| Abstract [eng] |
The aim of the study was to assess the ecological status of phytoplankton communities in the lakes of the Utena region studied in 2022. In this work, phytoplankton samples from lakes in the Utena region were analysed, biomass and abundance were calculated and the ecological status of the communities was analysed. Particular attention was paid to species diversity and its seasonal dynamics and correlation with other lake water parameters such as chlorophyll-a, temperature, total nitrogen, phosphorus and others. The sampling was carried out in 2022 in April-October in the Utena region. A total of 78 phytoplankton samples were analysed using inverse microscopy (Utermöhl technique). Two of the five lakes had the highest values for two parameters determining the hydrochemical-hydrophysical and hydrobiological characteristics in May: total phosphorus and chlorophyll a. The lowest mean water temperature (8.1 °C) was recorded in April, while the mean dissolved O2 concentration was the highest at 12.2 mg/l O2. The highest average water temperature was in the summer season, ranging from 20.2 to 23.9 °C, with a slight increase in total nitrogen concentration in July of 0.58 mg/l. The study found that total phytoplankton abundances and biomasses were highest during the spring season. Chrysophyceae were the most abundant in the spring months (about 70%), while in the summer season, green algae and blue-green algae start to dominate in terms of abundance. In the autumn months, algae of the genus Chrysochromulina and Zygnematophyceae were more abundant. Correlations between water parameters and phytoplankton communities in the lakes studied were analysed. Among the lakes studied, the ecological status of phytoplankton communities was the worst in Lake Suosa, while the best in Lakes Luokesai, Šiurpys and Šventas. Seasonal and temperature changes had the greatest impact on the ecological status of the lakes. A positive correlation was found between the main ecological groups of phytoplankton: Cryptophyceae, Chrysophyceae and Dinophyceae. The phytoplankton groups of green algae and blue-green algae are negatively correlated or not correlated at all with these groups. The knowledge, practice and results of the study have led to recommendations. It was suggested that the frequency of sampling should be taken into account in lake water surveys, which would give greater confidence in the results. This would allow future scenarios to be predicted through the assessment of biodynamic interactions, analysis of community structure and the use of modelling programmes. |
