Low-water Season Research Articles

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People and NatureVolume 3, Issue 1 p. 261-261 CORRIGENDUMOpen Access CORRIGENDUM First published: 22 December 2020 https://doi.org/10.1002/pan3.10175AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat In the article by Tregidgo et al. (2020), Figure 2 was originally published with "Low water" labelled as "High water" and vice versa. This was due to an error during article proofing. FIGURE 2Open in figure viewerPowerPoint Food insecurity and fishing activity in the high- and low-water seasons. Boxplots showing seasonal comparisons of (a) household food insecurity (log weighted score), (b) fish catch rate (CPUEb; log kg/hr) per trip, (c) household fish catch (kg caught within previous 72 hr by all adult household members) and (d) household fishing effort (hours spent fishing by all adult household members). Individual data points are jittered. Seasonal differences between all four variables were tested with linear mixed-effects models, and all were significant to p < 0.001 level. CPUEb, catch-per-unit-effort in biomass REFERENCE Tregidgo, D., Barlow, J., Pompeu, P. S., & Parry, L. (2020). Tough fishing and severe seasonal food insecurity in Amazonian flooded forests. People and Nature, 2, 468– 482. https://doi.org/10.1002/pan3.10086Wiley Online LibraryGoogle Scholar Volume3, Issue1Special Feature: Citizen ScienceFebruary 2021Pages 261-261 FiguresReferencesRelatedInformation

Ecological responses to flow variation inform river dolphin conservation

Many environmental flow (e-flow) studies and applications have predominantly used state—(i.e., at a single time point) and rate—(i.e., temporal change) based demographic characteristics of species representing lower trophic levels (e.g., fish communities) to build flow-ecology relationships, rather than using a process that incorporates population dynamics. Recent studies have revealed the importance of incorporating data on species traits when building flow-ecology relationships. The effects of flow on keystone megafauna species (i.e., body mass ≥ 30 kg) reverberate through entire food webs; however, the relationships between flow and these species are not well understood, limiting the scope of the relationships used in flow management. Here, we fill this gap by incorporating the habitat selection traits at different flows of a freshwater apex predator, Ganges River dolphin (GRD, Platanista gangetica gangetica), which plays a significant role in maintaining the structure, functions and integrity of the aquatic ecosystem. Using temporally and spatially measured GRD habitat selection traits, we quantified flow-ecology responses in the Karnali River of Nepal during the low-flow season when habitat was heavily reduced and water demand was highest. We define ecological responses as suitable habitat templates with enough usable surface area to support GRD fitness by improving reproduction and survival. We measured the available and occupied habitats to develop flow-ecology responses. Variation in flow resulted in substantial differences in the ecological response across time and space, suggesting that aquatic species adjusted in a variety of habitats to support their life histories and maintain viable populations. The limited availability of suitable habitats combined with uninformed water regulations by humans likely places GRDs under severe physiological stress during low-water seasons (i.e., January–April), suggesting that reduced flows contribute to the process of endangering and extirpating highly sensitive endemic aquatic biodiversity. Our study reveals that ad hoc or experience-based flow management is no longer tenable to maintain the integrity and functionality of aquatic ecosystems. We stress that quantifying the flow-ecology relationships of foundational species, particularly megafauna, in response to flow variation is crucial for monitoring the effects of water alterations and determining the minimum flows needed for maintaining healthy and functional freshwater ecosystems in the Anthropocene.

