Selenga River Delta Research Articles

TECTONOPHYSICAL ZONING OF ACTIVE FAULTS OF THE BAIKAL RIFT SYSTEM

Tectonophysical zoning of active faults of the Baikal rift system (BRS) was performed based on the degree of hazard caused by the generation of earthquakes of magnitude 7.0 and higher. The first basis for this procedure was the results of the natural stress state reconstruction, earlier performed from seismological indicators of rupture deformations (earthquake focal mechanisms). The second important element of fault zoning was electronic maps of active faults of Eurasia hosted on the GIN RAS sever. Within the algorithmic framework for Rebetsky’s method of cataclastic analysis, both of these datasets allowed calculating the Coulomb stresses for the segments of the BRS faults. During the study, a development of the cataclastic method has been carried out in using a diagram of brittle fracture as the Mohr–Coulomb model, considering a decrease in the range of positive Coulomb stress values with an increase in effective normal stress levels. Such an approach provides a more reliable identification of the fault segments with the maximum Coulomb stress levels. The performed calculations showed that in the BRS crust there are several up to 50 km long fault segments having critically high (80–100 % of the maximum) and high (40–80 % of the maximum) Coulomb stress levels. It is these corebased hazardous zones that are considered as places where seismogenic ruptures of future М>7.0 earthquakes may start. There have been distinguished three zones that present such hazard: 1) in the western segment of the BRS in the western part of the Tunka Valley in the Tunka, Khamardaban-Mondy and Baikal-Mondy fault systems; 2) in the Selenga River delta in the Proval, Delta, Ust-Selenga and Sakhalin-Enkhauk fault systems; 3) within the northeastern flank of the BRS on the fault system of the Muyakan basin (along the North Muya ridge). It is proposed to perform tectonophysical monitoring of changes in the stress state of these three zones and make observations of their surface motions using remote sensing methods.

Elemental Composition and Structural Features of Humic Acids from Floodplain Soils of the Selenga River Delta

The study of the elemental composition and structure of humic acids of floodplain soils of the delta of the Selenga River (Western Transbaikalia) was carried out. The research area belongs to the delta meadowmarsh and foreststeppe region, which is an area where deposits of sandy and silty fractions are actively carried out from the entire basin. Here, soils and vegetation are natural biofilters. Depending on the bioclimatic conditions, groundwater regimes, and sediment composition, soils are formed that differ in the composition of humus and humic acids (HA). The objects of research were alluvial (meadow, meadowmarsh, meadow saline) soils of the Selenga delta, according to the classification WRB – Fluvisols. The analysis of 13C-NMR spectra of HA preparations of the studied floodplain soils made it possible to identify ranges of chemical shifts belonging to carbon atoms of various functional groups and molecular fragments. NMR spectroscopy data showed that humic acids of alluvial meadow soil are more enriched in aromatic fragments than humic acids of meadowmarsh and meadow saline soils. A slightly higher degree of aromaticity in alluvial meadow and meadowmarsh soil is associated with environmental conditions and the component composition of the precursors of humification. An increase in the proportion of aliphatic structures and a decrease in the proportion of aromatic fragments in the composition of preparations of meadow salt marsh soil make it possible to judge the simplification of the structure of humic acid. Soil moisture in combination with salinization significantly reduces the rate of transformation of soil organic matter and leads to an increase in the proportion of non-oxidized aliphatic fragments. The use of NMR spectroscopy in the study of soils has significantly expanded the understanding of its composition and structure, deepened the understanding of the mechanisms of humification and transformation of soils of various genesis.

