Distribution Of Bottom Sediments Research Articles

The effects of wind-wave disturbances on sediment resuspension and phosphate release in Lake Chao

As a typical shallow lake with a wind-generated flow, the resuspension state of sediment and phosphorus release under wind field disturbance plays an important role in controlling lake eutrophication in Lake Chao. In this study, we proposed a combination of experimental analysis of dynamic disturbances, wind-wave disturbance shear stress calculation, and model simulation (experimental-calculative-modeling) to quantitatively investigate the effects of wind-wave disturbances on the resuspension state of Lake Chao bottom sediment and phosphorus release and distribution. The results showed that the release rate of phosphorus from the Lake Chao bottom sediment was affected by the wind field and bottom sediment content, which varied significantly spatially and showed some difference between different seasons. Under the condition of sufficient water body disturbance, the substrate in the Western Lake area of Lake Chao mainly adsorbed phosphate from the water body, while the substrate in the Central Lake area and the Eastern Lake area adsorbed phosphate along with the release. The magnitude of the phosphorus release rate due to sediment resuspension was mainly affected by wind speed, and the distribution of phosphorus content was influenced by the circulation generated by different dominant wind directions. The wind-wave disturbances have a significant effect on the spatial and temporal distribution of phosphorus in Lake Chao, and the proposed experimental-calculative-modeling ensemble can provide relevant technical support for the study of water pollution control strategies and comprehensive remediation and management of Lake Chao.

Zirconium-95 Distribution in Bottom Sediments of the Techa River in 1952–1955

Zirconium-95 Distribution in Bottom Sediments of the Techa River in 1952–1955

In situ bottom sediment temperatures in the Siberian Arctic seas: Current state of subsea permafrost in the Kara sea vs laptev and East Siberian seas

Features of sediment temperature on the shelf and continental slope areas of the Russian Arctic seas and its physical properties are important for understanding the current state of subsea permafrost and the gas hydrates stability zone. New data are reported for the Kara Sea region where the bottom sediment temperatures are influenced by warming effects from great Siberian rivers and the Atlantic currents. The data collected during marine expeditions in 2019–2022 are combined with results of earlier marine studies, drilling operations, and geophysical surveys in the Laptev and East Siberian seas, in order to identify major trends of in situ temperature and properties distribution of bottom sediments in the Russian Arctic region.Most (85%) of bottom sediments in the Kara Sea shelf, as well as in the Laptev and East Siberian shelves, consist of water-saturated silty clay and silt with rather uniform particle size distribution. The obtained thermal conductivity and heat capacity values for the Kara Sea sediments agree with the values of 1.0 W/(m·K) and 2900 kJ/m3, respectively, obtained previously from other Arctic seas. Thermal conductivity becomes up to 40% higher depthward from 0 to 2 m subbottom depth, possibly, because of lower moisture content and porosity in more lithified sediments.The bottom sediment temperatures in the Arctic seas are distributed unevenly, especially in the Kara Sea shelf (from +5.0 °C in the west to −1.4 °C in the east), where the high sediment temperatures in the western and central parts of the Kara Sea being due to the effect of warm water inputs. The distribution of bottom sediment temperatures correlates well with distribution of relic subsea permafrost. Ice-bearing permafrost in the Siberian Arctic shelf extends from the shoreline till sea depths of 80–100 m, within the respective offshore distances of ∼800–1000 km in some areas, but permafrost remnants may exist locally at sea depths within 120 m. Buried 100–600 m thick continuous subsea permafrost may occur in the Kara, Laptev, and East Siberian shelves under unfrozen (cryotic) saline shallow sediments. However, subsea permafrost is discontinuous and sporadic at sea depths ∼70 m and more. Thus, the bottom sediment temperature features in the Arctic seas can be used as a proxy of subsea permafrost extent contenting intrapermafrost and subpermafrost gas and gas hydrate accumulations.

