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The article provides information obtained during the monitoring of the spawning run of autumn chum salmon of the Amur River, conducted in 2023 near Tyr settlement. Data on the main biological indicators of autumn chum salmon are presented. Data on the dynamics of fishery indicators in the area over a number of years are also presented.

Based on simulations with an ensemble of CMIP6 (Coupled Models Intercomparison Project, phase 6) climate models using Bayesian averaging, an analysis of changes in the runoff of a number of Russian rivers—the Volga, Ob, Yenisei, Lena, Amur, and Selenga—has been carried out this century. Bayesian weights take into account the skill of runoff reproduction by models (long-term average runoff, linear runoff trend over a time interval with available runoff observations, and interannual and interdecadal variability). The skill of reproduction of runoff characteristics by individual CMIP6 ensemble models varies most widely for long-term average runoff; runoff trend; and, to a lesser extent, interannual variability. In the 21st century, the ensemble average runoff increases for most of the analyzed rivers, with the exception of the Volga. This increase is more pronounced in scenarios with large anthropogenic impacts. It is especially significant for the SSP5-8.5 scenario (Shared Socioeconomic Pathways, 14 5-8.5), in which the trend of increase in runoff in 2015–2100 relative to its modern long-term average value is (10 ± 4)% for the Ob, (16 ± 3)% for the Yenisei, (39 ± 7)% for the Lena, (36 ± 7)% for the Amur, and (18 ± 6)% for the Selenga. The main reason for changes in ensemble average runoff in the 21st century in models under all SSP scenarios is the changes in precipitation. Accounting for differences in model skill when reproducing river runoff on average for 2015–2100 reduces intermodel deviations relative to the corresponding values when uniformly weighting the model calculation results by 6–26%, depending on the SSP scenario and river catchment. [ABSTRACT FROM AUTHOR]

Abstract Primary production in the Sea of Okhotsk is largely supported by dissolved iron (dFe) transported by the Amur river, indicating the importance of dFe discharge from terrestrial environments. However, little is known about the mechanisms of dFe discharge into the Amur river, especially in terms of long-term change in dFe concentration. In the Amur river, extreme increase in dFe concentration was observed between 1995 and 1997, the cause of which remains unclear. As a cause of this iron anomaly, we considered the impact of permafrost degradation. To link the permafrost degradation to long-term variation in dFe concentration, we examined the changes in annual air temperature (Ta), accumulated temperature (AT), and net precipitation for three regions (northeast, south, and northwest) of the basin between 1960 and 2006. Ta and AT were relatively high in one out of every few years, and were especially high during 1988–1990 continuously. Net precipitation in late summer (July to September) has increased since 1977 and has stayed positive until 2006 throughout the basin. Most importantly, we found significant correlations between Ta and late summer dFe concentration with a 7-year lag (r = 0.54–0.69, p

The studies of the applicability of simulated precipitation in hydrological calculations and forecasts are presented on the example of the Amur basin rivers. It is shown that the use of simulated precipitation has a positive effect on forecasting rainfall floods in case of a sparse observational network. There is an especially noticeable lack of hydrological and precipitation data on the catchments of the Amur right-bank tributaries located in China (the Songhua River and its tributaries), whose runoff is a significant contributor to the water balance of the Middle and Lower Amur. It is revealed that the catchment-averaged fluctuations in simulated 5-day total precipitation above and below a certain threshold are linked to the temporal variations in water levels at the outlets of the Amur partial catchments. [ABSTRACT FROM AUTHOR]

This article considers exchangeable potassium levels in the floodplain soils of the Amur River. The accumulation of exchangeable potassium in these soils was found to be largely determined by their age and weathering extent. In the young and highly weathered soils, the content of exchangeable potassium was lower than in the middle-aged soils. In the humus-accumulating horizon, it was 100–400 mg/kg and 200 mg/kg in the Upper and Middle Amur River, respectively. As for the mineral horizons, it ranged from 20 mg/kg in the young alluvial soils to 150 mg/kg in the residual-floodplain rusty soils. Interestingly, a significant increase in exchangeable potassium was observed for the coniferous-birch forests of the Upper Amur River (reaching an average of 400 mg/kg), but not for the oak forests in the Middle Amur River. Due to the asymmetry of the rate and ratio of zonal processes in the floodplain soils of the Upper and Middle Amur River, the residual-alluvial soils turned out to be sharply differentiated by the exchangeable potassium profiles. On average, the brown soils (Fluvic Cambisols) of the Upper Amur River contained up to 350 mg/kg of exchangeable potassium. The Fluvic Cambisols of the Middle Amur River had the lowest content of exchangeable potassium as compared to other studied soils.

Accurate predictions of water surface elevation (WSE) in rivers at high spatial and temporal resolution are important for flood/drought risk assessment and flood/drought forecasting and management. WSE in a river is controlled by three main factors: discharge, riverbed geometry, and hydraulic roughness. In remote and poorly instrumented rivers, discharge and riverbed geometry are highly uncertain and WSE is therefore hard to predict. ICESat-2 laser altimetry provides accurate elevation transects across the river at very high spatial resolution (70 cm along track). This paper demonstrates how ICESat-2 elevation transects can be used to parameterize a basin-scale hydraulic model of a continental-scale river. The workflow is demonstrated for the transboundary Amur River in North-East Asia. Simulated WSE is subsequently validated against a large dataset of in situ and satellite altimetry observations, and we demonstrate that the model can reproduce available WSE observations throughout the basin with an accuracy of 1–2 m. [ABSTRACT FROM AUTHOR]

To study their feeding habits, Coregonus ussuriensis samples were collected seasonally in the Amur River, China. A total of 574 samples were collected, including 200 individuals with empty stomachs. The stomach contents of the remaining 374 samples were identified, counted, weighed, and analyzed. The results showed that the vacuity rate of Coregonus ussuriensis was 34.84% in total; the rates in summer and autumn were higher than in spring and winter. Prey items could be divided into three categories: fish, benthos, and mammals, with 62 taxonomic units. Of these, fish had the highest relative importance index (IRI), followed by benthos and mammals. Specifically, Exopalaemon modestus was the dominant species among the food species of Coregonus ussuriensis, and unidentified fish, Hydropsyche sp., Hemiculter leucisculus, Abbottina rivularis, and Saurogobio dabryi were important species. The average repletion index (RI, %) of Coregonus ussuriensis was highest in autumn (1.86), followed by winter (1.40), summer (1.26), and spring (1.02). The main food of Coregonus ussuriensis was benthos in spring and autumn, and fish in summer and winter. Cluster analysis showed that, according to the similarity level of the bait biological composition, the fork length group samples of Coregonus ussuriensis could be divided into three groups: 210–330 mm, 330–450 mm, and >450 mm. The highest IRI% of feed organisms in these three groups of samples were fish (73.67%), benthos (75.12%), and benthos (94.46%), respectively. It can be observed that with the growth of the fork length of Coregonus ussuriensis, the importance of benthos in its diet increases. The results of an RDA analysis on the relationship between main bait organisms and various factors indicated that season, river level, river width, and fish size have a significant impact on bait organisms and a positive or negative impact on the quality scores of some bait species. This study filled the gap in biological research on the feeding ecology of Coregonus ussuriensis and laid a research foundation for ecological research on this species and its resource protection and aquaculture.