Dynamics of Natural Resource Use in the Selenga River Delta as a Result of Regulating the Level of Lake Baikal

Dynamics of Natural Resource Use in the Selenga River Delta as a Result of Regulating the Level of Lake Baikal

Current and Retrospective Numbers of Anseriform Birds in Autumn Migration in the Selenga River Delta (Republic of Buryatia, Lake Baikal)

Current and Retrospective Numbers of Anseriform Birds in Autumn Migration in the Selenga River Delta (Republic of Buryatia, Lake Baikal)

THREE-DIMENSIONAL VELOCITY STRUCTURE OF THE CRUST IN CENTRAL LAKE BAIKAL FROM LOCAL SEISMIC TOMOGRAPHY

This work deals with the importance of studying seismicity and deep structure of the Earth’s crust in the region of the Baikal rift zone. The study presents a three-dimensional velocity structure of the Earth’s crust in the central part of Lake Baikal, obtained from the results of tomographic inversion of the travel times of P- and S-waves from more than 800 seismic events. Synthetic tests provide substantiation for the resolution of the tomographic inversion algorithm. The seismic structure of the crust was obtained to a depth of 35 km and has a direct relationship with the geological structure. The three-dimensional distributions of seismic P- and S-wave velocity anomalies are in good agreement with each other.The sharp contrast between the anomalies may indicate a difference in the material composition of the basement of the Central Baikal basin. At a 15-km depth below the Selenga River delta, there is observed a strong low-velocity anomaly which confirms the presence of a thick sedimentary cover therein. In the basement (at depths of 20 km or greater), to the northeast of the intersection between the Delta fault and the Fofanov fault, there occurs a high-velocity anomaly elongated towards the Olkhon Island. This anomaly is probably related to a rigid block in the earth’s crust. The same depths, on the western side of the Baikal-Buguldeika fault, show a reduced Vp/Vs ratio: 1.56–1.65 versus 1.70–1.75 in the adjacent areas. This indicates another type of basement rock composition and the presence of consolidated matter there.Besides, there has been made a more accurate hypocenter determination for further comparison between seismic events and active fault structures. For the central part of Lake Baikal, the distribution of seismicity mainly corresponds to depths of 10–22 km. The situation is different below the Selenga Delta – the only area where seismicity is observed at depths greater than 22 km, – which can be attributed to complex fault interactions.The velocity anomalies discussed herein are confined to reliably identified active faults and correlate well with the distribution of seismicity and gas hydrate structures.

Дистанционное слежение за орланами-белохвостами из Забайкалья, Россия: миграция, зимовка, летнее пребывание

Дистанционное слежение за орланами-белохвостами из Забайкалья, Россия: миграция, зимовка, летнее пребывание

Historical changes of biodiversity in Baikal Siberia and dynamics of nest settlements of the Great Cormorant (Phalacrocorax carbo L., 1758) in the first quarter of the XXI century

The article presents the history of nesting, disappearance from the fauna and the current spatial distribution of Great Cormorant (Phalacrocorax carbo L., 1758) breeding colonies in Baikal Siberia. The main research sites were the Selenga River Delta, Strait of the Maloye More and islands of the Chivyrkuy Bay, Upper Angara Bay on Baikal Lake; the Upper Angara and Barguzin hollows, Gusinoe Lake in the Pribaikalye and Transbaikalye, where this species once lived according to well-known literary sources in the XVII to the middle of the XX centuries. Direct accounting of newly nesting birds after a 50-year absence in known colonies with young birds that flew out by autumn, as well a non-breeding birds, allowed us to estimate the total number of cormorants in 2021 on Baikal Lake. It amounted to 39-40 thousand birds, which indicates the settlement of the species in the Baikal Lake ecosystem and population stabilization in accordance with the environmental ecological capacity.

HEAVY METALS AND FATTY ACID COMPOSITION OF RANUNCULUS CIRCINATUM (SIBTH.) SPACH. (RA-NUNCULACEAE) FROM THE DELTA OF THE SELENGA RIVER

Ranunculus circinatus Sibth. is a boreal, Eurasian species. The content of heavy metals and the composition of fatty acids in R. circinatum from the Delta of the Selenga River, which is the main tributary of Lake Baikal, was studied for the first time in this paper. Plants of R. circinatum of the Selenga river delta accumulated heavy metals in significant quantities, mostly Fe and Mn, and the content of Pb and Cd was below detection limit. Palmitic C16:0, myristic C14:0 and stearic C18:0 acids were the main saturated fatty acids. The content of unsaturated acids ranged from 53.67 to 58.60%, and they were represented by acids of n3-, n6-, n7- and n9-families. Unsaturated linolenic 18:3 ω3, linoleic 18:2 ω6 and palmitoleic 16:1n7 acids were dominant regardless of the place and year of sampling. The presence of iso-, anteiso- and 2-hydroxy acids was associated with the growth of microbial communities on plants, when the presence of 17:1 n7 and 20:3 n6 acids were associated with animals in vegetation bed of B. circinatum. The obtained data confirmed that plants contribute to the operation of such a powerful natural biofilter as the delta of the Selenga River.