Water-level fluctuations affect the alpha and beta diversity of macroinvertebrates in Poyang Lake, China

Water-level fluctuations (WLFs) are a key influence on aquatic biodiversity in seasonally inundatedfreshwater ecosystems. However, how unregulated WLFs affect macroinvertebrates in lake-floodplain systemsexperiencing considerable annual fluctuations remains unclear. We explored spatial and temporal variability intaxonomic α and β diversity in the largest fluctuating lake in China, Poyang Lake, during two hydrological seasons.We hypothesized that taxa richness (α diversity) is greater in the floodplain than in the lake channel due to greateravailability of trophic resources, and that variability in assemblage composition (β diversity) in the channel isgreater during the high-water season (HWS) than the low-water season (LWS) due to increased habitat heterogeneity.Benthic macroinvertebrate assemblages were sampled, water physicochemical and hydrological variables weremeasured, and geographical coordinates were determined at 34 sites during the HWS (October 2017) and LWS(January and April 2018). A total of 74 taxa were recorded. Macroinvertebrate α diversity was comparable in thefloodplain and the lake channel. Beta diversity in the channel was greater during HWS than LWS. Hydrologicalvariables influenced β diversity during LWS and geographical distance between sites increased β diversity duringHWS, whereas physicochemical variables did not influence β diversity in either hydrological season. Our resultssuggest that extensive WLFs altered macroinvertebrate biodiversity among hydrological seasons by extending waterinto floodplains during HWS and reducing substrate heterogeneity in the lake channel during LWS. We thushighlight the importance of WLFs that maintain such environmental seasonality in supporting the biodiversity ofbenthic macroinvertebrates in naturally dynamic freshwater ecosystems.

Seasonal variation characteristics and release potential of phosphorus in sediments: a case study of the Qiuxi River, a typical diffuse source pollution river in southwestern China

To better control and manage phosphorus (P) in the aquatic environment of the Qiuxi River, a typical river severely influenced by anthropogenic activities in southwest China, the morphological characteristics and the release potential of P in sediments during different water seasons were determined. The overlying water and sediment samples were collected from the Qiuxi River in the normal-water season (NWS), low-water season (LWS), and high-water season (HWS), and physicochemical properties were quantified. Total phosphorus (TP) in sediment and the inorganic phosphorus (Pi) fraction were analyzed using the standard measures technology (SMT) procedure, and organic phosphorus (Po) was further determined to be labile Po (LOP), moderately labile Po (MLOP), or non-labile Po (NLOP). The release potential of P from the sediments was studied by experiments under simulated conditions. The results showed that P pollution in the Qiuxi River was the most serious during the LWS, with mean TP concentrations in the sediment of 854.6 mg kg−1, and the release risk of the sediment P was also highest during this water season. The variation in P concentration was significantly influenced by the discharge of domestic sewage, agricultural diffusion, flow rate, and OM. The concentrations of P fractions varied with water season, but Pi was constantly higher than Po. HCl-extractable Pi (HCl-Pi) accounted for most of the P in the sediments, which was related to its characteristics and the geographical location of the Qiuxi River. The maximum P release (Rmax) was 25.9 mg kg−1 in the LWS and 15.3 mg kg−1 in the HWS, which were positively correlated with the TP (r2 = 0.848, p < 0.01) and OM (r2 = 0.847, p < 0.01) concentrations in the sediments and explained why the release risk of the sediment P in the LWS was higher than that in the HWS. Phosphorus pollution and the P release potential in the sediments of the Qiuxi River were most severe in the LWS, so more effective measures to restrain the release of P should be taken during the LWS. Moreover, OM in sediments should be given more attention owing to its significantly positive correlation with the risk of P release.

Seasonal flow dynamics exacerbate overlap between artisanal fisheries and imperiled Ganges River dolphins

Here we quantify the effects of artisanal fisheries on the ecology of a small cetacean, the Ganges River dolphin (Platanista gangetica gangetica, GRD), in a large river system of Nepal. We examine the size-classes of fisheries’ catches, behavioural changes in GRD in response to fishing activities, and diel overlap between GRD and fishing activity. We observed high human exploitation rates (> 60% of the total catch per effort) of GRD-preferred prey sizes, indicating risks of high resource competition and dietary overlap, especially during the low water season when resource availability is reduced. Competitive interactions in the feeding niches during the low water season, plus temporal overlap between the peak exploitation and critical life-history events (e.g., reproduction), likely have ecological consequences. Furthermore, we detected 48% (95% CI 43–52%) increase in the chance of behavioural changes among dolphins exposed to anthropopressure (fishing activity), risking social behaviour impairment in exposed dolphins. The higher diel overlap and increased diel coefficient as the surveys progressed towards the monsoon season suggest temporal shifts in GRD socio-behavioural states and seasonal effects on resource partitioning, respectively. This work identifies drivers of small cetaceans-fisheries interactions and their consequences, and can be used to help reduce biologically significant fishing impacts on small cetaceans. Mitigation strategies, together with river sanctuary and distanced-based approaches, should be urgently included in a framework of ecosystem-based management.