Dissolved iron (dFe) transported by the Amur River greatly contributes to phytoplankton growth in the Sea of Okhotsk. Nevertheless, there has been little research on the source of dFe to rivers, especially in the Amur‐Mid Basin, which is situated in a sporadic permafrost area. In the Amur‐Mid Basin, permafrost generally exists in wetlands in flat valleys, and these permafrost wetlands could be a source of dFe to rivers. To assess the importance of permafrost wetlands for dFe export, we conducted a local survey on land and soil characteristics of wetlands, and moreover analyzed the chemical composition (dFe, dissolved organic carbon [DOC], pH, and electrical conductivity [EC]) of 24 rivers with different watershed sizes in summer. As a result of local survey, the thickly accumulated peat soils in the permafrost wetland were almost saturated and rich in organic matter from the surface to a greater depth near the permafrost table. In addition, the coverage of such permafrost wetlands in watersheds showed significant positive correlations with dFe (r2 = 0.67, p = 1.7e−6) and DOC (r2 = 0.48, p = 1.8e−4) and a negative correlation with EC (r2 = 0.52, p = 7.7e−5). The dFe concentration was also correlated well with DOC concentration (r2 = 0.68, p = 7.3e−7) but not correlated with pH and watershed area. These findings are the first to indicate that permafrost wetlands in the Amur‐Mid Basin considerably contribute to dFe and DOC export to rivers, and their coverage primarily determines riverine dFe and DOC concentrations in summer. Plain Language Summary: Dissolved iron (dFe) is a key factor that limits phytoplankton growth in the ocean. In the Amur‐Okhotsk ecosystems, dFe transported by the Amur River greatly contributes to phytoplankton growth in the Sea of Okhotsk; however, there has been little research on the dFe source to rivers, especially in the Amur‐Mid Basin, which is situated in a sporadic permafrost area. In this study, we focused on permafrost wetlands in the Amur‐Mid Basin and investigated the soil characteristics and the relationship between wetland coverage and dFe concentrations in 24 watersheds. Permafrost wetlands contain waterlogged and organic‐rich peat soils, and more importantly, their coverage clearly shows strong positive relationships with riverine dFe and dissolved organic carbon (DOC) concentrations. This is the first study to show that permafrost wetlands impact water chemistry in the Amur‐Mid Basin, primarily as sources of dFe and DOC. Key Points: We provide water chemistry data from 24 rivers with different watershed sizes in the Amur‐Mid Basin during summerdFe and dissolved organic carbon concentrations showed a significant positive correlation with the coverage of the permafrost wetland in the watershedsPermafrost was confirmed underneath wetlands, and thickly accumulated peat soils were rich in organic matter [ABSTRACT FROM AUTHOR]

Among all observed natural disasters, water-related disasters are the most frequent and pose a serious threat to people and socio-economic development. River floods are the most relevant for the Russian Federation, and the importance of flood control, particularly in the Far East, was repeatedly stressed by Russian President Vladimir Putin. The quality of performance of various artificial intelligence methods on the task of predicting river floods in the Amur River basin was investigated. The uniqueness of the research lies in the fact that similar studies have not previously been conducted for this river. The main task of the work was the subsequent practical application of the obtained results in flood forecasting and risk management systems. For this purpose, the best method was searched among widely used methods on the market, which have a rich choice of auxiliary solutions: gradient tree binning, linear regression without regularisation and neural networks. The study design focus on achieving maximum reproducibility of the results. The gradient boosting over the trees in the domestic implementation of CatBoost showed the highest quality. The results of this work can be extrapolated to other rivers comparable in both area and volume of data collected.

In this paper, a mathematical model is constructed that reflects the dependence of the distribution of autumn chum salmon along the spawning tributaries stream of the Amur River from fishing on the tracks of an extended anadromous migration.

We developed an alternative approach to assessing raptor populations by fitting accumulation curves. This technique was applied to estimate the number of nesting territories of the Steller’s Sea Eagle Haliaeetus pelagicus in the northeast of Sakhalin Island and the lower reaches of the Amur River (Russian Far East). From 2004 to 2021, 428 nesting territories were found on NE Sakhalin and 422 nesting territories on the lower Amur. We selected four asymptotic functions of accumulation curves (negative exponential, Clench, Weibull and Hill) and tested three different measures of sampling effort. The best model was the one based on the negative exponential function with an offset from the origin (known as the von Bertalanffy equation), with the number of nests visited as the measure of effort. This model suggested the existence of 461 nesting territories on NE Sakhalin and 535 nesting territories on the Lower Amur. Taking into account an average territory occupancy of 69 %, we estimated the breeding population to be 318.2 territorial pairs on NE Sakhalin and 480.4 pairs on the Lower Amur. The total population was estimated to be 1079.8 birds (including 896.2 adults and 183.6 immatures) on NE Sakhalin and 1414.1 birds (1216.1 adults and 198.0 immatures) on the Lower Amur. Our experience suggests that fitting accumulation curves is a useful tool for estimating raptor populations in long-term studies, especially when total counts are impossible and objects are unevenly distributed.

