Composition and content of photosynthetic pigments in plankton of the Volga River reservoirs (2015-2016) Текст научной статьи по специальности «Биологические науки»

Труды ИБВВ РАН, 2018, вып. 81(84)

Transactions of IBIW RAS, 2018, issue 81(84)

УДК: 574.583(28):581

COMPOSITION AND CONTENT OF PHOTOSYNTHETIC PIGMENTS IN PLANKTON OF THE VOLGA RIVER RESERVOIRS (2015-2016)

N. M. Mineeva

Papanin Institute for Biology ofInland Waters Russian Academy of Sciences, Borok, Nekouzskii raion, Yaroslavl oblast, 152742 Russia, e-mail: [email protected]

Data on the composition and content of photosynthetic pigments in plankton of the Volga River reservoirs in the summer period of 2015 and 2016 are under consideration. Chlorophyll content determined by standard spectrophotometry and fluorescent methods correlate with each other (R2 = 0.78). The average concentration of chlorophylls (Chl a+b+c) in June in the Kuibyshev, Saratov, and Volgograd reservoirs was 4.0-5.5 ^g/L, in Gorky and Cheboksary reservoirs 10.0-14.7 ^g/L, in unregulated part of the Lower Volga 22.5 ^g/L. Chl a+b+c content in August was 20.5-34.4 ^g/L in five upper reservoirs of the cascade, 6.3 and 6.7 ^g/L in Kuibyshev and Saratov reservoirs (2015), 10.9 ^g/L in Gorky reservoir, and 16.3-26.4 ^g/L in others (2016). Chl a prevails in the fund of the green pigments (71-85% in June, 67-93% in August), the share of Chl c is 6-29%, the share of Chl b is 1-9%. Pheopigments content is equal to 26-78%, the plant carotenoids and chlorophyll content is commensurable. The contribution of blue-green algae (an average of 36-56% in June and 60-90% in August) and diatoms (40-60% and 9-40%) to the total amount of Chl a corresponds to the taxonomic composition of the Volga phytoplankton. The trophic status of the reservoirs of the Middle Volga in the early summer is characterized as mesotrophic and only Cheboksary reservoir is moderate eutrophic. At the height of the summer, Ivanko-vo, Uglich, and Cheboksary reservoirs are considered eutrophic category. The status of the Rybinsk reservoir during the study period varies from moderate eutrophic to eutrophic, Gorky reservoir from mesotrophic to eu-trophic, Kuibyshev reservoir from mesotrophic to moderately eutrophic. Reservoirs of the Lower Volga are characterized as mesotrophic.

Keywords: photosynthetic pigments, Volga River reservoirs, trophic state

DOI 10.24411/0320-3557-2018-1-0006

INTRODUCTION

The study of the autotrophic component of aquatic ecosystems is a crucial element of ecological research. In the process of photosynthesis, planktonic algae produce the main stock of organic matter in large lakes and reservoirs, creating an energy base for organisms of higher trophic levels. Among the indicators of the abundance and functioning of phytoplankton, a special place is given to photosynthetic pigments, which have been used extensively throughout the last decade to obtain operative information on the development and state of algocoenoses. Chlorophyll a (Chl a) that is the main pigment of green plants characterizes the production capabilities of algae, serves as a marker of their biomass, constitutes the basis of trophic classification of water bodies and is among the indicators of water quality [Vin-berg, 1960, Kitaev, 2007].

There are numerous, but scattered data on the content and composition of photosynthetic pigments in the plankton of the Volga. Most of the research was carried out at individual reser-

MATERIAL

The pigment content was determined by standard spectrophotometric method [SCOR-UNESCO, 1966; Lorenzen, Jeffrey, 1980] and fluorescent method [Gold et al., 1986; Gaevsky et al., 1993] at the river bed stations of the Volga reservoirs in August 2015 (64 stations), June and August 2016 (73 and 71 stations). Integral sam-

voirs, with only a few covering several reservoirs [Pyrina, 1966; Kovalevskaya, Karabanovich, 1975; Mineeva, 2006; Mineeva et al., 2008] and single studies describing the cascade as a whole [Mineeva, 1995, 2004]. However, it is the latter data that are of interest for a comparative assessment of the development and status of phyto-plankton in the cascade of water reservoirs located in different geographic zones. This is the data necessary for carrying out environmental monitoring, analysis and forecasting of changes that occur in the water ecosystem under anthropogenic impact and require constant control over the state of the aquatic environment.

The purpose of this work is to study the composition and content of photosynthetic pigments in the water of the Volga River reservoirs at the present stage, to estimate the distribution of phytoplankton and its major large taxa (divisions), to analyze the trends of long-term changes in the productivity of the Volga phytoplankton.

AND METHODS

ples obtained by mixing equal volumes of water taken from each meter of the water column from the surface to the bottom with an Elgmork plastic water sampler were used for the analysis. For spectrophotometry, algae were precipitated onto Vladisart membrane filters (pore diameter 3-5 ^m) covered with a layer of calcium carbonate

and silicon dioxide. Filters were stored in a refrigerator prior to analysis. The pigments were identified in 90% acetone extract on spectrophotometer Lambda25 (PerkinElmer), concentrations of chlorophylls (Chl a, Chl b, Chl c), their degradation products - phaeopigments and plant carotenoids were calculated by the respective formulas [Parsons, Strickland, 1963; Lorenzen, 1967; Jeffrey, Humphrey, 1975]. To assess the state of phyto-plankton, the pigment index E480/E664, the ratio of optical densities at the maxima of absorption of carotenoids and chlorophyll, was used [Watson, Osborn, 1979].

