Importance of the Variability of Geocryological Conditions in the Determination of the Significance of the Lakes in the Structure of Regional Water Discharge Abstract The dynamics of the talik zones, associated both with the internal cyclical nature of their development and with climate changes, leads to temporary differences in the volume of water exchange between groundwater and surface water in permafrost areas. Periodic fluctuations in the volumes of lake water are indicative of the unstable dynamics of flows between surface and groundwater. The region of investigation was located around the Chara Depression in Northern Transbaikalia of Russia. During fieldwork and remote sensing studies around the so-called “flickering” lakes on the middle and upper Pleistocene, sediments of end-moraines were identified in the Chara basin. This type of lakes is characterized by considerable fluctuations of water level with alternating complete drainage and subsequent re-filling of the lake depression. Fluctuations of level are not always synchronous in the lakes and do not uniquely depend on the regime of atmospheric precipitation. The authors link it with changes in permafrost conditions.

Simulation of Phytoplankton Community Transformations in the Ivankovo and Rybinsk Reservoirs: Graphical Analysis Abstract The paper describes a method of graphical analysis developed for freshwater ecosystems. The method was first used to analyze the structure of phytoplankton communities in the Ivankovo and Rybinsk reservoirs. Step-by-step spatial transformations of phytoplankton structure were revealed. Three scenarios of their transformation were highlighted.

The Impact of Climate Change on Surface, Subsurface, and Groundwater Flow: A Case Study of the Oka River (European Russia) Abstract The article considers an approach to evaluating the change in surface, subsurface and groundwater flow on a large river catchment exemplified by the Oka River basin. The study is based on the synthesis of a physical-mathematical model of runoff formation and atmosphere–ocean general circulation models. The paper presents the results of calibration and verification of a hydrological model over a period of history, as well as the assessment of reproduction accuracy of meteorological and hydrological characteristics according to the data of global climate models and observation data. Based on an ensemble of atmosphere–ocean general circulation models, the changes in meteorological (air temperature, precipitation, air humidity deficit) and hydrological (surface runoff, soil moisture content, groundwater flow) characteristics by the middle and the end of the 21st century have been calculated, under the scenarios RCP 2.6 and RCP 6.0 with regard to the historical period.

Modeling Water Pollution under Different Scenarios of Zinc Load on the Nizhnekamskoe Reservoir Watershed Abstract The potentialities of the physically-based model ECOMAG-HM for the study of zinc content formation regularities in the Nizhnekamskoe Reservoir basin have been demonstrated. The basin is characterized by high concentrations of heavy metals in natural waters due to the significant content of ore-forming elements in rocks and a high level of economic development. The daily zinc concentrations have been calculated, and the maps of mean annual zinc concentrations in the river network have been compiled. Local areas of the catchment not covered by hydrochemical observations and showing a significant level of river water contamination by zinc have been identified. The fields of the genetic components of zinc hydrochemical runoff have been calculated. The contribution of anthropogenic sources to the zinc runoff formation has been estimated, and it has been established that, with the current level of anthropogenic load, the contribution of wastewater point discharges does not exceed 4%. The scenarios and consequences of increasing the amount of zinc discharged as part of wastewater are considered. The time scale of the catchment self-purification from zinc has been evaluated. The results show that, in the absence of external impacts on the catchment area, a decrease in zinc content in river waters over a 400-year period will be about as little as 8%.

Modeling the Hydrological Regime of Small Testbed Catchments Based on Field Observations: A Case Study of the Pravaya Sokolovka River, the Upper Ussuri River Basin Abstract The aim of this study is to apply mathematical modeling to describe the hydrological regime of small testbed catchments located in the territory of the Verkhne-Ussuriisky Biocenological Experimental Station (Federal Scientific Сenter of the East Asia Terrestrial Biodiversity, Far Eastern Branch, Russian Academy of Sciences). The experience in data preparation and the calibration and application of two hydrological models, based on field observations, is presented. The interpretation of the results was based on the analysis of modeling errors, calibrated model parameter values and physical means, and simulated water balance elements. For all applied models and cases, the average and high flow values are close to the measurements, but the base flow is overestimated. A noticeable result is that the models parameters kept their physical sense and calculated water balance elements are comparable for both models used.

