of such lakes is a big amount of plankton, including phytoplankton, such as flagellar and diatomaceous algae,and zooplankton - infusorias, daphnias and cyclops. There is numerous and various microflora in the waters of sapropelic lakes, where the totalnumber of microorganisms includes 0.04 -2.6 mln. cells in 1 ml of water. The sapropelic formation behaviour in such lakes is based on the trophiclake conditions. The production processes of organic substances dominate their decomposition in eutrophic lakes, while in dystrophic lakes,conversly, the decay of animal and vegetation remains is prevalent. The dissolved organic substance and total nitrogen content, the (Na+K) to(Ca+Mg) ratio, and the oligotrophy index (the ratio of oligotrophic bacteria to the number of microorganisms growing in the plain agar) showthat the investigated lakes belong to the eutrophic type. Thus, such lakes have favourable conditions for the formation of sapropelic accumulations,as this accumulation process of organic substances is prevalent to its decay in these lakes.

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