Zooplankton of small reservoirs of the desert zone of Kazakhstan

Abstract

The purpose of the work is to study the abundance and biomass of zooplankton communities of small reservoirs to assess the possibility of their use for fishery purposes. The article presents the results of a survey of 10 reservoirs of the middle desert and desert plains of the Central Asian type in September 2020. Small reservoirs and lakes of the region (0.01–0.52 km²) are freshwater, shallow (average depth 0.5–2.3 m), with a high degree of overgrowth of coastal (25–60%) and aquatic vegetation (60–90%). Eight of them are at the lower level of mesotrophy in terms of organic matter content. Lakes Mozgovoy and Kosmurat are mesoeutrophic and oligotrophic reservoirs. In most reservoirs at the time of the study, summer water temperatures were noted during the day (18.3–23.7 °C). A feature of the six reservoirs was the high content of phosphorus ions. The optimal level of this element was in the three upper reservoirs of the Kenes cascade due to the inflow of water from the mountains. The species composition of zooplankton in September is poor, the number of species ranged from 2 to 13. The basis of quantitative characteristics were planktonic and benthic Copepoda or Rotifera. The exception was oz. Cerebral, in which Cladocera prevailed at the expense of representatives of the Chydoridae. The biomass of zooplankton in the lakes was also quite low from 5.3 to 832.5 mg/m³. Thus, according to S.P. Kitaev’s trophic scale, reservoirs belong to the oligotrophic type. A comparative analysis of the zooplankton state in autumn and in other seasons shows a consistently low productivity of arid cenoses in conditions of low water and significant overgrowth. To improve the productivity of reservoirs and their further fishery use, it is necessary to optimize the habitat of aquatic organisms with an improvement in the water content regime and a decrease in the level of overgrowth in them.