Currently, the validity of many nominal bivalve species of the genus Corbicula endemic to the Russian Far East and South Korea needs a critical reassessment. In this study, we clarify the taxonomic status of Corbicula species of this area based on a combination of molecular genetic, conchological and anatomical data. According to our results, four Corbicula lineages, corresponding to the nominal species Corbicula japonica , Corbicula elatior , Corbicula leana and Corbicula fluminea , can be delineated in samples collected in the Primorye and Khabarovsk regions of Russia and South Korea. Two species endemic to the Russian Far East (i.e. Corbicula finitima and Corbicula lindholmi) are considered here as junior synonyms of the species C. japonica , which is widely distributed in estuarine habitats around the Japanese Archipelago, Sakhalin Island, southern Kurile Islands, Primorye and Khabarovsk regions, Korean Peninsula and China. Three nominal species described from the Lower Amur basin (Corbicula amurensis , Corbicula nevelskoyi and Corbicula sirotskii) appeared to be synonyms of C. elatior , whose range covers the Korean Peninsula, Primorye and Khabarovsk regions and, perhaps, China. We delineated several colour morphs of C. fluminea and C. japonica. The distinctness between these colour morphs can be attributed to both heritable and environmental factors. [ABSTRACT FROM AUTHOR]

For the first time, the content of heavy metals in the river ice in the lower Amur River has been analyzed, taking into account the stratigraphic heterogeneity of the ice structure in the river channel. According to the conditions of origin and duration of formation, the main varieties of ice were identified – layered frozen ice, naled-type (icing) ice, and hummocky ice. The most widespread in the Amur ice cover is ice consisting of layers forming hummocky-frozen, hummocky-naled and homogeneous frozen ice sequences. The aim of the study was to determine the content of heavy metals in different ice varieties and the possibility of using this data to assess river pollution during the winter period. The highest content of heavy metals was found in the naled ice, which is due to its formation on the ice surface contaminated during the winter. The minimum content was found in the layered frozen ice, which is formed throughout the winter due to accretion from below. In the layers of hummocked ice formed for several days during the autumn ice drift, metals have average content and uniform distribution within the entire thickness. Influence of Khabarovsk city in winter period is most noticeable by the content of metals in the frozen variety of Amur river ice near its right bank, where the city is located. High concentrations were noted for Pb and Zn, and less pronounced for Cu and Ni. Ice is more informative object than water under the ice, and its chemical composition can serve as an indicator of the ecological state of the river during the freezing period.

As a result of expeditionary research on the Amur River and in the Amur Estuary in June–July 2021, it was revealed that the kaluga Huso dauricus and the Amur sturgeon Acipenser schrenckii were present throughout the entire Lower Amur, up to 1100 km from the mouth. The largest concentrations of these species in the river are noted up to 500 km from the mouth; in the estuary, their concentrations were confined to the waters near the mainland coast, mainly to the estuarine part of the Amur. In the Amur Estuary, the maximum density of kaluga aggregations reached 242.2 ind./km2, of Amur sturgeon aggregations, 320.9 ind./km2; in the river, 63.7 and 334.4 ind./km2, respectively. In the Amur River, mature kaluga individuals were not observed; young fish with a body length of 20.0–39.9 cm predominated; in the estuary, there were individuals of all size groups of this species with a predominance of juveniles 20.0–39.9 cm long and sexually mature fish 160–219 cm long. In catches in the Amur Estuary, the proportion of mature kaluga individuals was 36.9%. The proportion of mature Amur sturgeon individuals in the estuary was 7.2 times higher than in the river (35.7 versus 4.9%). The total abundance of the kaluga in the Amur River and in the Amur Estuary amounted to 233.1 thousand ind., biomass—4051.9 tons, of the Amur sturgeon—297.6 thousand ind., and 1589.4 tons, respectively. Compared to the data of 10 years ago, the abundance of the kaluga and the Amur sturgeon in the estuary has decreased. At the same time, in 2021, a multiple increase in the abundance of these species in the river was noted, which indicates a relatively favorable state of their populations. [ABSTRACT FROM AUTHOR]

The origin and distribution of the Pacific group of sturgeons (Acipenseridae) is considered on the basis of paleontological finds of Acipenseriformes in the eastern part of the Asian continent in regard to evolution of the river system of the Amur River basin. It is believed that Acipenseriformes originated in the late Paleozoic in the eastern part of Laurasia. Acipenseridae family also originated in the eastern part of Asia. The locations of fossil finds of representatives of Acipenseriformes largely coincide with the modern territory of the Amur River basin; the age of the fossils and basin evolution both indicate that this river system played the most important role in the genesis of the order in general and of the representatives of the Pacific group of species in particular. Part of the Chita Region, eastern and central Mongolia, northern and northeastern China, should be probably considered as the area of the initial radiation and long-term habitation of Acipenseriformes. The Bering land bridge (Beringia), which has repeatedly connected Eurasia and North America, contributed to the resettlement of the ancestral form of the Pacific group. The diversification of this form is probably associated with multiple significant ocean transgressions and regressions in the Eocene, Oligocene, Middle Miocene, Late Miocene, and Early Pliocene. This contributed to the development of isolates, as well as to the emergence of anadromous forms from the original potamodromous species. The formation of the Asian-Pacific group of sturgeons is associated with the diversification of species in terms of migratory behavior, temperature regime of reproduction, and water salinity demands. [ABSTRACT FROM AUTHOR]

Species composition and taxonomic structure of phytoplankton communities in the main channel of the Amur at Khabarovsk (Russia) were monitored from spring to autumn of 2018–2019. In total, 187 species, varieties and forms of algae and cyanobacteria were found belonged to 8 phyla (Cyanobacteria, Bacillariophyta, Charophyta, Chlorophyta, Heterokontophyta, Rhodophyta, Euglenozoa, and Miozoa) and 75 genera. Diatoms formed the basis of the algal flora (94.7 % of the total species number). Mass vegetations of the diatoms and charophytes were observed with dominance of Asterionella formosa, Aulacoseira islandica, A. ambigua, A. granulata var. granulata, A. granulata var. angustissima, Ulnaria ulna, Diatoma tenue, Nitzschia acicularis, Stephanodiscus sp., Tabellaria flocculosa, Hannaea arcus var. rectus, Melosira varians, Fragilaria capucina var. vaucheriae, F. crotonensis, and Mougeotia sp. ster. Total number and biomass of plankton algae and cyanobacteria varied in the ranges of 1.74–5724.39 million cells/L and 2.5–2648.5 mg/L in spring-summer and 0.07–0.62 million cells/L and 0.2–1.4 mg/L in autumn. The water quality was evaluated by Pantle-Buck method modified by Sládeček as the betamezosaprobic III class (slightly polluted).

