Mozhaisk Reservoir Research Articles

Features of Plankton Metabolism: Results of Automated Measurements in the Mozhaisk Reservoir

Features of Plankton Metabolism: Results of Automated Measurements in the Mozhaisk Reservoir

Gustera Blicca bjoerkna (Linnaeus, 1758) of small reservoirs of Central Russia

The question of the fishery significance of the gustera inhabiting the reservoirs of the Smolensk, Moscow, Ryazan and Kursk regions is considered. The occurrence of gustera in the catches of fixed nets with a mesh pitch of 30–50 mm is shown on the example of small reservoirs in Central Russia. Its share in net catches directly depends on the thermal regime of reservoirs and increases in the direction from north to south, from the Moskvoretsko-Vazuzskaya group of reservoirs to the reservoirs of the Kursk region. The greatest importance of the cluster is in the structure of ichthyocenoses of cooling reservoirs of nuclear power plants and GRES. Depending on the morphological features of reservoirs, the main biotopes of the gustera are the sublittoral zone and the flooded floodplain in the depth range from 2 to 8 m. Using the example of the Mozhaisk reservoir, it is shown that the share of gust in the structure of the fish part of the community has not changed significantly over the fifty-year period of its existence due to the relative stability of the ecosystem of this reservoir and operation in the mode of a drinking reservoir. The highest indicators of the weight growth of gust are characteristic of cooling reservoirs of nuclear power plants and GRES, as well as Kursk reservoirs. Significantly inferior to them is the gaster from the colder-water Vazuz and Moskvoretsky reservoirs. The onset of puberty in the gustera inhabiting the reservoirs of Central Russia, as well as growth, is closely interrelated with the thermal regime of these reservoirs and the duration of the feeding period. In the absence of industrial fishing and a low degree of development of the reserves of gustera by amateur fishermen, in most reservoirs of the group under consideration, a high biomass of this species is observed in the range from 25 to 116 kg/ha. When highly productive benthic fish are introduced, gustera will be their competitor in nutrition and significantly reduce the efficiency of reservoir stocking. It is recommended to suppress the number of gustera by intensifying amateur fishing and mass stocking of reservoirs with predatory fish species.

Features of Plankton Metabolism: Results of Automated Measurements in the Mozhaisk Reservoir

Plankton metabolism determines fluctuations in the oxygen concentrations of a water body, its ecological condition, and exchange of СО2 with the atmosphere. We used an automated device that allowed us to make mass measurements of intraday values of the gross primary production (GPP) and respiration (R) of plankton. During our studies of the Mozhaisk reservoir (Russia) in the summer of 2017, we established an important fact: the maximum values of GPP are observed essentially earlier in the daytime than those of R. This is explained by the fact that GPP is related to solar radiation (the maximum values are observed at noon), whereas R is related to the temperature of water, which reaches its maximum several hours after in the afternoon. As a result, the maximum value of dissolved oxygen is observed in the second half of the day, when GPP and R become even. The device we have designed may be used for continuous monitoring of metabolism of plankton and of its responses to various hydrometeorological, hydrochemical and anthropogenic impacts.

Methods for instrumental assessment of methane emission in reservoirs

Reservoirs are a significant source of methane in the atmosphere. Different estimations of the total methane emission from reservoirs vary greatly. In order to more accurately estimation of the methane emission from reservoirs, it is necessary to investigate the spatiotemporal variability of CH4 fluxes. To study this variability, detailed instrumental measurements of methane fluxes over a long period are required. Such measurements have been carried out for 6 years at the Mozhaisk Reservoir. These measurements showed that the determining factor of the spatiotemporal methane fluxes variability is the meteorological situation and the water level regime. These factors form the stratification of the water column. The highest values of methane flux into the atmosphere are observed in the middle part of the reservoir. The temporal variation of the methane flux is characterized by a general pattern for all years when the measurements were carried out. The methane flux increases during the summer period and reaches the highest values before the beginning of the autumn mixing stage. Also, high flux values observed during periods of storm events that cause mixing of the water column.

