The Species Structure of Plankton Communities as a Response to Changes in the Trophic Gradient of the Mouth Areas of Large Tributaries to a Lowland Reservoir

Abstract

The mouth areas of large rivers can serve as a good model of heterogeneity sites with a pronounced trophic gradient to assess the impact of the degree of eutrophication on different plankton communities. The aim of this research was to identify the possible response of the diversity indicators of phyto- and zooplankton communities to trophic gradients in the mouth area of two large tributaries of the reservoir, formed in the Middle Volga River (Russia). Both linear regression models and canonical correlation analysis (CCA) were used to assess the role of abiotic and biotic predictors in the structural organization of plankton communities and to assess the changes in the parameters of the species plankton community structure in the trophic gradient. It was found that the species diversity (Adjusted R2 = 0.116) and evenness (Adjusted R2 = 0.114) of phytoplankton significantly decreased with an increase in the degree of eutrophication, while the species diversity (Adjusted R2 = 0.059) and evenness (Adjusted R2 = 0.073) of zooplankton increased. According to the CCA models, electrical conductivity (EC) explained the largest proportion of the observed dispersion. The Trophic State Index (TSI) explained 3.0% of the total variance in the phytoplankton community species structure and 7.8% in the zooplankton one. The variation in phyto- and zooplankton dominant complexes generally corresponded to the well-known patterns of plankton species succession in the gradient of trophic conditions and can be considered as a classic manifestation of the cascade effect in the food chains of freshwater plankton communities. Our results highlight the necessity of studying the mouth river areas, as well as applying an integrated approach to investigating the response of plankton communities to eutrophication processes of continental water bodies.

Investigation of Water Dynamics Nearby Hydroelectric Power Plant of the Gorky Reservoir on Water Environment: Case Study of 2022

“…The authors analyzed such parameters of the phytoplankton communities as abundance (N (10 6 cells/L)) and biomass (g/m 3 ). A detailed description of the calculation of the indicators mentioned above is available in the work [34]. The dominant species included species with an abundance or biomass of more than 10% of the total value [35].…”

Biodiversity of zooplankton (Rotifera, Cladocera and Copepoda) in the tributaries of Cheboksary Reservoir (Middle Volga, Russia)

“…Rivers are the most widespread type of water body in the world. They have rich faunistic diversity and their estuaries act as refuges for zooplankton ( Krylov et al 2010 , Mukhortova et al 2015 , Zhikharev et al 2023a , Zhikharev et al 2023b ). River ecotones formed in estuaries maintain high biodiversity, bioproduction and nutrient transformation ( Ward and Wiens 2001 , Ward et al 2002 ).…”

“…In recent decades, the increasing anthropogenic impact on aquatic ecosystems has resulted in accelerated pollution, eutrophication and, as a consequence, changes in the biodiversity of aquatic communities ( Loreau et al 2001 , Naeem et al 2012 , Zhikharev et al 2023b ). Planktonic crustaceans and rotifers are sensitive to eutrophication of aquatic ecosystems and could change species diversity and spatial distribution of communities ( Shurganova et al 2018 , Afonina and Tashlykova 2020 , Krupa et al 2020 , Liang et al 2020 , Waite et al 2020 , Zhikharev et al 2021 ).…”