The impact of the wind-driven upwelling and the Amur River discharge on the thermohaline water structure off the northeastern coast of Sakhalin was analyzed using hydrographic data and satellite information on the sea surface temperature distribution. The interaction of upwelling water and the coastal current depends on wind conditions and the Amur River runoff. Coastal upwelling develops at relatively low river runoff values (summer low water). The increase in the Amur River discharge during the summer flood enhances the interaction of the upwelling and the coastal buoyancy current. The Amur River runoff flows directly along the shore, which tears cold upwelling water off the coast. The advection of the cold upwelling water from the coast towards the open sea increases with the consecutive alternation of upwelling and downwelling events. [ABSTRACT FROM AUTHOR]

In 2017, a spillover dam was constructed in the middle course of the Amazar River of Russia, forming a reservoir to provide water to the Amazar Pulp and Saw Mill project known as Polyarnaya. The dam uses an integrated approach, combining hydrochemical, hydrobiological, and ichthyological methods, as well as echo sounding. Comprehensive studies of the transformation of the Amazar River into a reservoir demonstrate the initially low biodiversity of hydrobionts characteristics for a semi-mountain river under the conditions of the sharply continental climate of the Trans-Baikal region. During the initial stage of formation, the reservoir was similar to the original watercourses in physical and chemical parameters and in the composition of the flora and fauna. It featured extensive shoals that were gradually turning into silt-covered and plant-filled shallow bays. These bays will eventually be locations of maximum concentration and diversity of hydrobionts and future nursery and spawning grounds for fish. The construction of the dam has significantly changed the hydrology of the Amazar River downstream of the dam. These findings reveal problems related to fish migration to the Thymallidae and Salmonidae spawning areas, as well as reductions in the biodiversity and quantity of the macrozoobenthos typical for run-of-river reservoirs.

Taking into account the unstable moisture regime and the diversity of landscapes within the Amur River basin, the problem of assessing the impact of climatic changes on the processes of surface water cycle in the region becomes multifaceted, associated with the solution of particular problems. This work studied the reaction of a river runoff to changes in the amount of atmospheric precipitation on the basis of the elasticity coefficient. Small and medium-sized river basins (52 in total) belonging to the system of the Middle and Lower Amur are the objects of this study. The data of standard observations at hydrological posts and meteorological points for the summer-autumn flood hazard period (June-September) were used. The data series were selected to include different moisture conditions. It was found that with an increase in precipitation by 1%, the river runoff in the flood hazard season has increased by 1.02–3.86% in 48 cases, and decreased in 4 cases. The results of the work are fundamentally close to the regional estimates within the basin of the Amur River on the base of the analysis of factual material (including the near abroad) and simulation results, as well as to the values of the runoff elasticity coefficient obtained in different geographic zones and given in the specialized literature. The relationship between the elasticity coefficient values of runoff with various basin indicators has been studied. For the rivers in the Primorsky Kray (catchment area of the Ussuri River), the relationship between the elasticity coefficient values and the seasonal runoff and precipitation, the runoff coefficient, average height, catchments slopes and average river network slopes has been revealed. The influence of local conditions of runoff formation on the river basins response to changes in the amount of atmospheric precipitation is discussed.

The analysis is carried out for changes in runoff of the Amur and Selenga rivers in the 21st century according to the CMIP6 (Coupled Model Intercomparison Project, Phase 6) climate model ensemble simulations using the Bayesian approach versus stream gage data on annual runoff and GPCP-2.3 dataset on annual precipitation over catchments on different timescales. For both catchments, significant intermodel differences are associated with the projections of multiyear mean runoff and interannual variability. The intermodel distribution of Bayesian weights indicates a high role of uncertainty related to initial conditions for model simulations. There is a positive trend in total runoff in the Amur River basin in the 21st century under all analyzed anthropogenic forcing scenarios. For total runoff of the Selenga River, there are no trends in the 21st century for all analyzed scenarios. No significant trends for the Amur and Selenga surface runoff were revealed for all algorithms for considering Bayesian weights and all anthropogenic forcing scenarios. At the same time, significant interdecadal variations in the interannual variability of runoff were found. [ABSTRACT FROM AUTHOR]

Morphological signs (32 plastic and 7 meristic) and biological parameters (size, weight, age and sexual structure, fecundity) are considered for weather loaches of gen. Misgurnus inhabiting the Pad Bolshaya (Jewish Autonomous oblast), with the body length Ad 60.2-182.4 mm, body weigh 2.3-55.3 g, age 1-8 years and sex ratio about 1 : 1 (53 % males, 47 % females). Sexual dimorphism is found for antedorsal, anteventral and ventroanal distances, tail fin base length, base length and height of pectoral, pelvic and anal fins, and maximum body height. Ontogenetic variability of morphological indices in dependence on body length is detected for 26 of 32 plastic signs, whereas the dependence of anteanal, antedorsal, pectoventral, and anteventral distances, and maximum and minimum body height on the body length is not statistically significant. Males grow slower than females. Age of puberty is 4-6 years, mean individual absolute fecundity is 7409 eggs. The analysis concluded that the weather loaches Misgurnus in the Pad Bolshaya belonged to the species Misgurnus nikolskyi (Vasil’eva, 2001).

This study examined the age, growth, and maturation of 1,064 Coregonus ussuriensis individuals that were collected monthly from the middle section of the Amur River, China between 2016 and 2018. The fork length (FL) ranged from 14.9 to 49.1 cm for males and 21.5 to 58.8 cm for females, and the body weight (BW) ranged from 72.6 to 1,348.7 g for males and 107.9 to 2,854.9 g for females. The relationship of BW and FL was expressed as: BW? = 0.0324 × FL2.708; BW? = 0.014 × FL2.963. The sample ages ranged from 2 to 8 years for males and 2 to 9 years for females. We used the von Bertalanffy function based on otolith reading and observed FL data to simulate Coregonus ussuriensis growth, which has been suggested to be similar to that of other Salmonidae fishes. No significant difference in growth was determined between males and females. The monthly gonad somatic index (GSI) value ranged from 0.16% to 1.69% for males and from 0.73% to 16.15% for females, with a peak in November. Additionally, the reproductive staging suggested that the Coregonus ussuriensis spawning season was mainly in November and December. The size at maturity (FL50%) for males and females was 34.9 cm and 37.9 cm respectively, and the corresponding age (T50%) was 4.5 and 5.1, respectively. This study provides basic information for understanding the biological characteristics of Coregonus ussuriensis and should aid in the assessment and management of fishery resources. [ABSTRACT FROM AUTHOR]

