by Galina LEONOVA, Dr. Sc. (Geol. & Mineral.), Vladislav BOBROV, Cand. Sc. (Geol. & Mineral.), Anna BOGUSH, Cand. Sc. (Geol. & Mineral.) and Anton MALTSEV, Junior Research Fellow, Sobolev Institute for Geology and Mineralogy, RAS Siberian Branch

Sapropel (<Gr. saprós, rotten, putrefying + pēlós, dirt or silt) is organic mud present in benthic sediments, a valuable raw material with many application domains in agriculture, industry, medicine and other areas. Although research scientists have been showing a long time interest in sapropels, these silts are not much in use for lack of credible information on their formative conditions, genesis, classification and chemical composition.

IN NATURE'S LABORATORY

Sapropels are found in the silt of stagnant bodies of water like lakes or ponds, old river beds and quiet seacoast inlets. Such organic mud is formed from plankton, a mix of dead benthic organisms, algae, aquatic plants (macrophytes) and also from organic matter (humus) and inorganic substances (clay, sand) carried in. All that is turned into sapropels through various biochemical, microbiological, mechanical and physicochemical processes.

Sapropels are akin to peats, though of finer structure. We also know of intermediate biogenic sediments, the peaty sapropels, found in shallow lacustrine waters overgrown with water plants. Such sapropels are high in

the remains, not decomposed in full, of water and land plants. In her monograph published in 1960 Dr. Nina Corde, expert in biostratification, ranked sapropels into those containing above 50 percent of organic matter and those low in it (from 4 to 50 percent).

Phyto- and zooplankton, or small water plants and animals, are playing a part in the formation of organic mud sapropels provided there are certain essential conditions for that, such as normal growth in a body of water, conservation of nondecomposed leftovers of organic matter in bottom sediments (chitinous, siliceous or carbonaceous mollusk shells and that sort of thing). Diverse planktonic organisms and proliferation of one particular species furnish adequate physicochemical conditions. Thus, blue-green algae (Cyanophyta) growing under aerobic (oxygen-rich) conditions in warm and shallow lakes and high in organic matter, give rise to cyanophytogenous sapropels rich in nondecomposed organic matter. Galina Leonova, one of the authors of the present article, has collected data on two small lakes, Dukhovoye and Kotokel, east and west of Lake Baikal, where such sapropels occur.

Certain lacustrine water plants (macrophytes) are likewise implicated; such macrophytes (like Naiadae for instance) are abundant in the littoral waters of shallow lakes, they often cover the entire floor turning it into a subwater meadow every now and then.

Sapropels as well as peat or turf take a long time to form according to Henry Potonier, a German paleobotanist and geologist, who found that more than a hundred years ago. This is confirmed by modern methods of instrumental analysis. Thus, the dating of lacustrine sediments by the radiocarbon method (by isotope ¹⁴C) shows they have been accumulating throughout the Holocene (for as long as 12,000 years), a period of excessive humidity. This study was made by Lubov Orlova, a doctoral candidate from the Sobolev Institute for Geology and Mineralogy. In the Western Siberian lakes we have explored, sapropels started taking body and form at different times: in Lake Kirek (Tomsk region), about 10,700 years ago; in Lakes Minzelinskoye, Bolshiye Toroki and Beloye (Novosibirsk region), in the Middle Holocene, i.e. 6,700, 6,600 and 3,400 years ago. Their accumulation rates in Siberian lakes during the 20th century have been evaluated by

Vladislav Bobrov, one of the authors of the present article, who took isotopes ³⁷Cs and ²¹⁰Pb to determine the age of the upper 10 cm sapropel layers. They were found to have low buildup rates in the 0.7-1.5 mm/yr range; for example, for Lake Beloye the figure was ~0.7 mm/yr; for Kirek, ~1.0 mm/yr; for Lakes Ochki and Dukhovoye (west and east of Baikal, respectively), ~0.8 and ~1.5 mm/yr.

