Ecological monitoring of phytoplankton in Lake Baikal

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Ecological monitoring of phytoplankton inLake BaikalG.I. Popovskaya aa Institute of Geochemistry , Siberian Branch of the Russian Academy ofSciences , Irkutsk, 664033, RussiaPublished online: 07 Nov 2008.

To cite this article: G.I. Popovskaya (2000) Ecological monitoring of phytoplankton in Lake Baikal, AquaticEcosystem Health & Management, 3:2, 215-225

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Aquatic Ecosystem Health and Management 3 (2000) 215-225

Aquatic Ecosystem Health & Management

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Ecological monitoring of phytoplankton in Lake Baikal

G.I. Popovskaya Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, 664033 Russia

Abstract

The results of the long-term investigations of phytoplankton of the whole of Lake Baikal summarizing almost 40 years of systematic observations are given in this paper. These studies draw attention to spatial heterogeneity of planktonic biomass across the basin during the spring maximal bloom. The research of vertical distribution of phytoplankton during different years allows us to specify the role of phytoplankton in the cycle of organic substances and in biological productivity of Lake Baikal. For the first time, Baikal picophytoplankton, peculiarities of its production, seasonal and inter-annual dynamics, biocoenotic interrelations and its role in the ecosystem of Lake Baikal have been described. Changes occurring in Baikal pelagial phyto- coenoses during the 1970-1990s in comparison with those of 1950-1960s have been revealed. © 2000 Published by Elsevier Science Ltd.

Keywords: Biomass; Picophytoplankton

1. Introduction

The phytoplankton of Lake Baikal plays an important role in generating primary organic substances, in providing an index of water quality and as a main component of the biotic cycle of the lake. Phyto- plankton reacts to changes in environmental conditions occurring in lakes. Algae thus serve as biological indicators by responding to changes in the ecosystem that may not be registered by other methods of investigation. Therefore, at present it is beneficial to continue long-term investigations on phytoplankton in the program of biological monitoring of Lake Baikal.

The first information on the flora of Lake Baikal began to accumulate at the end of the 19th century (Gutwinsky, 1891) and through the early part of the 20th century (Dorogostaisky, 1904). Meier (1930), Yasnitsky (1930), Skvortzow (1937), and later on Antipova and Kozhov (1957) all contributed to investigations of Lake Baikal and to knowledge of its algal

1463-4988/00/$20.00 © 2000 Published by Elsevier Science Ltd. PII: S 1463-4988(00)00021 -X

flora. Yasnitsky organized systematic year-round surveys on the phytoplankton of Lake Baikal in 1926-1928. These observations were centred on southern Lake Baikal in the region of Bolshie Koty where the biological station was established (Yasnitsky, 1930). For many years, Antipova (1955, 1963a,b) studied phytoplankton of Lake Baikal in relation to a wide range of problems about its long- term behaviour. From 1964 to 1990, we conducted continuous studies of phytoplankton in the pelagial region of the lake by means of a network of sampling stations. Some 70 samplings at standard cross- sections of the lake have been carried out. Approxi- mately 10,000 settled bottle samples have been exam- ined. Here, the results of the work undertaken between 1958 and 1990 are briefly discussed.

2. Distribution of phytoplankton biomass

The limnology of Lake Baikal is heterogenous

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216 G.I. Popovskaya / Aquatic Ecosystem Health and Management 3 (2000) 215-225

because of the large bays, shores and vast shoals that are adjacent to the mouths of large rivers. Peculiarities of composition, growth level, spatial distribution and the character of seasonal and inter-annual fluctuations in the pelagic plankton are related to this heterogeneity. For instance, it was found from long-term investigations that a higher level of phytoplankton growth is characteristic of Lake Baikal shores. Maximum phytoplankton biomass in the Rangatui, Posolsky and Istoksky shores were 93, 64 and 1 6 g m -3, respectively. According to the specific composition of the assemblages, to quantitative indices, to the blooms of blue-green algae in summer months and to the intensive production of diatom algae in spring and autumn, these shores might be referred to as eutrophic reservoirs. However, shores which are flushed by river waters (Proval Bay or Dubininsky shore, Severobaikalsky shore) have biomasses less than 2-3 g m -3. Blue-green algal blooms are slight, and diatoms dominate the sparse biomass.