GLDAS2.0 provides long‐term fine resolution gridded hydrometeorological data sets, which are necessary for water‐related studies, particularly in some transboundary rivers that are partially without observation. Yet, GLDAS2.0 has only been validated at limited locations, and few studies have been conducted to develop approaches to correct the GLDAS2.0 data for transboundary rivers. This work assessed the GLDAS2.0 data and developed approaches to correct their uncertainties for studies in large transboundary rivers in the Tibetan Plateau and Northeast China (NC). To achieve these goals, observational data from 1982 to 2010 and a water and energy budget‐based distributed hydrological model including biosphere after calibration and validation were employed. We find that the GLDAS2.0 data (except for wind speed) can reasonably replicate observed seasonal variations. However, its specific humidity and wind speed have large uncertainty, and precipitation has large uncertainty in summer. In NC, the trends of its precipitation, air temperature, downward longwave radiation, and wind speed are consistent with the observations. In the Yarlung Tsangpo, Lancang, and Nu Rivers, the trends of all GLDAS2.0 data reproduce the observation very well, that is, wetting, warming, and dimming trends. Validations show that the corrections are effective and the corrected forcing data can be successfully used in hydrological simulation with improved performance than the raw GLDAS2.0 data, which demonstrates the usefulness of the methodology and corrected forcing data to hydrometeorological studies in transboundary rivers in China as well as in other nearby regions/countries. Plain Language Summary: GLDAS2.0 provides long‐term hydrometeorological data sets, which are necessary for water‐related studies, particularly in some transboundary rivers that are partially without observation. This work assessed GLDAS2.0 data and developed approaches to correct their uncertainties for studies in large transboundary rivers in the Tibetan Plateau (TP) and Northeast China (NC). In NC, the trends of GLDAS2.0 precipitation, air temperature, downward longwave radiation, and wind speed are consistent with observations. In TP, the trends of all the GLDAS2.0 data reproduce observation very well. Validations show that the corrections are effective and the corrected data have improved performance than raw GLDAS2.0 data in hydrological simulation. Key Points: Specific humidity and wind speed have large uncertainty, and precipitation has large uncertainty in summerTrends of precipitation, air temperature, downward longwave radiation, and wind speed are consistent with observationEquations are developed to reduce forcing data uncertainty, and validations show that the equations are effective [ABSTRACT FROM AUTHOR]

In the Amur River, there are two ecological forms of pond smelt Hypomesus olidus: anadromous and freshwater. Generalized information about biology and fishery of the anadromous form of pond smelt is presented. The smelt migrate to the Amur for spawning in winter and spring, and for wintering in autumn. The most remote point of their spawning migration is Bolbinsky cliff (375 km from the mouth). The spawning herd is represented by three age groups: 2-, 3-, and 4-year-old fish; the two-year-old fish are the most numerous. The sex ratio of spawning smelt is close to 1 : 1, though females prevail slightly. Body length of the pubescent fish ranges from year to year from 7.6 to 13.2 cm, body weight — from 3.05 to 16.04 g; females are slightly larger than males. Absolute fecundity of pond smelt ranges from 0.7 to 12.4 thousand eggs, relative fecundity — from 199 to 1287 eggs/g. During migration to the spawning grounds, the smelt practically do not feed, but they go to active feeding after spawning. Pond smelt is a popular object of fishery in the Amur basin: on average 1569.2 t were caught annually in 2010–2019, during the spawning migration, mainly in the lower Amur River between Nikolayevsk-on-Amur and Bogorodskoe.

Inventory of spawning grounds is an important tool for estimation of pacific salmons abundance and adequate management of their stocks. A set of the most up-to-date, relevant and effective methods based upon geographic information system (GIS) is substantiated, designed, developed and scheduled to implementation for inventory of the spawning grounds in the Amur basin. Abilities of GIS-technologies for optimization of the surveys planning and conducting and for processing, analysis, visualization and presentation of their results due to accelerated, simplified and enhanced workflow are shown. Three components of modern corporative GIS are presented: server, desktop and mobile ones. The system is partially loaded with the data about spawning grounds, tested for the basic operations as data collection, multi-user editing, geoprocessing, spatial analysis, cartographic visualization, protected web publication, etc., and adjusted and improved using the results of this testing for further implementation in complex fisheries surveys in the Amur River basin. Proposed GIS-technology is modifiable and scalable, so can be spread to other species and areas after appropriate modification; the GIS can be specialized for certain practical tasks.

Current status of aquatic biological resources in the middle and lower parts of the Amur River basin, including Lake Khanka and the Amursky Liman, is assessed. Generally high abundance of the water organisms is noted, but a downward trend is revealed. In 2015–2019, the total annual catch in the basin by Russian fishermen changed between 15.9–69.6 . 103 t (on average 39.1 . 103 t), with the main portions of pacific salmons (31.9 . 103 t, or 81.6 % of total catch) and smelts (5.5 . 103 t, 14.1 %). After the peak in 2016, the salmons abundance in the Amur has decreased, particularly for summer chum salmon and pink salmon, the number of arctic rainbow smelt Osmerus dentex has decreased gradually in the last 3 years. The stocks of freshwater fish are generally stable, with a slight increase for some species. The program of fisheries research «Amur River Fishes» implemented for 2020–2024 includes intensifying of traditional monitoring of the stocks and their biological state, as well as organization of detailed comprehensive studies for key species. Improvement of data quality on status of the main stocks of pacific salmons, smelts, and freshwater fishes is planned, as the basis for fisheries forecasting. Besides, the program conducts quantitative assessment of the main components of the ecosystem (phyto- and zooplankton, macrozoobenthos, and fish) and their dependence on environmental changes. State of food base for the Amur fish will be evaluated, including the feeding of artificially reproduced juveniles of salmons and sturgeons. Results of these studies will allow to improve approaches to regulation of fishery and to promote development of fishery industry toward organization of effective fishery complex in the Amur River basin.