Water Blooming in the Reservoir with Long-Term Discharge Regulation

The factors of phytoplankton development in the stratified Mozhaisk Reservoir are analyzed on the basis of long-term observations and model calculations. To analyze the variability of phytoplankton biomass values, the weather contrast index based on the identification of synoptic cycles of water surface temperature was used. A comparative assessment of the water blooming intensity in different years was carried out based on the water blooming index, calculated as the sum of the daily values of phytoplankton biomass resulted from the model calculations. The study analyzes specific features of the development of diatoms and cyanobacteria in the reservoir depending on hydro-meteorological conditions and long-term changes in the values of water blooming and weather contrast indices.

Analysis of Long-Term Changes in Anoxic Zones in the Mozhaisk Reservoir Based on Model Calculations

The results of model calculations of the characteristics of anoxic zones in the Mozhaisk Reservoir over a 57-year period have been analyzed. A two-dimensional box hydrological model of the reservoir has been used to calculate variations of the values of ecological variables with a daily time step. The main regularities in the formation and development of anoxic conditions in different parts of the reservoir have been revealed. The factors that govern the space and time distribution of anoxic zones in the reservoir in different years have been identified. Empirical dependences of the volumes of anoxic zones on the characteristics of water mass stability in the reservoir and blooming index, which characterizes the rate of primary production in reservoir ecosystem, have been obtained. The identified trends toward an increase in anoxic zone volumes over the period under consideration characterize the progressive eutrophication of the Mozhaisk Reservoir.

On the relation of bottom valley-type reservoir hydrocarbon carbon flux and hydrological structure of water body

Circulation of carbon in water bodies is fundamental process of nutriens cycle in water ecosystems. Carbon flux from bottom sediments is the less studied chain of this circulation nowdays. The aim of investigation was the study of HCO3 flux from bottom sediments in the valley-type reservoir and identification of their relation with hydrological structure of water body. Field works and laboratory experiments were fulfilled at Mozhaisk reservoir in 2017-2019. These years differed by weather conditions, level regime and stability of water masses. Hydrological surveys were fulfilled three times during summer period of each year. They included measuring of vertical distribution of hydrological characteristic and sampling of water and bottom sediments. The Kuznetsov-Romanenko tube method was used to study exchange processes. Hydrocarbonate carbon flux from sediments into the water may have a wide range (50-900 mgC/m2day). By comparison of HCO3 flux with hydrological structure it was revealed that in deep (>8 m) regions it depends on stratification and thickness of uniform hypolymnion, where seiches and compensation currents may promote transsedimentation from shallow places to flooded river bed. At the regions with depth <8 m hydrocarbonate carbon flux from sediments depends much more from autochthonic organic matter, produced by phytoplankton. The relationship of the HCO3 flux with the content of organic matter in the soil and its hygroscopic humidity is insignificant.

Model Assessment of the Mozhaisk Reservoir Impact on the Transformation of Organic Matter Flow

The results of model calculations for the long-term balance of persistent and labile organic substances in the Mozhaisk Reservoir are analyzed. The model verification based on numerous hydrological and hydrochemical surveys of the reservoir demonstrated the adequacy of the model simulation of organic matter concentrations in the reservoir water. Long-term trends in the individual components of the organic matter balance in the reservoir are revealed. It is found that an average long-term decrease in the organic matter flow under the influence of intra-reservoir processes of its destruction makes up 28%, with the maximum values of the retention rate of organic substances during the spring flood phase.

Influence of hydrological factors on reservoir algal blooming

Based on model calculations of phytoplankton biomass over a long period in the Mozhaisk reservoir, the role of hydrological factors in fluctuations of production processes in the reservoir is analyzed. Among the hydrological factors, the most important for reservoir blooming is the reservoir filling mode in the spring and the volume of flood water intake in the summer. Sharp fluctuations in the phytoplankton development during the growing season are mainly due to the contrast of weather conditions, which determines the change of phases of cold weather to hot windless.