СОДЕРЖАНИЕ ПОЛИЦИКЛИЧЕСКИХ АРОМАТИЧЕСКИХ УГЛЕВОДОРОДОВ В ДОННЫХ ОТЛОЖЕНИЯХ ОЗЕРА БАЙКАЛ В РАЙОНАХ СИЛЬНОГО АНТРОПОГЕННОГО ВОЗДЕЙСТВИЯ

Up-to-date data on the concentration of polycyclic aromatic hydrocarbons (PAHs) in the upper 2-centimeter layer of bottom sediments in the areas of strong anthropogenic impact are presented. These areas are the following: that of the municipal wastewater discharge in the city of Baikal’sk, the impact area of the Baikal-Amur Mainline in the north of the lake, the area at the Selenga River delta front, and the one in the Maloe More region. Based on the results of long-term studies, concentrations of polyarenes in different lithological types of bottom sediments at the controlled test sites were determined. The most severe PAH contamination was observed in the sandy sediments of the test site in the area of municipal wastewater discharge in the city of Baikal’sk. In the other areas, the PAH content does not generally exceed background values.

The Rupturing Phenomena in the Deltaic Deposits of Cape Rytyi on the Northwestern Shore of Lake Baikal

Abstract —We present materials of aerial photography of Cape Rytyi, a unique and most mysterious place on the northwestern shore of Lake Baikal. Photogrammetric survey was carried out using a DJI Phantom 4 Pro V2.0 UAV and provided an orthophoto and a digital terrain model of an 11.074 km2 area. When deciphering the images obtained in the Rita River deltaic sediments composing the cape, surface ruptures trending north and northeast at 30–150 m from the shore of Lake Baikal were discovered. The ruptures are a clearly localized zone 2.9 km in total length. The performed analysis showed that the structural features of the zone obey the general laws of the development of faults resulted from prevailing extension. It has been established that the formation of the ruptures was predetermined by tectonics and is a secondary effect of resonant oscillations from the M = 5.2 earthquake of 08.13.1962, the epicenter of which was located ~35 km southeast of Cape Rytyi, in the Morskoi fault zone. The seismic event initiated the formation of surface ruptures, which led to a gravitational subsidence of coarse deposits of the fan in the shore zone. It is concluded that the development of modern geomorphologic forms in the peripheral part of the Rita River fan on land is similar to the formation of an underwater topography in the region of the Selenga River delta. It occurs under the influence of seismogenic rupturing and following gravitational movements, which intensify in a water-saturated environment and are subsequently complicated by erosion processes.

The December 9, 2020, Mw 5.5 Kudara earthquake (Middle Baikal, Russia): internet questionnaire hard test and macroseismic data analysis.

The article discusses the macroseismic data on the December 9, 2020, Mw 5.5 Kudara earthquake which occurred in the Selenga River delta (Middle Baikal, Eastern Siberia, Russia). This is the strongest seismic event in the study area over a 50-year period. The bulk of macroseismic data was obtained with internet questionnaire posted on the website of the Baikal Branch of the Geophysical Survey of the Russian Academy of Sciences. In total, 1433 responses were received from 120 places (villages, towns and cities) in Eastern Siberia, with most of them was obtained from large cities. In addition, a field survey was carried out in the near-field, which revealed slight non-structural damage to buildings in several settlements. The maximum intensity assessed VI–VII MSK-64 or VI EMS-98 was observed in the Kudara village. Taking into account the macroseismic data obtained, we have prepared a map of intensity data points. The largely observed shakings (intensity IV MSK-64/EMS-98) were noted at epicentral distances of over 500 km; intensity II MSK-64/EMS-98 was noted at a distance of up to 980 km. The Kudara earthquake allowed us to test the internet questionnaire in real conditions of strong seismic impact. The results obtained confirm the rather high efficiency of the internet questionnaire in the conditions of the Baikal region, however, some limitations associated with the responses spatial distribution are exist. A detailed study of the Kudara earthquake allowed us to gain new experience useful for the further development of macroseismology in Eastern Siberia.