Influence of hydrodynamic conditions on the bacteriobenthos distribution in the upper reaches of the Zhiguli hydroelectric power station of the Kuibyshev reservoir

The paper presents the results of our expedition studies of bacteriobenthos in the water area of the Kuibyshev reservoir in the autumn period of 2020 and the influence of the dynamics of currents on its spatial distribution. The relevance of the study is determined by the need to study the internal load (secondary pollution) of large reservoirs from bottom sediments. The Kuibyshev reservoir is one of the largest flowing reservoirs in the world, where features of the coastal configuration, the heterogeneity of the bed, the unsteady hydrodynamic regime, the sediment regime and its composition determine the spatial distribution of bottom sediments and the bacteriobenthos community therein, which is an important link in the circulation processes of organic and biogenic substances in the ecosystem of the reservoir. An assessment of the regime of currents and sediments was carried out by calculation on a 2D mathematical model of the Priplotinny Reach of the Kuibyshev reservoir, implemented in the software package «VOLNA». The model was verified, and a series of numerical calculations of the flow velocity was carried out taking into account the regime of water flow control at hydraulic units. The spatial geometry of the currents and the sediment flow distribution dynamics were obtained. According to the data of our expedition studies, the total numbers and biomass of bacteria were estimated, which varied in the range of (2.47–27.55)×109 cells mL-1 and 0.10–2.43 μg mL-1, respectively. As a result of the conducted studies, patterns of the spatial distribution of the bacterial community in the water area of the Priplotinny Reach of the reservoir were revealed, and the nature of the relationship between the total numbers of bacteria and the sedimentation rate, the flow velocity, and the content of organic matter in bottom sediments was established. The influence of the circulation zones of currents in shallow waters on the nature of the distribution of bottom sediments and changes in the quantitative characteristics of bacteriobenthos is shown.

DISTRIBUTION OF BOTTOM SEDIMENT BEFORE AND AFTER RECLAMATION AT CENTER POINT OF INDONESIA (CPI) MAKASSAR CITY

Characteristics and distribution of bottom sediment is one of the important parameters in determining the management plan and land use in coastal areas. The purpose of this study was to determine the condition of the distribution of bottom sediments and to compare the changes that occurred in the distribution of bottom sediment before and after the reclamation of the Center Point of Indonesia (CPI) in Makassar City. Sediment sampling was carried out using a grab sampler at four stations, namely stastions on the island adjacent to the reclamation area and two other stations in the water around the reclamation area. The results showed that the bottom sediment in the waters around the reclamation area consisted of coarse sand and medium sand with an organic matter content of 14.92% in the sediment. On the islands adjacent to the reclamation area, the bottom sediments are move varied, consisting of coarse sand, medium sand and fine sand with lower organic matter content of 4.92% to 5.38%.

Granulometric, elemental and isotopic composition of bottom sediments of lakes of mountainous areas as a reflection of transformations in their watersheds

The article provides a brief description of the geological and tectonic structure and technogenic transformations in the drainage basin of two lakes of the Krasnodar Krai (Malyy Liman and Abrau). They belong to a single natural-technogenic system. On the example of these mountain lakes, the grain-size distribution, elemental (mercury) and isotopic (cesium-137) composition of bottom sediments was studied. The use of a set of methods and technologies, including those developed by the authors, made it possible to determine the parameters of the anthropogenic impact layer in bottom sediments and the chronology of its formation. It is closely related to natural and man-made events in the drainage basin.

