Abstract
The Peipsi-Pskov Lake is the largest freshwater body in Europe, ranking fourth in area and fifth in volume. It is characterized by shallow water and a high level of trophy. The water in the lake is poorly mineralized and has little transparency due to suspended sediments and the development of plankton. Phytoplankton acts as a primary link in trophic chains, quickly reacts to changes in the aquatic environment and serves as a convenient object in monitoring studies.The average concentrations of total nitrogen in the lake during the observation period were in the range of 525-818 µg/dm3. The content of ammonium, nitrate, and nitrite nitrogen in the samples was mostly below the detection limits. The values of total phosphorus varied from 20 µg/dm3 to 54 µg/dm3, and its concentrations were lower than the sensitivity of the method during the flood recession.The maximum values of total nitrogen and phosphorus were recorded in August: in Lake Peipsi - 1.12 mg/dm3 and 0.09 mg/dm3, in Lake Pskov - 1.59 mg/dm3 and 0.14 mg/dm3, respectively. BOD5 values ranged from 1.96 mg/dm3 in autumn to 4.26 mg/dm3 in summer.During the growing season of 2020, 244 species taxa of phytoplankton from 8 phylums were identified in the Peipsi-Pskov Lake: Chlorophyta, Bacillariophyta, Cyanobacteria, Chrysophyta, Euglenophyta, Cryptophyta, Dinophyta and Xanthophyta. Floristic complex was characterized as сhlorophyta-diatom-cyanobacterial.The number of phytoplankton varied between 2.1 and 16.2 million cells/l depending on the season. The average number was 7.6 million cells/l. The biomass values ranged from 0.9 g/m3 to 3.6 g/m3. The average biomass was 2.3 g/m3.According to the ecological and geographical characteristics of the lake, widespread freshwater forms of microalgae predominated, preferring stagnant-flowing, slightly alkaline waters.Saprobiological analysis showed that the waters of the Peipsi-Pskov Lake were classified as moderately polluted, class III of water purity quality.
Highlights
Peipsi-Pskov Lake is located on the border between Estonia and the Pskov and Leningrad regions of Russia, and is the fourth largest lake in Europe
The maximum content of total phosphorus in August was observed in Lake Pskov at station 27-20 μg/dm3, in Lake Peipsi - at station 7 - 38 μg/dm3
In October, the waters of Lake Pskov were characterized by a higher content of total phosphorus compared to Lake Peipsi
Summary
Peipsi-Pskov Lake is located on the border between Estonia and the Pskov and Leningrad regions of Russia, and is the fourth largest lake in Europe. The area of the water mirror of the lake at an average water level is 3555 km, the volume is 25 km, the average depth is 7.1 m, the largest is 15.3 m. The height above sea level is 30 m. Lake Peipsi is an unstratified eutrophic lake. The water, especially in the southern part of the lake, is rich in nutrients. The lake is characterized by high productivity. Macrophytes occupy 5-8 % of the entire water area. The lake is home to more than 30 species of fish [1]
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