Экологические проблемы землепользования и загрязнения почв естественных, пахотных и залежных земель дельты реки Селенги

In the summer of 2017–2018 we researched the landscape-geochemical and socio-geographical aspects in the delta of the Selenga river (southeast coast of Lake Baikal). The structure of land use is dominated by hayfields and pastures. The study area is important for the development of meat and dairy farming in Buryatia. The cultivated crops here are cereals, legumes, cold-resistant silage crops, potatoes and other vegetables. In the Selenga river delta various types of soils have been formed: fluvisols, folic-podburs, and gray metamorphic and folic-gray soils. The fertile soils of the high floodplain with chernozems and phaeozems are used for arable land. The agricultural land of terraces with gray and folic-gray soils is used for pasture. The soils of the low floodplain of waterlogged meadows are included in agricultural circulation. We revealed that the soils of most agricultural lands have a satisfactory agronomic quality. The upper horizons of gray soils under the forest and chernozems under the steppe have high humus concentrations in their natural state. In constantly used agricultural soils humus content is reduced. In fallow lands, its concentrations are restored. The water pH level of soils is mostly neutral. It is revealed that the soils of the Selenga delta are mainly light soils. It was revealed that gray soils after forest clearing and using them for arable land, quickly degrade and lose their fertility. Soils of the steppes show good resistance to agricultural use. Soil deposits and arable land, previously located under forest, are infertile and require introduction of nitrogen and potassium fertilizers. Soils recently introduced for agricultural use require phosphorus and potassium fertilizers. Chernozems and gray soil of natural landscapes, as well as anthrosols, previously located under steppe, are in good and satisfactory agronomic condition. Near the settlement of Kabansk we established high concentrations of some heavy metals in alluvial soils, exceeding the MPC. An increased content of oil products, phosphates, fluorides and heavy metals in the waters of the Selenga river was revealed. The coastal waters of Lake Baikal at the mouth of the Selenga river still meet sanitary and hygienic requirements. Alluvial soils of the Selenga river delta acts as a geochemical barrier to the migration of pollutants into Lake Baikal.

Transformation of accumulative landforms in the area of the Selenga river delta under the influence of changes in Baikal level

Transformation of accumulative landforms in the area of the Selenga river delta under the influence of changes in Baikal level

Drivers and extent of surface water occurrence in the Selenga River Delta, Russia

Study regionSelenga River Delta (SRD), Russia. Study focusHow is water occurrence changing in the SRD, and what are the hydroclimatic drivers behind these changes? The presence of water on the surface in river deltas is governed by land use, geomorphology, and the flux of water to and from the Delta. We trained an accurate image classification of the Landsat satellite imagery during the last 33 years to quantify surface water occurrence and its changes in the SRD. After comparing our estimations with global-scale datasets, we determined the hydrological drivers of these changes. New hydrological insights for the regionWe find mild decreases in water occurrence in 51% of the SRD's surface area from 1987–2002 to 2003–2020. Water occurrence in the most affected areas decreased by 20% and in the most water-gaining areas increased by 10%. We find a significant relationship between water occurrence and runoff (R2 =0.56) that does not exist between water occurrence and suspended sediment concentration (SSC), Lake Baikal's water level, and potential evapotranspiration. The time series of water occurrence follows the peaks in the runoff but not its long-term trend. However, the extremes in SSC do not influence surface water occurrence (R2 <0.1), although their long-term trends are similar. Contrary to expected, we find that the Delta has a relatively stable long-term water availability for the time being.