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

Sulfide Sulfur in Water Objects with Different Mineralization Abstract Hydrogen sulfide, like other sulfides, is formed in aquatic environments due to sulphate reduction processes and putrefactive decomposition of organic matter of bottom sediments, as well as due to the influx of wastewater containing it. It is toxic for water objects used for fishery and drinking water supply. It decreases organoleptic properties and water quality and causes death of hydrobionts, while this gas is an important therapeutic component or water objects with therapeutic mud. The authors have analyzed the literature and original data on the concentration of hydrogen sulfide in freshwater reservoirs and streams, as well as in water objects with elevated mineralization (seas, bays, estuaries, and mud lakes) of the Russian Federation. Water mineralization in the studied water objects varies from <1 g/dm3 to >400 g/dm3, and dissolved oxygen varies from <0.6 to 10.0 mg/dm3. The total hydrogen sulfide content of water (H2S, HS–, S2–) varies within a wide range from 0.0 to 50 mg/dm3. Freshwater and streams relative to water objects with a high salinity are characterized by lower concentrations of sulfide sulfur. The concentration of sulfide sulfur (∑H2S) in water has a close inverse relation to dissolved oxygen. In addition to the natural factors and processes that affect the distribution of sulfide sulfur concentration in water, the pollution and eutrophication of water bodies also play a major role. For instance, the salt Big Tambukan Lake shows an inverse relationship between the concentrations of ∑H2S in water and the depth of bottom sediment, and this gas is chiefly linked to sulfides.

Standardization as an Instrument of Environmental Regulation of Water Use Abstract World experience is analyzed to show that the role of standardization in water use management has increased considerably in the recent years. The state of the technical regulation of water use in the Russian Federation is considered, and the use of standardization in this sphere is shown to be not perfect. The main functions of standardization as an instrument of environmental management are determined. Examples are discussed to show that the lack of standards causes errors in the application of the Russian legislation now in force. An example shows how the described approach to standardization can be used to solve the problem of control of water advanced treatment by criterion of maximal benefit.

Weather Radar Data for Hydrological Modelling: An Application for South of Primorye Region, Russia Abstract This paper describes the experience of using weather radar data to simulate a catastrophic flood caused by intense rains that occurred in the period from August 5 to 8, 2017 in the south of Primorye, Russia. The Amba River (243 km2), where historical discharge peak was measured, was chosen as the test watershed of this study. Weather radar hourly precipitation fields with a spatial resolution of 1 km and a modified version of the kinematic-wave-based geomorphologic IUH model were used to estimate the hydrograph at the watershed outlet. The simulation was performed with an hourly time step; using the precipitation grids obtained from initial radar reflectivity data, and then using bias-correction based on precipitation measurement at the closest meteorological station. In the preliminary tests, the simulated discharge was found underestimated about two times in comparison with the observed discharges. After performing a precipitation bias-correction, the simulated and observed discharges showed good accordance.

Statistical Modeling of the Global River Runoff Using GCMs: Comparison with the Observational Data and Reanalysis Results Abstract Specific methods are proposed to assimilate the results of the “historical” experiments on 28 climate models. The results of the analysis confirm the hypothesis regarding a stationary character of changes in the global river runoff during “instrumental” period (approximately 150 years). Part of the models (about one third) reproduces the non-stationary changes in the global runoff with respect to the mean. At the same time, the number of such models indicating increased runoff is exactly equal to the number of models that indicate a decrease in runoff. The models generally reproduce well the coefficient of variation of global river runoff in comparison with the observational data, as well as the small value of the coefficient of asymmetry. The model of the Gaussian white noise is optimal for the description of the majority of the annual time series of global river runoff generated by the GCMs.