The main source of the organic substance primary output is the water plants inhabiting the thick of the water (phytoplankton) as well as the bottom (phytobenthos). Mostly stony shores which are subject to the strong surf throughout the iceless period do not let marsh and water plants, which are common for regular lakes, inhabit the lake. Only in some places with conditions different from the Baikal ones (sors, river mouths, some coves of the Chivyrkui gulf and others) variable marsh and water vegetation is highly developed. But the area of this non-Baikal vegetation is very insignificant compared to the Baikal one.
Studying the Baikal water plants was started in the end of the previous century by R. Gutvinsky and V.Ch. Dorogostaisky. But this research did not discovered the specific nature of the world’s greatest lake’s flora and vegetation. Later K.I. Meyer (1922, 1930) proved that the Baikal flora is special, it is generally endemic and unique and incomparable as well as the fauna. All the later researchers confirmed K.I. Meyer’s conclusions who also discovered the main components of the Baikal phytoplankton. V.N. Yasnitsky organized all-the-year-round research throughout several years. Before this work everybody had been surprised at unusual poorness of the Baikal phytoplankton. V.N. Yasnitsky’s works (1930) demonstrated that its quantity is rather great, develops under the ice from February to May, sometimes to the early June. After ice break-up the phytoplankton disappears. It turned out that the huge area of the ice free Baikal is extremely unfavourable for the plankton organisms. Incessant winds cause constant and variable water flows. That is why the Baikal phytoplankton is as if covered with ice and carries out its live functions under the ice in spring. But it also turned out that there is abundant phytoplankton in summer, too, represented by blue-green algae - synechocytis, which was discovered and described by G.I. Popovskaya (1968).
In the pre-war years the main device for collecting phytoplankton was the plankton net though other methods were known before. In the post-war years sedimentation method became universally recognized alongside with the filtering one, though many authors used both of them alongside with the net one, because the filtering method researches very small quantity of water. All the modern methods were introduced into practice of the Baikal phytoplanktologers’ work.
Overwhelming majority of the Baikal vegetation is composed of algae, a group of lower plants which are represented in the fresh waters by unicellular and colonial organisms. The algae, hydrophytes and hydatophytes are absent from the Baikal itself with the exception of very rare individual evidently depressed representatives. But in some places with changed conditions as well as in the Baikal sors or in the river mouths the marsh and water vegetation is very abundant.
All in all in the Baikal flora and in the lakes connected with it 1,085 taxons of water plants 852 of which are endemics and 233 are sub-species, varieties and forms have been discovered by now.
The water plants endemism of the Baikal is not so profound as the endemism of its fauna, it is not further than genera though some of them make a special development branch which can be distinguished as a separate family or sub-family.
A great majority of the algae species which have been discovered in the Baikal can be referred to the ones widespread in the fresh waters of Eurasia. The general number of endemic species and varieties is rather big, it is about 200 taxons out of which there are 6 genera, 133 species and 62 varieties and forms. But it makes up only about 28% of the general number of taxons found in the open lake.
Let us consider the meaning of different algae groups in the Baikal flora.
Blue-green algae (Cyanophycees) inhabit the open Baikal. Almost all of them are widespread species which live in different conditions, in stagnant and flowing waters, hot and cold springs, out of the water, on the walls of different structures, in the soil etc.
Gold algae (Chrysophycees) is a group which is not numerous in the Baikal, it consists of 29 taxons 13 out of which inhabit the open sea. There are 4 species of endemics, others are widespread in the fresh water plankton. In general it is characteristic for golden algae to be adapted to cold waters and seasons, that’ s why their settling in Lake Baikal is quite natural. Two endemics can be referred to the plankton, Epichrysis melosirae C. Meyer (Chrysosphaera melosirae (C. Meyer) Bourr) and Crysospherella baikalensis Popovsk. Two other endemics out of the number of the golden ones are the benthos organisms: Teterasporopsis reticulata C. Meyer, Chrysothaltus baikalensis C. Meyer.
Pirrophyte algae (Pirrophytae) are a very small group in the Baikal including 7 taxons. All of them are found in the open sea, and only some of them inhabit the gulfs and the sors. Peridinium baikalense J. Kiss, et Zwetkow is very peculiar. Three endemic taxons are also interesting referred to the non-testaceous genus of Gymnodinium. Three taxons of this group are widespread. One of them is Ceratium hirundinella (O.F. Mull) Bergh, it can be considered to have settled in the Baikal but its main habitats are sors.