On all the shores, three seasonal maxima may be observed in terms of numbers and the biomass of algae. The range of seasonal and inter-annual variations in shores is not so high as in the pelagial lake. In the 1970s, the total numbers of phytoplankton in shores increased four-fold, and biomass five-fold times over general levels in the 1950-1960s (Popovs- kaya, 1977). Through the 1980s, the level of phytoplankton growth continued to increase.

The large bays of Baikal (Chivyrkuisky, Bargu- zinsky, Maloe More Strait) differ from the shores in their greater depths, lower average temperatures and the great influence they experience from the open waters of Lake Baikal. Blue-green algal blooms are typical only in Chivyrkuisky Bay, where, in summer, the highest biomass exceeds 10 g m -3. In Bargu- zinsky Bay and Maloe More spring biomass measures 2-3 g m -3. As in the shores, there are three peaks of phytoplankton growth in bay areas. The range of seasonal and inter-annual variations in number and biomass is less than in the pelagial lake, but is greater than in the shore areas. Phytoplankton standing crop in the 1980s was three to five times greater than it was in the 1960s and sometimes as much as 10 times greater. According to the level of phytoplankton growth, the bays could be compared in quality to mesotrophic reservoirs with some features of eutro-

phication during recent years (Popovskaya, 1977, 1986).

Long-term investigations on the Selenga River showed that, during the 1980s, there was a sharp increase in the number of small centric diatoms of the genera Cyclotella and Stephanodiscus, with a simultaneous decrease in the numbers of Nitzschia acicularis. In the 1980s, quantitative indices of plankton in the Selenga River were 15-18 times higher in comparison with those in the 1960s. Hence, the tendency towards eutrophication of the Selenga River noticed in the 1970s still continues.

A significant increase of phytoplankton also occurred in the biological productivity of the Selenga shoal that is fed mainly by waters of the Selenga River. Biomass in the shoal was from 0.1 to 1.5 g m 3 in the 1950-1960s, while in the 1980s it was 2 - 9 g m -3 (Popovskaya, 1991). Phytoplankton cell numbers increased eight-fold on average, and biomass five-fold. According to this level of phytoplankton biomass, the Selegan shoal could be referred to the mesotrophic-eutrophic type, with features of eutrophication occurring during recent years.

Phytoplankton of pelagial Lake Baikal has a specific character of growth. In the course of long- term investigations of seasonal growth, spatial distribution and inter-annual differences, I have chosen particular periods in the life of the lake to study plankton algae which are, to some extent, representative of the productivity during the whole year and so permit some perspective on the eutrophication of the lake. As the level of phytoplankton biomass in spring usually determines the productivity of the whole year, more detailed surveys were performed in spring after thawing of the ice, from south to north. Samples of phytoplankton collected along the whole of Lake Baikal during ice break-up are taken to reflect the scales of productivity of algae during the period of ice cover. Production of high standing crops of algae under ice is typical in the southern and central basins of Lake Baikal.

The largest crops of algae in southern and central Baikal are usually observed in March but sometimes at the end of April and the second half of May, that is, around the time of ice break-up. At this time, the most prolific production by diatoms, dinophyte algae and cysts occurs. The level of phytoplankton biomass attained under the ice is subject to sharp inter-annual

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G.I. Popovskaya / Aquatic Ecosystem Health and Management 3 (2000) 215-225

.¢1 f f t t . z t • . ¢J lJ .

. a ~ u r a

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= 200 rng/m 3

Fig. 1. Horizontal distribution of phytoplankton biomass in Lake Baikal in spring 1975 in the 0-25 m layer (mgm-3). English translations for Russian script appearing in the above figure, left hand side, top to bottom: Nizhneangarsk, Baikalskoe, Cape Elokhin, Cape Pokoiniki, Uzur, Cape Ukhan, Olkhonskiye Vorota Strait, Cape Karsny Yar, Goloustnoe, Listvyanka, Cape Polovinka, Cape Sharyzhalgay. Right hand side, top to bottom: Cape Nemnyanka, Cape Tompa, Davsha, Cape Orlovy, Cape Krestovy, Turka, Cape Sukhinsky, Kharauz Channel, Posolsk, Tankoi, Murino, Bezymyannaya.

