U.V. Zhakova1, G. Badino2, V.T. Khmurchik3
1Science Natural Institute of PSSRU, Perm,
2Turin University, Turin,
3Science Natural Institute of PSSRU, Perm,
In the world there are a lot different karstic lakes which was classifying by composition of bearing strata, by belonging to different hydrodynamic zones, by supply conditions, by thermal regime, mineralization, chemical composition of water. Cheric-Kel’ lake is the unique by the some of these parameters. It is concurrently us the several unique native objects: karstic shaft (abyss), karstic spring and naturally, lake. Lake is the extended mouth of ascending spring. Discharge of the spring is quite big – giant, in the world classification.
There are more than 8 millions lakes in the World, more than 2 million in Russia. Total stock of fresh water in the carstic spring are 16 км3. Among Russian lakes Cheric-Kel’ has the 7th position.
Table 1. Deepest Lakes Of Russia
|№||Lake ||Region||depth, m||area, km2|
|1||Baikal||Buryatiya, Irkutsky||1642||31 722|
|2||Caspian Sea ||Dagestan, Kalmykia, Astrakhan ||1025||371 000|
|3||Khantayskoye||Krasnoyarski Kray ||420||822|
|6||Lama||Krasnoyarski Kray ||300||318|
|7||Cheric-Kel’ ||Kabardino-Balkaria ||258||0,0216|
|9||Noion-Khol’ ||Tuva republic ||225||52|
|10||Manyi-Khol’ ||Tuva republic ||180||30,7|
The surface area of Blue Lake is quite small in comparison with its depth.
The other deep lakes from this table has not the karstic genesis, so Cheric-Kel’ lake is the
deepest karstic lake in Russia.
There are a lot of deep karstic lake in the World. The deepest and one of the impressive karstic lake is Crveno Jezero - the largest karst landform in Dinaric mountains and one of the largest sinkholes in whole world. This sinkhole containing a karst lake near the city of Imotski, Croatia. Limestone walls rise over the medium level of this lake 240-260 m tall, dwarfing the forest which grows around it. Total known depth of the sinkhole is approximately 530 m. Width of sinkhole is 450-500 m.
Diameter of the lake is some 200 m. The known depth of lake is 280-290 m. Data about the depth of lake are somewhat controversial, explained - the level of lake may change per 30-50 m.
So Cheric-Kel’ and Crveno lakes seasonally fight for priority of the deepest World kastic lake.
It should be noted that Crveno Jezero most likely has been formed by collapse of enormous cave hall, but Cheric-Kel’ lake is a spring-lake, most likely not collapsed. Cheric-Kel’ Lake is the deepest karstic lake of the World.
There are two genesis hypothesis of Cheric-Kel’ Lake: has been formed by collapse; due to dissolution of Limestone by the ascending spring. During international expedition 2012 was studied not only lake but also karst of surrounding. The lake has constant water inflow, there is a small variation of the water surface, temperature and chemical composition. All this facts indicate us that the lake as a spring associated with pressure aquifer. According to cave-divers dates and instrumental deep-water investigation the walls of the lake sinkhole has a negative inclination and the cross-section is conic flask with convex bottom and splay mouth. The cause of this conic form is growth of saturation rate of the rising water, and decrease of water solvent capacity. In the upper part of the lake formed the bell connected with water discharge. There is no significant amount of rock block in the bottom.
Why this lake appeared exactly in this place? There are some facts which helped for this event. The depth of limestone in this zone is 1700 m, so here can appear quit big vertical karstic form. The water-bearing formation of this zone is the most water-abundant in Caucasus folded region, with recharge area in Rocky ridge, and it is also helped for huge karst formation (fig. 1).
Fig. 1. Cheric-Kel’ lake from Google Earth
In the tectonic map of Nothern Caucasus we can see that the main tectonic fractures (in conformity with water-conductive zone) are parallel to Greater Caucasus Mountain Range.
Almost all big karstic forms and associated with them lakes (Upper Blue lakes, Sekretnoe, Suhoe, Nizhnee) are along the direction of line related with tectonic fractures.