Towed dredge for collection of microplastics from the surface of the bottom through density separation

The publication reflects the problematic issues related to the need to create effective equipment for the selection of microplastics from the bottom surface of water areas, which is one of the relatively new types of pollutants in aquatic ecosystems. The existing methods and tools for its selection are considered and their advantages and disadvantages are determined. The design of the device for the selection of microplastics from surface bottom sediments, alternative to the existing options, is proposed. The methodological approach to the creation of such a construction is based on the expediency of simultaneous planar sampling using a towing device with the primary distribution of bottom sediments in the sampling process due to density separation. This is achieved by implementing a number of structural solutions that allow not only the selection of the upper semi-liquid layer of bottom sediments, but also the separation of the heavy mineral component, carrying out the targeted selection of substances with low density, including microplastics. Some issues remain methodologically unfounded, in particular, the possibility of recalculating the number of microplastic particles per unit volume of the substance of bottom sediments, their solution consists in conducting long-term experimental work. The principle of operation of the device, based on the conducted analysis of literary sources, has no analogues, and, in case of successful completion of experimental tests, it can become an effective and, at the same time, affordable tool for researching the surface of water areas bottom in the future.

Facies partitioning of fluvial, wave, and tidal influences across the shoreline-to-shelf architecture in the Western Interior Campanian Seaway, USA

Abstract The influence of bottom currents and tectonic activity on shelf sedimentary processes and sand distribution remains poorly constrained. A growing body of research highlights the importance and variability of the shelf sandstone bodies. To explore the roles of fluvial, wave and bottom current-controlled sediment distribution in the Western Interior Seaway, 21 marine sandstone outcrops in Wyoming and Colorado were analysed. Recurring facies associations include: paralic, tide-influenced coastal margins; mainly east and SE prograding, wave-dominated delta-fronts and shorefaces; heavily bioturbated, glauconitic sandstones; and traction current-dominated, tidally influenced, open-marine subaqueous delta and shelf deposits, with southward palaeocurrent directions. Intense reworking by a moderately diverse ichnofauna occurs in wave-dominated and glauconitic facies. Minimal burrowing occurs in cross-stratified subaqueous delta and shelf deposits. Lithofacies associations are interpreted to change basinward with increasing water depth. Ichnoassociations reflect the proximity of river mouths. Widespread, southward palaeocurrent directions, not restricted to a narrow longshore zone, on the shallow-marine shelf indicate the persistence of strong, along-shelf sand-transport which has not been previously documented in detail. Palaeobathymetric complexity caused by uplift of Laramide structures amplified and accelerated bottom and tidal currents and facilitated the erosion, transport and deposition of older sediments.

DISTRIBUTIONS OF 210PB, 137CS AND PHYSICAL PROPERTIES IN BOTTOM SEDIMENTS OF WEST NANAO BAY, JAPAN.

This study revealed sedimentation processes based on 137Cs and 210Pb distribution, grain size and magnetic susceptibility of bottom sediments in West Nanao Bay, Japan. Surface sediment concentrations and inventories of these radionuclides were relatively low in the middle and eastern areas of the bay and high in the western area, which has several major river mouths, suggesting that the contribution of riverine input affected only the western area. In the middle and eastern areas, the level of 137Cs inventory was much lower than that of the soils, and the excess 210Pb inventory was at the same level or lower. These results indicate that removal effects are stronger than accumulation effects (riverine input) in these areas. The patterns of radionuclides were consistent with the results, that grain size was relatively large in the middle and eastern areas, implying strong current conditions, and that fine sediment accumulated less in these areas.

Factors controlling 137Cs distribution in bottom sediments of Koronowo Reservoir (Poland)

