Nutrients, Organic Matter, and Trace Elements in Lake Gusinoe (Transbaikalia)

: Lake Gusinoe is the second largest freshwater lake in Transbaikalia. Lakes serve as a source for drinking water, irrigation, and as a water source for the electricity, aquatic production, and tourism industry. Currently variations of content nutrients and organic matter differ in different areas of the lake. The content of total nitrogen, phosphorus, organic matter, and dissolved oxygen are distinguished more than 1.2–2.0 times. In accordance with the behavior of elements in the water, three groups of elements can be distinguished. The ﬁrst group of elements, including Li, Ga, Ge, As, Rb, Sr, Mo, Cd, W, and U, were directly correlated with variations of major elements. The ﬁrst group of elements showed decreasing concentrations with an increasing amount of total dissolved salt (TDS). The second group of elements, including Fe, Y, Nb, Th, and REE, were correlated oppositely with variations of TDS. The behavior of the third group of elements, including Mn, Zn, Ni, Cu, and Pb, decoupled with TDS. The value of the Eu anomaly was positively correlated with TDS. The water of Lake Gusinoe was extremely enriched by W, Mo, V, U, Li, Sr, and Ga; moderately by Ni, Cu, Ge, As, Rb, Cd, and Pb; and minimally by Al, Cr, Mn, Fe, Co, Zn, Y, Th, and REE.


Introduction
Lake Gusinoe (51.2 • N, 106.5 • E) is a freshwater lake in the southwest of Transbaikalia, the second largest body of water after Lake Baikal. It has a watershed area of about 924 km 2 ; a maximum width and depth of 8.5 km and 25-30 m; a water surface area of 164 km 2 ; a volume of water of 2.4 km 3 ; and a shoreline length of 25 km. The tributaries of the lake are represented by 72 small rivers and their total length is 312 km. The river Tsagan-Gol (85% of the inflow) is in the southwest, river Zagustai is in the northeast, smaller rivers flow from the Khambin Ridge into the lake. The streams of the Monostoi Ridge are insignificant and seasonal. Part of the lake is fed by underground sources. The reservoir has a single flow out at the southern end of the lake. The Bayan-Gol River flows out at the left tributary of the Selenga River. At the northeast, the city Gusinoozersk is located on the slopes of Monostoi and the Zagustai valley adjoins the lake. The Tamchinskaya flatplain is southwest of the reservoir (Figure 1).
The region has a severely continental climate with negative average annual temperatures (−2 to −3 • C), a short frost-free period (95-100 days), and a relatively small amount of precipitation (200-300 mm). The negative average monthly air temperature continues for six months; therefore, the lakes freeze to significant depths of 1.2-1.4 m. The region has a severely continental climate with negative average annual temperatures (−2 to −3 • C), a short frost-free period (95-100 days), and a relatively small amount of precipitation (200-300 mm). The negative average monthly air temperature continues for six months; therefore, the lakes freeze to significant depths of 1.2-1.4 m. The banks are treeless and have steppes, and only in the northwest at the mouth of the Yelnik stream, there is a small massif of coniferous forest with an area of about 1 km 2 . The western, northern, and partly southern coasts of Lake Gusinoe are swampy, especially at the mouths of rivers which streams flow into. The coastal bottom is muddy and covered with aquatic vegetation. For the most part, the eastern coast for 20 km forms a narrow sandy beach with clear water, suitable for recreational purposes. The bottom of A specific geologic feature of the study area is the presence of late Mesozoic carbonatites on the northwestern flanks of the Gusinoe Ozero-Orongoi and Ivolga depressions [4]. Carbonatites are present as dikes, manto deposits, and steeply dipping breccias; they are associated with alkaline high-K rocks and are referred to as both REE (Arshan and Yuzhnoe (southern) occurrences) and essentially Ba-Sr (Khalyuta and Oshurkovo) types.
Onego represents an important freshwater resource used to supply cities, residential areas, and large industrial centers, but suffers from industrial, urban, and agricultural pollution. The lake connects to the White Sea through the White Sea-Baltic canal and connects to the Caspian and Black Seas through the Volga-Baltic waterway and Volga River, thus representing a major transportation route. Eutrophication and chemical pollution derive from point sources [11]. The results of comprehensive hydro-physical, hydrobiological, and hydro-chemical studies are summarized by several authors [12][13][14][15][16].
The expansive and economically important North American Great Lakes are subjected to multiple stressors and understanding their responses to those stresses is important for understanding system-wide ecological controls. Phytoplankton production is an important factor in determining both ecosystem stability and the provision of ecosystem goods and services. These changes indicate that the lakes have undergone gradual oligotrophication coincidence with and anticipated by nutrient management implementation [17][18][19][20][21][22][23][24][25][26].
Lake Baikal is located in eastern Siberia in the center of a vast mountain region. Even though the lake is regarded as a unique and pristine ecosystem, there are existing sources of anthropogenic pollution to the lake. The concentrations of the potentially toxic trace elements As, Cd, Pb, Hg, and Se were analyzed in water, plankton, invertebrates, and fish from riverine and pelagic-influenced sites in Lake Baikal. Concentrations of Cd, Hg, Pb, and Se in Lake Baikal water and biota were low, while concentrations of As were similar or slightly higher compared to that in other freshwater ecosystems [27].
In recent years, regarding the rapid development of the local economy in the Siberia of Russia and the subsequent intensive uses of water resources, surface water pollution has become increasingly serious, restricting the sustainable development of the local economies. Anthropogenic activities result in a significantly decreased surface water quality in the aquatic systems in watersheds.
The goal of this paper is to determine changes in the aquatic ecosystem of Lake Gusinoe, as impacted by anthropogenic influences of varying intensities.