Exomorpholithogenesis of the Selenga River delta at the present stage of the hydroclimatic cycle

The materials of complex interdisciplinary studies of the relief forming in different periods of water availability in the Selenga River delta are presented since the technogenic level rise of Lake Baikal. Four water and sediment runoff anomalies, synchronous with water level fluctuations in the Lake are identified. The current boundaries of the Selenga River mouth area (RMA), floodplain complex, flooding territories in the maximum water ability conditions are identified. The RMA covers the territory from the main channel bifurcation nod to Lake Baikal, includes subaerial and subaqueous parts of the protruding delta, the interaction zone fluvial processes and different-aged terraces deposits and adjacent lagoons Proval and Cherkalov Sor. Semi-empirical models and data on the water runoff and sediment yield are presented.

TRACES OF HIGH SEISMIC ACTIVITY IN THE UPPERMOST SEDIMENTS OF LAKE BAIKAL, SIBERIA

Sedimentation in Lake Baikal is significantly affected by continuous seismic activity in the Baikal Rift Zone. Our study shows that historical earthquakes, as well as recent seismic events, considerably influenced sedimentation in this deep tectonic basin. Here we present some of the results of extensive international research activities during the period of 1996–2019. To identify traces of seismic events in the uppermost sediments (&lt;1.5 m), short cores were recovered from many coring stations throughout the entire lake. Based on lithological descriptions, measurements of magnetic susceptibility, and concentration of inorganic and organic components, we identified earthquake indicators in the sediment cores. Impacts of historical earthquakes were traced within South Baikal (near the Sharyzhalgai Station and the Station 106-km of the Circum-Baikal railway, hereafter CBR) and Proval Bay (near the Selenga River delta).

Quantifying the actual sediment load flux into Lake Baikal: A case study of the main tributary – The Selenga River (Russia)

The significant reduction of sediment load flux into Lake Baikal from its main tributary – the Selenga River began in the mid-1970s, and can be explained by climate change and socio-economic activities. Integrated analysis was done of changes in hydro-meteorological parameters (water discharge, sediment load, air temperature, and precipitation) and their tendencies over periods of 1946–1975 (baseline) and 1976–2017 (warming). Changes in natural processes and human activity were negligible during the baseline period. In the warming period, against the background of an increase in temperature, the water discharge had a slight decreasing trend (−13%) whereas the sediment load has significantly decreased (−53%) these are consist with the precipitation change (−9.4%). Analysis of hydro-climatic data using statistical methods showed that in the warming period the greatest reduction in river sediment runoff occurred in the interval 1996–2017. In this period the sediment load was 768 × 103 t/yr, which is less than the average value during the warming period – 1048 × 103 t/yr. Considering sedimentation in the Selenga River delta, the actual sediment load flux from the Selenga River into Lake Baikal amounted to 515 × 103 t/yr, which is three times less than the average multiyear value 1535 × 103 t/yr for observation period (1946–2017).

Paleoseismic Investigations in the Selenga River Delta (Lake Baikal)

Paleoseismic Investigations in the Selenga River Delta (Lake Baikal)

Modeling of the Suspended Matter Balance in the Selenga River Delta Using Remote Sensing Data

Modeling of the Suspended Matter Balance in the Selenga River Delta Using Remote Sensing Data

Quantitative development and structure of zoobenthos in channels on the left margin of the Selenga River delta

Abstract. There are only a few studies on zoobenthos in the delta of the Selenga River located at the junction of Lake Baikal and its largest tributary. The present work provides the results of research on zoobenthos in the southern (left) Selenga delta channels in 2002. Baikal amphipods and bivalves are widespread up to the upper delta. The direction and velocity of the water flow in the delta induced change of a river zoobenthos complex for a limnophilous one. Baikal amphipods are responsible for high quantitative indicators of zoobenthos in the southern channels of the delta. Low parameters of quantitative development of zoobenthos were registered during summertime. Organic matter from the catchment area of the Selenga River provides trophic resources for zoobenthos. Amphipods, bivalves and oligochaetes are involved in the transformations of suspended, sedimented and buried fractions of allochthonous matter. The authors obtained evidence on maintenance of the principal properties of the delta ecosystem as an ecotone at the time of research.