PurposeThe main aim of this study was to investigate factors influencing the long-term distribution of 137Cs activity concentrations in the bottom sediments of the dam lake, Koronowo Reservoir, 32 years after the Chernobyl nuclear power plant accident. For this purpose, selected properties of the collected sediment samples, such as grain size, mineralogical composition, and organic matter (OM) content, were investigated.Materials and methodsThe samples of lake sediments were collected with a Kayak-type gravity corer. The spatial and vertical distributions of 137Cs and 40K activity concentrations in the bottom sediments were investigated based on gamma spectrometry measurements. The particle size distribution of surface lake sediments was determined using a laser particle size analyzer. SEM and XRD were used for the mineralogical analysis of the collected sediment samples. Additionally, the content of organic matter was examined in all samples using an elemental analyzer.ResultsThe 137Cs content was significantly elevated in the case of fine-grained (< 63 µm) surface lake sediments (classified as silts, which are deposited in the profundal zone of Koronowo Lake) and ranged from 12.5 ± 4.1 to 29.2 ± 4.0 Bq kg−1. It was found that the increased concentration of 137Cs activity is more closely related to the content of the silt fraction (2–63 µm) than to the clay fraction (< 2 µm) in the collected surface lake sediments. The content of clay minerals also showed a significant positive correlation with 137Cs activity concentration in the surface lake sediments of Koronowo Lake. A similar relationship was noticed for the OM content, but it may be suspected that it is the result of radiocesium-bearing particle accumulation in OM-rich sediments.ConclusionThe most important factor influencing the spatial distribution of 137Cs activity concentrations in the surface lake sediments of Koronowo Lake, apart from the bottom morphology and grain size of sediments, is the content of clay minerals. Moreover, the increased detrital inflow to the lake after the construction of the dam could have probably affected the vertical distribution of 137Cs activity concentrations in the bottom sediments, as evidenced by, e.g., the measurements of 40K activity concentration.

Assessment of heavy metals distribution and environmental risk parameters in bottom sediments of the Pechora River estuary (Arctic Ocean Basin)

The article is devoted to the study of the content of heavy metals in the bottom sediments of the estuary of the Pechora River, which is the largest river in the European Arctic of Russia. In addition to metals, the particle size distribution and physicochemical parameters of river sediments were analyzed, such as the content of carbonates, organics and ash components. Average concentrations of heavy metals in the sediments of the Pechora Delta sediment have been found to be significantly lower than terrestrial values. The assessment of pollution and toxicity of sediments in the Pechora delta, made using various parameters Igeo, Cf, Cd, EF and ERI, showed a low level of heavy metals in bottom sediments, coupled with a low level of environmental risk. Despite the fact that high concentrations of heavy metals of anthropogenic origin are continuously recorded in the water of the Pechora River, (almost throughout the entire length), there is no accumulation of pollutants in the sediments of the delta. Thus, the estuary of the Pechora River, unlike other large estuary systems, does not act as a filter or sediment trap, which contributes to the penetration of heavy metals deep into the Barents Sea and the widespread distribution of pollutants in the ecosystems of the Arctic.

Regime of Reservoir: Experience in Modeling Riverbed Processes with a Movable Bed

The paper presents the results of the interrelated calculation of the unsteady uneven movement of the river flow and the re-formation of the bottom of the largest flowing Kuibyshev reservoir in Eurasia in different phases of water content. These calculations are based on the hydrodynamic model “Wave” and algorithms for calculating solid runoff (analytical formula for sediment flow rate), changes in the transport potential of the flow and, as a result of the latter, changes in the bottom marks. In this case, the dynamics of the bottom marks is taken into account in subsequent calculations and is one of the arguments of the model. Based on the model calculations, the spatial distribution of bottom sediments in the water area of the reservoir was investigated and maps of accumulation and erosion of the bed in different phases of water content were constructed. It is shown that for the entire calculation period, an uneven redistribution of sediments in the reservoir is observed: erosion occurs in the upper part, and accumulation occurs in the middle and lower parts. In general, for the Kuibyshev reservoir, the contribution to siltation only by river sediment is insignificant. On average, over the 150-day modeling period for the entire reservoir water area, sediment accumulation is 0.5 mm/period. The weak dynamics of currents in the vast water area of the reservoir reaches does not contribute to active channel transformations. The most intensive processes of bottom transformation occur in places of narrowing of the water area, where the contribution of the non-stationary regime to the formation of the bottom relief during the rise and fall of the flood is best expressed. More full-flowing years will also lead to a more intensive redistribution of solid runoff and bottom sediments coming from the upper strata.