Materials and Methods
In sampling the water, suspended materials were examined monthly from March to October for three years during 2016-2018. The sampling sites are shown in Figure 1, while their list and locations are summarized in Table 1. Table 1. Sampling site and their location within Lake Gusinoe.

Sample Site
Location and Anthropogenic Impact

S1
The inflow of the Telya river. Production areas of the electricity power station. S2 The inflow warming water of the electricity power station.

S3
Wastewater after treatment (WWTP) from the city of Gusinoozersk inflows in Zagustai River.

S4
Agriculture and animal husbandry of the rural population. S5 The center of the lake, involved in fishing.

S6
Mine water of the coal-bearing Cholboldze deposit.

S7
The inflow of the Tsagan-gol River that flows out from the Temnik mountain river, resting in natural conditions. The railway station is at a distance of 0.8-1.3 km.
Water samples were collected by 3 L polypropylene bottles at 0.5 and 2.5 m below the surface at the 7 sampling sites. The water samples were immediately preserved at 4 • C in darkness and analyzed within 48 h.
The temperature T • C, pH, and DO were determined directly at each sampling site. The pH was measured by the pH meter Beckman Model F8 253 (Beckman, Pasadena, CA, USA), the DO by a YSI oxygen meter, Model 57 (YSI, Yellow Springs, OH, USA), and the temperature by the RST 07953 (Sweden-China).
The filter, which was situated through a 0.45 µm pore size, was used for the determination of dissolved inorganic nitrogen NH 4 -N (mg·L −1 ) and NO 2 -N + NO 3 -N (mg·L −1 ), Water 2021, 13, 2958 5 of 16 as well as for dissolved inorganic phosphate PO 4 − -P (mg·L −1 ), which were determined by standard methods and measured using spectrophotometric determination NH 4 -N (λ = 630 nm), NO 2 -N -(λ = 543 nm), TN (λ = 207 nm), and PO 4 -P (λ = 882 nm). Total nitrogen TN and phosphorus TP were determined in unfiltered samples. The concentration of organic phosphorus P org , Norg, was determined from the difference between the concentrations of the total phosphorus and the mineral phosphorus. The chemical oxygen demand, COD (COD Cr ), and biological oxygen demand, BOD 5 , were determined in unfiltered samples [28][29][30].
The trace and REE elements were determined by the ICP-MS method on a doublefocusing mass spectrometer and an ELEMENT XR cross-flow atomizer (Thermo Finnigan, Bremen, Germany) in the Lab of Physical Methods of Analysis at the Geological Institute, Siberian Branch, Russian Academy of Sciences. The index for the water pollution (WPI) was calculated as follows.
where C i corresponds to the concentration of the water parameter and MPC i corresponds to the maximum permissible concentration ( Table 2).
At site S7, the Tsagan-gol River inflows into Lake Gusinoe. The TDS of the water samples varied from 63 to 86 mg·L −1 ; the content of anions was determined as HCO 3 − 48-52 mg·L −1 , SO 4 2− 6.4-9.1 mg·L −1 , and Cl − 5.1-7.2 mg·L −1 ; and the content of ions was Ca 2+ 11.2-14.5 mg·L −1 , Mg 2+ 1.5-1.8 mg·L −1 , and Na + 12.3-15.4 mg·L −1 . It is well known that the chemical composition of Tsagan-gol River water inherits the composition of the fractured-vein waters of the mountain frame and has a low mineralization. There is no anthropogenic activity in the watershed area of the Tsagan-gol River.
Following seasonal variation, the concentrations of Na + and SO 4 2− increased at sites S1-S6 during to the occurrence of open water, which is due to the input of river water under anthropogenic impact and the runoff of mine waters. Seasonal changes in the content of these ions differ more than 1.5-2 times In contrast, at site S7, where the Tsagan-gol River flows into the lake, the concentrations of these ions do not differ significantly [32].
Thus, the greatest impact of the anthropogenic impact on Lake Gusinoe occurred at sampling sites S1-S3. There was no anthropogenic impact on sampling site S7, except for the atmospheric transport of pollutants. Sampling sites S4-S6 were located far from the objects of the anthropogenic impact and were influenced by the processes of mixing and exchange with the water of the great lake.
Annually, water temperature ranged from 0 to 25.6 • C. The temperature of the water was higher during July (21-25.6 • C) and lower, at 0 • C, from November to April. The pH of the lake water ranged from 7.1 to 9.3 (average 8.6), indicating the alkaline conditions at all times and sampling sites.
Nutrients. Nutrient concentrations varied between different sampling sites and different seasons ( Table 3). The highest TP (32 µg·L −1 ) and PO 4 -P (19 µg·L −1 ) concentrations occurred during the winter at sampling site S3, which could reflect wastewater treatment plant (WWTP) releases and P diffusion from the sediments. The mean values of TP and and PO 4 -P were 24-26 and 11-13 µg·L −1 , respectively. Discharge from Gusioozersky WWTP could explain the warmer and denser waters occupying the near-bottom layer during the winter months. Sites S4-S7 exhibited lower TP concentrations (mean of 14-16 µg·L −1 ). Observations indicated that the TP content of Lake Gusinoe was changed significantly in space and with time. The highest concentrations of TP and PO 4 -P at sampling sites S1-S3 were observed during the year. These sampling sites were under intense anthropogenic impact at the confluence of rivers Telya and Zagustai.  Table 3. Cont. The distribution of N in Lake Gusinoe exhibited a distinctive pattern ( Table 3). The concentration of NO 3 -N resembled that of Norg (~0.2 mg L −1 ) and was the highest value (0.47 mg·L −1 ) in the winter. The NH 4 -N concentration was low (0.006-0.008 mg L −1 ). The highest value of NH 4 -N (0.07-0.09 mg·L −1 ) was determined in the spring. The concentration of NO 2 -N was 0-0.002 mg·L −1 and did not vary significantly in terms of time and space. The highest value of TN was 65 mg·L −1 at site S1 in the winter.

