Water Quality Monitoring in the Volga Headwaters

Water Quality Monitoring in the Volga Headwaters

1. Introduction

The hydrosphere contains about 1.386 million km3 water [1], but about 97.5% of the global water is salt water vs. only 2.5% freshwater, of which 68.9% is stored in glaciers and permanent snow cover, 30.8% in the groundwater (including soil moisture), and only 0.3% in rivers and lakes [2]. The annual net transport from the sea to the land is 40,000 km2, and the river flow to the oceans also amounts to 40,000 km2 per year [3]. Thus, among freshwater resources, rivers are often referred to as lifelines [4,5,6,7,8] or arteries [9,10,11,12], as lotic systems often formed the cradles of civilizations [13]. But we also need to take into account “flying rivers” [14] and that 40% of terrestrial precipitation originates from land evaporation [15]. In the context of long-distance moisture transport, the theory of the biotic pump run by forests was developed, which predicts that forests supply moisture as well as the winds that carry it [16]. The large boreal forests of Scandinavia and Russia provide about 80% of the rainfall in China [15].
The catchment of Europe’s largest river, the Volga, is located in the southern taiga, and a major part of the runoff comes from boreal forests [17]. Due to large forests and minor anthropogenic activities, the headwater section of the Volga is of great interest regarding long-term monitoring [18]. In Agenda 2030, water is highlighted in Goal 6, “Clean water and sanitation”, and goal 15, “Life on Land” (which includes terrestrial and inland freshwater ecosystems) [19], but de facto is each of the 17 goals related to water and water availability.
In the Russian Federation, the governmental monitoring of running waters (according to RD 52.24.309-2016 [20]) includes quantity (discharge) and quality (physico-chemical parameters) [21], and some scientific campaigns include biological parameters to assess water quality [18,22]. In general, monitoring programs about physico-chemical parameters consider biogenic elements as well as organic substances [23]. Biogenic elements include mineral substances that are actively involved in the life of aquatic organisms, i.e., compounds of nitrogen, phosphorus, and silicon. Also, insufficient iron content can be one of the limiting factors in the development of phytoplankton; therefore, iron is often also included in the group of biogenic elements of water [21]. Organic substances in natural waters are compounds of carbon with other elements. The simplest and most common way to characterize the content of organic matter is the method of determining the oxidizability of water by the amount of oxygen consumed for the oxidation of this substance. Depending on the oxidizing agent used, permanganate or bichromate oxidizability is distinguished (COD—chemical oxygen demand). The quantitative assessment of easily oxidized organic substances by the amount of oxygen is estimated by the BOD (biochemical oxygen demand) [21].

Herein, we present results from long-term water-quality monitoring campaigns in the headwaters of the Volga in order to exemplify (a) the hydrochemical regime of the Upper Volga in the summer low-flow period, (b) the temporal and spatial variability of physico-chemical parameters, (c) the problem of “natural pollution”, as well as (d) changes in the content of biogenic elements and indicators of organic matter in the water of the Ivankovskoye Reservoir.