Effectiveness of protected areas for jaguars: the case of the Taiamã Ecological Station in Brazil

The largest feline in the Americas and the third largest in the world, the jaguar is an apex predator in the food chain and a key species in the ecosystems where it occurs, developing important ecological functions in maintaining ecosystem balance. In Brazil, the Pantanal is considered an important refuge for the species, and protected areas such as the Taiamã Ecological Station (TES) are relevant for conservation of pristine ecosystem where the species persist. Thus, considering that this area is located in one of the regions with the highest concentration of this large cat in the Pantanal, the objective of this study was to evaluate the effectiveness of the protection given by the TES for the jaguar population. The station is a flooded island in the middle of the Paraguay river and surrounded by extensive wetlands. We monitored ten jaguars using GPS collar at the TES and its surroundings. The samples were separated into high-water season (January to June) and low-water season (July to December), and the estimated home ranges were grouped as: 1) residents only and 2) all monitored individuals. The stabilization of the home ranges of eight jaguars, considered residents, was determined through variograms. When all jaguars were analysed together there was 55% overlap between the clustered areas of the two analysed seasons. In the analysis excluding non-resident individuals there was 72% overlap between the clustered areas. The type of land cover inside these areas was very similar between these periods. The range of this protected area is not sufficient to effectively protect these jaguar populations, since the grouped home ranges of the resident animals studied are 3.5(wet)/2.5(dry) times larger than the area of the TES. However, the surroundings of the TES have low human impact and no deforestation and, in this way, the landscape context of the station may have a significant effect on the persistence of a large carnivore like the jaguar. However, it is necessary to create more protected areas in order to prevent possible future environmental changes in the areas surrounding TES.

Mercury biomagnification in an ichthyic food chain of an amazon floodplain lake (Puruzinho Lake): Influence of seasonality and food chain modeling

Mercury (Hg) biomagnification in fish food chains is a relevant subject due to the high fish consumption of the Amazonian population and the high toxicity of this metal. In the Amazon, floodplain lake hydrodynamics change considerably along the four seasons of the hydrological cycle (rising water, high water, falling water and low water), which can influence Hg bioaccumulation in fish. The main aim of this study was to evaluate if Hg biomagnification is influenced by seasonality in a floodplain lake (Puruzinho Lake) in the Brazilian Amazon. Additionally, the influence of food chain modeling on measurement of Hg biomagnification was tested. Hg concentrations and stable isotope signatures (carbon and nitrogen) were estimated in four species, Mylossoma duriventre (herbivorous), Prochilodus nigricans (detritivorous), Cichla pleiozona (piscivorous) and Serrasalmus rhombeus (piscivorous). The “trophic magnification slope” (TMS) of the food chain composed by the four species was calculated and compared among the four seasons. There was no significant seasonal variation in TMS among rising water, high water, falling water and low water seasons (p = 0.08), suggesting that Hg biomagnification does not change seasonally. However, there was significant variation in TMS among different food chain models. Lower TMS was observed in a food chain composed of detritivorous and piscivorous fish (0.20) in comparison with a food chain composed of the four species (0.26). The results indicate food chain modeling influences TMS results.

