Zooplankton under the conditions of lake eutrophication and acidification

Abstract

Bogging processes are accompanied by the accumulation of humic acids, pH decrease, and low values of oxygen dissolved in water. Environmental conditions that are unfavorable for hydrobionts affect zooplankton communities and change their structure. We studied zooplankton of 14 lakes in the Middle Volga region (Russia). The lakes are acidified to different degrees; three groups of lakes were distinguished according to the degree of acidification: acidic (pH 5–5.5), transitional (pH 5.6–6.5), and neutral (pH > 6.5). The purpose of the study was to reveal the peculiarities of the structure of zooplankton communities under the conditions of natural bogging and acidification. The abundance of zooplankton was of the same order in the acidic and transitional lakes and about three times higher in the neutral ones, while rotifers were dominant in the acidic mesotrophic and neutral eutrophic lakes, where they comprised about 80% of the population. The biomass in the acidic and neutral lakes was low and did not exceed 1 g/m3. Changes in the abundance of prevailing zooplankton groups by the pH gradient were revealed. With the decrease in the acidity, the following changes were observed: Conochilus hippocrepis (Schrank, 1803) was replaced by C. unicornis Rousellet, 1892; the proportion of the genera Kellicottia, Keratella, and Ceriodaphnia increased; Postclausa hyptopus (Ehrenberg, 1838) appeared; and the abundance of the genus Eudiaptomus increased. In the neutral lakes, the proportion of the genus Keratella, as well as that of the genera Asplanchna, Polyarthra, and Trichocerca, increased and the species composition became typical for the eutrophic lakes of the Middle Volga region. In the acidic lakes, an increase in the number of microdetritivores of the genus Diaphanosoma (biomass) was noticed. Its value decreased in the transitional lakes, where they were replaced by the genus Daphnia and the genus Ceriodaphnia. In the transitional lakes, compared with the acidic ones, the proportion of coarse filter feeders of the genus Eudiaptomus increased. In the neutral lakes, they were replaced by crustaceans of the genus Thermocyclops and their juvenile stages. The pecies diversity of zooplankton increased in the direction from the acidic to neutral lakes.

Keywords

• zooplankton
• bog
• acidification
• waterlogging
• structure
• community
• bioindication
• lake