Sensitivity Assessment of a Runoff Formation Model in the Mozhaisk Reservoir River Basin

The physically based model of river runoff formation with a daily resolution ECOMAG was adapted for the Mozhaisk Reservoir with an area of 1360 km2. A large series of numerical experiments were carried out in order to investigate the sensitivity of the model to the spatial resolution of land surface characteristics and the size of calculation cells. Digital elevation models (DEMs) of three different spatial resolutions (50, 100 m, and 2 km) were used along with model schematizations of the catchment area and river network with varying detail. In addition, the model sensitivity to sets of calibration parameters when modelling genetic runoff components was studied, as a part of the approaches to mitigating the problem of equifinality. The importance of incorporating additional hydrochemical information for a correct description of the spatial and temporal genetic structure of river runoff is shown.

Influence of hydrological structure on exchange processes between water and bottom sediments in Mozhaysk Reservoir

The results of studies of exchange processes at the “water – bottom sediments” border for the summer period 2017–18 at the Mozhaisk reservoir are presented. The factors that determine the intensity values of methane and mineral phosphorus fluxes from bottom sediments as well as their spatial non-uniformity, associated with the soils distribution characteristics in the valley-type reservoir, are analysed.

Seasonal variation of methane flux from Mozhaisk reservoir

The paper present the results of methane flux measuring from the surface of valley type reservoir with a long water residence time. The factors of its spatio-time variations are revealed. The results of calculation and measurements of diffusive flux are compared.

Methane Emission From the Surface of the Mozhaisk Valley-Type Reservoir

This article deals with spatio-temporal changes in methane emission from the surface of the Mozhaisk reservoir. Seasonal changes in methane content and flux were revealed for different morphological areas of the reservoir, based on field observation data obtained in 2015–2018. In the low-flow Mozhaisk reservoir, the methane content in the boundary and bottom layers of the deep-water areas at the end of the summer stratification period may differ by three orders of magnitude. According to results from measuring with floating chambers in the central area of the reservoir from early June to the end of the period of direct stratification (August–September) the total methane flux increased from less than 1 to 16 mgC-CH4/(m2/hr). Time-coincident measurements with floating chambers of two types revealed characteristic values of the methane flux components and their change over the sampling period. It was found that at the period of stratification the diffusive flux predominates with the mean values 0.2 mgC-CH4/(m2/hr). A further increase in the total methane flux is associated with an increase of its bubble component. According to calculations, the diffusive flux reaches its maximum values in late summer in the shallow zone of the reservoir. It is established that a significant increase of the values of the total methane flux is observed when the upper boundary of the oxygen-free zone reaches the lower boundary of the epilimnion. The methane flux density reaches its largest values prior to destruction of the direct stratification. Comparison of field measurements with literature data showed that the magnitude of emission from reservoirs with a slow water exchange in the temperate zone can be underestimated in the evaluation of global methane emission.

New Possibilities of the Classical Method: Automated Determination of Primary Production and Destruction of Organic Substance in a Reservoir by the Oxygen Method

A device for the automated determination of the primary production (PP) and destruction (D) of organic matter in a water body by the oxygen method is presented. It consists of light and dark bottles with optical dissolved oxygen sensors (Onset, YSI) and the pump changing water in bottles through a predetermined period (3 h). Results of 3-day measurements performed in the Mozhaisk Reservoir have shown that the device describes the studied processes fairly well, significantly facilitating field research. The gross PP obtained during the experiment constituted about 4 mg O2/(L day), which corresponds to the eutrophic status of the reservoir. The device can be used for studying the functional characteristics of aquatic ecosystems under changing environmental factors such as temperature, illumination, and content of biogenic elements.