Spatial Variability and Associated Risk Assessment of Nitrate and Ammonium Concentration in Hail Haor Wetland, Northeastern Bangladesh

Nitrate-nitrogen and ammonium-nitrogen concentration were evaluated to assess the current nutrient condition of an ecologically as well as economically important wetland of Bangladesh. The contamination condition of surface water nitrate and ammonium of Hail Haor wetland was assessed to understand its probable risk to human health using the water samples collected from total-fifty monitoring stations, 25 each for two different seasons within 2018 to 2019. Nitrate concentration was measured using the spectrophotometer by colorimetric method, whereas ammonium was quantified using the micro Kjeldahl's distillation method. Statistical and geo-spatial analysis revealed an extensive understanding of the temporal and spatial variability as well as possible source identification of the nutrients in the studied area. Medium to a low level of nitrate ranging from 0.95 up to 9.25 mg/L and high ammonium with values from 0.32 up to 1.92 mg/L was a sporadic trend observed in wetland water, with low water season having more concentration than that of wet high water season. Hazard quotients (HQ) obtained from wetland water for four individual age groups recognized wetland water to be safe for consumption (HQ&lt;1) based on its nitrate level. Wetlands can provide valuable ecosystem services, conserve the native and exotic wetland inhabitants and mitigate flood along with their purifying properties of nutrient removal to lessen the public health concerns about nitrate-nitrogen in drinking water. Therefore, appropriate rein in measures, incentivizing water use efficiency, and continuous monitoring of water quality will ensure safety for wetland habitats, also may aware of the risks or opportunities associated with using wetland water for both drinking and agricultural use.

Миграция тяжелых металлов в системе «береговой грунт – донные отложения – растения» реки Ходца в период летней межени 2019 года

The article describes the purpose of the work, which is determining the distribution and relationships between the composition of pollutants in coastal soil, bottom sediments and higher aquatic vegetation in the small river Khodtsa. There have been presented the data of the laboratory research based on the results of the field work onselecting samples, on concentration of toxicants (cadmium, lead, iron, nitrogen, ammonium and petroleum products) in deposit media, as well as &#x0D; in Carex aquatilis plants of the small river Hodza. This plant species is limiting throughout the river due to the low intensity of biological absorption. The studies were carried out during the summer low water season in 2019 on the river section from the source (Elektrostal city) to the river mouth in the area of Pavlovsky Posad. In all the studied objects there have been found increased concentrations of iron. In the coastal ground and bottom sediments the pollution with heavy metals is manifested to a much greater extent: at the source and intermediate point. Petroleum products and ammonia &#x0D; nitrogen are distributed unevenly in space. A correlation analysis of the experimental data obtained in the components of the environment of the studied territory (the Khodtsa river) was performed. &#x0D; In general, the highest measurement results are observed in the upper reaches of the small river Khodtsa in the industrial city of Elektrostal. The obtained data on the heavy metals migration &#x0D; in the system “сoastal ground – bottom sediments – higher aquatic vegetation” of the small river Khodtsa can be successfully used as indicators an environmental monitoring system and serve as the basis for organizing further research, as well as for developing a strategy for environmental management and environmental protection in the Moscow Region.

Hydrocarbons at the Geochemical Barrier the Northern Dvina–the White Sea

Aliphatic and polycyclic aromatic hydrocarbons have been studied in suspended matter and bottom sediments at the geochemical barrier the Northern Dvina–Dvina Bay during spring flood and low-water season. The increase in the concentrations during spring flood (for aliphatic hydrocarbons, on the average, 154 µg/L) compared with those during low-water season (on the average, 52 µg/L) has been shown to be short-time. The losses of hydrocarbons at this geochemical barrier are governed by variations of water salinity, river flow, and lunar phases and can reach 96% (August 2017). The composition of alkanes and polycyclic aromatic hydrocarbons in river water mostly showed the predominance of petroleum components. In the course of sedimentation and as salinity increases, petroleum hydrocarbons decompose, making their effect beyond the gravitational part of the marginal filter of the Northern Dvina minor. The effect of redox processes in the sediment stratum on hydrocarbon distributions is stronger than that on Corg.

