By Valery NOVIKOV, Cand. Sc. (Geol. & Mineral.) director of the "Ugra" National park; and Tatyana GORDEYEVA, senior researcher

The river Zhizdra, meandering through the Kaluga Region south of Moscow, is flanked on both sides by a string of lowland lakes with rather peculiar hydrological, hydrochemical and hydrophysical characteristics. These bodies of water were but little studied until recently. The tables were turned as this area was elevated to a national park status, something that spurred comprehensive research and nonstop monitoring.

According to the origin of their basins, Kaluga lakes are predominantly fluvial plain bodies of water (mort-lakes). But here and there one may come upon solution, or sink lakes, and glacial (glacier) lakes; and one of them, Ozerki, is thought to have appeared in a kettlehole left by a meteorite (by tentative estimates of a geological team from Lomonosov Moscow State University). Most of these lakes are situated along the Oka and its major tributaries, the Ugra and the Zhizdra. The flood plain of the latter is particularly rich in mort-lakes, more than 100 in number; of these over seventy with a total water surface area of about 20 hectares (50 acres) lie within the bounds of our national park.

Hydrochemical studies of these bodies of water were launched in 1998 and, on a broader scope, in 1999. In keeping with the project of the Global Ecological Fund (an international organization financing nature conservation projects), teams of experts from Moscow, Kaluga, Obninsk and other places got down to comprehensive studies of the Zhizdra plain so as to determine its geological structure, hydrological and hydrochemical characteristics, the degree of eutrophication (ageing) of lakes and other things. One of our goals was to describe the valuable plant and animal species inhabiting these lakes, and work out measures toward preserving and rehabilitating the unique ecosystems. Also, we were to draw up scientific recommendations for a network of ecology-friendly tourist itineraries and for protection regulations. Overall, something like 30 fluvial plain bodies of water are covered by our studies, with only 11 studied in full so far.

The Zhizdra empties into the Oka 1,157 kilometers away from its mouth. This tributary rises from natural springs in the district of Lyudinovo. It is 233 kilometers long (compare the total extension of the park, 92 km), its basin is 9,170 sq km in area, its mean depth is around 1 meter, and the average flow rate- 0.3 m/s; the annual consumption of water is equal to 36.6 m ³ /s. The river bed is smooth and sandy. Buried in the deposits of the bed, flood plain and terraces just above the plain are the abundant remnants of tree trunks, including those of the water-seasoned oak. The Zhizdra's bed has a moderately, or else strongly winding, mean-

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dering* course. The river bed is 20 to 40 meters wide in the middle, and 50 to 60 m in the lower reaches.

The river valley (0.5 to 5 km wide) has a distinct flood plain on both sides (1 to 3 km wide in the middle and lower reaches), and three above-the-plain terraces, with sand drifts and hills complementing the relief features.

The Zhizdra's alimentation (recharge) varies-the mean contribution of meltwater over many years accounting for 60 percent, subsoil (ground) water adding a little over 30 percent, and precipitation contributing but only 5 percent. In recent years, according to Veniamin Semyonov representing the Obninsk-based World Data Center for Hydrometeorology, there have been significant changes in the water balance components: the contribution of subsurface water is up 15 to 20 percent against the background of a corresponding decrease in the thawing water input.

The river level conditions are characterized by high-water spring freshets and interseasonal floods in summer and autumn due to rainfall; and there is always a lower amount of moisture in wintertime. True, the water level may rise in winter too as a result of snowmelt and precipitation during thaws, a trend that has surfaced in the last few years. In springtime the Zhizdra's water rises by 6 to 7 meters and floods the fluvial plain.

As shown by observation data over the past sixty years, the plain is flooded if the water level is up by 2.5 - 3 meters (what happens every 8 years out of 10). The high water may stay on at this level from one day to one month. In the past 30 years the water regime has been characterized by lower rises in the springtime, and therefore the fluvial plain is flooded not as often as before: only every other year in the last decade. The time of high water has been down too.

The first ice appears on the Zhizdra in the middle of November, and by the end of this month the river is icebound for

* From meander, here a bend in a level-land river course. Such bends occur under the effect of currents that do not coincide with the direction of the main flow, as surface streams head for the concave, and benthic streams-for the convex shore.- Ed.

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good. Toward the end of the winter the ice thickness is up to one meter. The river breaks up early in April and is cleared of ice toward the first decade of this month.

Possessing a fairly high natural capability of diluting technogenic impurities, the Zhizdra is subjected to a comparatively low anthropogenic load. The level of its water pollution is thus rather low too.

The mort-lakes, which are actually fragments of the Zhizdra's old bed, appeared in the process of the river's meandering through the flood plain. This is seen in their elongated, sinuous and shoe-like form, and in small dimensions. Such ponds are usually not longer than 500 meters. The shore line of the largest is over 3.5 kilometers long. The largest lakes are Bolshoye Kamyshinskoye, Karastelikha and Zheltoye. The width of mort-lakes depends on the size of the old bed and is not above 50 meters. Some lakes are joined by channels with one another or with the river.