- = 200 mg/m 3

Fig. 2. Horizontal distribution of phytoplankton biomass in Lake Baikal in spring 1982 in the 0-25 m layer (mg m 3). English translations for Russian script appearing in the above figure, left hand side, top to bottom: Nizhneangarsk, Baikalskoe, Cape Elokhin, Cape Pokoiniki, Uzur, Cape Ukhan, Olkhonskiye Vorota Strait, Cape Karsny Yar, Goloustnoe, Listvyanka, Cape Polovinka, Cape Sharyzhalgay. Right hand side, top to bottom: Cape Nemnyanka, Cape Tompa, Davsha, Cape Orlovy, Cape Krestovy, Turka, Cape Sukhinsky, Kharauz Channel, Posolsk, Tankoi, Murino, Bezymyannaya.

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Fig. 3. Horizontal distribution of phytoplankton biomass in Lake Baikal in spring 1976 in the 0-25 m layer (rag m-3). English translations for Russian script appearing in the above figure, left hand side, top to bottom: Nizhneangarsk, Baikalskoe, Cape Elokhin, Cape Pokoiniki, Uzur, Cape Ukhan, Olkhonskiye Vorota Strait, Cape Karsny Yar, Goloustnoe, Listvyanka, Cape Polovinka, Cape Sharyzhalgay. Right hand side, top to bottom: Cape Nemnyanka, Cape Tompa, Davsha, Cape Orlovy, Cape Krestovy, Turka, Cape Sukhinsky, Kharauz Channel, Posolsk, Tankoi, Murino, Bezymyannaya.

J~.,o

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Fig. 4. Horizontal distribution of phytoplankton biomass in Lake Baikal in spring 1979 in the 0-25 m layer (rag m 3). English translations for Russian script appearing in the above figure, left hand side, top to bottom: Nizhneangarsk, Baikalskoe, Cape Elokhin, Cape Pokoiniki, Uzur, Cape Ukhan, Olkhonskiye Vorota Strait, Cape Karsny Yar, Goloustnoe, Listvyanka, Cape Polovinka, Cape Sharyzhalgay. Right hand side, top to bottom: Cape Nemnyanka, Cape Tompa, Davsha, Cape Orlovy, Cape Krestovy, Turka, Cape Sukhinsky, Kharauz Channel, Posolsk, Tankoi, Murino, Bezymyannaya.

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G.L Popovskaya / Aquatic Ecosystem Health and Management 3 (2000) 215 225

variation. In low-production years, the biomass does not exceed 0.1 g m -3. In high-production years, the biomass can attain levels comparable to those of highly eutrophic lakes. During such years, the prin- cipal species of diatoms (Aulacoseira baicaIensis, A. islandica, Syndera acus vat. radians, S. ulna var. danica, Stephanodiscus binderanus, Nitzschia acicularis) achieve masses of 1-8 g m -3 or under 30 gm 3. During mass growth of the dinoflagellate Gymnodinium, biomass in the upper layer of water usually reaches 10-30g m -3, but at times up to 250 g m -3 (in 1979) or 1.5-2 kg m 3. Such high values are quite transient, however (Popovskaya, 1987).

3. Seasonal patterns of phytoplankton

Continuous long-term investigations on spring phytoplankton reveal a wide range of inter-annual changeability in the whole pelagial lake, The first samples showed that surveys conducted on one or two sites in southern Baikal were not representative of the whole lake. The growth of the major species of algae in open Lake Baikal is quite irregular. Often there may be a mass development in the south when there are low concentrations in the north, and vice versa (Figs. 1 and 2). More rarely, there are years with slow growth of algae through the whole lake or, in contrast, when high numbers and biomass typify the entire pelagial lake (Figs. 3 and 4).

Large crops of typical species have occurred in 1- 3 years, occasionally in as many as 5 -7 years and sometimes in two consecutive years. The absence of a clear recurrence in the growth of a few dominant species emphasizes the dependence on the complex interactions associated with hydrophysical factors, predominantly the extent of mixing of the water masses.