Microplastics distribution in bottom sediments of the Baltic Sea Proper

An abundance of microplastics particles (0.2–5 mm, MPs) in bottom sediments is analyzed based on 53 samples (3 to 215 m deep) obtained in 8 cruises of research vessels across the Baltic Sea Proper in March–October 2015–2016. MPs content varied between stations from 103 up to 10,179 items kg−1 d.w., with the bulk mean of 863 ± 1371 items kg−1 d.w., showing a statistically significant increase with water depth. As many as 74.5% of MPs are of fibrous shape, followed by films (19.8%) and fragments (5.7%). The distributions of fibres, fragments, films, and different types of natural bottom sediments are significantly different, highlighting the specific behaviour of each of these kinds of bottom deposits. A statistically significant correlation between water depth and fibres content is found. Based on the analysis of oceanographic factors and sedimentological principles, an erosion/transition/accumulation pattern for fibres in the Baltic Sea Proper is outlined. Fibres can be considered as a specific type of “synthetic sediment”, while principles of distribution of other MPs are not yet certain.

In-situ temperatures and thermal properties of the East Siberian Arctic shelf sediments: Key input for understanding the dynamics of subsea permafrost

Significant reserves of methane (CH4) are held in the Arctic shelf, but the release of CH4 to the overlying ocean and, subsequently, to the atmosphere has been believed to be restricted by impermeable subsea permafrost, which has sealed the upper sediment layers for thousands of years. Our studies demonstrate progressive degradation of subsea permafrost which controls the scales of CH4 release from the sediment into the water-atmospheric system. Thus, new knowledge about the thermal state of subsea permafrost is crucial for better understanding of the permafrost -hydrate system and associated CH4 release from the East Siberian Arctic Shelf (ESAS) – the broadest and shallowest shelf in the World Ocean, which contains about 80% of subsea permafrost and giant pools of hydrates. Meanwhile, the ESAS, still presents large knowledge gaps in many aspects, especially with respect to subsea permafrost distribution and physical properties of bottom sediments. New field data show that the ESAS has an unfrozen (ice-free) upper sediment layer, which in-situ temperature is −1.0 to −1.8 °C and 0.6оС above the freezing point. On one hand, these cold temperature patterns may be related to the presence of subsea permafrost, which currently primarily occurs in the part of the ESAS that is shallower than 100 m, while ice-bearing sediments may also exist locally under deeper water in the Laptev Sea. On the other hand, the negative bottom sediment temperatures of −1.8 °C measured on the Laptev Sea continental slope sediments underlying water columns as deep as down to 330 m may result from dissociation of gas hydrates or possibly from dense water cascading down from the shelf. In contrast, data collected on recent expeditions in the northern Laptev shelf, zones of warmer bottom temperatures are coinciding with methane seeps, likely induced by seismic and tectonic activity in the area. These warm temperatures are not seen in the East Siberian Sea area, not even in areas of methane seeps, yet with little seismic activity.The thermal conductivity and heat capacity of bottom sediments recorded in the database of thermal parameters for the ESAS areas mainly depend on their lithification degree (density or porosity), moisture content, and particle size distribution. The thermal conductivity and heat capacity average about 1.0 W/(m·K) and 2900 kJ/(m3·K), with ±20% and ±10% variance, respectively, in all sampled Arctic sediments to a sub-bottom interval of 0–0.5 m.