TWO ASPECTS

We might as well note here that bottom sediments have been building up in most of the lakes of the earth's humid zone and also in some of the seas (like the Mediterranean and the Black Sea), and hence they are an object of close studies. Some research scientists suppose sapropel sediments must have produced material for carboniferous sedimental rocks, such as black and combustible shales, Paleozoic dull coals, and bituminous clayey shales. As Mikhail Zalessky, our paleobotanist, sees it, conglomerations of green (protococcal) algae have been a formative basis for pristine bioliths (biological stones), in particular, the Cheremkhovo sapropel coal (cheremkhite, a sapropel with alga remains) and the Kasyanovo coal deposit in the Irkutsk region (kasyanovite). Many researchers supporting the theory of organic origins of petroleum, postulate the plankton to be a major producer in maritime paleobasins. Such old deposits are viewed as source oil suites, and among these is the Bazhenovo suite (formation) in Western Siberia--its organic matter is composed largely of sapropel planktonogenous material.

Acad. Alexei Kontorovich (Trofimuk Institute of Oil-and-Gas Geology and Geophysics) says in his works that the amount of biogenic siliceous and carboniferous (planktono- and bacteriogenic) material is above 50 percent within the Bazhenovo formation in the central part of the basin. In deposits of the Kuonamo Cambrian suite in the eastern part of the Siberian platform (marine deposits of the Low and Middle Cambrian high in bitumen), according to Dr. Fabian Gourari (Siberian Research Institute for Geology, Geophysics and Mineral Raws), planktonogenous organic matter likewise predominates.

Stratigraphy data on lacustrine sapropels formed during the Holocene are used for paleoreconstructions to learn how water ecosystems responded to climate changes. Doing such research east and west of Lake Baikal are Dr. Sergei Krivonogov (Sobolev Institute) and Dr. Yelena Bezrukova (Vinogradov Institute for Geochemistry).

In practical terms sapropels are of great interest as an organic and mineral raw for various industries. In her work Biostratification and Typology of Russian Sapropels Dr. Nina Corde traces the history of explorations and use of these benthic depositions since the late eighteen-hundreds and the early nineteen-hundreds. Back in 1919 the Russian Academy of Sciences set up a Sapropel Committee which in subsequent twelve years fulfilled a large amount of research and applied work with the aim of using sapropels in agriculture, industries, medicine, mud treatment and veterinary medicine. In 1931 a sapropel laboratory was estab-

lished in Leningrad reorganized later, together with the Biochemistry Department of the national Academy of Sciences, into a Sapropel Research Institute that explored into the conditions of genesis of this raw material and the possibility of its practical chemical and technological uses. In 1934 this center gave birth to another research institution, the Moscow Institute for Combustible Minerals under the umbrella of the national Academy of Sciences. But then the work on sapropels slowed down due to the discovery of petroleum-rich provinces in Siberia. True, the interest in sapropels is alive today as ever.

FROM FERTILIZER TO DRUGS

The application area of these heteroorganic sediments and their byproducts is very wide. Sapropels go to produce grade organomineral fertilizer good for any soil and plant species, for it increases the concentration of humus, nitrogen and microelements there. Sapropels boost soil fertility and improve soil structure, they bring down excessive acidity, and increase the presence of mobile forms of phosphorus and potassium. As a result, the productivity of grain crops, vegetables and tubers is up 40 to 50 percent. Sapropels also act as a natural biostimulator. Yet another asset: unlike organic composts, sapropels carry no weed seeds and no pathogenic bacterial and floral species. Unlike many kinds of mineral fertilizer, sapropels are ecofriendly, and have no deleterious effect on man and animals--quite the contrary, they reduce the concentration of nitrates, nitrites, and salts of heavy metals. Thanks to the low solubility of bioactive substances sapropels provide for a balanced nutrition of plants.

Sapropels hold out good prospects, too, in minimizing the toxic effect of industrial pollution. The humin acids of organogenic metals form tight bonds with metal ions and thus serve as a reliable geochemical bar against dangerous substances.

Sapropels are also supplemented as nutrient and vitamin additives to mixed feed and grass fodder granules to enhance the effect of biologically useful components.

As to the human organism, sapropels exert a positive effect on the nervous, endocrine and cardiovascular systems; they improve the condition of the locomotory system, and stimulate metabolic processes in the liver. The presence of antibiotics and the absence of pathogenic microorganisms makes sapropels quite good in arresting inflammations and for a quick cure of eczemas, burns and dermatitides by boosting the fagocytic activity of white blood cells and tissue regeneration processes. Sapropels are also effective for phlegmons, mastitides, furunculosis, chronic gastritis, gastric and duodenal ulcers...