In spite of the fact that the composition of dominant species and the level of their spring crops during some years are so variable between basins and among years, a single complex of cold-loving species prevails. The values of spring phytoplankton were sorted as being high-production years (biomass in a layer of 0-25 m is more than 1 g m 3), average production (from 0.5 to 1 g m -3) and low production (less than 0.5 g m 3). There have been more high-production years in the

219

south and more low-production years in the north (Table 1). In the pelagial lake, 1 year can differ from another 10- or even a 100-fold. Average long- term numbers of algae in southern Lake Baikal is five times and average biomass is three and a half times higher than in northern Lake Baikal. Faster rates of productivity of algae in southern Lake Baikal are supported by the nutrients supplied by the Selenga River, by the longer vegetation period and by better light conditions under thinner ice with less snow.

Production of summer phytoplankton in the pelagial lake is poor (Figs. 5-8), except of blue-green algae in those years which exhibit maximum heating of the water and calm weather.

Anabaena lemmermannii has a mass development which causes an intensive algal bloom. A major frac- tion of the pelagial biomass in summer is nanoplank- tonic: small centric diatoms, crysophyte algae and cysts.

Small crops of autumn plankton are typical for Lake Baikal (Figs. 5-8). The absence or paucity of an autumn maximum of phytoplankton in pelagial Lake Baikal is due to high winds which take algae into the aphotic zone as well as to the highest populations of zooplankton, especially of the phycophagous Epischura baicalensis. The maximum algal biomass in autumn is much less than that of the spring maximum, during some years 100 times lower and, typically, some two to eight times.

Net primary production typically occurs in Lake Baikal for about 11 months out of every 12. The average phytoplankton biomass during the vegetation period is 0.5-1 g m -3 in high-production years, and around an order of magnitude less in low-production years.

The extreme depth of the lake and intensive vertical mixing greatly influences the biology of phytoplankton in the whole water mass. Most of the year, deep layers of the lake are inhabited by algae in various concentrations. The majority of algae are beyond the euphotic zone (wherein photosynthesis is possible), but are alive and not necessarily subject to decay at once or to settling. Under ice cover, the main mass of phytoplankton is concentrated in the upper 5 - 10 m layer of the water (Fig. 6). After ice breakup, high concentrations of algae are confined mainly to the upper 100 m layer (F?gs. 6-8). In July, under the conditions of full isothermy, phytoplankton can be

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Table 1 Long-term changes of phytoplanton biomass in spring in Lake Baikal in the 0-25 m layer (mg m -3)

Years Southern Baikal Central Baikal Northern Baikal

1964 2830 1972 251 1965 1278 236 468 1966 84 243 29 1967 31 846 1562 1968 4163 1859 895 1969 828 110 22 1970 46 71 14 1971 204 574 245 1972 426 149 338 1973 68 492 31 1974 2380 311 97 1975 37l 717 128 1976 1575 688 778 1977 513 487 107 1978 226 552 103 1979 2366 1181 1222 1980 629 602 53 1981 58 435 24 1982 1394 2342 176 1983 1259 2012 334 1984 1653 1515 31 1985 99 1271 81 1986 92 592 93 1987 1345 1050 97 1988 200 920 102 1989 282 720 120 1990 2833 1840 1232

evenly distributed in the 500 m layer of water. In July-August, the phytoplankton biomass in the productive 0-25 m layer accounts for not more than 3-10% of the total algae biomass in the water column. In autumn, 85-95% of the planktonic mass is beyond the zone of photosynthesis at depths of 300-500 m. Through the whole depth of Lake Baikal (0-1400 m), phytoplankton biomass per m 3 of the lake varies between 9 and 70 mg -3 in low-production years, and between 80 and 500 mg 3 in high-production years. The algae in the extensive aphotic layers are important for the deep-water bacterioplankton, protozoa, zooplankton and so on, that is, to the entire production of Lake Baikal. Even in high-production years, little phytoplankton is buried in bottom sedi- ments, but is processed within the water column. This inertness and economy of the 'activity' of the unique and bioproductive system of Lake Baikal is largely

due to the lake's great depth and is reminiscent of ocean systems.

