Assessment of the restoration of the zooplankton community in lake Chishmyale after ecorehabilitation activities

Lake Chishmyale is located in Kazan (Russia), in an area with multi-storey residential development. In the 2010s, the lake was completely filled up due to the planned development of this area. However, the work was stopped, because there was an accumulation of surface water on the site, which led to the re-formation of a small reservoir. In 2015, it was decided to restore the lake and create a public garden. Eco-rehabilitation measures included the restoration of the lake to its former boundaries, artificial recharge of the reservoir, and shore strengthening with gabions. The aim of this work is to assess the recovery of the zooplankton community following the implementation of eco-rehabilitation activities. During the growing seasons of 2016–2018, the physicochemical indicators of water were measured, samples of zooplankton were taken. The data obtained were compared with the results of studies performed before recovery. The analysis of satellite images showed that the area of the newly created reservoir is less than the previously existing one by 46 %. The water in the lake has an average mineralization, the environment is neutral. A deficiency of dissolved oxygen in water, developing in July-August, was revealed. During the post-rehabilitation period, 51 species were found in zooplankton. The average number of species in the sample increased from 4.8 ± 0.7 in 2016 to 7.9 ± 0.8 in 2018. Comparison of the species richness on the same dates before and after recovery demonstrates a statistically significant increase in this parameter. The quantitative indicators of zooplankton in the post-rehabilitation period were low, the average abundance over the growing season varied from 10.59 ± 3.15 to 40.24 ± 24.56 thousand ind./m3, and the biomass – from 0.031 ± 0.010 to 0.098 ± 0.050 g/m3. The values of the Shannon Species Diversity Index were not high. The saprobic index values corresponded to the β-mesosaprobic zone. Thus, despite the positive aspects associated with the restoration of the lake and the improvement of the coastal zone, the zooplankton communities are still characterized by low species richness and low quantitative indicators.