Fluorescence of chlorophyll was measured on board of the research vessel in natural water on a stationary fluorimeter PFL-3004 (Krasnoyarsk University). Modification of the method is based on the specifics of light-harvesting pigmentprotein complexes of the diatoms (containing Chl a, c and fucoxanthin), blue-green (Chl a and phycobilins), and green (Chl a and Chl b) algae. The fluorescence intensity Fx0 was measured in the red region of the spectrum (~ 680 nm) when excited by light with wavelengths (X) of 410, 490 and 540 nm. The measurement was repeated after the addition of ETC inhibitor simazine (at a concentration of 10-5 M) to the cuvette, thereby increasing the fluorescence yield to a maximum level of FXmax. To introduce a correction for the presence of colored organic matter, at the same wavelengths, fluorescence of water (Ff filtered through a membrane filter with a pore diameter of ~ 0.5 ^m, i.e., devoid of algae, was measured. For calculations, a system of linear equations including a "pure" fluorescence signal (FXmax-FXf and Fx0-Fxf) was used for the three indicated wave-

RESULTS AND

The study of the summer phytoplankton is of considerable interest, as negative trends caused by eutrophication or climate changes become apparent in the ecosystem of the reservoir during this season. Observations carried out in June refer to the seasonal change of plankton communities -the end of the spring forms vegetation and the beginning of summer forms development. During this period, the abundance of phytoplankton usually decreases. The data obtained in August are confined to the period of maximum warming of the water and, as a rule, capture the summer maximum of phytoplankton, which is indicative of the state of the reservoir.

Spectrophotometric method allows obtaining a set of characteristics, the attributes of the state and degree of community development. The green pigment pool is formed by the total content of chlorophylls a, b, c (Chl a+b+c). In June 2016 it fluctuated having values typical for early sum-

lengths [Gold et al., 1986; Gaevsky et al., 1993]. Total Chl a content was calculated as the sum of its concentration in diatom, blue-green and green algae (respectively, Bacillariophyta - ChlBac, Cy-anophyta - ChlCyan, Chlorophyta - ChlChlor).

For calculations, statistical processing of data and plotting charts, standard programs for a personal computer were used.

Trophic status of reservoirs was evaluated by the average content of Chl a, considering values of 3-10, 10-15 and 15-30 ^g/L respectively, as boundary for mesotrophic, moderate eutrophic and eutrophic waters [Mineeva, 2000b]. Distribution of phytoplankton over the water area in reservoirs was assessed using a coefficient of variation (CV) in the average concentrations of Chl a.

Volga River cascade spans for over 2500 km from north to south and consists of eight large (surface area from 249 to 6150 km2) relative shallow (average depth 3.4-10 m) water reservoirs, differing in morphometry, drainage area, intensity of water exchange, as well as a number of hydrological and hydrochemical characteristics. From the Upper Volga to the Lower Volga, the transparency of water and the total sum of ions (electrical conductivity) increase, and the color of water decreases. The high content of nutrients throughout the cascade does not limit the development of phytoplankton [The River Volga ... , 1979; Rivers of Europe, 2009]. During the study periods, the average water temperature in the reservoirs was 16.9-18.7°C in June, and with the maximum warming of the water column in August, 18.0-20.9°C in 2015 and 21.9-24.7°C in 2016.

DISCUSSION

mer: the minimum was 1.5-5.7 ^g/L, the maximum - from 9.0 to 37.8 ^g/L, in reservoirs of the Middle and Lower Volga. Maximum values for individual reservoirs differed by a factor of 4-9. The average concentration of Chl a+b+c varied from 4.0-5.5 ^g/L in Kuibyshev, Saratov, and Volgograd reservoirs to 10.0-14.7 ^g/L in Gorky and Cheboksary reservoirs and was maximum (22.5 ^g/L) in the unregulated Lower Volga area from Volgograd to Astrakhan (Table 1).

In August, the content of Chl a+b+c was typical for the summer peak of phytoplankton. In 2015, the minimum values for water bodies varied from 2.4 to 18.4 ^g/L, maximum - from 9.9 to 96 ^g/L, mean - from 20.5 to 34.4 ^g/L in the five upper reservoirs and decreased to ~ 6 ^g/L in Kuibyshev and Saratov reservoirs.

Table 1. Phytoplankton pigment composition in the Volga River reservoirs based on spectrophotometry method