Station PO 4 -P TP NH 4 -N NO 3 -N Norg TN
In order to highlight the difference between sampling sites, statistics multiple regression was applied.    Organic matter. The organic matter (OM) concentrations varied considerably between different samples ( Table 4). The OM composition during ice-free periods depended largely on the annual precipitation and hydrometeorological conditions, which control the intensity of the water exchange. Given the high precipitation during the spring of 2017, there were elevated levels of dissolved oxygen, DO (11.8 mg·L −1 ), chemical oxygen demand, COD (21.8 mg·L −1 ), and total organic carbon, TOC (16.2 mg·L −1 ), content. The concentrations of the chemical oxygen demand (COD) and biological oxygen demand (BOD 5 ) were much higher in the summer, at 36,5 and 5.3 mg·L −1 , respectively, compared to those measured in the winter. At the same time, for example, the concentration of dissolved oxygen (DO) exhibited a decrease in the highest concentrations from 10.8-11.8 to 9.3-9.8 mg·L −1 at sites S1-S3. The results of the statistics multiple regression are displayed in Figure 3. The distribution pattern indicates that organic matter (OM) concentrations were at the highest values at sites S1-S3.  are displayed in Figure 3. The distribution pattern indicates that organic matter (OM) concentrations were at the highest values at sites S1-S3. At sampling sites S1-S3, the content of the organic matter and nutrients were increased and higher by almost two times than that in sites S4-S7. In contrast, the dissolved oxygen (DO) was decreased by 1.25 times as a result of production and destruction biological processes (Figure 4). At same time the pH values showed less variation, ranging from 7.1 to 9.12.
There were significant differences in the distribution of mass ratios C/N and C/P depending on the sampling site ( Table 4). The highest value of ratios C/N (70) and C/P (1950) were observed in the spring and summer at site S7, higher by 1.1-1.4 times than that of the values in other sampling sites. At sampling sites S1-S3, the content of the organic matter and nutrients were increased and higher by almost two times than that in sites S4-S7. In contrast, the dissolved oxygen (DO) was decreased by 1.25 times as a result of production and destruction biological processes (Figure 4). At same time the pH values showed less variation, ranging from 7.1 to 9.12.
There were significant differences in the distribution of mass ratios C/N and C/P depending on the sampling site ( Table 4). The highest value of ratios C/N (70) and C/P (1950) were observed in the spring and summer at site S7, higher by 1.1-1.4 times than that of the values in other sampling sites. logical processes (Figure 4). At same time the pH values showed less variation, ranging from 7.1 to 9.12.
There were significant differences in the distribution of mass ratios C/N and C/P depending on the sampling site ( Table 4). The highest value of ratios C/N (70) and C/P (1950) were observed in the spring and summer at site S7, higher by 1.1-1.4 times than that of the values in other sampling sites.  The monitoring data were compared with the Russian standard from the hygienic norms, specifically "Maximal Permissible Concentration of Chemical Substances in water of the Water Sources of Drinking and Communal use" [31]. Figure 5 illustrates the weights of the six parameters analyzed at the seasonal value of WPI, with these parameters established according to the result of the C i /MPC i (see Equation (1)). According to the graphic representations, the weight of the parameters varies from one season to another. BOD 5 and DO contribute, to the largest extent, to the final results of WPI, as recorded in all seasons. This is because these variables significantly exceeded the maximum permissible concentration in different seasons. In the summer, the contribution of N-NH 4 had an important contribution to WPI. This is explained by the fact that in open water, the content of N-NH 4 increased. However, the WPI index did not have a high sensitivity for different sampling sites in Lake Gusinoe. The authors of the works [33,34] showed that the WPI can be used particularly to determine the level of pollution, with the results showing only the exceedances of the maximum allowed concentrations. The value of WPI varied between 0.22 0.29 at all sampling sites during the year. Currently, according to the Russian water quality classification based on WPI [31], the water of Lake Gusinoe is pure. The monitoring data were compared with the Russian standard from the hygienic norms, specifically "Maximal Permissible Concentration of Chemical Substances in water of the Water Sources of Drinking and Communal use" [31]. Figure 5 illustrates the weights of the six parameters analyzed at the seasonal value of WPI, with these parameters established according to the result of the Ci/MPCi (see Equation (1)). According to the graphic representations, the weight of the parameters varies from one season to another. BOD5 and DO contribute, to the largest extent, to the final results of WPI, as recorded in all seasons. This is because these variables significantly exceeded the maximum permissible concentration in different seasons. In the summer, the contribution of N-NH4 had an