4. Discussion

Our study provides a holistic view on the physico-chemical condition of the headwaters of the Volga. The hydrochemical features of the region are mainly associated with a large number of mires and consist of increased values of chromaticity, oxidability, and high concentrations of iron, manganese, zinc and copper [35,42]. At the border of the mire and forest landscapes, surface waters are intensively saturated with various inorganic and organic substances, which is explained by the contact of acidic mire waters containing large amounts of fulvic acids with mineral soil and the subsequent formation of water-soluble and colloidal complexes. This is described herein as “natural pollution”. Further, data from Ivankovskoye VDHR revealed that the bottom sediments accumulated in reservoirs under certain conditions became a source of secondary water pollution, in particular manganese.
Based on the calculation of modal intervals of values of hydrochemical indicators in accordance with the criteria of the Hydrochemical Institute of Roshydromet, we assign the status of the Volga River ecosystem on its uppermost 670 km section as “balanced“. It is important to note that the specific combinatorial index of water pollution (UKIZV; see RD 52.24.643-2002 [43]) is currently used to assess the quality of surface waters in Russia. This indicator has a significant drawback since its value is also influenced by naturally caused exceedances of MPC of such indicators as oxidizability, iron, manganese, copper, zinc, and phenols. In accordance with the values of the UKIZV in the monitoring points of Roshydromet, the uppermost 670-km section of the Volga River is officially characterized as “very polluted” [31]. The system for assessing the quality of surface waters based on comparison with the country-wide MPC standards does not take into account the regional hydrochemical specifics of water bodies and leads to a distorted view of water quality (worse than it actually is). Thus, modal values of hydrochemical parameters determined on anthropogenically undisturbed sections of the river flow can be an alternative to MPC for assessing water quality.
Within different scientific projects biological sampling is also carried out. Based on this data, the free-flowing section between the Upper Volga Lakes and Tver is characterized as beta-mesosaprobic based on phytoplankton [44] and macroinvertebrates [18]. Also, the free-flowing section provides important habitats for rare species, such as the mayfly Prosopistoma pennigerum [45].
Our long-term data from the Volga headwaters reveal a good overview of dynamics and seasonal changes in water quality. However, from the scientific point of view, the existing data (mostly monthly time series) have limitations regarding the identification of extreme (minimum and maximum) values. This can be overcome with automatic observation stations that allow for studying the dynamics of hydrochemical indicators with minimal time discreteness, i.e., real-time water quality (RTWQ) monitoring [46,47]. An attempt to create such a station was made by the Tver division of Roshydromet in 2018 on the Volga River in Staritsa (Figure 7). Water was pumped continuously through the station, where temperature, oxygen, pH, Eh (redox potential), conductivity, as well as turbidity were measured at 10 min intervals. If critical changes were recognized, automatically, the samples were filled within the station and stored in a fridge. Unfortunately, due to technical reasons (blockage of the intake system by sediments), this station worked only for less than a year. Future research and monitoring campaigns along rivers, i.e., longitudinal studies, should consider the construction of automatic observation stations, as well as the joint use of hydrochemical and hydrobiological methods for assessing the status of the aquatic environment.
An analysis of the literature sources [27,39,40,41] and data from our own field studies showed that over a long period in the water of the Ivankovskoye Reservoir, the concentrations of ammonium and nitrate nitrogen increased, which is evidence of a deterioration in the sanitary condition of the reservoir. The concentrations of total iron and the values of permanganate oxidizability, due to natural factors, on average, change in the same ranges as in the first years of the reservoir’s existence. The intra- and inter-annual variability of all analyzed indicators is still noted. The study in 2021 confirmed the earlier conclusion that it is necessary to clarify the critical concentrations of nitrogen and phosphorus at which intensive algal blooms can occur in the reservoir. It is also necessary to take a number of environmental measures (e.g., riparian vegetation) to reduce the ingress of nitrogen and phosphorus into the reservoir.
The characteristics of the chemical composition of the water of the Ivankovskoye Reservoir at the beginning of the backwater (Tver, 100 m below the mouth of Tvertsa River) and in front of the Ivankovskoye HPP in the first years after the creation of the reservoir (1938, 1944–45) were published by D.D. Kudryavtsev [39]. Total iron concentrations in 1944–1945 downstream of Tver ranged from 0.12 to 0.60 mg/L; ammonium nitrogen concentrations ranged from 0.04 to 0.23 mgN/L, and the maximum concentrations of nitrates did not exceed 0.16 mgN/L. In 1938, the values of oxidizability in the water of the reservoir varied from 9.9 (September) to 15.8 mg/L (June), and in 1944, they ranged from 11.2 to 17.1 mg/L.
Analyses of the current state of surface water quality in the upper Volga basin make it possible to assess the existing levels of pollution, trends in change, and possibilities for its restoration. In order to assess the possibility of restoring water quality, it is necessary to determine the concentrations of pollutants. Nutrients, primarily nitrates and phosphates, are the limiting factors of water “blooming”, which is typical for shallow water bodies of slow water exchange, in particular, the Ivankovo reservoir. Previous studies [40] showed that the maximum concentration of phosphorus and mineral nitrogen, at which the phytoplankton biomass did not exceed its background value (0.81 mg/L), was 0.07 mg/L, respectively 1.5 mg/L.
Concentrations of ammonium nitrogen in the water of the Ivankovskoye Reservoir in the period from 2018 to 2021 changed, on average, in the range of 0.03–1.61 mgN/L and were higher in certain periods than in the first years of existence [40]. An increase in concentrations is evidence of a deterioration of the sanitary condition of the reservoir. The concentrations of nitrate nitrogen in the water of the reservoir in recent years have fluctuated in the range of 0.06–0.88 mgN/L and were higher than in the first years of the existence of the reservoir [40,41] but below the limit at which the phytoplankton values exceed the background values.
Total iron concentrations from 2018 to 2021, on average, fluctuated in the range of 0.06–0.34 mgN/L. The maximum concentrations were recorded in winter at the Bezborodovo gauge. The range of their change in comparison with the first years of the existence of the reservoir [39] has practically not changed, which is not surprising since the content of iron in the water of the reservoir is determined mainly by natural factors. The seasonal dynamic in the iron concentrations in rivers with paludified catchments is also known from other catchments, e.g., [48,49], which is linked to fluctuating pH [48] as well as the source (surface water vs. groundwater) [50].

The maximum values of color and permanganate oxidizability in recent years in all observation sites were noted in spring. The range of values varied from 24 to 90 degrees (Pt-Co scale), respectively, from 6.6 to 21.2 mgO/L. The range of changes in permanganate oxidizability in recent years, on average, has remained the same as in the first years of the reservoir’s existence. But the minimum and maximum observed values in some years differed from those observed in the first years of existence. For indicators of the content of organic matter and biogenic elements, spatio-temporal variability is characteristic under the influence of changes in water discharge and anthropogenic load.

Since 2004, the ECOMAG (ECOlogical Model for Applied Geophysics) model has been used for the simulation of hydrological characteristics and water inflow into reservoirs of the Volga–Kama cascade [51], and recently, heavy metals were also included in the model [52,53]. A future application can be the modeling of nitrogen loads toward the Ivankovskoye Reservoir based on the data presented herein.
In the last century, in European rivers and lakes, the water temperature rose in the range from +0.05 to +0.8 °C per decade, and our case study along Tudovka—a tributary of the Volga in Tver region—revealed an increase of 0.20 °C/decade [54]. For the free-flowing section of the Volga River in the Tver region, we are currently analyzing the available dataset in order to compare the data from a mid-sized tributary with the main channel.

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