Floodplain soils function as long-lasting stock or source of different substances, including pollutants. The main factor determining biochemical processes in fluvisols is flooding. Global climate change, which is causing more frequent and massive floods, is urging us to assess the potential environmental risks and create appropriate environmental management strategies. This study was performed to estimate the impact of a heavy flood on the total content of major elements and both total and mobile trace elements in fluvisols of one of the longest rivers in the world, the Amur. The study was conducted in field conditions by sampling from the same soil profiles before and after the flood. As a result, 10 major and 42 trace elements were distinguished. Major-element composition was determined with X-ray fluorescent method, trace-element composition - with the inductive coupled plasma mass spectroscopy. Maximum decrease of concentration was determined for CaO, MnO, P2O5 (up to 60%) and Sr, Cd, Ba, Tl and Pb (up to 40%). Significant increase was in concentration of Ni, Cu, and Mo (up to 160%). Among mobile trace elements, increase was observed in concentration of Sc, Ni and Th (up to 400%). With the correlation analysis, it was also established that the main causes of changes in elemental composition of the soils were decrease of pH, development of redox environment and washing out of organic matter. The main factor determining the influence of the flood on fluvisols was floodplain relief, which affected the length of the inundation, flood water velocity and the way allochthonic matter retained.

istribution of fishes and prawns in the Amur River (40–960 km from the mouth) is described on results of the beam-trawl survey conducted in September-October, 2003 (57 trawl stations at the depth of 1.5–23.0 m). In total, 2584 ind. of 22 fish species and 1077 ind. of 1 invertebrate species (prawn Palaemon modestus) were caught. The highest species richness was registered for orders Cypriniformes (13 species) and Siluriformes (4 species). The fish and prawn stocks were evaluated as 32.161 . 106 ind. (583.8 t) for bottom and near-bottom fish and 4.887 . 106 ind. (8.8 t) for prawns. Two commercial fish species were the most abundant: catfishes Tachysurus brashnikowi (16.26 . 106 ind. or 32.9 % of total biomass) and T. sinensis (4.32 . 106 ind. or 24.0 % of total biomass); other 6 fish species with considerable biomass were lizard gudgeon Saurogobio dabryi (12.6 %), ussuri catfish T. ussuriensis (9.7 %), amur white-pinned gudgeon Romanogobio tenuicorpus (7.8 %), amur sturgeon Acipenser schrenckii (5.6 %), amur gudgeon Gobio cynocephalus (2.4 %), and kaluga Huso dauricus (0.6 %). Distribution density varied in the range of 0.01–2.57 g/m2 (on average 0.45 ± 0.27 g/m2) for fish and 0.005–0.044 g/m2 (0.021 ± 0.012 g/m2) for prawns. Abundance of both fish and prawns increased multifold towards the Amur mouth that correlated with increasing of forage benthos biomass in the same direction. So, the main portion of fish biomass (82.4 %) was distributed in the Amur River downstream (40–400 km from the mouth) and the prawn stock was concentrated completely in its lowermost part (50–150 km from the mouth).

Abstract GLDAS2.0 provides long‐term fine resolution gridded hydrometeorological data sets, which are necessary for water‐related studies, particularly in some transboundary rivers that are partially without observation. Yet, GLDAS2.0 has only been validated at limited locations, and few studies have been conducted to develop approaches to correct the GLDAS2.0 data for transboundary rivers. This work assessed the GLDAS2.0 data and developed approaches to correct their uncertainties for studies in large transboundary rivers in the Tibetan Plateau and Northeast China (NC). To achieve these goals, observational data from 1982 to 2010 and a water and energy budget‐based distributed hydrological model including biosphere after calibration and validation were employed. We find that the GLDAS2.0 data (except for wind speed) can reasonably replicate observed seasonal variations. However, its specific humidity and wind speed have large uncertainty, and precipitation has large uncertainty in summer. In NC, the trends of its precipitation, air temperature, downward longwave radiation, and wind speed are consistent with the observations. In the Yarlung Tsangpo, Lancang, and Nu Rivers, the trends of all GLDAS2.0 data reproduce the observation very well, that is, wetting, warming, and dimming trends. Validations show that the corrections are effective and the corrected forcing data can be successfully used in hydrological simulation with improved performance than the raw GLDAS2.0 data, which demonstrates the usefulness of the methodology and corrected forcing data to hydrometeorological studies in transboundary rivers in China as well as in other nearby regions/countries.

The results of histological analyses of the status of muscle and liver tissues in the Amur sturgeon Acipenser schrenckii and kaluga Huso dauricus are presented. Samples have been collected in the mouth of the Amur River in 2007. Pathological changes in most specimens of both species are found. The frequency of occurrence of the most distinctive abnormalities in muscles (curvature and exfoliation of muscle fibers, connective tissue insertions, and destructions of myofibrils) and liver (inflammable infiltrates, necrosis, fibrosis of vascular walls, and decomposition of hepatic cords) is estimated. These abnormalities are presumably a consequence of the Amur River water pollution. The degree of manifestation of the abnormalities found in some specimens varied from low to extremely high. The results were compared with similar data on sturgeon species inhabiting the Caspian Sea and the Volga River. [ABSTRACT FROM AUTHOR]

Background. This study was initiated for the morphological comparison of two species of recently described Amur graylings collected in the unique zone of their sympatry. This provided an infrequent opportunity for the estimation of the species-specific morphological diversification not determined by environmental conditions dissimilarity. This study aimed to compare the seismosensory systems of two species of Amur grayling, the lower Amur grayling, Thymallus tugarinae Knizhin, Antonov, Safronov et Weiss, 2007, and yellow-spotted grayling, Thymallus flavomaculatus Knizhin, Antonov et Weiss, 2006, collected in sympatric habitats with the inclusion of the published data on other northeast Asia grayling species. Materials and methods. The comparative study was based on samples of T. tugarinae and T. flavomaculatus specimens collected at species sympatric habitats in the middle stretch of the Anyuy River, one of the biggest tributaries of the Amur River. The lateral line system was stained, the topology was examined, and seismosensory system canal pores were counted. Differences in canal pore numbers between examined species were estimated with Wilcoxon signed-rank test. Also, cluster analysis was carried out. Results. Examined sympatric species were found to differ in the number of pores and secondary canaliculi topology but were similar to geographically distant grayling species. Conclusion. The results revealed sympatric morphological divergence of studied species and demonstrated parallelism of interspecies variability of examined features which are likely determined by conditions of species ecological optima. Comparative morphological analysis of the species and forms with questionable taxonomic status should be carried out using material that is collected in different parts of the habitation areal, paying special attention to the sympatry zones, if there are any such cohabitation regions, because the environmental factors have similar effects on all of the analysed species within such zones.