important contribution to WPI. This is explained by the fact that in open water, the content of N-NH4 increased. However, the WPI index did not have a high sensitivity for different sampling sites in Lake Gusinoe. The authors of the works [33,34] showed that the WPI can be used particularly to determine the level of pollution, with the results showing only the exceedances of the maximum allowed concentrations. The value of WPI varied between 0.22 0.29 at all sampling sites during the year. Currently, according to the Russian water quality classification based on WPI [31], the water of Lake Gusinoe is pure. In this study, the variables of nutrients and organic matter in the lake were identified. The results suggest that anthropogenic activities had significant effects on the water. The power electricity industry and WWTP of Gusinoozersk presented serious negative feedbacks for water pollution. In this study, the variables of nutrients and organic matter in the lake were identified. The results suggest that anthropogenic activities had significant effects on the water. The power electricity industry and WWTP of Gusinoozersk presented serious negative feedbacks for water pollution.
Trace element. The input of chemical elements into lake water is controlled mainly by the supply ground, surface waters, and antropogenic impact, and their further concentration is determined by the processes of vaporization, by the physico-chemical properties of the elements themselves, and by the geochemical conditions of the environment. The saturation of supply water with trace elements depends on their extraction from rocks, which is controlled by the processes of the water-rock interaction [35][36][37][38][39].
Trace element concentrations in the lake water spanned with 6-7 orders of magnitude. The maximum concentrations within n 100 µg·L −1 were observed for Sr. The concentrations within n 10 µg·L −1 were typical for Li and Mo, as well as within n µg·L −1 -for Al, Mn, Cu, Zn, Rb, and U; within n 0.1 µg·L −1 for V, Ni, As, W, Cd, and Pb; within n 0.01 µg·L −1 for Co, Ga, Ge, Y, La, Ce, Pr, and Nd; and within n 0.001 µg·L −1 for Ga, Th, Sm, Eu, Gd, Tb, Dy, Er, and Yb (Table 5).  In accordance with the behavior of elements in the waters feeding the lake and in the process of evaporation of lake water, three groups of elements could be distinguished. As shown in [32], the smallest TDS was determined at site S7. A clear distinction existed between trace elements whose abundance followed the abundance of major elements or TDS, and whose concentrations were decoupled from the variations of major ions. In Lake Gusinoe, three categories were revealed. The first set of elements, including Li, Ga, Ge, As, Rb, Sr, Mo, Cd, Ba, W, and U, were directly correlated with variations of major elements. The first set of elements showed decreasing concentrations with increasing TDS (site S1-S6). The second set of elements, including Fe, Y, Nb, Th, and REE, were correlated oppositely with variations of TDS, in contrast to the elements of the first set. The behavior of the third set of elements, including Mn, Zn, Ni, Cu, and Pb, decoupled from the major elements and their variations at the sampling sites were not correlated with TDS.
In order to assess the processes of vaporization and the anthropogenic impact, the concentration ratio of the trace elements at sites S1, S5, S6, and S7 were calculated. Sampling sites S1, S5, and S6 represented the anthropogenic impact and the central part of the lake with missing waters. Figure 6 displays the distribution of the concentration ratios. In accordance with the behavior of elements in the waters feeding the lake and in the process of evaporation of lake water, three groups of elements could be distinguished. As shown in [32], the smallest TDS was determined at site S7. A clear distinction existed between trace elements whose abundance followed the abundance of major elements or TDS, and whose concentrations were decoupled from the variations of major ions. In Lake Gusinoe, three categories were revealed. The first set of elements, including Li, Ga, Ge, As, Rb, Sr, Mo, Cd, Ba, W, and U, were directly correlated with variations of major elements. The first set of elements showed decreasing concentrations with increasing TDS (site S1-S6). The second set of elements, including Fe, Y, Nb, Th, and REE, were correlated oppositely with variations of TDS, in contrast to the elements of the first set. The behavior of the third set of elements, including Mn, Zn, Ni, Cu, and Pb, decoupled from the major elements and their variations at the sampling sites were not correlated with TDS.
In order to assess the processes of vaporization and the anthropogenic impact, the concentration ratio of the trace elements at sites S1, S5, S6, and S7 were calculated. Sampling sites S1, S5, and S6 represented the anthropogenic impact and the central part of the lake with missing waters. Figure 6 displays the distribution of the concentration ratios.  1-11.8). The water of the lake was extremely enriched by these elements. The elements Al, Cr, Mn, Fe, Co, Zn, Y, Th, and REE had values of less than 1.0. These elements minimally accumulated in the lake water. The enrichment elements Ni, Cu, Ge, As, Rb, Cd, and Pb had values of between 1.4 and 6.3, and thus they moderately accumulated in the water of Lake Gusinoe.