Authigenic Minerals of the Derbent and South Caspian Basins (Caspian Sea): Features of Forms, Distribution and Genesis under Conditions of Hydrogen Sulfide Contamination

This paper presents the results of complex lithological, mineralogical, and geochemical studies of bottom sediments of deep-water basins of the Caspian Sea (Derbent and South Caspian Basins) in areas contaminated by hydrogen sulfide. In the course of complex studies, numerous manifestations of authigenic mineral formation associated with the stage of early diagenesis have been established. Authigenic minerals belonging to the groups of sulfates (gypsum, barite), chlorides (halite), carbonates (calcite, low Mg-calcite; kutnohorite), and sulfides (framboidal pyrite), as well as their forms and composition, have been identified by a complex of analytical methods (X-ray diffractometry (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS); atomic absorption spectroscopy (AAS); coulometric titration (CT)); the nature of their distribution in bottom sediments has been assessed. Carbonates and sulfates are predominant authigenic minerals in the deep-water basins of the Caspian Sea. As a part of the study, differences have been established in the composition and distribution of associations of authigenic minerals in the bottom sediments in the deep-water basins. These are mineral associations characteristic of the uppermost part of the sediments (interval 0–3 cm) and underlying sediments. In the Derbent Basin, in sediments of the interval 3–46 cm, an authigenic association is formed from gypsum, calcite, magnesian calcite, siderite, and framboidal pyrite. An association of such authigenic minerals as gypsum and calcite is formed in sediments of the 0–3 cm interval. In the South Caspian Basin, in sediments of the interval 3–35 cm, an association of such authigenic minerals as gypsum, halite, calcite, magnesian calcite, and framboidal pyrite is formed. The association of such authigenic minerals as gypsum, halite, calcite, magnesian calcite, kutnohorite, and framboidal pyrite is characteristic of sediments of the 0–3 cm interval. We consider the aridity of the climate in the South Caspian region to be the main factor that determines the appearance of such differences in the uppermost layer of sediments of the basins. Judging by the change in the composition of authigenic associations, the aridity of the South Caspian increased sharply by the time of the accumulation of the upper layer of sediments (interval 0–3 cm). Taking into account lithological, mineralogical and geochemical data, the features of the processes of authigenic mineral formation in the deep-water basins of the Caspian Sea under conditions of hydrogen sulfide contamination have been determined. Analysis of the results obtained and published data on the conditions of sedimentation in the Caspian Sea showed that hydrogen sulfide contamination recorded in the bottom layer of the water column of the deep-water basins of the Caspian Sea may affect the formation of authigenic sulfides (framboidal pyrite), sulfates (gypsum), and carbonates (calcite and kutnohorite) associated with the activity of sulfate-reducing bacteria in reducing conditions.

Forms of transfer of microelements in river network and their distribution in bottom sediments in coal mining regions

Forms of transfer of microelements in river network and their distribution in bottom sediments in coal mining regions

Геоморфологические аспекты преобразования крупного равнинного водохранилища (по данным измерений на Краснодарском водохранилище)

The article considers the results of the analysis and generalization of the materials of bathymetric surveys of the Krasnodar reservoir in 2005, 2016 and 2021. The Krasnodar reservoir occupies a key position in the Kuban reclamation complex, so its transformations caused by siltation cannot be underestimated. Special attention is paid to the geomorphological aspects of the transformation of the reservoir bed in the process of siltation, which directly affects the morphometric characteristics of the reservoir. According to a series of bathymetric surveys, digital elevation models of the basin and maps reflecting the distribution of bottom sediments and the processes of morpholithogenesis of the bed were constructed. During the period 2005–2021, the volume of sediment accumulation in the main reservoir, excluding the separated Tcshikskoe reservoir and deltaic sediments of the dividing bridge, amounted to 127 million m³. The greatest contribution to geomorphological transformations is made by fluvial processes, with the participation of which deltas of rivers flowing into the reservoir (Kuban, Belaya, Pshish, etc.) and estuarine avandeltas are formed. So, for 2016–2021. within the mouth of the Kuban seashore, the volume of sediments amounted to 9.36 million m³ or 38 % of the total volume of the siltation body in the reservoir, and the increment of the siltation layer over 5 years reached 2–3 m or more. Within the zone of variable backwater in the open part of the water area, bottom sediments are distributed relatively evenly with an increment of the sediment layer over 5 years of 0.01–0.4 m. The lowest rates of sediment layer increment were observed in the dead volume zone—less than 2 cm per year. During the study period, a decrease in the average annual volume of situation was recorded, which presumably indicates a gradual attenuation of the siltation process as the volume of the reservoir decreases.