Water Year, Chl a+b+c, Chl a, % Chl b, % Chl c, % Phaeo- Carote- E480/E664,

reservoir month ^g/L pigments, % noids, |SPU/L Rel. units

Ivankovo 2015, 14.1-67.4 78-92 2.0-9.7 5.2-12 31-72 9.0-39.7 0.73-1.11

VIII 27.3±4.4 89±1.3 6.0±0.7 7.1±0.6 49±4.5 16.1±2.7 0.87±0.04

2016, 13-59 52-91 2.1-13 6.9-35 23-66 8.6-51.4 0.85-2.41

VIII 26.4±5.0 77±4.6 7.0±1.1 16±3.9 43±4.4 18.9±4.1 1.29±0.16

Uglich 2015, 17.2-41.7 87-92 3.0-5.8 5.3-7.8 31-48 10.3-22.1 0.73-0.85

VIII 28.7±3.2 89±0.5 4.3±0.3 6.8±0.3 40±1.8 16.1±2.0 0.78±0.01

2016, 16.5-38.1 82-91 2.6-7.6 6.3-12 25-65 10.8-26.3 0.85-1.06

VIII 22.9±2.5 86±1.0 4.7±0.7 8.9±0.6 36±5.7 15.6±1.9 1.00±0.03

Rybinsk 2015, 18.4-47.4 89-96 0.0-2.7 5.6-8.7 20-48 18.5-35.5 0.79-1.28

VIII 30.6±2.4 93±0.5 1.1±0.2 7.0±0.2 37±2.6 25.8±1.2 1.07±0.04

2016, 11.0-39.5 54-94 0.6-9.3 4.3-36 15-46 7.3-36.6 0.93-2.34

VIII 18.1±2.1 71±3.7 4.5±0.5 24±3.4 30±2.1 16.1±2.1 1.54±0.12

Gorky 2015, 12.6-25.7 86-94 0.3-5.1 5.4-9.9 26-48 8.4-22.6 0.76-1.24

VIII 20.5±1.2 90±0.7 2.7±0.4 7.6±0.4 36±2.1 14.3±1.2 0.99±0.04

2016, 3.6-17.9 67-88 2.7-12 8.3-21 39-74 2.3-11.7 0.83-1.53

VI 10.0±1.3 80±1.5 6.3±0.8 13±0.9 54±3.1 7.0±0.8 1.17±0.05

2016, 5.4-24.5 57-90 1.5-7.2 6.7-36 41-68 6.1-28.9 0.90-2.40

VIII 10.9±1.5 67±3.6 4.2±0.5 29±3.5 48±2.6 10.8±1.6 1.93±0.17

Cheboksary 2015, 6.0-96.1 83-94 1.3-7.4 4.7-9.5 30-69 2.6-48.5 0.67-1.09

VIII 34.4±10.7 90±1.2 3.8±0.7 6.7±0.5 45±4.2 18.2±5.0 0.83±0.06

2016, 4.0-37.8 68-89 2.9-14 8.3-19 59-91 2.1-24.8 0.92-1.35

VI 14.7±3.5 80±2.4 7.7±1.1 12±1.3 70±3.5 9.7±2.4 1.10±0.05

2016, 6.5-67.4 78-95 0.5-6.8 3.8-15 18-50 5.7-43.7 0.84-1.46

VIII 18.9±7.1 87±2.3 3.7±0.9 9.0±1.6 35.4±4.1 12.7±4.2 1.03±0.07

Kuibyshev 2015, 2.4-11.3 81-95 0.1-7.4 4.6-14 11-49 1.6-8.0 0.79-1.15

VIII 6.8±0.8 89±1.4 2.9±0.7 8.1±0.8 26±3.1 4.2±0.6 0.95±0.03

2016, 2.0-9.3 54-86 3.1-14 11-32 46-95 0.9-5.4 0.81-1.69

VI 4.0±0.6 71±2.7 8.2±1.0 20±2.0 78±5.5 2.6±0.3 1.30±0.07

2016, 6.8-36.6 86-95 0.5-7.9 4.6-8.2 16-41 5.0-21.5 0.81-1.11

VIII 16.3±3.2 91±1.0 3.1±0.9 6.1±0.5 28±3.0 11.4±1.9 0.97±0.03

Saratov 2015, 3.5-9.9 87-95 0.4-3.3 4.2-10 24-40 2.3-7.1 0.85-1.00

VIII 6.3±1.0 91±1.4 1.7±0.5 7.1±0.9 30±2.3 4.1±0.9 0.89±0.02

2016, 1.5-9.0 61-89 0.8-11 10-28 44-82 1.0-5.1 0.86-1.58

VI 4.6±1.0 79±3.8 4.7±1.4 16±2.4 61±5.1 2.9±0.6 1.08±0.09

Volgograd 2016, 2.5-18.6 65-84 6.8-13 8.8-24.0 33-68 1.2-10.6 0.82-1.26

VI 5.5±1.6 75±2.1 8.9±0.7 15±1.6 46±3.7 3.0±0.9 1.06±0.05

Unregulated 2016, 5.7-35.8 78-87 3.6-8.7 7.5-13 30-71 3.4-25.9 0.84-1.08

Low Volga VI 22.5±2.5 85±0.6 5.0±0.3 10±0.3 51±3.2 14.4±1.7 0.92±0.02

Note. Here and in Table 2 top - limits, bottom - average values close to 1 mg used to measure carotenoids.

In 2016, the minimum concentrations of Chl a+b+c were 5.4-16.5 ^g/L, the maximum concentrations - 24.5-67.4 ^g/L, the average concentrations - from 10.9 ^g/L in the Gorky reservoir to 16.3-26.4 ^g/L in all other. Maximum values differed by a factor of 2-5 for each reservoir, i.e., to a lesser extent than those seen in June, and only in the Cheboksary reservoir they differed by an order of magnitude. In August 2015, in most reservoirs, the concentrations of Chl a+b+c were higher than in August 2016, despite the less intense warming of the water column. Only in the Kuibyshev reservoir higher values were obtained in 2016. Inter-annual differences in Chl a+b+c were 1.4-1.9

with standard error. SPU - Specific Pigment Unit - unit

times in Uglich, Rybinsk, Gorky, and Cheboksary reservoirs, but were absent in Ivankovo reservoir (Table 1).

The results of the correlation analysis showed that at the height of summer the chlorophyll content did not depend on the water temperature (R2 <0.05 in August both years). This is consistent with the previously assessed complex effect of abiotic factors on the development of Volga phytoplankton [Litvinov, Mineeva 1997]. At the same time, the correlation was close in June (R2 = 0.85) during the warming of the water column (Fig. 1).

Fig. 1. Dependence of chlorophyll content on water temperature (reservoir mean values). 1 - June 2016, 2 - August 2015, 3 - August 2016.

The basis of the green pigment pool of freshwater phytoplankton is Chl a, which is contained in all plant cells. As before [Mineeva 2000a], the content of Chl a and the total amount of chlorophylls closely correlate with each other (R2 = 0.98). The relative amount of Chl a in the Chl a+b+c pool varied within 54-89% in June, being 71-85% of this pool on average in reservoirs. In August, the share of Chl a increased as compared to June: the limiting values up to 7896% in 2015 and 52-95% in 2016, the average for reservoirs - respectively up to 87-93% and 6791% (Table. 1).