Diatom algae (Diatomorphycees) are the most numerous group in the Baikal, the general number of their taxons is 715. In the open parts of the Baikal 576 taxons are found.
On the list of the Baikal flora there is a great number of widespread species, such as Navicula radiosa, N. Bacillum, Cocconeis placentula, Cymbella ventricosum and many others.
The Baikal is connected with many lakes, a lot of rivers flow into it and it is natural that the diatoms developing in these lakes are washed and accumulated as folds on the bottom of Lake Baikal.
The group of the North Alpine diatoms is well represented in the Baikal, they are Melosira arenaria Moore, M. Scabrosa Ostr., Tetracyllus lacustris Ralfs., Diatoma hiemale (Lyngb.) Heib., Eunotia praerupta Ehr., Frustulia rhomboides (Ehr.) D.T., Diploneis finica (Ehr.) Cl., Cymbella stuxbergii and others.
In the Baikal there are also diatoms which are peculiar to salty lakes and even seas. The bigger part of the diatom endemic species is of course of fresh water origin and in general the appearance of the Baikal endemics is more of fresh water than of sea character with the exception of some above mentioned cases. Almost all the endemic diatoms are within the existing genera. The exception is only several species which need further research.
Green algae (Euchlorophycees), this very big and important group of fresh water vegetation is relatively scanty in the Baikal, there are only 224 taxons. The main part of them is peculiar to gulfs and sors, in the open parts of the lake only 49 green algae are registered.
Volvoxes (Volvocales) have 13 taxons in the Baikal out of which only 4 species are discovered in the open parts of the lake. Two of them, Swarchewskiella rotans Jasn. and Chlorophy-sema hemisphaerica C. Meyer are endemics. The third species, Chlorogonium popovae Ustyuzh., inhabits the Selenga and the Selenga shoal under the ice. The fourth one, Eudorina, lives in the sors and gets to the lake pelagic from there.
The groups of Tetrasporales and Chlorococcales have 111 taxons in the Baikal, the bigger part of them live in the sors, shallow bays, while in the open Baikal 11 taxons are registered. But out of those taxons only two are really Baikal ones, Tetraspora bullosa C. Meyer (T. cylindrica (Wahlenb.)) Ag. var. bullosa C. Meyer and Sykidion gomphonematis C. Meyer. Other Tetrasporales and Chlorococcales are brought to open Lake Baikal from the sors.
Out of the numerous group of Ulotricophycees including 17 families, representatives of only three families live in the open Baikal, Ulotricacees, Chaetophoracees, Cladophoracees, and they make up the main vegetation mass.
In the family of Ulotricacees, Ulotrix zonata Kutz. has an important meaning, it is a rheophilic organism widespread in clear and cold waters. In the Baikal it has very favourable conditions in the surf zone. Another species of this family, Binuclearia tatrana Wittr. (Binuclearia lauterbornii (Schmid.) Pr. – Lavr.), is abundant in the Maloye sea plankton and some other parts of the lake.
The greatest meaning in the Baikal flora green algae is ascribed to Chaetophoracees and Cladophoracees. Chaetophoracees in the Baikal contain three endemic genera, Ireksokonia C. Meyer, Myxonemopsis C. Meyer and Drapamaldioides C. Meyer et Skabitsch. In the present time the genus of Myxonemopsis C. Meyer can be considered the only endemic Baikal species. All the three above mentioned genera are connected genetically.
The group of Cladophoraceae is very interesting in the Baikal, it unites 4 genera out of which 2 are endemics, Gemmiphora Skab. and Chaetocladiella C. Meyer et Skab.
The genus widespread in fresh waters and seas, Cladophora, is the richest in endemic species, there are 7 of them. This number includes 3 species of Cladophora itself and 4 species described by C.I. Meyer as Aegagropila.
The genus of Chaetomorpha includes three species, all of them are endemics. Two of them, Ch. baikalensis C. Meyer and Ch. moniliformis Skab., are scanty while Ch. curta Skab. is spread all over the Baikal.