Generally, elements known to be present as oxyanions (As, Mo, W, U, and others) in oxidized water exhibit some coherence with major solute variations.   (14-14.6), Sr (9.4-9.7), and Ga (94. 1-11.8). The water of the lake was extremely enriched by these elements. The elements Al, Cr, Mn, Fe, Co, Zn, Y, Th, and REE had values of less than 1.0. These elements minimally accumulated in the lake water. The enrichment elements Ni, Cu, Ge, As, Rb, Cd, and Pb had values of between 1.4 and 6.3, and thus they moderately accumulated in the water of Lake Gusinoe.
Generally, elements known to be present as oxyanions (As, Mo, W, U, and others) in oxidized water exhibit some coherence with major solute variations. The best examples of decoupling between major solutes and trace elements derive from REEs. As shown in [37], the lowest concentrations of REEs in river waters are found in the rivers with the highest pH. In Lake Gusinoe at sites S1-S6, as they are greatly influenced by carbonate dissolution, high pH and alkalinity values were determined and found to be present at very low REE concentrations, in contrast to site S7. Elements such as Th and Y, and to a lesser extent Fe, Al, Mn, and Zn, are correlated with REE concentrations in lake water. The close association of these elements with DOC has been shown by other authors [38,39].
Total concentrations of Al, Fe, and Mn showed increases across the sites, with higher values in the northern sites (S1-S3) compared to the other sites (S4-S7). The differences between the particulate and dissolved concentrations were highest for Al, Fe, and Mn, with particulate concentrations that were, on average, 57, 28, and 24 times greater, respectively, than the dissolved concentrations in the 2016 monitoring campaign, and 36, 12, and 8 times greater, respectively, in the 2017 campaign. As, Cd, Cr, Cu, and Mo had dissolved concentrations of the same order of magnitude as their total concentrations. V and Zn showed varying behaviors, exhibiting both higher dissolved and particulate concentrations depending on the sampling site.
As shown in [40,41], the precipitation of gibbsite and ferrihydrite was predicted to be the dominant control of Al and Fe, with these particulate fractions generally limiting their solubility by 90-100%. In others works [42][43][44], 40-50% was predicted to occur as soluble organic complexes (bound to DOC). In other locations, only minor fractions of Fe (up to 10%) were predicted to exist as complexes with organic matter. Metal-organic complexation also had a large impact on the speciation of Pb and Zn, and these elements were predicted to form soluble complexes with DOC, on average, governing their speciation by 50% and 30%, respectively. Sorption processes to ferrihydrite and gibbsite mainly controlled the solubility of V, Pb, and Zn. V, Cr, and Pb were predicted to sorb only to ferrihydrite, on average, by 60%, while Zn was predicted to sorb to both ferrihydrite and gibbsite (on average, by 65%), but with predominant sorption to gibbsite over ferrihydrite (under pH conditions above 8).
The content of REE and their fractionation degree by indicator (La/Yb) N is presented in Table 5. The total content varied for ΣREE = 0.016-0.024 µg·L −1 . In the REE patterns for most sampling sites, HREE strongly dominated over LREE: (La/Yb) N = 0.29-0.60. The exception was water from site S2, where (La/Yb) N = 1.35. The content of Σ HREE was higher at site S7 by 1.2-2.0 times than at other sites.
There was a difference in the value and sign of the Ce and Eu anomaly. The distribution of REE when normalized to NASC [45] is shown in Figure 7. Cerium anomalies were not observed at sites S1-S5 (Ce/Ce* = 0.089-0.342). The negative anomaly Ce/Ce* = 1.504 was recorded at site S6, which was due to the mine water of the coal-bearing Cholboldze deposit. The REE normalized profile was characterized by deeper positive anomalies (Eu/Eu* = 2.8-12.7). The lowest value (Eu/Eu* = 2.818) derived from the water from site S7, where the anthropogenic impact was minimal. The value of the Eu anomaly was positive correlated with TDS. From these results, it follows that the Eu anomaly is an indicator of anthropogenic influence and of the process of vaporization in Lake Gusinoe.
The Malo-Khamardaban volcanogenic association is one of the largest and typomorphic structures of the Jurassic-Cretaceous rift magmatism of the western Transbaikalia. It is mainly made up of bimodal volcanogenic trachybasalt-trachyte series with subordinate amounts of trachyandesites, trachyrhyodacites, and trachyrhyolites. As shown by several authors [46][47][48], the mineralogical-petrographic, mineralogical-geochemical, and geochemical features of trachyandesites as well as of some syenite porphyries (subvolcanic analogues of trachytes) indicate their hybrid nature. The trachyandesites were formed by mixing trachybasaltic magma with trachytic magmas (endohybridisation), and trachy-basaltic magma with contaminated trachytic magma. Trachybasalts and trachytes contain weak positive Eu anomalies (Eu/Eu* = 1.24-0.84) for the normalized primitive mantle.
Water 2021, 13, x FOR PEER REVIEW Figure 7. Normalized distribution of rare earth elements in the lake water.