Chum salmon in the Amur River basin are represented by two races: summer and fall ones. For the summer race, one population with specific type of spawning grounds is known, but the fall race includes three populations with different types of spawning grounds. In total, four eco-geographical groupings of the species are separated in their reproduction by geographical boundaries of geomorphological zones, as well as temporally and ecologically. Chum salmon do not spawn in the Chinese part of the Amur basin in more than 50 years. In the Russian part, the summer chum salmon spawn completely in the hyporheic waters in late July — August, the major grouping of fall chum (77.1 %) spawns in the spring waters in September-November, other two groupings spawn in the hyporheic waters of the lower Amur in September (20.4 %) and in the spring waters of the lakes near the Amur mouth in October-November (2.5 %).

The Amur River is one of the largest rivers in Asia and the world. The initial data on major, trace geochemistry of the bulk composition of recent sediments from upper, and middle Amur River suggests that concentrations of most major and trace elements in the Amur sediments correspond to the upper continental crust. However, there are significant differences in the bulk composition of recent sediments in different river parts, e.g. ƩREE, (La/Yb)n, Eu/Eu*. Besides, from "Upper Amur" down the river to "Amur–Zeya valley" the values of indices CIA, CIW, PIA, V increase, whereas STI and R values decrease. Farther down the river to "Khingan canyon" the opposing process occurs. That may be explained by the changes of river reaches, namely from mountain to valley and contrariwise. The statistical analysis results show a significant positive correlation of ƩREE with indices PIA, CIA, CIW, and a significant negative correlation with STI and R indices. Eu/Eu* values have a positive correlation with WIP. The correlations may be explained by the peculiarities of sorting and transporting river sediments, not chemical weathering. [ABSTRACT FROM AUTHOR]

Results of the layer-by-layer studies of distribution of organic matter (OM) and mercury in ice cores sampled from the Amur River near the Khabarovsk city: its mainstream and the Pemzenskaya and Amurskaya branches, are presented. Comprehensive investigation of ice performed at the end of the freeze-up period allows making a retrospective analysis of the river ecosystem pollution during winter. Analysis of the total content of dissolved organic substances and aromatic compounds, determining a level of humification of the aquatic environment, was carried out with a spectrophotometer Shimadzu UV-3600 at 254 and 275 nm. The mercury content was determined by inductively coupled plasmamass spectrometry (ICP-MS). The number of cultured heterotrophic bacteria, sulfate-reducing bacteria (SRB) and their resistance to mercury (0.0005 and 0.001 mg/L) were used as indicators of biogeochemical processes going on in vitro. The maximum resistance to mercury at concentration of 0.001 mg/l was revealed from the sulfate-reducing bacteria in cores taken from the upper ice layer (0-10 cm) near the right bank of the Amurskaya branch. Periodical high mercury contamination of ice (up to 0.71 mkg/L) is estimated as a risk factor. In Pemzenskoy branch, the main factors for the mercury methylation in the ice were fine detritus, coming at the reservoir discharges, and the SRB resistant to mercury. These microorganisms were found in upper layers of the ice (10-35 cm) near the left bank and in the middle of the water stream (60–80 cm). A layer of ice (70–117 cm) with conditions also favourable for the sulfate reduction and the mercury methylation had been revealed in the mainstream of the Amur River near its right bank that is the cross-boundary area in the zone of influence of the Songhua river runoff. Among these conditions are high levels of OM, the presence of heterotrophic bacteria, which are destructors of high-molecular compounds, the potential producers of metabolites with methyl radicals, and the activity of the SRB resistant to mercury.

The content of microelements is determined within the alluvial soils of the flood plain situated near the river bed in the middle flow of Amur River. The impact of the catastrophic flood of 2013 on their content is also revealed. The microelements were determined by using mass spectrometry in samples collected from genetic horizons. The principal component analysis has been applied to characterize the relationship between microelements, alluvial soil properties and macroelements composition. The associations of accumulation (Rb, Sr, Ba) and association of dispersion (Zr, Ta), having a lithogenic nature, are separated. The content of other microelements is lower than the average one for the world's soils. However, their concentration increases as the distance from the river bed increased. It is revealed that trace elements under the impact of flood waters are not accumulated only. They are also leached. Their migration is influenced significantly by floodplain topography: microelements are more affected to washing out in soils which are located near the river bed. Other factor which affects the microelements migration is the soil properties. Some microelements (Sr, Cd, Ba, Pb) are washed out from all types of soils. While the other ones (Y, Sc and Cr) are accumulated only. Flood affected greatly Mo (+43% average for the soil), Sc (+38%), Cu (+27%), Cd (-23%), Pb (-12%) and Sr (-12%). However, before the flood, significant correlation between microelements were observed only for exchangeable manganese and oxides aluminum and magnesium. Significant correlation between texture, organic matter and soil pH appeared after a long flood in all studied soils. These changes are probably caused by a decrease in the redox potential during flooding and the washing out of calcium oxide.

The morphological variability of nine characters in six samples of Siberian taimen Hucho taimen from the Amur River was studied. The differences in the level of fluctuating asymmetry of fish from different tributaries are small, which indicates the similarity of the conditions of embryonic and early postembryonic development; significant differences between the samples were noted only in six cases. The maximum fluctuations in the coefficient of variation are characteristic for the number of postorbital bones and channels of the seismosensory system on the 1st postorbital bone; the minimum, for the number of soft rays in the pectoral fins and channels of the seismosensory system on the preopercular bones. The largest sum of the variation coefficients values for individual characteristics differs in the sample from the Bikin River; the smallest, the Limuri River. These difference positively correlates with the length and area of ​​the basin of these tributaries. A regular decline in the mean values in the fish sampled at increasing distance from the mouth of the Amur River concerns only the number of postorbital bones. Clustering according to the mean values ​​of the features, revealed that the samples form three clusters: (1) the rivers Bol'shaya Ussurka and Tyrma (2nd order tributaries, the farthest from the Amur mouth), (2) the Limuri River (the least distant from the Amur mouth), 3) the rivers Anyui, Khor and Bikin (geographically close populations). Revealed features may indicate the similarity of the conditions of early development and the likelihood of gene exchange between the last three groups. [ABSTRACT FROM AUTHOR]