Monitoring the spatio-temporal dynamics of the wetland vegetation in Poyang Lake by Landsat and MODIS observations

Poyang Lake, the largest freshwater lake of China, provides critical ecological functions for water circulation and biodiversity conservation as a dynamic wetland system. However, recent climate change and human activities exerted strong pressures on this ecosystem. In this paper, we applied object-based image analysis (OBIA) and Radom Forests (RF) classifier to ten Landsat images to examine the land cover composition and its change during 1987–2017 low water season at Poyang Lake. NDVI time series (2000–2017) derived from MODIS imagery was used to document the changes of vegetation growth status. To investigate the potential driving mechanism of the inundation patterns, we differentiated the spatial-temporal changes of vegetation coverage and NDVI accumulation on eight elevation bands. Major result indicates that the vegetation area increased by 15.5% of the lake area during 1987–2017. A much faster-increasing rate (58.0 km2 year−1) can be observed during 2001–2009 as compared to that of the overall study period (18.4 km2 year−1). Analysis of NDVI accumulation showed that 42.1% of the lake's area displayed a significant increasing trend during 2000–2017. Spatially, the increase of vegetation area and NDVI accumulation mainly took place in the 11–12 m elevation band in the lower lake center. Early dry season and prolonged exposure period after the operation of Three Gorges Dam (TGD) was the major reason for the spatio-temporal evolution of the wetland vegetation in Poyang Lake. The Lake's water level started to fall below 12 m before 9th November might cause a boost of vegetation growth in the low lake center, and in turn, triggering xerophilization for the vegetation in the highlands and a shift in foraging patterns of waterbirds due to phenology variations. The findings of this study provide a clear reference for sustaining the inter-annual stability of the ecosystem by controlling the depth of water in the lake.

Numerical study on the sedimentation at intake of the new water supply project in the LaoYeMiao area of Poyang lake

The water intake of a new water supply project of Lushan City is located on the opposite side of the LaoYeMiao in Poyang Lake. Dredging is required between the shore and the deep trough to allow water to be introduced into the intake during low water season. Based on the intake dredging project, this study established a numerical model of water and sediment transport of the research area. The model is verified in terms of water level, flow velocity, erosion-deposition rate using hydrological and topographical data. The characteristics of water flow and erosion-deposition, before and after the implementation of different dredging schemes, are studied and the influence by dredging project are analyzed from the hydrodynamics perspective. The simulation results show that the water level and flow velocity change before and after the dredging project is less than 0.002m and 0.1m/s. The dredging area before and after the project shows deposition, and the average deposition rate changed by 0.01m/year. research shows that the dredging project only affects the erosion and deposition of the dredging area. The adjustment of the dredging scheme will not have a significant impact on the deposition rate and distribution of the area. The research results can provide a scientific basis for the argumentation and optimization of the water intake dredging scheme.

Initial Geochemical Study of Planned Impact Zones of the Separated Parts of Launch Vehicles by OneWeb Project (Inclination 87°, Russia)

The results in the article have both practical and scientific significance. The practical significance is due to the need to determine the parameters of the initial condition of natural landscapes in the impact zones (IZ) of the separated parts of launch vehicles, which will be used to identify changes in the process of their operation. Scientific significance is associated with the low knowledge of the studied landscapes, because of their inaccessibility. The main components of the landscape, which may be adversely affected by space rocket activity (surface water, snow cover, plants, and soils), were used as the objects of the study. Samples were taken in three stages: autumn, winter, and summer-autumn. During the autumn stage, water samples were taken; during the winter, snow samples; and during the summer-autumn, water, soil, and plant samples. Acidity (pH), chemical oxygen demand (COD), hydrocarbons, and ionic composition were determined in water and snow samples; pH, hydrocarbons and total organic carbon, elemental composition, and cation exchange capacity (CEC) were determined in soil samples; elemental composition was determined in plant samples. During the autumn low-water season, the chemical properties of water in all rivers did not differ significantly, except for Junguele river, which had a lower acidity and more intense chemical oxygen demand, as well as a higher concentration of Mg2+ and K+ ions. In the winter stage, it was revealed that the snow cover of all planned IZ will turn into slightly acidic or neutral waters with a slight concentration of hydrocarbons, NO3−, Mg2+, Zn2+, Mn2+, and Al3+, the distribution of which is uniform within the boundaries of each IZ. During the summer-autumn stage, despite the flood, no significant changes in the chemical composition of water in the studied rivers were detected.