Here there is a discharge zone of strong ascending spring.
Apparently, the Cherek doline widening in the region of Cheric-Kel’ lake is connected with
depressed tectonic zone crossed by Cherek River.
Let’s note other interesting hydrogeological peculiarity of the Cheric-Kel’ lake.
Periodically lake has a smell of hydrogen sulfide with different intensity. The divers also pointed to the springs with whitish color of water at the different depth.
Hydrogen sulfide appearance in the water is quite usual in this region. In the hydro geo- chemical point of view the region has sulfate-calcium mineral sulfide underground water. There are several spring with hydrogen sulfide in the region, including the spring discharging to the Cherek River downstream from Cheric-Kel’ Lake. It is interesting the nature of pulsating entering hydrogen suflide water to the Lake. The limestone massif of Cheric-Kel’ Lake is the interchange of water-resistant and water-bearing layers. The discharging throw this layer to the Lake is unevenly and forming complex hydraulic system. In certain circumstance there are conditions for intensive discharge from the hydrogen suflide saturated layers.
Irregular discharge to reduce to temperature anomaly stratification by the depth and also quite quick change of level (5-10 cm) and discharge of the lake.
The lake bowl stratums has a not regular composition and water content. Due to this facts in the Lakes walls can be karst processes and formed horizontal cave. Further research of this unique object can give us discovery a new underwater cave.
The different natural processes are quite intensive in the karst region - in full view of the people a sinkholes formed, appear and disappear karstic lakes, the discharge of rivers changes by thousands times during short period. The human operation in this dynamic and unstable system can became a reason for activation of negative processes and backwash effect.
The first mention of Blue Lake dates back to 1887-1890 (Dinnik I., 1890). The active geographical investigation of the Blue Lake region started at the beginning of 20th centures by Shookin I.
Blue Lake was partly studied and described by professor of Petersburg mine institute Ivan Kuznezov in 1926-27. He was awarded a silver medal of Russian Geographical society for this work.
The next exploration was made by expedition of geographical institute of Giorgian academy of science in 1980. They made morphological research of the lake (the length is 233 m, width is 146 m), for bathymetry they used portable echo-depth-sounder “Yaz”.
During expedition of 2011-2012 was made observation about hydrological regime, miner- alogical research of the bedrock and bottom sediments and also microbiological investigation.
Microbiological investigation. Microbiological investigations of natural objects are often based on cultivation technique and so labour- and time-wasting: for example, the determination of the number of chemolithoautotrophic nitrifying bacteria could be as long as three months or longer.
As we had not so much time, we present here the preliminary results of our investigations, that is rather quick and less labour-intensive, namely, the number of heterotrophic and ammonifying bacteria in lake water and sediments.
The life and biological processes in lake are determined with landscape and geographical conditions, the main of which are type of soil, plant associations, amount of precipitation. Bacteria are most adapted to unfavourable environment conditions in reservoirs, but quick react on their changes at the same time.
The heterotrophic microorganisms are the important part of the lake ecosystem. They destruct organic matter in water and sediments using it in constructive metabolism and as an energy- source. The cycles of the main biogenic elements – N, P, S, Fe, Mn, Ca etc. – are interrelated to the carbon cycle. So, heterotrophic bacteria take an active part in biogenic elements recycle [1, 2].
The ammonifyind bacteria mineralize the proteins of dead hydrobionts releasing NH4+ ions into environment. Ammonifying process determines the succession of over bacterial processes of N-cycle: denitrification, nitrification and N2-fixation.
The intensity of organic matter destruction is determined with reservoir’s type and properties. There is an exchange in metabolites between water column and sediments, so, the organic matter, that not be destructed in water column, enters sediments to be destructed there.
We studied samples of water and sediments elicited from the depth of 40 m below water surface. The number of physiological groups of microorganisms was determined with serial 10-fold dilutions technique using McCrady tables (fig. 2). Medium for heterotrophic bacteria: 10-fold diluted meat-pepton broth plus glucose, 1 g/l. Medium for ammonifying bacteria: 2% peptone plus pH-indicator. All dilutions and media are prepared on mineral salt solution, which roughly corresponds to salt content of lake water [3, 4, 5].