The distribution of fish and prawn in the bed of the lower Amur River (within 40–960 km from the mouth) is described based on the results of a beam-trawl survey (57 trawl taw at depths of 1.5–23.0 m) conducted in September and October 2003. A total of 2584 ind. of 22 fish species and 1077 ind. of one invertebrate species (the prawn Palaemon modestus) were caught. The most frequently occurring fish species were members of the orders Cypriniformes (13 species) and Siluriformes (4 species). The total number of benthic and demersal fish was estimated at 32.161 million ind.; the total number of prawn was estimated at 4.887 million ind. The most abundant fish were two commercial catfish species: the Brazhnikov's catfish Tachysurus brashnikowi (estimated at 16.26 million fish) and the Chinese catfish T. sinensis (4.32 million fish). The abundance of both fish and prawn increased by many times towards the mouth of the Amur, which correlated with the increasing biomass of the benthic food supply in the same direction. The total biomass of fish and prawn equaled 583.8 and 8.8 t, respectively. The fish biomass varied in the 0.012–2.572 g/m2 range (with an average of 0.450 ± 0.270 g/m2) and the prawn biomass varied within 0.005–0.044 g/m2 (0.021 ± 0.012 g/m2). The major portion of the fish biomass (82.4%) was recorded mainly from the lower reaches of the Amur River (40–400 km from the river mouth); the entire prawn biomass was concentrated in the lower reaches (50–150 km from the mouth). The following fish species were dominant in catches in terms of biomass: Chinese catfish (32.9%), Brazhnikov's catfish (24.0%), Chinese lizard gudgeon Saurogobio dabryi (12.6%), Ussuri catfish T. ussuriensis (9.7%), Amur whitefin gudgeon Romanogobio tenuicorpus (7.8%), Amur sturgeon Acipenser schrenckii (5.6%), Siberian gudgeon Gobio cynocephalus (2.4%), and kaluga Huso dauricus (0.6%). [ABSTRACT FROM AUTHOR]

The distribution of desalinated waters from the Amur Estuary in the northwestern Sea of Okhotsk during the summer period is analyzed using satellite data on the sea surface height (SSH), sea surface salinity (SSS), temperature, and concentrations of particulate organic carbon. There is a good agreement between the spatial distributions of SSS (data from the SMAP satellite) and SSH (AVISO data) in the study area. Identification of the Amur Estuary waters in terms of surface water temperature and concentration of particulate organic carbon is confined by Sakhalin Bay and the coastal zone of Sakhalin Island. An increase (a decrease) in the Amur River discharge during the spring–summer high-water period leads to an increase (a decrease) in the SSH in the northern part of Sakhalin Bay in July. Strengthening of the northwestern (southeastern) winds in September reduces (increases) the inflow of waters with low salinity and causes an elevated SSH in the water area to the north of Sakhalin Bay. [ABSTRACT FROM AUTHOR]

The chum salmon in the Amur River basin is represented by two races, that is, summer-run and fall-run races. In the summer-run race, one population is known to use a specific type of spawning grounds. The fall-run race includes three populations with different types of spawning grounds. These four populations correspond to four eco-geographical groups separated reproductively by geographical boundaries of the geomorphological zones, as well as temporally and ecologically. In China, chum salmon has not been recorded from the spawning grounds of the Amur basin for already more than 50 years. In the Russian Federation, 100% of summer-run chum salmon spawn completely at parafluvial springs in late July and August; 77.1% of fall-run chum spawn at orthofluvial springs in September–November; 20.4% of fall-run chum spawn in the downstream part of the spawning range at parafluvial springs in September; and 2.5% of fall-run chum spawn in lakes near the Amur River mouth at orthofluvial springs in October and November. [ABSTRACT FROM AUTHOR]

Background. This study was initiated for the morphological comparison of two species of recently described Amur graylings collected in the unique zone of their sympatry. This provided an infrequent opportunity for the estimation of the species-specific morphological diversification not determined by environmental conditions dissimilarity. This study aimed to compare the seismosensory systems of two species of Amur grayling, the lower Amur grayling, Thymallus tugarinae Knizhin, Antonov, Safronov et Weiss, 2007, and yellow-spotted grayling, Thymallus flavomaculatus Knizhin, Antonov et Weiss, 2006, collected in sympatric habitats with the inclusion of the published data on other northeast Asia grayling species. Materials and methods. The comparative study was based on samples of T. tugarinae and T. flavomaculatus specimens collected at species sympatric habitats in the middle stretch of the Anyuy River, one of the biggest tributaries of the Amur River. The lateral line system was stained, the topology was examined, and seismosensory system canal pores were counted. Differences in canal pore numbers between examined species were estimated with Wilcoxon signed-rank test. Also, cluster analysis was carried out. Results. Examined sympatric species were found to differ in the number of pores and secondary canaliculi topology but were similar to geographically distant grayling species. Conclusions. The results revealed sympatric morphological divergence of studied species and demonstrated parallelism of interspecies variability of examined features which are likely determined by conditions of species ecological optima. Comparative morphological analysis of the species and forms with questionable taxonomic status should be carried out using material that is collected in different parts of the habitation areal, paying special attention to the sympatry zones, if there are any such cohabitation regions, because the environmental factors have similar effects on all of the analysed species within such zones. [ABSTRACT FROM AUTHOR]

Wildfires affect biodiversity at multiple levels. While vegetation is directly changed by fire events, animals are often indirectly affected through changes in habitat and food availability. Globally, fire frequency and the extent of fires are predicted to increase in the future. The impact of fire on the biodiversity of temperate wetlands has gained little attention so far. We compared species richness and abundance of plants and birds in burnt and unburnt areas in the Amur floodplain/Russian Far East in the year of fire and 1 year after. We also analysed vegetation recovery in relation to time since fire over a period of 18 years. Plant species richness was higher in burnt compared to unburnt plots in the year of the fire, but not in the year after. This suggests that fire has a positive short-term effect on plant diversity. Bird species richness and abundance were lower on burnt compared to unburnt plots in the year of the fire, but not in the year after. Over a period of 18 years, high fire frequency led to an increase in herb cover and a decrease in grass cover. We show that the effects on biodiversity are taxon- and species-specific. Fire management strategies in temperate wetlands should consider fire frequency as a key driving force of vegetation structure, with carry-over effects on higher trophic levels. Designing fire "refuges", i.e., areas that do not burn annually, might locally be necessary to maintain high species richness. [ABSTRACT FROM AUTHOR]