Great groups of Zygonematales are absent from the open Baikal, while in the sors and gulfs about 50 species were found, and all of them are widespread in Eurasia.
Charophycees of the Baikal are not studied enough. In the sors three species of this group are known. They can be found in the Baikal itself, e.g. near Bolshiye Koty. Unfortunately they were observed without the reproductive organs that’s why their sex is not defined.
Rhodophyta (Rhodophycees) are very scarce in Lake Baikal. It is interesting to note that two species of Batrachospermum usually inhabiting clear and cold waters do not grow in the Baikal itself, but can be seen in the sors.
Besides the algae there is one peculiar underwater lichen, Collema ramenskii Elenk, found by V.N. Yasnitsky in the coves of the Olkhonskiye Vorota (the Olkhon Gate). Besides the Olkhon Gate coves C. ramenskii has been seen only near the village of Bolshiye Koty.
The Baikal waters phytoplankton has been studied much better than the phytobenthos. The history and the essence of the problem are very well expounded in the book by K.K. Votintsev, A.I. Meshcheryakova and G.I. Popovskaya (1975).
First of all it is necessary to mention that the open Baikal pelagic species are not numerous. In the open Baikal about 30 species of phytoplankton live. It includes both endemics and non-endemics.
An interesting peculiarity of the Baikal phytoplankton is its under-ice development first described by V.N. Yasnitsky (1930). The considerable increase of plankton starts in February and goes on as far as May or early June, i.e. the time when the Baikal ice breaks up. After that the complex of the spring species drops out of the plankton.
Another peculiarity of the Baikal is extremely unfavourable life conditions in its open pelagic. The upper water layer is always on the move under the influence of incessant winds of different directions, and the waters are mixed up, the upper layers go down, the deep waters go up. This continuous movement is as unfavourable for the phytoplankton as the fast river current. Perhaps because of this the mesoplankton develops intensively in spring protected with the ice. The main components of the spring phytoplankton are the diatoms, peridineas, chrysophytes, the organisms which are satisfied with faint lighting under the ice.
In summer mesoplankton is represented by the forms which usually develop in small numbers and carried out of the sors and rivers.
Littoral area. The ground vegetation occupies the littoral and sublittoral areas. The Baikal littoral is similar to the sea one in one of the main factors, the surf force and the tidal current caused by it. This permanently active factor caused forming special algae devices which allow them to endure the load of the tidal wave and the current.
The Baikal littoral vegetation is situated in regular belts.
The first belt, the Ulotrix belt, is situated at the very water edge where the mechanic effect of the waves is felt to the greatest extent. The belt is about a metre wide, sometimes more. It surrounds the whole of Baikal and is interrupted only opposite the river mouths and in some sandy places. In the Ulotrix belt numerous diatoms settle.
The second belt, Tetraspora – Didymosphenia, borders on the Ulotrix belt and goes 2-2.5 m down. Didymosphenia covers stones all over and its cover looks like downy brown and grey fur. Tall leaf-like emerald-green Tetraspora bullosa talloms raise over Didymosphenia forming the second tier. Didymosphenia is inhabited by epiphytes, such as different diatoms, Swarchewskiella rotans Jasnitsk., Sykidion, Chrysostallus. In that belt Tetrasporopsis and Nostoc verrucosum can be found. The second belt is not clearly manifested everywhere; in some places Didymosphenia overgrowth is weakly developed, in other places Tetraspora is found in small quantities or is absolutely absent.
The third belt, Draparnaldioides – Cladophora, the most productive one, is from 2-2.5 to 12-20 m deep. The lower tier is made with low algae. Round cushion-like cladophora species and diatomeas grow there in great numbers, attached to the stones. The cracks and hollows in the stones are filled with Gemniphora compacta, Tetrasporopsis, Nostoc verrucosum, Tolypothrix distorta are also found there, Cladophora pygmaea, C. flocossa, Chaetomorpha microscopica are less common. Diatoms are abundant on the stones as well as green algae, especially Cladophora. The second tier is represented by Draparnaldioides species, the most original and biggest algae. They do not make up a closed cover but grow as either separate bushes or in small groups. At the lower border of the littoral area, 15-20 m deep, Ireksokonia, Myxonemopsis and charous algae can be seen, too.