Reconstruction of the Long-Term Dynamics of Particulate Concentrations and Solid–Liquid Distribution of Radiocesium in Three Severely Contaminated Water Bodies of the Chernobyl Exclusion Zone Based on Current Depth Distribution in Bottom Sediments

Given the importance of understanding long-term dynamics of radionuclides in the environment in general, and major gaps in the knowledge of 137Cs particulate forms in Chernobyl exclusion zone water bodies, three heavily contaminated water bodies (Lakes Glubokoe, Azbuchin, and Chernobyl NPP Cooling Pond) were studied to reconstruct time changes in particulate concentrations of 137Cs and its apparent distribution coefficient Kd, based on 137Cs depth distributions in bottom sediments. Bottom sediment cores collected from deep-water sites of the above water bodies were sliced into 2 cm layers to obtain 137Cs vertical profile. Assuming negligible sediment mixing and allowing for 137Cs strong binding to sediment, each layer of the core was attributed to a specific year of profile formation. Using this method, temporal trends for particulate 137Cs concentrations in the studied water bodies were derived for the first time and they were generally consistent with the semiempirical diffusional model. Based on the back-calculated particulate 137Cs concentrations, and the available long-term monitoring data for dissolved 137Cs, the dynamics of 137Cs solid–liquid distribution were reconstructed. Importantly, just a single sediment core collected from a lake or pond many years after a nuclear accident seems to be sufficient to retrieve long-term dynamics of contamination.

Reconstruction of time changes in radiocesium concentrations in the river of the Fukushima Dai-ichi NPP contaminated area based on its depth distribution in dam reservoir's bottom sediments

Radionuclide depth distribution in bottom sediments in deep-water zones of dam reservoirs, where no sediment mixing occurs, can be used to reconstruct time changes in particulate activity concentrations of radionuclides strongly bound to bottom sediments. This approach was used to analyze the 137Cs concentration profile in a bottom sediment core collected from Ogaki dam reservoir on the Ukedo River in the Fukushima Dai-ichi nuclear power plant contaminated zone in October 2019. The derived 137Cs particulate concentrations provided a basis for estimating the dissolved concentration and its temporal trend in the Ukedo River, using the mean value of the apparent 137Cs distribution coefficient. The reconstructed particulate and dissolved 137Cs concentrations and their temporal trends are consistent with monitoring data. The annual mean particulate and dissolved 137Cs wash-off ratios were also calculated for the period of eight years after the accident. Interestingly, the particulate 137Cs wash-off ratios for the Ukedo River at Ogaki dam were found to be similar to those for the Pripyat River at Chernobyl in the same time period after the accident, while the dissolved 137Cs wash-off ratios in the Ukedo River were an order of magnitude lower than the corresponding values in the Pripyat River. Both the particulate and dissolved 137Cs wash-off ratios in the Ukedo River declined faster during the first eight years after the FDNPP accident than predicted by the diffusional model, most likely, due to greater natural attenuation and, to some extent, remediation measures implemented on the catchments in Fukushima.

Spatial distribution of bottom sediments of the near-dam ples of Kuibyshev Reservoir

The composition of bottom sediments and the patterns of their spatial distribution are determined by external (type of underlying surface of the catchment area, anthropogenic development, intensity of soil erosion) and internal (water regime, intensity of water exchange, morphometry of the basin) factors. The analysis of the granulometric composition of the bottom sediments of the near-dam ples of the Kuibyshev Reservoir showed the relative uniformity of the ples soil in terms of size. At the same time, depending on the location of the sampling points, certain patterns of distribution of the size of bottom sediments in space are traced.