High (> 90%) relative content of Chl a indicates a prevalence of blue-green algae that do not contain additional Chl b and Chl c. At the height of summer in 2015 and 2016 such values were noted at 27 and 18 stations, respectively. The mean concentration of Chl a for these stations made 27.5±3.3 pg/L and was close to the 30 pg/L that is the boundary value for the water bloom [Sirenko, Gavrilenko, 1978]. (We should point out that the lower proportion of Chl a corresponded to its lower concentration: at a fraction <70%, it was 8.0±2.5 pg/L, at 70-90% it was 17.3±1.5 pg/L). In general, the percentage of Chl a became higher in total amount of chlorophylls compared with the early 1990s when the mean values for reservoirs were 46-70% in June and 60-85% in August [Mineeva, 1995, 2004].

The relative amount of Chl c contained in the cells of the diatoms ranged from 7.5 to 28% in June; from 4 to 14% in August in 2015 and up to 38% in 2016. The average for reservoirs was 1020% in June, 7-8% and 6-29% in August of two years. The proportion of Chl b, a component of the pigment complex of green algae, was less variable and varied from <1 to 10-13% in all observation periods, with an average of 5-9% in June and 1-7% in August (Table 1). The contribution of additional chlorophylls to the green pigment pool at the height of summer did not decrease as much as early in the summer, as was noted in 1990s. [Mineeva, 1995, 2004].

Phaeopigments, the products of chlorophyll decomposition formed with the dying out of algae and their consumption by zooplankton, remain in the seston and sediments for a long time, and always present in the waterbody. The concentration of phaeopigments is closely related to the concentration of chlorophyll (Fig. 2).

Fig. 2. Relationship between chlorophyll a (Chl) and phaeopigments (Phaeo) in the Volga River reservoirs.

The regression coefficient in the equation makes it possible to estimate the average percentage of chlorophyll derivatives, and the free term is explained by the constant presence of phaeopig-ments in the water column. The relative amount of phaeopigments in the Volga reservoirs is represented as typical values for fresh waters, as a rule, maximum in early summer and late autumn and lower in the height of summer [Mineeva, 1995]. The limits are 30-95% in June and 11-72% in August of both years, and the averages are 4678% and 26-49%, respectively (Table 1).

The content of plant carotenoids that carry out light-harvesting and protective functions of excessive insolation in the cell, is commensurate with the content of chlorophyll. At different observation periods, it varied from a minimum of 118 pSPU/L to a maximum of 5-51 pSPU/L at a mean of 2.6-25.8 pSPU/L (Table 1). The dynamics of carotenoids repeats the dynamics both of Chl a (R2 = 0.96) and the total content of green pigments (R2 = 0.98). On the basis of this relationship, the yellow pigments are considered as a marker of phytoplankton biomass [Foy, 1987]. However, the quantitative ratio of yellow and green pigments, the indicator of the physiological state of the algocoenoses, is more widespread, and the excess of carotenoid content over chlorophyll is a sign of the algae unfavorable state [Paerl et al., 1983]. The lowest values of E480/E664 index (marginal 0.67-1.28, average 0.78-1.07) were observed in August 2015 - the period of the summer peak of phytoplankton in most reservoirs. In 2016, higher values of E480/E664 (limiting 0.812.40, average 0.93-1.93) were obtained, with the highest values in June coinciding with low Chl a content during seasonal change of communities (Table 1). At present, the E480/E664 values have increased in comparison with 1989-1991. Plant

carotenoids dominated in the early summer, along with the decline in the development of algae, and the values of the pigment index E480/E664 > 1. At the height of summer, the ratio E480/E664 (as well as the percentage of phaeopigments) decreased and, with a few exceptions, fluctuated around 1.0 [Mineeva, 1995]. The dynamics of pigment ratio E480/E664, as well as dynamics of phaeopigmets, corresponds to the degree of development of algo-coenoses. During the periods of seasonal highs, viable active cells are present in the waterbody, the sign of the physiological well being of which is the predominance of green pigments over yellow (E480/E664 below or slightly above 1), and the predominance of the active form of chlorophyll (low relative content of phaeopigments). Both indicators increase along with the decline in the development of algocoenoses.

The source of additional information on the development of phytoplankton is the data of the fluorescent method, which makes it possible to estimate the chlorophyll content of the three algae divisions typical for freshwater waterbodies. With differences in the specific content of chlorophyll in algae of large taxonomic groups [Mineeva 2011; Mineeva, Schur, 2012], these data do not quantify the biomass of divisions, but are of interest for a comparative analysis of their dynamics.

Results of fluorescent and spectrophotometry determination of chlorophyll are closely correlated with each other (Fig. 3).

Fig. 3. Ratio of chlorophyll concentrations obtained by spectrophotometric (Chlsph) and fluorescent (Chlfi) methods. 1 - August 2015, 2 - June 2016, 3 - August 2016.

Regression equation shows that the differences are 30% on average. Higher chlorophyll concentrations are obtained by measuring fluorescence in natural water where there are small-celled algae with a delicate membrane. These forms can be lost during filtration needed to prepare samples for spectrophotometry. The difference between two methods is almost lacking in June at relatively low chlorophyll concentrations and increases in August.

According to the data obtained by fluorescent method, chlorophyll content for each of the three algae divisions in Volga reservoirs fluctuat-

ed within a broad range. All minimal values were < 1pg/L. Maximal chlorophyll content of green algae (ChlChlor) did not exceed 1-4 pg/L, with average usually being < 1pg/L. The contribution of ChlChlor into the sum Chl a varied very little both within the cascade as well as during the observation periods, with average being 1.3-6.8% in August and 3.5-5.2% in June (Table 2).

Chlorophyll content of blue-green algae (ChlCyan) in June was 2.1-12.5 pg/L, average of 0.9-5.5 pg/L. Despite the low concentration, the contribution of ChlCyan in total Chl a was appreciable and reached 54-87% (average 36-56%). In August of both years, the absolute and relative amount of ChlCyan increased: the maximum up to 8.7-49.1 pg/L (2015) and 84-98% (2016), the average up to 9.5-20.7 pg/L and 60%-90%. The highest percentage of ChlCyan was recorded in the Gorky and Saratov reservoirs (Table 2).

