Assessment of the influence exercised by the hydrodynamic regime on the phytoplankton development and the water quality of the Kuibyshev Reservoir

Abstract

This paper presents the results of the field hydroecological observations performed within the Kuibyshev Reservoir during the period of 2016–2017. The high relevance of the research stems from the need to reduce the cyanobacterial bloom and to improve the water quality by increasing the flow rate during the summer low-water period. Among a number of climatic and anthropogenic factors that define the production processes in the reservoir, the flow rate was considered as adjustable, which is of certain value for preventing the negative consequences of eutrophication. The flow rate in the reservoir was determined using a two-dimensional numerical hydrodynamic model developed on the basis of the shallow water equations and implemented for the reservoir section on a rectangular spatial grid at 200 m intervals. The numerical modeling was performed for the depth-averaged flow rates in the reservoir. A series of model calculations was carried out, and the dependence of phytoplankton development on the flow control regime was analyzed. The impact of the hydrodynamic regime on phytoplankton development and water quality was assessed. The analysis of the observational data and the simulation results showed that the specific growth rate of phytoplankton is by an order of magnitude higher than the rate of water exchange in the reservoir. It was found that the phytoplankton biomass changes as a power function along with changes in the average flow rates of the reservoir. The data obtained confirm that an increased flow rate during the summer low-water period significantly reduces the amount of organic matter in the water and even prevents cyanobacterial bloom. The conclusion was made that phytoplankton development during the growing season is determined more by the intra-annual redistribution of the runoff than by the dryness of the year. The change of the water regime can play a no less important role in the healing of large reservoirs than the external organic load reduction.

Keywords

• phytoplankton
• eutrophication
• water quality
• hydrodynamics
• hydrochemistry
• numerical model
• kuibyshev reservoir