Biogeochemistry of Lake Baikal Stony Littoral

The problem of biogenic income from rocks into a water ecosystem and of their use by hydrobionts is considered by the example of Lake Baikal biogeocenoses. A complex interreaction of stony material and Baikal water occurs on the stony littoral of Lake Baikal with an active participation of benthic and planktonic hydrobionts. Biogeochemical processes enable income of biophile elements providing productivity of stony littoral and hydrobionts biodiversity. A particular role in the littoral zone belongs to symbiotic organisms: lichens and sponges. They extract from the tocks a wide spectrum of macro- and micro- elements including phosphorus, fixe nitrogen and consume carbon. Biodiversity and bioproductivity of stony littoral depend on the diversity of petrographic composition of the rocks and on their geochemical peculiarities. Increase of anthropogenic impact onto the stony littoral manifested by income of biogenic elements and alien microbial cenosis flow results in degradation of primary aquatic biogeocenoses.


Introduction
Riftogenic Lake Baikal is a very good object for studies of biochemical peculiarities of interreaction of fresh waters with rocks. Main agents of this interreaction are endemic plants and organisms in the littoral, which disappeared in major part of the lakes worldwide. Lake Baikal remains a unique object of studies of protobiogeochemical processes.
Chemical state of the Earth crust and biosphere is completely determined by the life of organisms, water influence and chemicals migration (Vernadsky, 1962). A particular role in this system belongs to interreaction between water and rocks with biota participation as only due to this interreaction, the elements Journal of Geoscience and Environment Protection necessary for functioning of aquatic cenosis are supplied permanently (Shvartsev, 2007).
Besides organogens C, H, O, N, P, S, basis of any living system includes nutrients K, Na, С, Mg, Mn, Fe, Co, Cu, Zn, Mo, biogenic non-metallic elements Cl, Br, Si, As and metals Li, Sn, Ti, V, Cr. Metals, thanks to their high catalytic ability, provide a high activity of metalloenzymes and of other metalliferous biomolecules (Haraguchi, 2004). The most important role of metals as primary catalysts in formation and evolution of metabolic systems and metals mineral sources are presented in the papers by М. А. Fedonkin (Fedonkin, 2003). He believes that during the Earth evolutional process, the geochemical basis of life is narrowing. Burying of chemicals on stable continents supposes their excision from the geochemical turnover. In rift zones and on continents tectonic margins, one can observe primary processes of biogeochemical interreactions of water and biota with ancient magmatic and metamorphic rocks. The accessibility of biophile macro-and microelements determines the productivity and biodiversity in the shore zone of the interreaction between water and rocks. The stony littoral of Lake Baikal represents a unique object for study of protobiogeochemical processes and for revealing of the role of biota in the involving of macro-and microelements into biogeochemical turnover and into re-distribution of chemicals between rocks, benthic and planktonic organisms and water (Suturin et al., 2003) (Figure 1).
Almost the half of Lake Baikal shore is represented by hoes consisting of bedrocks. Tectonic genesis of Lake Baikal and seismic activity provide permanent income of clastogene material and its deposition in the bench zone. Shores abrasion and landslides bring each year into the lake basin more than 1550 thousands m 3 of stony material. The bench stony material under the conditions of a freshwater body may serve as a source of biophile elements diversity for benthic organisms.
For ultraoligotrophic lakes such as Lake Baikal, the income of biophile elements only from aquatic environment is limited. The processes of rocks decomposition occur under the impact of Baikal water, and its aggressiveness towards the majority of materials is determined by undersaturation by majority of ions