The lake shores are usually gentle and poorly swamped; but there occur now and then lakes with steep and bluff shores, their bench height being up to 1.5 m. The riparian ground is of sandy loam and clay. The bottom relief features are rather varied. Judging by geo-radar sounding data, most of the mort-lakes have trough-like basins, often with alternate rises and depressions. Such morphological elements vary in number and parameters: seven rises have been detected in Lake Bolshoye Kamyshinskoye, and six - in Zheltoye. The differential between the bench marks of rises and depressions is in the range of 1.3 - 3 and 0.8 - 4.3 meters. On one hand, this is explained by the elevations of bedrock, and by the erosional activity of the river and its tributaries, on the other.

Georadar studies carried out by a team of Moscow University geophysi-cists under Igor Modin have yielded data on the profile of lacustrine basins and on the nature of water accumulation within. The lithological boundaries

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between different sedimentation complexes are rather sharp and irregular. Most of the lakes have a trilayer structure from bottom up: bedrock, alluvial deposits corresponding to the fluvial formation of water reservoirs, and contemporary silt deposits.

Alluvial deposits in the form of obliquely laminated sands are found at depth down to 10 meters (Lake Tsarskoye). Deposits (predominantly flatlaminated, clayey and sapropelic* silts) have the greatest thickness in depressions (sags): from 1.5 to 2 m (Lakes Tsarskoye, Gorozhenoye, Bolshoye Kamyshinskoye) and from 3 to 4 m (Knyazheskoye, Zheltoye, Gorka). Deposits fill these basins from the center to the periphery, and the floor is leveled out as a result. Sometimes landslip deformations are detected on the periphery of lacustrine basins and in depressions.

The age of the Zhizdra fluvial plain lakes is within the chronology of the Holocene; this is also confirmed by archeological evidence, for one, by a Bronze Age encampment discovered on the shore of Lake Lenivoye. Since relics of this period are confined to various bodies of water, Lake Lenivoye is thought to have been in existence for at least 4 thousand years. Dr. Sergei Kuznetsov of Lomonosov Moscow State University has found the age of 13 local lakes to be between 5.9 and 9.5 thousand years.

The water mass of mort-lakes is formed by fluvial and thawing waters, and by precipitation. The Zhizdra lakes depend on the inflow of subsoil water; yet in most of them such recharge is either absent or else is too small. Geophysical research data indicate the presence of subsoil water relaxation zones that empty directly into lacustrine basins, as can be seen in the example of numerous springs (from 5 to 14 to each lake).

Most of the Zhizdra lakes have entered a eutrophic (old age) stage: they heat well and have profuse water vegetation. The fullest of them, Bolshoye

* Sapropel(ic)-from the Greek sapros- rotten, putrid and pelos- dirt, silt-in reference to organic silts composed mostly of organic substances and deposits of aquatic organisms.- Ed .

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Kamyshinskoye, is in the mesotrophic (intermediate) stage, while Gorka and Maloye Kamyshinskoye are as far as the dystrophic stage, that is they are swamped and contain a large amount of humin substances.

The hydrological regime of morte-lakes depends on the Zhizdra's conditions, though their water level may be higher than of the river's. During springtime freshets the Zhizdra floods the plain, it fills the lakes with new water. In summer, autumn and winter, when their water level is at its lowest, most lakes are replenished by subsoil water; but small ponds may go dry in full during hot and dry summers.

The water recharge of the Zhizdra lakes tells on their mineral and chemical composition. They, devoid of underground springs, are characterized by the weakly alkaline (especially in winter) or neutral reaction of water, low water hardness (< 2.0 mmole/1), by the low concentration of chloride and sulfate ions, and consequently, by a low level of water mineralization (< 150 mg/1).

All the lakes studied by us boast of good oxygen conditions in the summer season. The concentration of dissolved oxygen varies from 5.1 mg/1 (Lenivoye and Podkova), that is 64 percent saturation, to 9.2 mg/1 (Gorozhenoye), or 114 percent. These lakes have as good as no oxidized biogenic elements-such as nitrates, nitrites and phosphates.

As shown by hydrochemical studies, Gorozhenoye is the cleanest lake in the Zhizdra area. The electrical resistivity of its water is equal to 150  which means a low salt concentration. This phenomenon that occurs only in the Far North is quite unique for the Moscow area. Lake Gorozhenoye has well-nigh distilled water prone to self-purification.