The number of heterotrophic and ammonifying bacteria was not exceed 10 cell/ml. We revealed the same results in subsurface water of SO4-Ca hydrochemical type during winter season. Water of Cheric-Kel’ lake is SO4-Ca type too, that can explain the result obtained.
The number of heterotrophic and ammonifying bacteria in lake sediments was several millions cells/g wet weight.
The gas bubbles containing H2S and other gases and occuring near lakeshore periodically are indicative to anaerobic bacterial processes – sulfate-reduction (H2S-producing) and, probably, methane-genesis. The content of SO42- ions in water and sediments determines which of these processes became dominative one in organic matter destruction. On the other hand, both processes can proceed simultaneously in the presence of SO42- ions. So, the analysis of gas bubbles content is needed. The lakeshore’s soil is the source of dissolved organic matter filtering to lake water through the soil column .
Hydrological investigation. The shape of Сheric-Kel’ effluent gives a very clear clue to understand the lake hydrological regime: the water flux is closed in a double conduit.
This means that the floods are never too heavy, and that the water circuits are at high impedance, then not in large karstic conduits. This is also confirmed by our measures. A discharge of 0.3 m3/s after a long period of temperatures below 0 °C means that hydrological circuit continues to drain with a very big time delay (delayed component of water flow) (Fig. 3).
Fig. 2. Microbiological inoculation.
Fig 3. Hydrologic section at the point of Cheric-Kel’ lake discharge.
We can compare with another important spring, at the same latitude, the Fontaine de Vaucluse, which is well known to drains water from deep karst, with low impedance. The average discharge is 20 m3/s, the maximum exceed 5 times this figure, and the historical minimum has been 3.7 m3/s .
Local inhabitants said us that at the maximum discharge, few hours after big storms, the water level could rise up to the top of small bridge in front of effluent (section A) a total discharge that probably does not exceed 10 m3/s, for a little more than one hour, then a total flux not exceeding 105 m3.
Considering typical summer heavy storm rain precipitation (0.2 m3/m2 in an hour), we have that these floods are due to rains above an area of 0.5 km2, that is the lake itself and immediate surroundings, including Dry Lake but excluding the region South of lake which surely drains directly in Cherek River. This a fast but small component of water flux (prompt component of water flow).
The average yearly temperature in Mineralnye Vody is 9.5 °C at an altitude of 314 m, and that of Piatigorsk (512 m asl) is 8.6 °C (www.worldclimate.com).
The expected average temperature in Babugent (820 m asl) is then 6-6.5 °C. In a first ap- proximation the water springs feeded by local water infiltration (same altitude) has to have a similar temperature, or lower if the feeding water infiltrates at higher altitudes.
Therefore actual lake temperature looks higher than expected, but a big correction has to be done.
The precipitation are highly concentrated during warm periods (see graphic) and the region is covered by snow for a significant part of the year, and then there is no infiltration during winter, when the air is significantly below zero centigrade.
Fig. 4. Average temperature and precipitation per month by the data of Pyatigorsk meteostation.
Meteorological data from Piatigorsk can be used to extrapolate temperatures and precipitations in Babugent.
The average air temperature results in 6.7 °C, but if we weight this figure with precipations, month by month, we obtain an average temperature of 10.4 °C, and if we admitting that the winter precipitation enters at 0°C and not at the air temperature (which is below 0 °C), this figures still increases and the average temperature estimation of infiltrating water becomes 11 °C, if the infiltrationg waters are at the same altitude of Babugent (fig. 4).
We can then estimate the average altitude of lake catch basin.
The atmospheric average temperature, and then that of precipitations, decrease of 6.5 °C per kilometre of altitude rise. During its flow underground the water temperature increases of 2.5-3 °C per kilometre of descent. Let us consider a spring at altitude A, where it outflows water caught at an altitude ∆H higher than A. The local infiltration temperature at A is TA, but the spring water was caught at (TA-6.5+∆H) and heated of (2.5*∆H) along the underground flow, then it results (4*∆H) degrees cooler than TA.