Objects and Methods
Petrographyc analysis of hoe and bench rocks from different sites of Lake Baikal was performed. The rocks of stony littoral were studied additionally for graining degree, character of surface sculpture, minerals resistance to processes of aquatic hydrolysis. Stones from the depths of 3 -15 m were provided by divers. For each sample, species composition of hydrobionts was described, links between hydrobionts amount and diversity and rocks composition and their variety degree were determined.
Washed samples were placed in plastic cups with deionized water and subjected to ultrasound impact. Samples of sponges of branchy shape were divided into parts differing by density, color, amount of mechanical admixtures. Sponges of ball and crust shapes were divided into samples of outer and inner layer, anchoring sole and skeleton.
Samples washed from the admixtures were rinsed with bidistilled water and brought to airy-dry state. Then they were pounded in an agate mortar, and mean samples were composed. Using quartening method, an analytical sample was Elemental composition of samples was determined using ICP-MS method.
The analysis was performed at quadrupole mass-spectrometer "PlasmaQuad PQ2 + " of British company "VG Instruments". All samples and elements standard solutions represented solutions in 2% HNО 3 . The character of interreaction between rocks and biota was determined using electronic microscopy.

Results and Discussion
Near-shore outcrops are represented by pre-Cambrian metamorphic rocks subject to an intensive cataclasis and weathering processes. Rocks weathering degree is important for the development of benthic algae, epilithic crustoce lichens and sponges. Great porosity of stones outer frame, preliminary decomposition of primary rocks provide better anchoring of hydrobionts and simplifies getting of minerals from the rocks (Figure 4).
Even within one stone, one can see difference in minerals resistance to chemical and biological decomposition. Quartz grains, garnet strings and albite contractions remain fresh, not subjected to weathering and not occupied by lichens, algae and crust sponges ( Table 1). The degree of minerals resistance to interreaction of Baikal water was determined using petrography and electronic microscopy of the rock surfaces, to which benthic organisms attached themselves.
Only quartz remained non-variable among all the minerals.   The analysis of stony littoral bogeocenoses showed an important role of hydrobionts in rocks destruction. An especial role in aluminosilicates decomposition belongs to diatom algae. The algae cover first of all weathered, clayed rocks; while destroying clays, they get necessary for them deficit silica.
Such symbiotic organisms as lichens and sponges play an important role in stony littoral biogeocenoses. They provide extraction of phosphorus from rocks and nitrogen fixation. Symbiont cenosis of a fungus with green and blue-green algae includes as well azotobacter. Polysymbiont cenosis get the ability to fixe dissolved in the water nitrogen. Terrestrial crustose lichens form up to 250 acids.
Oxalic acid provides calcium extraction. Chelation is basic process of rocks disintegration and extraction of metals, calcium and magnesium by lichens.
Study of biogeochemical role of underwater lichens showed that they inhabit stony littoral selectively according to petrographic and mineralogical composition. Maximal lichens abundance is found in near-shore, shallow-water (up to 3 m) zone. Crustose lichens are mainly found on amphibolites, as well as on mica string in plagiogranites. The intensity row of elements consuming by lichens is specific:

Conclusion
Biogeocenoses, in which bedding stone substratum serves as a source of biophile elements for zoo-and phytobenthos, form in Lake Baikal littoral zone. Income of additional components into benthic biocenosis occurs both due to leaching of elements with water from rocks and due to life activity of symbiont organisms.
Petrographic and geochemical composition of stony substratum is important for biogeocenoses productivity and biodiversity. Biogeochemical processes on Lake Baikal stony littoral provide biodiversity and bioproductivity of benthic hydrobionts. Process of biogeochemical extraction of macro-and microelements from rocks has similar features for stony littoral of oceans and rift lakes. The biogeocenosis of Lake Baikal stony littoral, which formed during several millions of years, is destroyed due to surface and subaquatic drainage of anthropogenically polluted waters (Kulikova et al., 2017;Suturin et al., 2016). On one hand, the incoming flows of biophile elements replace complex biogeochemical processes of extraction of necessary elements from rocks. On the other hand, heterotrophs and micromycetes of intestinal flora annihilate symbiotic cenosis of the stony littoral. Such non-characteristics for Lake Baikal littoral biocenoses as Spirogira and Elodea start developing instead of existing endemic benthic belts of algae.
Ecological crisis in Lake Baikal littoral is mainly anthropogenic processes resulting in destruction of existing benthic biocenoses.

Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this paper.