Sapropels are treated in a variety of ways--by heat and combined heat-and-chemical procedures (low-

temperature carbonization, thermal dissolution, express thermolysis) and chemical methods (extraction, hydrolysis, oxidation). Tar, phenols, ammonia, acetone and gaseous products (H₂S, CH₄, N₂ and other compounds) as well as a wide array of carbon-containing materials and sorbents used to collect oil slicks on water and any other hard surfaces and treat effluents--such is the range of substances obtained in heat-and-chemical treatment of the stock material.

THIS IS JUST THE START

As little as 2 percent of sapropels has been explored so far. Today we may speak only of inferred deposits proceeding from the number of lakes and statistical average data. In his article on heat-and-chemical treatment of lacustrine sapropels, Dr. Georgi Plaksin of Omsk State University surveys the available data on the overall reserves of sapropels estimated from 38 to 250 bln m³ by various sources for Russia's natural humidity zones. As we see, the hiatus is very wide. And here are data furnished by the Torfgeologia enterprise specializing in peat prospecting: the total sapropel resources in the Russian Federation are estimated at 91 bln tons; of these 31.5 bln tons is found in the North, 17.2 bln tons in Western Siberia, 14.5 bln tons in Eastern Siberia, 12.8 bln tons in the Far East, and 7.9 bln tons in the Urals.

Although vast deposits of sapropels are buried in Western Siberian lakes, their actual reserves are not yet known in practical terms: only a few bodies of water have been explored thus far. Dr. Plaksin adduces data whereby 300,000 large and small lakes in the Tyumen Administrative Region may contain as much as 1,398.7 mln tons of sapropel. For Novosibirsk and its region the explored resources are determined at 25 mln m³ (inferred resources, 2.5 bln m³), and for Omsk and its region, at 300 to 350 mln m³.

In Western Siberia the lead sapropel-mining enterprise and the only one in Russia engaged in sapropel processing is Vega-2000-Sibirskaya Organika at Omsk. It has determined the chemical composition of sapropel deposits in some of the lakes that have been registered in due course and supplied by hygienic certificates. These lakes have been proved environmentally friendly in a series of industrial experiments; Omsk sapropels have been recommended as feed additives for poultry, hogs and cattle. Vega-2000 is also producing sorbents for collecting oil slicks from water surfaces. Another research center, the Institute on Problems of Hydrocarbons Refining (operating under the wing of the RAS Siberian Branch) is researching into methods of oxidation and heat dissolution of sapropels thus converted into liquid fuels, phenols and other products.

The Tomsk and Novosibirsk regions are lagging behind: sapropels have been explored but little there for practical uses, barring a few exceptions. True, the For-

tuna Company is recovering sapropels at Lake Kirek for medical and balneological (mud cure) purposes. Another research center, the Institute for Kurortology (health resorts) is also there, at Lake Kirek: it has carried out comprehensive studies of the chemical, biochemical and microbiological makeup of Kirek sapropels. And at Novosibirsk, the Sapropel Company is mining and processing Lake Beloye sapropels.

BIOGEOCHEMICAL RESEARCH

The physical and geographical conditions of Western Siberia's south are favorable to sapropels--flat lowlands sloping gently northwards, no rough relief features, the temperate climate with excessive moisture. This goes along with wind erosion and weathering processes; washed out, a large amount of biogenic compounds is carried off into lakes. These are small and slow-flow or stagnant bodies of water, with depositions of organic matter and ferrum built up on the bottom, a thing typical of humid zones. The climate south of Lake Baikal is rather mild--intermontane lowlands are under lakes and swamps there.

The authors of the present article have been exploring Siberia's lakes ever since 2004. In Western Siberia we have centered on six sapropel lakes: Beloye, Minzelinskoye, Bolshiye Toroki, Itkul, Sargul (Novosibirsk) and Kirek (south of Tomsk). West of Lake Baikal we have been studying two lakes, Ochki and Dukhovoye, and Lake Kotokel, east of Baikal. We were sinking wells in summertime from a pontoon by percussion drilling, which allowed us to get intact sapropel core samples 7.5 cm across, and 3.5 to 14 m long. In laboratory we cut them down to 2.5 cm or 10 cm chunks, and determined their humidity. Thereupon we desiccated and homogenized our samples and, if necessary, baked them in a muffle furnace to steady weight. Prepared by standard techniques, the samples were assayed by high-sensitivity methods for a wide range of chemical elements (as many as 55) at the Analytical Center of the Geology and Mineralogy Research Institute and in the laboratories of the Siberian Science Center credited with international certificates.