With the continuous presence of the diatoms in phytoplankton, the concentrations of ChlBac varied throughout the observation period within a wide range (Table 2). The maximum of ChlBac in individual reservoirs in June was from 5.8 to 22.2 pg/L, in August - mainly from 11.7 to 31.4 pg/L, exceeding 60 pg/L in Cheboksary (2015) and Ivankovo (2016) reservoirs. The minimum of ChlBac was observed in Saratov reservoir. In June the share of ChlBac in total Chl a was the highest: from 5.9-41% to 81-94%, on average -40-60%. The low values (average < 5 pg/L) were observed both in June and August. Early in the summer, ChlBac formed about the half of total Chl a, with the low content of the latter, in Kuibyshev, Saratov, and Volgograd reservoirs. At the height of summer, in Ivankovo and Saratov (2015), Gorky and Kuibyshev (2016) reservoirs with the dominance of ChlCyan, the contribution of Chl Bac was much lower (from 9 to 29%). Average concentrations of ChlBac in limits of 5-10 pg/L in June were obtained in the Gorky and Cheboksary reservoirs, where ChlBac made about half of total Chl a, and in August - in Uglich, Rybinsk (both years) and Cheboksary (2016) reservoirs - about a third of this pool. High (average >10 pg/L) concentration of ChlBac was recorded in Ivankovo (August 2016, about a third of Chl a) and in Cheboksary (August 2015, about 40%) reservoirs, as well as in the unregulated section of the Lower Volga from the dam of the Volgograd HEP to Astrakhan (June, 88%). This section with high flow velocities was distinguished by the maximum absolute and relative content of ChlBac, due to the high abundance of the diatoms.

Table 2. Chlorophyll a content in basic phytoplankton taxa in the Volga River reservoirs according to fluorescent method