Sublittoral area. The sublittoral area spreads itself from the border of the littoral (11-20 m) to 60-116 m. In the sublittoral area the next two belts can be distinguished, the fourth and the fifth ones (Skabichevsky, 1934, 1966). The fourth belt is from 11-13-16 to 20-35 m deep and is located on clean coarse-grained reddish, less often yellow, sands (the northern part, the bays of Ayaya, Lakanda, Frolikha, Pongonye, Yakshakan, Davsha and others). Its characteristic algae are very small green ones, such as Cladophore meyerii, Chaetocladiella microscopica, Cladophora floccosa, C. kursanovii, C. pulvinata, Chaetomorpha tnoniliformis, Ch. curia, Chaetocladiella pumila, blue-green algae, such as Tolypothrix, Chamaesiphon and a great number of various diatom algae. The fifth belt at the eastern shore is located from 20-35 m to 30-78-116 m deep on very silted sand. The main components of that belt are Chaetomorpha curia, Eunotia clevei, Gomphonema bergii, Cocconeis ptacentula and others.
The role of endemics is great in the phytobenthos of the littoral area. The basic mass of the littoral phytobenthos algae is made up of chrysophyta and especially green algae.
To sum it up it is necessary to say that the original flora of Lake Baikal is in general of fresh water origin. The exception is only some species of diatoms which are undoubtedly related with sea ones. It is impossible to say how they penetrated into Lake Baikal.
Prevalence of endemics in the Baikal vegetation, especially in the group of the phytobenthos green algae which are of primary importance in the life of littoral and sublittoral, allows up to think that the Baikal isolated itself from the flora of Eurasian lakes long ago. E. Mair (1947) thinks that great ancient lakes are similar to ancient islands lying far off in the ocean. It is impossible to say this about the Baikal flora because there is no impassable obstacle between the Baikal and other lakes, like for ocean islands.
Moreover, the Baikal is directly connected with the lakes inhabited by common Siberian algae. Nevertheless the Baikal endemics do not spread beyond the limits of the Baikal, and vice versa, green, euglenous, rhodophyta and bigger part of other groups inhabiting the surrounding lakes, do not penetrate into Lake Baikal. The exception is only some diatoms, blue-green algae, only some species of which play an important role in the Baikal flora. Ecological factors prevailing in the Baikal are obstacles for common Siberian flora penetration into the lake. The Baikal endemics do not become widespread because they are very specific and adapted to the life in the specific Baikal conditions.
In the Baikal as well as in the seas and oceans, the main source of the primary organic substance of the water thick is its autochthonous production by phytoplankton. Owing to the vital activity of the plankton algae about 4 mln tons of organic substance is formed in the lake throughout a year, which makes 89% of its total acquisition into the lake.
The Baikal phytoplankton, together with its gulfs, sors, shallow parts, is characterized by great variety. Moore than 400 species of plankton algae have been discovered in it. The number of algae species in the typically open pelagic parts of the lake is not big owing to severe hydrological conditions. For the last 10 years we have discovered 95 phytoplankton species in the Baikal pelagic area, they can be referred to 5 types of algae: Cyanophyta (20), Chrysophyta (10), Bacillariophyta (30), Pyrrophyta (6), Chlorophyta (28). Most species are not regular or numerous in the plankton. It is especially true for green and blue-green algae which come to the lake pelagic from the gulfs and the Baikal lake-sor zone.
In the lake pelagic area itself 31 forms of plankton algae live and develop, the leading role belongs to diatom, chrysophyta and peridinia algae. Green and blue-green ones are not numerous in the lake pelagic. Among the forms typical of the open Baikal, only 12 species are mass ones: Melosira baicalensis (C. Meyer) Wisl., M. islandica O. Mull., M. binderana Kutz., Synedra acus subsp. radians (Ktitz.) Skab., 5. ulna subsp. danica (Ktitz.) Skab., Cyclotella tnituta (Skv.) Antip., Nitzschia acicularis W. Sm., Peridinium baicalense Kiss. et. Zwetkow, Gymnodi-nium baicalense var. minor Antip., Cyclotella baicalensis Skv., Dinobryon cylindricum Imh., Anabaena lemmermannii P. Richt. Owing to them the number and biological mass of phytoplankton is formed.