Conclusions
Lake Gusinoe is the second largest freshwater lake in Transbaikalia. Lakes source of drinking water and irrigation, and as a water source for the electricit production, and tourism industry. The electricity industry and sewages discha affect water quality. The combined influence of these two main sources depen intensity of the bay-lake exchange, which in turn varies with annual precipit hydrometeorological conditions. In the winter, the hydrochemical regime dep marily on the Telya and Zagustai River inflow because the water exchange be bay and the central lake is restricted during its ice-covered period. In this p content of nutrients was highest for TP (32 μg·L −1 ) and TN (0.65 mg L −1 ), while ration varied from 72% to 98%. In the spring, summer, and autumn, when b masses experience wind-induced and thermal mixing, open lake water e strongest influence on chemical composition, evident by the lower mean conce of TP (9-11 μg·L −1 ), TN (0.24-0.26 mg·L −1 ), and DO (8.1-8.3 mg·L −1 ), as well highest content of COD (36.5 mg·L −1 ) and BOD5 (mg·L −1 ).
Seasonal monitoring indicated that sewage from power stations and Gusi which bothndischarge sewage into the peripheral areas of the lake, exerted on effects on the bay water quality during the spring and autumn period of mi open waters of the greater lake. In water sample sites S1-S3, which were und thropogenic impact, the content of the organic matter and nutrients were inc almost 2 times compared to other sampling sites which had less influence from sources.
The water of Lake Gusinoe is extremely enriched by W, Mo, V, U, Li, Sr moderately by Ni, Cu, Ge, As, Rb, Cd, and Pb; and minimally by Al, Cr, Mn, F Y, Th, and REE. In most areas of the water, HREE strongly dominated over L cerium anomaly was not observed in most of the lake, except for the area wh waters of the coal-bearing Cholboldze deposit inflow. The normalized distri REE was characterized by a deeper positive Eu anomaly, which was due to chemical features of trachybasalts and trachytes of the Malo-Khamardaban vol association.

