Zveza društev gradbenih inženirjev in tehnikov slovenije
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Objavljeno v: Gradbeni vestnik - 61-64 - 1958,1959

Avtorji

Janko Sketelj, ing.
dr. Marjan Rejic

PRELIMINARNO POROČILO O PREISKAVI BLEJSKEGA JEZERA - RECENZIJE

UDK: 627.175.001.5(Bled)

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PRELIMINARY ACCOUNT ON THE EXAMINATION OF LAKE BLED

PRELIMINARY ACCOUNT ON THE EXAMINATION OF LAKE BLED
The surface of the lake amounts to 1,438 square kilometers, its volume comes to 27,69 millions of cubic meters, the greatest depth found amounts to 30,2 meters, while the calculated mean depth is 17,9 meters. The hypolimnium ration to volume comes to 0,056. The pricipitation area covers 9,3 square kilometers, while the average precipitations in the priod from 1901—1056 amount to 1614 millimeters, their minimum being 773 millimeters and their maximum coming to 2352 millimeters. The exchange of water was estimated to come to 40 per cent of the lake’s volume a year. Usually the lake is frozen 45 days a year. It is sheltered from the wind, the intensity of which is too weak for being able to cause the spring- or autumn-circulations. The subsistence of strata for the period of October 1954 to March 1956 came to 119,452 — 341 Mpm. Quantity of heat emitted by the lake to the surroundings, in the period from 1955—1956, amounts to 207,6 millions of M cal.
The water’s transparency, trifling in spring and coming to its maximum in autumn, carries together 7,9—9,5 meters. Colour of water is 10—20 Mg. Pt/1. The smallest light transfer exists in the yellow part of the spectrum but there is a noticeable light transfer in the green region. The selen’s fhoto-cells are still capable of perceiving light in a depth of 16 meters. In the upper strata, at sufficient development of phytoplancton, a biological discaltiation occurs. In such occasions a shortage of carbon dioxide takes place. In monimolimnium its quantity will do. In the aerobe atmosphere rH is positive and dissolved oxy-gene is to be found. On the other hand in the anaerobe atmosphere rH is negative and hydrogene sulfide occurs. The presence of hydrogene sulfide is oscillating. In the course of the year it occurs at depths of 12—20 meters. On the other hand in monimolimnium it occurs during the whole of the year.
Up to the depth of 12 meters the lake’s mud is impregnated with mineral salts and does not smell of hydrogene sulfide. From that level downwards the mud moulds strata and smells of hydrogene sulfide. If the strata are analysed, it becomes ciear that there were hard conditions at the bottom of the lake about at least 40 years ago.
The structure of the lake’s plants, to be found in the higher strata and of the plancton, is recognizable out of the list. If former analyses are consulted, it becomes clear that the quality of water has grown worse. Two specimens, belonging to the plancton, have disappeared: Cyclops sp. and Bosmina longinostris cornuta typica, which were to be found in the lake before 1914. Bental belongs in greater part to the anaerobic zone, where bacilli and anaerobic mono- cellulars are able to exist. In the pelagial’s anaerobic zone there is a great number of Iarvas, belonging to the specimen of Corethra plumicornis, and mono-cellulars, belonging to the specimen of Stentor coeruleus. An examination also showed that in the north and east parts of the coast, at an extention of 10 meters, excretion bacilli exist during the whole of the year but they are absent in the south and west and in the pelagdal. In the anaerobic zone of bental and pelagial there are sulphur bacilli.
The present state of Lake Bled is a result of aging, culture also contributing its part to this phenomenon. Lake Bled is a lake of a well type, in a wind sheltered position, it has a small water exchange, and a small precipitation area. Owing to this conditions the growing entrophy is inevitable. An improvement of this situation may be obtained only by increasing the yearly exchange of water from the actual 40 per cent to 100 percent of the whole volume. This solution of the problem is quite possible becouse of the favourable position of the lake.

The surface of the lake amounts to 1,438 square kilometers, its volume comes to 27,69 millions of cubic meters, the greatest depth found amounts to 30,2 meters, while the calculated mean depth is 17,9 meters. The hypolimnium ration to volume comes to 0,056. The pricipitation area covers 9,3 square kilometers, while the average precipitations in the priod from 1901—1056 amount to 1614 millimeters, their minimum being 773 millimeters and their maximum coming to 2352 millimeters. The exchange of water was estimated to come to 40 per cent of the lake’s volume a year. Usually the lake is frozen 45 days a year. It is sheltered from the wind, the intensity of which is too weak for being able to cause the spring- or autumn-circulations. The subsistence of strata for the period of October 1954 to March 1956 came to 119,452 — 341 Mpm. Quantity of heat emitted by the lake to the surroundings, in the period from 1955—1956, amounts to 207,6 millions of M cal.

The water’s transparency, trifling in spring and coming to its maximum in autumn, carries together 7,9—9,5 meters. Colour of water is 10—20 Mg. Pt/1. The smallest light transfer exists in the yellow part of the spectrum but there is a noticeable light transfer in the green region. The selen’s fhoto-cells are still capable of perceiving light in a depth of 16 meters. In the upper strata, at sufficient development of phytoplancton, a biological discaltiation occurs. In such occasions a shortage of carbon dioxide takes place. In monimolimnium its quantity will do. In the aerobe atmosphere rH is positive and dissolved oxy-gene is to be found. On the other hand in the anaerobe atmosphere rH is negative and hydrogene sulfide occurs. The presence of hydrogene sulfide is oscillating. In the course of the year it occurs at depths of 12—20 meters. On the other hand in monimolimnium it occurs during the whole of the year.

Up to the depth of 12 meters the lake’s mud is impregnated with mineral salts and does not smell of hydrogene sulfide. From that level downwards the mud moulds strata and smells of hydrogene sulfide. If the strata are analysed, it becomes ciear that there were hard conditions at the bottom of the lake about at least 40 years ago.

The structure of the lake’s plants, to be found in the higher strata and of the plancton, is recognizable out of the list. If former analyses are consulted, it becomes clear that the quality of water has grown worse. Two specimens, belonging to the plancton, have disappeared: Cyclops sp. and Bosmina longinostris cornuta typica, which were to be found in the lake before 1914. Bental belongs in greater part to the anaerobic zone, where bacilli and anaerobic mono- cellulars are able to exist. In the pelagial’s anaerobic zone there is a great number of Iarvas, belonging to the specimen of Corethra plumicornis, and mono-cellulars, belonging to the specimen of Stentor coeruleus. An examination also showed that in the north and east parts of the coast, at an extention of 10 meters, excretion bacilli exist during the whole of the year but they are absent in the south and west and in the pelagdal. In the anaerobic zone of bental and pelagial there are sulphur bacilli.

The present state of Lake Bled is a result of aging, culture also contributing its part to this phenomenon. Lake Bled is a lake of a well type, in a wind sheltered position, it has a small water exchange, and a small precipitation area. Owing to this conditions the growing entrophy is inevitable. An improvement of this situation may be obtained only by increasing the yearly exchange of water from the actual 40 per cent to 100 percent of the whole volume. This solution of the problem is quite possible becouse of the favourable position of the lake.

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