Modeling the Genetic Components of River Runoff for the Mozhaisk Reservoir Watershed

The physically-based ECOMAG model of river runoff formation has been adapted to simulate the processes in the Mozhaisk Reservoir watershed. The main goal of the study was to correctly simulate the genetic components of the runoff considering the hydrochemical methods of identifying the water masses in calibrating the model parameters. To break down the runoff hydrograph by genetic components, a technique was applied, based on the chemical–statistical analysis of the composition of the water mass mixture. The many years’ runoff hydrographs from 3 gauging stations and hydrochemical data from which the genetic components of the river runoff have been determined were used to calibrate model parameters. A satisfactory agreement has been obtained between the runoff hydrographs from gauge stations and the hydrographs simulated by the model and obtained by analyzing hydrochemical data of the genetic components of the river water. The regularities of the annual distribution of the genetic runoff components have been analyzed and the genetic types of waters prevailing in different phases of water regime have been demonstrated. The proposed method of determining model parameters by hydrometric and hydrogeochemical data allows simulation of the behavior of the water sources and description of the spatial-temporal genetic structure of the river runoff.

The Rate of Oxygen Release from Freshwater Bodies

The annual regimes of estimated rates of oxygen and carbon dioxide exchange between water surface and the atmosphere was compared for two water bodies with different sizes and hydroecological conditions: the deep oligotrophic Lake Baikal and the small mesotrophic–eutrophic Mozhaisk Reservoir with water exchange rate 150 times greater than that of Baikal. The obtained, very large, differences between the rates of gas evasions and invasions in the lake and the reservoir allow the rates of these processes to be used as integral characteristics for the parameterization of the self-purification capacity of freshwater bodies from organic pollutants.

Correlating the concentration of mobile manganese with redox- and acid–base properties in sediment column of the Mozhaisk Reservoir in the period of its formation (1970-1975)

Data of 1970-1971 and 1974-1975 for six layers of the Mozhaisk Reservoir were used to analyze the within-year relationships between Mn concentration and silt Eh and pH. The character of these relationships is explained. For the first time, a critical Eh zone, where Mn concentration abruptly changes, was identified. The redox processes involving Mn were shown to gradually stabilize over time.

Assessment of the role of reservoir morphology in parameterizing its ecological regime under extreme hydrological conditions

The results are presented of scenario calculations of water quality parameters and biological productivity in three areas of morphologically different types of reservoirs in the years with extreme water conditions. Three models of reservoirs with the same size and flowage are used: river-, lake-, and mixed-type reservoirs. The study is based on the morphometric parameters and bathygraphical curves from 18 stretches of the Mozhaisk Reservoir. The revealed differences in the intensity of algae bloom and anoxia in hypolimnion in the simulated reservoirs are compared with the criteria of the norm and risk of the ecological regime of the reservoirs being the sources of municipal water supply.

Changes in the contents of strontium, barium, and lead in scales of bream Abramis brama from the Mozhaisk Reservoir over a quarter century.

The heavy metal contents in the scales of bream (Abramis brama) from the Mozhaisk Reservoir collected in the second half of the 1980s were compared to the current values. The concentrations of three out of the seven elements studied in the bream scales have changed severalfold during the past quarter century: that of strontium has decreased, and those of barium and lead have increased. Short-term variations of heavy metal contents have proved to be smaller than the observed long-term differences. There is grounds to believe that these long-term differences adequately reflect the changes that have occurred in the water body.

Time variations of the concentration of mobile forms of Fe, Mn, and P in silts of the Mozhaisk Reservoir

Layer-by-layer concentrations of Fe, Mn, and P compounds in the channel silts of the Krasnovidovo Pool, the Mozhaisk Reservoir, was studied in 1970–1971 and 1974–1975. The mean annual concentration of those elements in a sediment column was found to increase by factors of 1.1, 2, and 1.4 for Fe, Mn, and P, respectively. The factors that caused such changes are discussed.