Water reservoir Year, month ChlCyan ChlBac ChlChlor Sum,

^g/L % ^g/L % ^g/L % ^g/L

Ivankovo 2015, VIII 3.0-42.0 26-86 0.8-11.7 8.5-58 0.3-3.9 1.2-18 4.3-49.0

12.8±3.6 64±6.3 4.7±1.0 29±5.5 1.1±0.3 6.8±1.4 18.6±3.8

2016, VIII 4.8-49.1 37-87 1.7-73.4 12-61 0.5-3.0 0.8-11 8.4-120

19.7±5.4 62±4.2 12.7±6.8 32±4.2 1.2±0.3 5.5±1.1 33.7±11.1

Uglich 2015, VIII 2.2-28.5 20-84 3.2-14.2 12-74 0.3-1.7 1.6-6.6 17.1-35.2

16.6±3.0 62±6.3 8.0±1.2 35±6.0 0.8±0.1 3.4±0.5 25.3±3.6

2016, VIII 10.9-27.1 40-85 3.9-26.1 14-57 0.3-1.6 1.2-4.8 16.7-45.9

18.2±1.5 68±4.2 8.6±2.2 29±4.0 0.8±0.2 2.8±0.4 27.6±2.8

Rybinsk 2015, VIII 6.3-20.5 24-93 1.0-19.5 6.5-74 0.0-0.6 0.2-3.6 8.6-29.1

12.0±2.2 67±9.4 6.8±2.7 32±9.3 0.2±0.1 1.3±0.6 19.1±3.0

2016, VIII 13.1-35.8 72-96 4.6-18.3 25-61 0.5-2.6 2.6-7.3 18.2-47.0

20.7±2.3 68±4.6 8.4±1.3 29±4.3 0.6±0.2 2.1±0.4 30.1±2.5

Gorky 2015, VIII 7.2-27.8 46-91 2.6-14.0 8.6-53 0.0-2.1 0.0-6.1 15.6-36.1

19.9±1.6 71±4.0 7.6±1.0 28±3.8 0.3±0.2 0.9±0.4 27.8±1.5

2016, VI 0.4-12.5 2.1-63 0.9-16.3 35-95 0.0-1.2 0.1-6.5 2.5-20.5

5.5±0.8 45±4.1 7.0±1.0 51±4.0 0.5±0.1 3.5±0.4 13.0±1.4

2016, VIII 6.4-36.6 76-98 0.3-6.4 2.2-22 0.0-1.1 0.0-2.5 8.5-44.1

17.7±2.3 90±1.8 1.8±0.5 8.9±1.6 0.1±0.1 0.7±0.3 19.6±2.7

Cheboksary 2015, VIII 0.5-26.1 1.5-89 1.6-63.2 9.9-97 0.0-0.4 0.0-1.1 16.2-81.5

17.8±2.6 60±10 18.3±6.8 40±10 0.2±0.0 0.5±0.1 36.3±6.9

2016, VI 0.8-4.0 18-54 0.8-14.4 41-81 0.1-1.0 1.0-9.9 1.8-19.0

2.2±0.2 36±2.8 5.2±1.0 60±3.1 0.3±0.1 4.5±0.5 7.7±1.2

2016, VIII 3.8-18.7 14-97 0.5-31.4 2.8-82 0.0-1.3 0.1-6.7 5.2-38.1

10.4±1.9 66±6.3 6.7±1.2 30±5.7 0.6±0.1 3.7±0.8 17.7±2.2

Kuibyshev 2015, VIII 1.6-22.8 59-93 0.6-13.6 6.7-35 0.0-2.5 0.0-6.3 2.2-38.9

10.6±2.0 78±2.9 2.7±0.9 21±2.6 0.3±0.2 1.4±0.5 13.6±2.8

2016, VI 0.1-2.8 2.0-87 0.0-6.7 5.9-94 0.0-0.3 0.8-14 0.5-7.1

0.9±0.1 53±4.6 1.3±0.3 42±4.6 0.1±0.0 5.2±0.7 2.3±0.3

2016, VIII 6.7-47.2 44-95 0.6-11.9 4.7-46 0.1-3.0 0.2-12 7.9-49.9

17.6±2.0 79±2.9 3.5±0.6 17±2.2 0.8±0.2 3.7±0.7 21.9±2.0

Saratov 2015, VIII 4.0-18.4 74-88 1.0-2.6 10-26 0.0-0.3 0.5-1.6 5.1-20.8

9.5±1.3 82±1.3 1.7±0.2 17±1.4 0.1±0.0 0.9±0.1 11.3±1.4

2016, VI 0.1-2.7 2.6-58 0.6-5.8 40-93 0.0-0.3 1.8-5.0 1.2-7.0

1.3±0.2 37±4.1 2.8±0.4 60±4.0 0.2±0.0 3.5±0.2 4.2±0.4

Volgograd 2016, VI 0.9-7.1 3.9-75 0.8-22.2 18-94 0.2-0.5 1.9-8.0 2.1-23.6

3.5±0.3 56±3.5 4.0±1.1 40±3.6 0.3±0.0 4.4±0.4 7.8±1.0

Unregulated 2016, VI 0.0-2.1 0.1-14 5.2-49.0 82-96 0.1-2.3 2.0-6.3 5.6-51.3

Volga 0.9±0.1 7.5±0.9 13.2±1.6 88±1.0 0.6±0.1 4.1±0.2 14.7±1.6

Fig. 4. Relationship between chlorophyll content in the diatoms (ChlBac, fluorescent method data) and chlorophyll c (Chl c, spectrophotometry data).

Comparison of ChlBac with another diatoms marker - the content of Chl c, which is determined spectrophotometrically, demonstrates a close relationship between them. This confirms the validity

of the results of both methods and makes it possible to obtain a quantitative dependence that is approximated by a linear equation (Fig. 4).

Dynamics of ChlCyan and ChlBac correspond to seasonal development of the Volga phytoplankton, which is characterized by the dominance of diatoms in spring and autumn, and the dominance of blue-green (or blue-green and diatoms) in summer. This is quantitatively expressed by the presence of spring, summer and autumn rises and early summer depression [Korneva, 2015].

In the last years, vegetation of the blue-green algae becomes more abundant and more prolonged at the intensification of phytoplankton development taking place simultaneously with temperature increase due to climate warming considered as eutrophicating factor [Jeppesen et al., 2005]. The latter is confirmed by the increased

amount of ChlCyan in all reservoirs in June, as well as by the data on the long-term dynamics of ChlCyan in the Rybinsk reservoir [Mineeva, 2016].

Reservoirs of the Volga River are characterized by a complex hydrodynamic regime (flow, intensive mixing, developed network of tributaries, the presence of dissimilar water masses). This fact is responsible for the uneven horizontal distribution of phytoplankton, the most pronounced for a large (> 1000 m) scale [Mineeva, 2004]. During the study period, the macroscale distribution of Chl a was characterized by a different degree of inhomogeneity. Coefficients of variation (CV) of Chl a average concentrations in most cases were from 30 to 70%, indicating a moderate

Table 3. Coefficients of variation (%) in the average chlorophyll content in the Volga River reservoirs during the study periods

heterogeneity in the distribution of algae. The most uniform distribution of Chl a was observed in the Gorky reservoir in August 2015 (CV = 21%), while the most heterogeneous - in Cheboksary reservoir during the whole period of studies (CV = 75-102%) and in Volgograd reservoir in June (CV = 96%) (Table 3). In each of the last two reservoirs, the maximum Chl a content was noted at a single station: in the mouth of the Oka River in Cheboksary reservoir (32 pg/L in June, 63 and 86 pg/L in August) and at the near-dam site in Volgograd reservoir (15.5 pg/L).

Water reservoir ChlCyan ChlBac Chl a

2015 2016 2015 2016 2015 2016

VIII VI VIII VIII VI VIII VIII VI VIII

Ivankovo 89 85 66 - 58 54 - 56

Uglich 54 - 25 46 - 78 32 - 47

Rybinsk 44 - 44 96 - 62 37 - 33

Gorky 29 73 42 48 70 86 21 49 55

Cheboksary 43 47 46 111 87 89 81 75 102

Kuibyshev 70 73 68 121 137 95 42 61 57

Saratov 53 68 - 37 75 - 41 60 -

Volgograd - 57 - - 160 - - 96 -

Lower Volga - 70 - - 71 - - 55 -

Note. Chl a - according to the spectrophotometry method; here and in Table 4, dash - absence of data.

Distribution of ChlCyan in the majority of cases was moderately heterogeneous (CV = 4273%), but more discrete in Ivankovo reservoir (CV >80%), and more uniform (CV = 25%) in Uglich reservoir (August 2016). For the distribution of ChlBac, on the contrary, a high degree of variability was revealed, especially in June when CV values exceeded 100% (Table 3).

If we consider the Volga cascade as a whole, the previously revealed tendency to decrease the chlorophyll content from the upper reservoirs to the lower ones remains [Mineeva, 2004]. Similar distribution is seen for phytoplank-ton biomass [Korneva, 2015]. The increase of flowage and drainage volume downstream of the Volga River as well as decrease of lateral tributaries volume explain this.