How does the lake ecosystem exist when the production of phytoplankton is low? Investigations have shown that, in low-production years, an abun- dant picophytoplankton dominated by small blue- green algae develops in spring and summer in the pelagial lake. Their spatial and temporal dynamics, ecosystem interactions and productive capability have been investigated. A new species, Synechocystis limnetica, 1.5-2 mm in diameter, has been found to account for 90% of the picophytoplankton (Popovs- kaya, 1968a,b, 1985; Votintsev et al., 1972, 1975). Picophytoplankton is widely distributed over the pelagial lake, and its abundance is inversely proportional to the level of biomass of large phytoplankton. In low- production years, the number of picoplankton is 50- 80X 106 cell 1 -~ in spring, but in the years of high crops of phytoplankton, only 2-5 X 106 cell 1-1. Such reciprocity is observed every year. The highest crop of picoalgae around the whole pelagial lake is observed in summer. Maximum growth is typical in northern Baikal, where the number of picoplankton is 60-80 x 106 cell 1 1. In low-production years, picoplankton biomass is 40-60% of phytoplankton biomass, but in high-production years, only 5-15%. Due to the small size of its cells, populations of Syne- chocystis limnetica have a relatively small biomass, 60-180 m g m -3. Mass growth of picoplankton in Lake Baikal occurs due to high rate of division (up to 2.5 d -~) and to high rate of assimilation of nutrients. Having a large specific cell surface, these organisms are able to grow at concentrations of nitrogen and phosphorus that are close to analytical limits of detection. Increased content of chlorophyll in small cells promotes a more effective cell-specific absorp- tion of light and high rate of division.

These findings on the picophytoplankton have provided answers to many questions that arose during earlier investigations on Lake Baikal and have made possible a new estimate of the functional role of this group of organisms in the lake ecosystem. Mass development of picoplankton smooths the striking seasonal and inter-annual differences in the production and biomass of phytoplankton. It explains to some extent the discrepancy between high values of primary production and phytoplankton biomass in summer months, and low values of transparency in

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G.L Popovskaya / Aquatic Ecosystem Health and Management 3 (2000) 215-225 221

~D

Y ¥1 Yll yll[ ~ X

f00-

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Fig. 5. Vertical distribution of phytoplankton biomass in central Baikal in 1976. One point on the horizontal axis equals 25 mg m -3.

August due to slow growth of algae. The scales of productivity of picophytoplankton and its role in lake ecosystem makes Lake Baikal similar to the oceans. The growth under the ice of large forms of phytoplankton and the dominance of picoplankton algae which can sustain high rates of reproduction in the period of open water ensure the optimal functioning of the whole biome.

The growth of phyto- and picophytoplankton in the pelagial lake, practically throughout the whole year, and their significant concentration (especially per m 3) allow us to classify Lake Baikal with reservoirs of high bioproducing potential (Pastukhov and Popovskaya, 1984). The availability of high concentrations of golomyanka sculpin fish and

high numbers of seals in open Lake Baikal presum- ably testify to this fact.

4. The present state of Lake Baikal

Long-term studies of the species composition, structure and functioning of Lake Baikal phytoplankton allow us to determine the state of the lake and to draw conclusions about the direction of change and to propose quantitative and qualitative indices for the future. The material reviewed here shows that, over the last 10-15 years, there have been quite significant changes in the Baikal phytoplankton. Earlier (1950-1961), high-productive years were

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a~

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dominated mainly by A. baicalensis and Cyclotella baicalensis. The biomass of other algae in the 1950s and the 1960s was extremely low. Between 1960 and 1968, high numbers of A. baicalensis were observed in southern Baikal in two or three of the years, but were quite rare in two others. During the period from 1969 to 1990, there were only 3 years which produced rich crops of Aulacoseira, that is, the intervals between Aulacoseira years had increased to 5 - 8 years with a simultaneous decrease in its biomass levels (Table 2). On the other hand, the proportion of Aulacoseira islandica in the plankton of open Lake Baikal has increased: from 1 x 105 cell 1-1 in the 1950-1960s, to 1 x 10 6 cell 1 -~ in the 1970-1980s. During the last decade, the number of Synedra acus var. radians increased several times, to 2 X 10 6 cell 1 I. Nitzschia acicularis was also intro- duced, and there has been a mass growth of this species during the last years. This species is widely