Factors affecting the persistence of endangered Ganges River dolphins (Platanista gangetica gangetica).

The Ganges–Brahmaputra–Meghna and Karnaphuli (GBMK) River Basin in Nepal, India, and Bangladesh is among the world's most biodiverse river basins. However, human‐induced habitat modification processes threaten the ecological structure of this river basin. Among the GBMK’s diverse flora and fauna of this freshwater ecosystem, the endemic Ganges River dolphin (Platanista gangetica gangetica; GRD) is one of the most charismatic species in this freshwater ecosystem. Though a >50% population size reduction has occurred since 1957, researchers and decision‐makers often overlook the persistence (or evolutionary potential) of this species in the highly fragmented GBMK. We define the evolutionary potential as the ability of species/populations to adapt in a changing environment by maintaining their genetic diversity. Here, we review how evolutionary trap mechanisms affect the dynamics and viability of the GRD (hereafter Ganges dolphin) populations after rapid declines in their population size and distribution. We detected six potential trap mechanisms that might affect the Ganges dolphin populations discretely or in combination: (a) habitat modification; (b) occurrence of finite and geographically restricted local populations; (c) ratio of effective to estimate population size; (d) increasing risk of inbreeding depression in genetically isolated groups; (e) at‐risk behavioral attributes; and (f) direct fisheries–dolphin interactions. Because evolutionary traps appear most significant during low water season, they adversely affect demographic parameters, which reduce evolutionary potential. These traps have already caused local extirpation events; therefore, we recommend translocation among populations, including restoring and preserving essential habitats as immediate conservation strategies. Integrative evolutionary potential information based on demographic, genetic, and environmental data is still lacking. Thus, we identify gaps in the knowledge and suggest integrative approaches to understand the future of Ganges dolphins in South Asian waterways.

Long-term changes in water flow of the Volga basin rivers

The long periods/phases (with a duration of more than 10-15 years) of increased and decreased water flow of rivers in the Volga river basin were identified. The annual and seasonal water flow (over snow-melt flood period, as well as summer–autumn and winter low-water seasons) of six representative rivers over observation periods more than a century in duration, starting from the 1870s–1890s up to 2016, was used. In addition to this, periods with the average runoff close to its normal value were also observed. The boundaries of contrast phases were determined using normalized cumulative deviation curves in combination with Student’s test of the statistical homogeneity of the data series. The duration of the phases varies from 10 to 96 years. The phases of lower runoff were generally longer than those of higher runoff (this is especially typical of the winter and summer–autumn low-water season). The identified contrast phases show a statistically significant difference between the annual and seasonal runoff. The analysis of the data series of alteration of phases with increased and decreased water flow in hydrological seasons of the year allowed the authors to identify three major types of their long-term dynamics within the Volga river basin.

Maximum water level calculation based on 2-dimensional DELFT-3D model, the case study of the Oka river

This research represents methodical approach and main results of water level hydrodynamic modeling for real summer low-water season and extreme spring flood of 1% probability. The object of modeling is 105 km length section of the Oka River in Moscow region between Kashira and Kolomna urban districts. Modeling object includes also the Moscow River section downstream the Severka River mouth. Two-dimensional hydrodynamic model constructed using DELFT-3D. To build the model we used the detailed elevation model and hydrological conditions based on in-situ measurements in 2019, special estimated discharge and water level time-series of 1% exceedance probability based on reference year observations and distributed Chezy coefficient calibration. The model implementation resulted in the actual detailed distribution of the water discharge, velocity and level along the Oka River section (including the downstream Moscow River) for low-water and extremely high water periods. These results are used for the flood zone delineation in the Kashira and Kolomna urban districts.