At the same time, the distribution of total Chl a, distribution of ChlBac and ChlCyan along the Volga cascade are characterized by the alternation of rises and falls. All water reservoirs have areas with elevated abundance of phytoplankton. In June, when Chl a concentrations were low overall, a local peak of its content was observed in the upper part of Cheboksary reservoir with maximum

downstream of the Oka River inflow; in the upper reach of the Volgograd HEP and (the most significant) - in the unregulated Lower Volga (Fig. 5). During this period, the overall chlorophyll pool was formed mostly by ChlBac as its content was significantly higher than that of ChlCyan in majority of cases. Concentrations of ChlBac from 3 to 10 pg/L were obtained at a third of the stations, concentrations over 10 pg/L at 11 stations, including the sites in Gorky reservoir, the mouth of the Oka River, and the Lower Volga. An increase in the content of ChlCyan to 5-7 pg/L was observed only in the upper part of Volgograd reservoir (near the mouth of the Bol'shoi Irgiz and Kurdyum rivers), and up to 9-13 pg/L in the middle part of Gorky reservoir, including the Kostroma expansion (Fig. 6). At these stations, the concentrations of ChlCyan were higher than ChlBac. In August 2015, Ivankovo, Uglich, Gorky and the upper part of Cheboksary reservoir were characterized by a high content of Chl a, which decreased significantly towards the lower stations of the latter and not changing in the Kuibyshev and Saratov reservoirs (Fig. 5).

Fig. 5. Distribution of chlorophyll a in the Volga River reservoirs in August 2015, June and August 2016 (1-3, respectively). Data of the spectrophotometry method. Reservoirs: Iv- Ivankovo, Ugl - Uglich, Gork - Gorky, Cheb - Cheboksary, Kuib - Kuibyshev, Sarat - Saratov, Volg -Volgograd, UnLV - unregulated section of the Lower Volga.

This decrease could be a consequence of the specific conditions of the high-water river areas with high flowage, which inhibits the development of algae. The Chl a pool was mainly formed by ChlCyan, the content of which was from 10 to 30 pg/L at 2/3 of the stations, reaching maximum of 42 pg/L in the Shosha reach of Ivankovo reservoir. In the upper part of the latter, as well as in the estuarine zones of rivers, the amount of ChlBac (8-14 pg/L) was noticeable (Fig. 6). In August 2016 the content of Chl a was maximal in the Upper Volga, declining in the Gorky and Cheboksary reservoirs and increasing in Kuibyshev reservoir below the confluence of the river Sviyaga (Fig. 5). The content of ChlCyan in most cases was > 10 pg/L and exceeded the content of ChlBac by 2 times or more, and at 16 stations (mainly in the Middle Volga) - by an order of magnitude. Only at three stations, with a high abundance of algae (the mouth of the Medveditsa River, Shosha Bay, the mouth of the Oka River), ChlCyan quantitatively yielded to ChlBac, significantly so in the Oka River mouth (Fig. 6).

Concentrations of Chl a over 30-60 pg/L, characteristic for the water bloom of varying intensity [Sirenko, Gavrilenko, 1978], were noted in the Volga cascade only locally. The Shosha Bay in Ivankovo reservoir and the mouth of the Oka River in Cheboksary reservoir constantly belong to such areas and sometimes they include also the lower part of Ivankovo reservoir, the upper part of Uglich reservoir and its estuary zones, the Kostroma expansion in Gorky reservoir.

A comparison of the current data and those dating back to the end of the 20th century shows that the chlorophyll content, which characterizes the degree of phytoplankton development, became

significantly higher in Uglich reservoir and slightly decreased in Saratov and Volgograd reservoirs. In Rybinsk and Gorky reservoirs (2015), in Cheboksary and Kuibyshev (2016) reservoirs, chlorophyll concentrations are commensurate with those obtained earlier. However, lower concentration of Chl a were seen in Rybinsk and Gorky reservoirs (2016), as well as in Kuibyshev reservoir (2015), while greater values were demonstrated in Cheboksary reservoir (2015) (Table 4).

Photosynthetic pigments characterize not only the development and functioning of phyto-plankton, but are also used to assess the trophic status of water bodies and water quality [Vinberg, 1960; Kitaev, 2007]. According to the average content of Chl a, the Volga River reservoirs correspond to different trophic categories that are associated with the development of biological communities and, considering the high dynamics of this development, are subject to seasonal and in-terannual fluctuations. In the beginning of summer the reservoirs of the Middle and Lower Volga were characterized as mesotrophic (<10 pg/L Chl a), with only Cheboksary reservoir - as moderate eutrophic. In August 2015, five upper reservoirs were classified as eutrophic (15-30 pg/L), Kuibyshev and Saratov reservoirs - mesotrophic. In August 2016 Gorky reservoir corresponded to mesotrophic type; Rybinsk and Kuibyshev reservoirs - moderate eutrophic (10-15 pg/L); Ivanko-vo, Uglich, and Cheboksary reservoirs - eutrophic (Table 4).

Modern assessment of trophic status of reservoirs in some cases differs from that obtained in the second half of the 20th century, when Uglich, Saratov, and Volgograd reservoirs were characterized as mesotrophic, Rybinsk and Kuibyshev res-

ervoirs - moderate eutrophic, Ivankovo, Gorky, and Cheboksary reservoirs - eutrophic [Mineeva,

2004]. Nowadays concentrations of Chl a correspond to a higher trophic category in Uglich and

Fig. 6. Distribution of chlorophyll in blue-green (ChlCyan, 1), diatom (ChlBac, 2) and green (ChlCUor, 3) algae in the Volga River reservoirs in June 2016, August 2015 and 2016 (a, b, c, respectively). The remaining notations, as in Fig. 5.

Table 4. Chlorophyll a content in the Volga River reservoirs in different years.