distributed in reservoirs of different types. This species was first seen in 1969 when its number exceeded l X 106 cell1-1. In the beginning, the interval between productive Nitzschia years was 7 years; then it decreased to 2 - 3 years (Table 2). The maximum numbers of this species have been 4 - 7 x 10 6 cell 1-1 during recent years. Its maximum abundance is in spring, which is typical of all the mass species of diatom plankton of the pelagial Lake Baikal.

Some changes have also been observed in the phytoplankton of central Lake Baikal: Stephanodiscus binderanus, Synedra and small species of centric diatoms have been prevalent in the last few years.

It is harder to detect changes in the phytoplankton of northern Baikal because the leading role during most of the vegetation period belongs to picophytoplankton. In the summer months of the 1980s, there have been blooms of blue-green algae, Anabaena

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223

x

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! Fig. 7. Vertical distribution of phytoplankton biomass in southern Baikal in 1979. One point on the horizontal axis equals 25 mg m 3

lemermannii, which was seen in smaller quantities in previous years.

The reorganization of planktonic biocenoses does not readily influence the quantitative indices. In consequence of the partial substitution of large cell species of phytoplankton (A. baicalensis) by small- cell species (N. acicularis, Stephanodiscus binderanus), the numbers of phytoplankton cells have increased two times in southern Baikal during the last 10-15 years, in central Baikal by three times and in northern Baikal by one and a half times. As for phytoplankton biomass, it has changed very little. In southern and northern Baikal it is practically unchanged and in central Baikal it has increased two times.

In the long-term, phytoplankton biomass in pelagial Lake Baikal will probably not change significantly in the future due to the huge water mass, the capacity of its environment and the peculiarities of the cycle of organic production. The disturbance of recurrence of dominant species of phytoplankton during the last years may be explained by the warming global

climate, which greatly influences the time of freezing and thawing of the lake, the annual snowfall, the movements of the water masses and consequently the return of nutrients from deep layers to the surface. The eutrophication of open Lake Baikal, as is the case in other deep lakes of the world (Malawi, Tanganyika and so on) is unlikely in the future. In the shallow water regions of Lake Baikal, however, phytoplankton quickly responds to human activities; for example, in the bays and tributaries of large rivers the effect of anthropogenic eutrophication has already been marked.

Acknowledgements

I express my deep gratitude to Dr M. Munawar for his interest in these investigations on phytoplankton of Lake Baikal and for the help in publishing this paper, as well as to Prof. Yu. Kusner, Head of Limnology Laboratory, Institute of Geochemistry, Irkutsk, Russia, for the assistance in this research.

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G.1. Popovskaya / Aquatic Ecosystem Health and Management 3 (2000) 215-225

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Fig. 8. Vertical distribution of phytoplankton biomass in southern Baikal in 1982, One point on the horizontal axis equals 25 mg m 3.

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Table 2 Long-term changes of number of Alacosira baicalensis and Nitzschia acicularis in Southern Baikal in spring in the 0-25 m layer (10 3 cell I -l)

Years Aulacosira baicalensis Nitzschia acicularis

1964 239.0 0.3 1965 0.4 1.7 1966 1.7 0.1 1967 2.2 0.1 1968 212.3 0.1 1969 0.1 1208.0 1970 3.5 1.0 1971 19.5 4.1 1972 1.0 2.4 1973 2.0 8.1 1974 157.5 0.1 1975 5.2 8.4 1976 2.9 4.7 1977 0.1 1066.0 1978 0.1 98.2 1979 46.0 2.5 1980 0.7 1509.0 1981 1.0 0.9 1982 132.8 2.4 1983 3.5 7.4 1984 13.9 4244.0 1985 2.8 20.4 1986 3.6 82.3 1987 13.3 3308.0 1988 14.0 10.0 1989 15.0 13.0 1990 182.0 0.9

References

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Ecological monitoring of phytoplankton in Lake Baikal