Conclusions
Lake Gusinoe is the second largest freshwater lake in Transbaikalia. Lakes serve as a source of drinking water and irrigation, and as a water source for the electricity, aquatic production, and tourism industry. The electricity industry and sewages discharges both affect water quality. The combined influence of these two main sources depends on the intensity of the bay-lake exchange, which in turn varies with annual precipitation and hydrometeorological conditions. In the winter, the hydrochemical regime depends primarily on the Telya and Zagustai River inflow because the water exchange between the bay and the central lake is restricted during its ice-covered period. In this period, the content of nutrients was highest for TP (32 µg·L −1 ) and TN (0.65 mg L −1 ), while DO saturation varied from 72% to 98%. In the spring, summer, and autumn, when bay water masses experience wind-induced and thermal mixing, open lake water exerts the strongest influence on chemical composition, evident by the lower mean concentrations of TP (9-11 µg·L −1 ), TN (0.24-0.26 mg·L −1 ), and DO (8.1-8.3 mg·L −1 ), as well as by the highest content of COD (36.5 mg·L −1 ) and BOD 5 (mg·L −1 ).
Seasonal monitoring indicated that sewage from power stations and Gusinoozersk, which bothndischarge sewage into the peripheral areas of the lake, exerted only minor effects on the bay water quality during the spring and autumn period of mixing with open waters of the greater lake. In water sample sites S1-S3, which were under the anthropogenic impact, the content of the organic matter and nutrients were increased by almost 2 times compared to other sampling sites which had less influence from pollution sources.
The water of Lake Gusinoe is extremely enriched by W, Mo, V, U, Li, Sr, and Ga; moderately by Ni, Cu, Ge, As, Rb, Cd, and Pb; and minimally by Al, Cr, Mn, Fe, Co, Zn, Y, Th, and REE. In most areas of the water, HREE strongly dominated over LREE. The cerium anomaly was not observed in most of the lake, except for the area where mine waters of the coal-bearing Cholboldze deposit inflow. The normalized distribution of REE was characterized by a deeper positive Eu anomaly, which was due to the geochemical features of trachybasalts and trachytes of the Malo-Khamardaban volcanogenic association.

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The studies were carried out in accordance with the state assignment of the Siberian Branch of the Russian Academy of Sciences.

Informed Consent Statement:
The consent of the expert commission of the Geological Institute on the publication and access of data in the open press is available.