Water Chlorophyll a, |rg/L

reservoir VIII 1989-1991* VIII 2015 VI2016 VIII 2016

Ivanovo 25.5+2.4 24.0±4.0 - 20.7±3.7

Uglich 7.9+0.8 25.5±2.8 - 17.7±3.0

Rybinsk 24.4+2.5 24.8±3.6 - 12.9±1.8

Gorky 17.9+1.0 18.4±1.1 8.2±1.2 7.5±1.3

Cheboksary 14.6+1.4 29.6±8.1 12.2±3.1 16.9±6.7

Kuibyshev 11.5+1.0 6.1±0.8 3.0±0.5 14.8±2.8

Saratov 8.1+1.0 5.7±1.0 3.8±0.9 -

Volgograd 8.9+1.0 - 4.3±1.5 -

Note. * - according to Mineeva, 2004

Rybinsk reservoirs and to a lower one in Gorky reservoir. At the same time, the values obtained in Ivankovo, Uglich, and Cheboksary reservoirs correspond to the same trophic gradation in both years of observation, whereas they differ in Rybinsk, Gorky, and Kuibyshev reservoirs. These

changes are caused by the interannual and long-term dynamics of phytoplankton revealed by continuous long-term observations at the Rybinsk reservoir [Mineeva, 2016], and indicate a high dynamic development of the ecosystems in the Volga River reservoirs.

CONCLUSION In the summer of 2015 and 2016 the content of photosynthetic pigments in reservoirs of the Volga River is represented by the values typical for the early summer depression of phyto-plankton in June and the summer maximum in August. The average concentration of chlorophylls (Chl a+b+c) in early summer is 4.05.5 pg/L in Kuibyshev, Saratov, and Volgograd reservoirs; 10.0-14.7 pg/L in Gorky and Cheboksary reservoirs. At the height of summer 2015 and 2016 higher values were obtained (16.3-34.4 pg/L), generally. Determination of chlorophyll by standard spectrophotometric and fluorescent methods showed good convergence of the obtained results (R2 = 0.78). Chlrophyll a prevails (71-85% in June, 67-93% in August) in the pool of green pigments of phytoplankton, its share became higher than at the end of the 20th century. An increase in the fraction of Chl a indirectly indicates an intensification of the development of blue-green algae, which is confirmed by the high amount of ChlCyan in all reservoirs, not only in August, but also in June. The relative content of Chl c is 6-29%, Chl b is 1-9%, phaeopigments are 26-78%, the content of plant carotenoids and Chl a is commensurate. The contribution of ChlCy-an (an average of 36-56% in June and 60-90% in August) and ChlBac (40-60% and 9-40%)

in the total amount of Chl a corresponds to the taxonomic composition of the Volga phytoplank-ton and the dynamics of its main divisions. Close relationship (R2 = 0.69) is established between the content of diatoms markers - Chl c, determined spectrophotometrically, and ChlBac, determined by the fluorescent method.

With a general tendency towards a decrease in phytoplankton biomass from the upper water reservoirs to the lower ones, its distribution in the Volga cascade is characterized by alternating rises and falls in the concentration of Chl a. Local increase in Chl a up to 30-60 pg/L is constantly observed in the Shosha Bay in Ivankovo reservoir and the mouth of the Oka River in Cheboksary reservoir.

The trophic status of the reservoirs of the Middle Volga in early summer is characterized as mesotrophic, with only Cheboksary reservoir - as a moderately eutrophic. At the height of the summer, Ivankovo, Uglich, and Cheboksary reservoirs are eutrophic. The trophic status of Rybinsk reservoir during the study varied from moderately eutrophic to eutrophic, Gorky reservoir from mes-otrophic to eutrophic, Kuibyshev reservoir from mesotrophic to moderately eutrophic. Reservoirs of the Lower Volga are characterized as meso-

trophic.

The author expresses sincere gratitude to the employees T.P. Zaikina, O.S. Makarova, and V.V. Solov'eva (Laboratory of Algology of IBIW RAS) for collecting field material.

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СОСТАВ И СОДЕРЖАНИЕ ФОТОСИНТЕТИЧЕСКИХ ПИГМЕНТОВ В ПЛАНКТОНЕ ВОДОХРАНИЛИЩ ВОЛГИ (2015-2016 гг.)

Н. М. Минеева

Институт биологии внутренних вод им. И.Д. Папанина РАН 152742 пос. Борок, Ярославская обл., Некоузский р-н, e-mail: [email protected]

Приводятся данные по составу и содержанию фотосинтетических пигментов в планктоне водохранилищ Волги летом 2015 и 2016 гг. Определение пигментов выполнено стандартным спектрофотометриче-ским и флуоресцентным методами, результаты которых коррелируют между собой (R2 = 0.78). Средняя концентрация хлорофиллов (Хл a+b+c) составляет в июне в Куйбышевском, Саратовском и Волгоградском водохранилищах 4.0-5.5 мкг/л, в Горьковском и Чебоксарском - 10.0-14.7 мкг/л, на незарегулиро-ванном участке Нижней Волги - 22.5 мкг/л. В августе содержание Хл a+b+c равняется 20.5-34.4 мкг/л в пяти верхних водохранилищах каскада, 6.3 и 6.7 мкг/л в Куйбышевском и Саратовском (2015 г.), 10.9 мкг/л в Горьковском и 16.3-26.4 мкг/л в остальных водохранилищах (2016 г.). В фонде зеленых пигментов преобладает Хл a (71-85% в июне, 67-93% в августе); доля Хл c составляет 6-29%, доля Хл b - 1-9%, количество феопигментов - 26-78%, содержание растительных каротиноидов и хлорофилла соизмеримо. Вклад в суммарное количество Хл а синезеленых (в среднем 36-56% в июне и 60-90% в августе) и диатомовых водорослей (40-60% и 9-40%) соответствует таксономическому составу волжского фитопланктона. Трофический статус водохранилищ Средней Волги в начале лета характеризуется как мезотрофный, лишь Чебоксарского - как умеренно эвтрофный. В разгар лета Иваньковское, Угличское и Чебоксарское водохранилища устойчиво относятся к категории эвтрофных. Статус Рыбинского водохранилища в годы исследования меняется от умеренно эвтрофного до эвтрофного, Горьковского - от мезо-трофного до эвтрофного, Куйбышевского - от мезотрофного до умеренно эвтрофного. Водохранилища Нижней Волги характеризуются как мезотрофные.

Ключевые слова: фотосинтетические пигменты, водохранилища Волги, трофический статус.