Local lakes and ponds are remarkable for a specific microclimate and for singular biocenoses that include rare and relict plant and animal species. Mammalians are represented by the Russian muskrat, musquash (common muskrat), European beaver and even by the American mink. As to the Russian muskrat, or desman (Desmana moschata),

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this is the only representative of Kaluga's animal kingdom to be entered in the Red Data Book of the Russian Federation and Kaluga as a very rare and endangered species. In the late 1940s and mid-50s only a few animals of this species occurred in the Zhizdra basin. But after, in 1959 and 1960 as many as 206 acclimated muskrats had been let out in several lakes off the lower reaches of the Zhizdra, the muskrat population marked an uptrend and reached a maximum of over a thousand by 1969. In the course of several seasons muskrats came to populate the Zhizdra valley (nearly 100 km long) and even penetrated as far as the basin of the Oka. But then came a downturn, and by 1976 their population in the Zhizdra district had contracted to two hundred. It stayed at this level up until 1986 when another downturn set in: in 1996 only seventy burrows were registered with an estimated population of 120 to 150. In the last three years the muskrat population in the Zhizdra plain has been stabilized at 220 - 250 thanks to tougher protective regulations and essential biotechnical measures carried out by the Ugra National Park.

Now what concerns the wild and water fowl. These are the moor hen, mullard and wild duck (Anas querquedula, Anas crecca). The Zhizdra lakes are also the haunt of the gray heron and black kite. Among the nesting and migratory birds, these are the kingfisher as well as fowl of the Tringa ochropm and Tringa nebularia species. You can also find the snipe and a varied duck population, including the diving and tufted ducks and those of the Anas penelope variety. The Zhizdra flood plain is one of the main migration routes of birds of passage, including the water fowl, birds of prey and various sparrow species. Since 2000 the river valley has been a key ornithological territory of international significance.

Now the fish population which is typical of central Russia's fluvial lakes. Overall, twenty piscine species have been identified. The crucians predominate-namely the golden and silver carp (Camssius camssius and Camssius aura-

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tusgibelio, respectively), yellow bunting (yellow-hammer), tench, perch, roach and pike. Here and there one can find the bream, ide, ratan goby (Perccottus glehni)... Some lakes are inhabited by the redfish of the carp family (Scardinius crythrophthalamus), by the carp species (Blicca bjoerknd) related to the bream; occasionally, by the bleak (Alburnus alburnus), dace, bitterling, sheatfish, turbot (eelpout), gudgeon, loach, chub... These fishes find good fodder and spawning-grounds here. Yet many perish in periodic "scourges" in wintertime as a result of oxygen starvation under ice sheet, especially in stagnant and shallow ponds. But such lakes as Staraya Rechka-2, Borovoye, Peremoynoye, Podkova-1 and Gorozhenoye give reliable protection to the fish population against periodic "scourges". The others do not.

Lake shores of the Zhizdra plain are the habitat of three reptile and nine amphibian species: the toad (Bufo bufo), and the frogs-the lacustrine ( Rana ridibunda), pond (Rana lessonae), sharp-snouted (Rana arvalis) and brown frog (Rana temporaria) as well as the grass snake (Natrix natrix) and the common lizard (Lacerta vivipara). Less frequent are the common viper (Vipera berus), the bombina (Bombina bombina), the spotted and crested newt ( Triturus vulgaria and T. cristatus, respectively) and the spade-footed toad (Pelobatesjuscus).

The water fauna of fluvial lakes is quite diverse as well. Their hydrobios comprises representatives of 8 types, 20 classes, over 30 families and 80 species. In spring and early in summer zooplankton is particularly profuse, with the genus Daphnia and cyclopes found among them. Many mollusks and larvae inhabit the benthal. Sponges occur in nearly all lakes.

The Zhizdra mort-lakes are original sites of the vestal flora, with over 150 species of higher plants and 150 or so different algae which hug the river edge. Their zones have been identified: shore and near-shore hydrophytes* and float-

* Hydrophytes-water plants rooted in the ground and rising above water.- Ed.

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Russian muskrat population dynamics in Zhizdra lakes (according to V. Margolin).

ing leaves. All water plants are sturdy and rather lush in their growth.

The water chestnut ( Tmpa natans) is a very rare floral species entered in the Red Data Book of the Russian Federation in 1988. The bulk of its population is concentrated in Lake Gorozhenoye, with a few individual representatives also found in two neighboring lakes, Yamnoye and Oreshnya. Among the rare species are also these: the long-leaved buttercup (Ranunculus lingua), the perennial broad- leaved umbellate (Slum latifolium), potamogetons (Potamogeton trichoides et lucens), the inshore sorrel (Rumex hydrolapathum), the amphibian buckwheat (Polygonum amphibium) and such plant species as Utricularia vulgaris, Thelypteris palustris and Salvinia natans - the latter species that inhabits nearly all the mort-lakes of the Kaluga region is not found elsewhere.

The best lakes on the right side of the Zhizdra plain (a stretch from the community of Nizhniye Pryski to Kamyshinka) are under special protection as unique natural objects and sources of drinking water, and as splendid sites for tourist and health recreation activities.

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