Sapropels are made of the components, which are interacting with each other – organic and mineral fraction as well as the living organisms.
A. The organic matter of sapropels
The organic matter of sapropels may be defined in various ways:
• the undissolved remains of hydrobionts and the colloidal autochthonic substances, which are brought in the terrigenous water flow. It is a combination of biological and organic components’ ;
• low-molecular-weight organic compounds, biopolymers, and adsorption composites with minerals.
B. Compounds contained in the composition of sapropel
Sapropels are combustible fossils, which are made of various compounds of chemical groups. The most rational use of the sapropel is determined depending on the content of various group compounds in its organic mass.
Division of different compound groups in the organic mass of sapropels is based on the methods of its fractionation; therefore, depending on these methods several classifications and variations of separate components in the composition were created.
The composition of the organic mass of sapropel divides as follows:
• substances dissolving in water;
• easily hydrolysable substances, including, humic acids and fulvic acids;
• residue, which is not hydrolysable.
C. Chemical composition of the mineral matter in sapropels
The combination of the mineral components in the sapropel is an important diagnostic indication in its classification002E. Formation of the mineral components in the sediments of lakebeds is related to the terrigenous flow, the sequential sedimentation of minerals as well as the biological and chemical sedimentation of mineral ions dissolved in the water body. Usually the minerals of terrigenous water flow is quartz (SiO2), dolomite (CaMg(CO3)2), silicate and alumosilicate (feldspars, hydromica, chlorites, kaolinite, etc.). As a result of biochemical processes, calcite and aragonite (carbonates Mg, Ca, Sr, Ba, Fe, Mn), pyrite (Fe2), gypsum (CaSO4-2H2O), hematite (Fe2O3), and marquisate (FeS2) accumulate in sapropels of the water bodies.
The brown oxides are dominating the iron minerals – triad iron oxyhydroxides, goethite and hydrogeothite (FeOOH), in rare occasions – iron pyrite and phosphates, very rarely – siderite (FeCO3). The iron sulfate heptahydrate minerals or common for the deepest layer of the sapropel, in section where siderite and part of the iron phosphates are formed. It is related to the decomposition and deoxidization conditions of the organic matter. Iron phosphates like the iron brown oxides are common in all of the genetic types of sapropels – the content of iron phosphates increase when the content of carbonates decreases. Content of these phosphates in carbonatic sapropels is 0.4%, mixed sapropels – 0.8%, and silicon containing – 1.4%. The formation of mineral sediments is common to the final phase of ice age. During the Holocene, the dynamics of the formation of the mineral fraction of organic-mineral sapropels was determined by the flow of the water body, while in nowadays it is the use of the area around the water body for agriculture. The proportion of the regional deviation (SiO2>Al2O3>Fe2O3, K2O>Na2O) may be related to the conversion of previous sediments.
D. Living organisms in the composition of sapropel and its biological activity
The biological component in freshwater ecosystems is formed by hydrobionts and their life cycle facilitate active accumulation of the organic matter in the ecosystem in form of sapropel sediments.
The research shows that sapropels contain an extremely large amount of microorganisms – in 1 g of fresh sapropels there are 12 billion microorganisms in its top layer. In the lower layers, starting from around 0.6-1.0 m from the lakebed surface the amount of microorganisms decreases.
Antibiotics and sulfanilamide in sapropels are synthesized by fungus and actinobacteria, while vitamins by bacteria and algae. Azobacteria facilitate transformation of hydrogen in form, which is accessible by plants.
Various bacteria and water fungus groups are specific destructors (they decompose the necrotic hydrobionts down to separate fragments) of the organic matter and take part in biochemical processes – synthesis of the secondary organic matter of sapropels (humification).
The living organisms contained in sapropels are involved in various processes for transformation of substances, not only forming the sapropel sediments, but also regenerating and preserving them. Thanks to the microorganisms, mineralization and synthesis of the organic matter takes place in sapropels; they determine composition of various gases (hydrogen sulfide, ammonium, methane, and others) and their content in sediments. Biologically active and antibacterial substances accumulate in the sediments and they play a big role in balneology. Also some physical-chemical properties in sapropels are determined by the biochemical substances produced by microorganisms.
The list of substances that can be found in sapropel is given below:
The amount of given substances may vary in different sapropels.
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