We have to admit, though, that the type-design practice for lacustrine sapropels (in particular, with respect to their heteroorganic composition) is not yet elaborated well enough. In our view, their classification, as suggested by Dr. Nina Cordé, is the best among those known to us in its genetic substantiation. Adopting her approach (by using biological and chemical indices characterizing the probable conditions of sedimentation), we are working out biochemical type designs for sapropels of small Siberian lakes--we are singling out biological types on the basis of organic matter genesis and making use of certain essential characteristics (occurrence, concentration of calcium, ferrum and other elements).

Lithostratigraphy of a sapropel core sample from Lake Minzelinskoye. 1 (0-291 cm), macrophytogenic sapropel; 2 (291-307 cm), peaty sapropel; 3 (307-318 cm), peat with a cluster of gastropod shells; 4 (318-460 cm), peaty sapropel with gastropod shells; 5 (460-500 cm), sand.

According to biological indicators, we distinguish between the planktonogenic and macrophytic types of sapropels (with plankton the principal producer of organic matter, and macrophytes, the main producers of the same substance). First of all we are studying the present-day lacustrine biocenosis, for one, the dominating sapropel-producing species accounting for the greatest biomass. The genesis of fossil organic matter is determined by the carbon/nitrogen ration (C_org/N), pointing indirectly to a genetic connection of sediments with the stock material: plankton and macrophytes, or ground plants.

Summing up our data over many years, we come to a tentative conclusion: the different physical, geographical and climatic conditions in small lakes west and east of Baikal favor formation of planktonogenic sapropels (Lake Dukhovoye, Ochki, Kotokel), while the lakes of Western Siberia's south accumulate sapropels of macrophyte origin (Lakes Beloye, Bolshiye Toroki, Minzelinskoye). Lake Kirek (Tomsk) produces two kinds of sapropels: planktonogenic (in the middle, and to 7 m deep) and macrophytogenic (inshore and to 5 m as deep). A close study of deposition strata enabled us to get a clear idea about the genesis of organic matter in strata formed throughout the Holocene.

In these two biological kinds of sapropels we identify three biogeochemical varieties of sediments. First, a macrophytogenic sapropel high in calcium and low in ferrum and organic matter, and occurring in many zones (high zoning); second, a planktonogenic sapropel low in calcium and high in ferrum, with middlelevel zoning; and third, a planktonogenic sapropel low in calcium and ferrum (Fe ≤ 3 percent) having a low zonality and rich in organic matter. The formation of these three varieties largely depends on the chemical composition, physical-and-chemical conditions of lake waters and on organic matter producers (plankton, macrophytes, peat-forming plants).

We cannot bypass ecological matters either, for one, the impact of the human (technogenic) factor on the

Lithostratigraphy of a core sample from benthic sediments of Lake Dukhovoye. 1 (0-180 cm), planktonogenic sapropel; 2 (180-205 cm), clayey silt, loose, dark; 3 (205-393 cm), clayey silt, compact, bluish-gray; 4 (393-445 cm), dark-gray clays; 5 (445-574 cm), sandy clays.

chemical composition of lacustrine sapropels. By and large, the lakes we have explored do not exceed background pollution values. However, the total atmospheric pollution of the atmosphere in the 20th century by chalcophilic elements (Hg, Cd, Pb, Zn, Cu, As, Sb, etc.) getting into the atmosphere with aerosols and dust, and often carried rather far, affects the chemistry of the upper horizons of lake sapropels. Falling with rain water, these elements become actively implicated in biodifferentiation processes. At the atmosphere/water interface in small lakes the plankton acts like a filter involving chemical elements into the biological turnover. At this barrier the plankton takes in mobile chalcophilic elements from the water, and these, with the plankton dying off, get down, together with the detritus, to the upper sapropel layers. Yet the concentration of technogenic chalcophilic elements in surface layers of lacustrine deposits does not exceed regional background values, and consequently such sapropels are fit for industrial uses.

The results of our biogeochemical explorations may become a base for practical recommendations for rational uses of Siberian sapropels and help in answering many questions bearing on the history of benthic deposits and their formative conditions in the geological time framework.

This work was done with financial support of the Russian Fund for Basic Research (grants 04-05-65168, 08-05-00392, 11-05-00655, 11-05-12038) and Interdisciplinary Integrated Project No. 125 of the RAS Siberian Branch.