During the ice period phytoplankton is mainly produced in the lake pelagic by the algae of great size; almost all representatives of the Baikal complex are among them – M. baicalensis, M. islandica, Cyclotella baicalensis, Dinobryon cylindricum, Peridinium baicalense, Synedra, the species of Gymnodinium genus. G.I. Semina (1974) points out that the biggest algae cells in the Pacific ocean live in the quietest water, and vice versa. There is a similar phenomenon in the Baikal, too.
The works on the biology of the main phytoplankton representatives have found out that the Baikal algae complex has adjusted to the mass development in the conditions of very low water temperatures and faint lighting. The exception is the group of non-testaceous peridineas of the Gymnodinium genus which, on the contrary, is light-requiring and vegetates mostly in spring in the uppermost layers of water.
One of the peculiarities of the Baikal phytoplankton development is its vigorous vegetation in the under-ice period which is generally caused by clear transparent ice and little snow in the bigger part of the lake. The beginning of the algae development is usually timed to the second half of February. At that time cold-loving complex of algae develops, such as Melosira, Synedra, Gymnodinium, Dinbryon, Chrisosphaerella baicalense Popovsk. and Mallomonas sp.
After the lake breaking-up of ice until the end of June the phytoplankters’ life conditions change considerably. The water temperature goes up, the water circulation becomes more intensive, the quantity of light increases. Diatom and chrysophyta algae become prevailing in the plankton.
Summer and autumn Baikal phytoplankton (July-August) is very poor compared to the spring one. The difference between the phytoplankton biological mass in spring and in autumn is dozens or even hundreds times.
Besides phytoplankton, rich ultra-nano-plankton algae world inhabits the Baikal waters and develops all over the lake pelagic in great numbers, it consists of several species of green and blue-green algae. The most numerous representative of this group is Synechocystis limnetica Popovsk.
Ultra-nano-plankton algae are widespread all over the Baikal and vegetate intensively from May till October. They are most numerous in the summer months, when the regular plankton is poor.
In the general balance of the organic substance in the Baikal the main component is its primary output by phytoplankton, about 90% of the income part.
It is stated that in summer photosynthesis can be observed in the Baikal as deep as 25 m, and sometimes as deep as 50 m and even more. In May, i.e. soon after the ice breaking up, there are great numbers of it as deep as 10-15 m. In June and in July the phytoplankton photosynthesis intensity at the depths of 0-25 m is not different in the vertical direction and is not great in general. In August in the upper water layer photosynthesis intensity is maximum for summer. In September its number decreases throughout the studied water column which is connected with the beginning of the summer algae forms decay and their sinking into the deep water layers. In October, when autumn forms of the diatoms start developing, photosynthesis in the upper layer increases again, and decreases at the depth of 5 m and down.
The primary output values characterize the Baikal as oligotrophic or even ultra-oligotrophic lake. In such lakes with very low values of photosynthesis intensity in a water volume unit owing to high water transparency this process penetrates into relatively great depths of the Baikal, down to 50-70 m in summer. As a result gross primary output under the unit of the lake surface is quite great. Benthos attached algae forms down to 115 m deep show that the process of photosynthesis is going on very deep.
The primary output figures of the open parts of Southern and Middle Baikal are very close to each other and make up 130 g Corg under 1 sq. m of the lake surface a year. The Northern Baikal is less productive, its yearly primary output is 119 g Corg under 1 sq. m. On the whole the average primary output is 127 g Corg under 1 sq. m of the lake surface a year.
The seasonal changes of the primary output values are characterized by minimum daily indices in November-March, spring maximum in April-May, July minimum, August summer maximum and gradual reduction of the values in the following autumn months.
The comparison of the Baikal and other lakes outputs has shown that such lakes as the Superior, the Michigan and in summer – some lakes of the Kola peninsula and the Arctic Urals are the closest to Lake Baikal. Of course, their yearly output is much lower than the Baikal output.
Throughout a year an average of 3,925 thousand tons Corg of the primary output is formed in Lake Baikal. At that time phytoplankton utilizes 286 thousand tons of mineral nitrogen and 62 thousand tons of mineral phosphorous.
The process of organic substances primary output in Lake Baikal is one of the main processes of migration and transformation of many chemical components in the lake.