In our case the infiltration temperature TA at the lake is 11 °C. The lake temperature at -50 m was 7.4 °C in June 1980, a temperature difference of 3.6 °C, which correspond to an average altitude difference between catchment area and lake of 900 m.
Fig. 5. The cross-section of concretion.
Fig. 6. The flat columnaris crystal of calsite with combination pinakoid and rhombohedron inside split and pores of concretion. By HITACHI TM 3000, 75 kVScale bars: A)500um; B)300um; C)200um; D)100um
In fact we have not included in this estimation the thermal sedimentation inside the lake – water temperature at -125 m was 8.7 °C, which corresponds to a ∆H=600 m, which is probably due to its morphology and different feeds, and above all the fact that the water is likely heated by geothermal energy flux, a fact that would increase the ∆H estimate. In any case, if there are no local large anomalies in geothermal flux, we can estimate that the average altitude of catchment basin is around 1600-1800 m asl.
Mineralogical investigation. Two samples were taken. The first is stalactite from the wall on depth 60 м. The second one is concretion from the slope on depth 40 м. The first sample is looks like f stalactite but in fact it is concretion.It is composed of consistent close-grain aggregation. The external edge of this concretion (thickness is near 5 mm) is consist of cavernous aggregate calcite. Inside of concretion there are cracks and pores with flat columnaris crystal of calsite with combination pinakoid and rhombohedron, which are formed by offset clayey – dolomite pelitomorphic material.
In the thin section it is possible to see two zones (fig. 7). The fist is composed of fine-grain white limpid calcite crystals. Then the zone enriched with detritus material. This zone contain the foraminiferan shells (diam 0,2 мм). Calcite in the detritus zone is pelitomorfic.
The second samle is concretion of septarium (Fig.8). Probably were formed by the ammonite shell. The shape of sample is spheric. Such characteristic of shap allow us to say that concretion are formed at the diagenesis stage on the ductile substratum – limestone «gruel» with clayey pelitomorphic material. Due to karstic process concretion was leaching and transformed.
Fig. 7. The zone enriched with detritus material with foraminiferan shells.
Fig. 8. Concretion of septarium.
In future we are planning to reveal genesis of the Lake, formation of natural laws, contemporary situation and characteristics of interaction with the components of environment, dynamics and chemical regime of water, using modern techniques and methods.
We’ll made a model (using cartografical, graphical, mathematical modeling) of unique karstic spring, which then can be useful for development a new methods of protection underground water of karstic region and also like the scientific basis for efficient using and guarding of unique karstic object.
1. Аникиев В.В., Лукомская К.А. Руководство к практическим занятиям по микробиологии. – М., Просвещение, 1983. – 127 с.
2. Кузнецов И.Г. Озеро Церик-кель и другие формы карста в известняках Скалистого хребта на Северном Кавказе // Изв. гос. русск. геогр. общества -1928. – Т. LX. – Вып. 2. – С. 245-293.
3. Кузнецов С.И., Дубинина Г.А. Методы изучения водных микроорганизмов. – М., Наука, 1989. – 288 с.
4. Кузнецов С.И., Саралов А.И., Назина Т.Н. Микробиологические процессы круговорота углерода и азота в озерах. – М., Наука, 1985. – 213 с.
5. Романенко В.И. Микробиологические процессы продукции и деструкции органического вещества во внутренних водоемах. – Л., Наука, 1985. – 295 с.
6. Хмурчик В.Т. Бактериальная активность и физиологические группы микроорганизмов цикла азота в подземных водах Пермского Прикамья. – Автореф. дисс. … канд. биол. наук. – Пермь, 1997. – 23 с.
7. The karst system of the Fontaine de Vaucluse, Blavoux, Mudry, Puig http://www.springerlink.com/content/x621x13781m358l2/
8. Stankeev, E.A. (1986) Genetic mineralogy.
9. Stepanov, V.I. (1998): Structures and textures of mineral aggregates, which form in the free space of caves. Speleology in Russia. Vol. 1, Moscow, pp. 70-91.