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Lakes

Lakes

There are about 120 lakes on the territory of the park, of which about 70 are glacial, divided into several characteristic groups, according to the territory in the National Park (Marichini, Musalenski, etc.). The total volume of water in the lakes is about 80x106 m 3. The lakes have a significant regulatory impact on the formation of river runoff from the park.
Glacial lakes are most often located at the bottom of circuses, circus terraces or less often in trough valleys. The glacial lakes in Rila are scattered throughout the mountain, located mainly on northern exposures. The largest glacial lakes in Rila are Smradlivoto (21.2 Ba) and Gornoto Ribno (17.6 Ba) (both on the territory of Rila Monastery Nature Park), and the deepest lake is Okoto (37.5 t). The lakes in Rila are located between 1900 and 2600 tons above sea level and according to their area are distributed as follows: 1-1.5 Ba - 73.4%, 1.5-4.0 Ba - 20%: over 4 .0 Ba - 6% The lakes most often have an oval shape, which depends on the shape of the circus, but there are lakes with an elongated shape such as Upper Fish Lake, triangular shape such as Yakoruda Lake or kidney-shaped like Lake Kidney. fed by streams, temporary streams, solid and liquid precipitation, giving rise to some of the rivers flowing from the Rila or feeding lower lakes.The maximum water quantities in the lakes are in the period May-July, when the snow melts and is the maximum rainfall, and the minimum is in September, when rainfall is scarce and evaporation is significant.Most lakes drain superficially, but there are exceptions with an underground drain, such as the Dry Lake, whose waters are filtered through the washed moraine materials.
The waters in Rila National Park are extremely soft with one of the lowest electrical conductivities in Bulgaria - varying so far from 6.1 µS / sm (in one of the measurements of Karagyol Dam - in phytobenthos sampling) to 79 µS / cm (Leevshtitsa River ). Practically in the Rila lakes and dams no electrical conductivity has been measured more than 20 µS / sm.
There are no established problems with dissolved oxygen (resp. Oxygen saturation), which is about 9 mg / l and resp. about 100% saturation, which is normal for this type of water;
The acidity of the water (measured as pH) varied between 7 and 8, and only in Karagyol Dam and Yonchevo Lake was the pH measured just below 7 (pH = 6.81), which is normal for this type of water.
All inorganic forms of nutrients (ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, orthophosphates) are below the limit of detection of analytical methods and show that the river and lake waters in Rila National Park are extremely poor in nutrients (oligotrophic and ultraoligotrophic).
The total phosphorus (organically bound and inorganic) is also below the limit of quantification of the analytical method in river and lake waters within the boundaries of Rila National Park.
Only low values ​​of total nitrogen (organically bound and inorganic) were registered in some of the points: for rivers ranging from <0.2 mg / l to 0.93 mg / l (Kriva river); in lakes ranging from <0.2 mg / l to 1.9 mg / l (Karagyol dam). These final values ​​exceed the norms for good condition laid down in Ordinance H-4, but it should be borne in mind that these norms are for average annual values ​​and it is not correct to compare them with one-time measurements, especially in the period close to snowmelt. (when is the biogenic annual maximum of dissolved forms).
The values ​​of COD (chemical oxygen demand), which is an indicator of total water pollution, are in most cases below the limit of quantification of the method of 5 mg / l or slightly above it, reaching a maximum of 7.2 mg / l (Leevshtitsa River) , which are extremely low values ​​for this indicator.
The indicator for total organic pollution (BOD5 - biochemical oxygen demand) has very low values, ranging from <0.5 mg / l (Beli Iskar dam) to 1.59 mg / l (Karagyol dam), which shows waters with very high drinking water. quality.
The river and lake waters in Rila National Park are characterized by very high quality in the main groups of physicochemical parameters (oxygen status, acidification / acidification, nutrient load, salt regime), and no cases of clear anthropogenic pollution have been registered in the park. (in the surveyed 17 rivers and 18 lakes).