Local environmental factors influence beta-diversity patterns of tropical fish assemblages more than spatial factors.

A major goal in ecology is to understand mechanisms that influence patterns of biodiversity and community assembly at various spatial and temporal scales. Understanding how community composition is created and maintained also is critical for natural resource management and biological conservation. In this study, we investigated environmental and spatial factors influencing beta diversity of local fish assemblages along the longitudinal gradient of a nearly pristine Neotropical river in the Colombian Llanos. Standardized surveys were conducted during the low-water season at 34 sites within the Bita River Basin. Physical, chemical, and landscape parameters were recorded at each site, and asymmetric eigenvector maps were used as spatial variables. To examine the relative influence of dispersal and environmental variables on beta diversity and its components, distance-based redundancy analysis (db-RDA) and variation partitioning analysis were conducted. We proposed that spatial scale of analysis and position within the river network would constrain patterns of beta diversity in different ways. However, results indicated that in this system, high beta diversity was consistent among species assemblages no matter the scale of analysis or position within the river network. Species replacement (turnover) dominated beta diversity, an indication of the importance of species sorting. These findings suggested that conservation of fish diversity in tropical rivers requires maintenance of both habitat heterogeneity (spatial variation in habitat conditions) and connectivity at the scale of entire river basins.

Hydrological and hydrochemical research of the mouths of the small rivers flowing to the White sea in the winter low water season of 2019

In the winter low water season in March and the first week of April 2019, complex hydrological and hydrochemical studies were carried out at the mouths of two small rivers of the White Sea catchment basin (the Mudyuga river, which flows into the Dvina Bay, and the Tamitsa river, which flows into the Onega Bay). The results indicate significant differences in the short-period variability of hydrological and hydrochemical parameters in the winter in the studied river mouths compared with the characteristics observed in the tidal estuaries of large and medium rivers, as well as in the mouths of small rivers of the southern seas.

The response of water flow, suspended sediment yield and erosion intensity to contemporary long-term changes in climate and land use/cover in river basins of the Middle Volga Region, European Russia

The Middle Volga Region is one of the most populated and agriculturally developed geographic regions of the East European Plain within European Russia, where noticeable changes in climate and land use/cover were observed since the 1980s and the early 1990s respectively. The long-term year-to-year (trend) variability (during mainly 1960–2016) in water flow and suspended sediment yield of 14 small and medium-size rivers in the Middle Volga Region was analyzed in the paper. It is shown that in all the studied rivers there was a statistically significant decrease (on average, by 77.2 ± 4.5%) in the intra-annual irregularity of the water flow between 1960–1979 (as a baseline period) and 2002–2016 (the period of the greatest relative climate change in the region). This decrease was caused by a statistically significant reduction in the water flow during the snowmelt period (on average, by 37.4 ± 9.8%) and by an increase in the water flow during the low-water (baseflow) seasons – during the winter months (by 145.2 ± 57.6%) and the river-ice-free period (by 94.9 ± 39.7%). The intensity of snowmelt-induced flood flow has also statistically significantly decreased (by 40.4 ± 8.2%). At the same time, a reduction in the river suspended sediment yield was more significant – by 27.9 ± 26.9 times; it was the result of great changes in soil/rill/gully erosion intensity in the region. This reduction is confirmed by an analysis of sedimentation rates within one of the small (dry valley) catchments in the north of the studied region over the past 60 years. The changes in climate (chiefly a decrease in the depth of freezing of the soil during the snowmelt period, mainly April) and land use/cover, associated basically with reduction in cultivated land area (especially in the 1990s, after the collapse of the Soviet Union), are considered to be as the main reasons for the aforementioned trends that were characteristic in general for almost the entire southern half of European Russia.

Long Periods of Increased/Decreased Runoffs of Large Russian Rivers

Long series of annual and seasonal runoffs of large Russian rivers (the Volga at Volgograd, the Don at Razdorskaya, the Yenisei at Igarka, and the Lena at Kyusyur) since the 1870s for the Russian Plain rivers and since the 1930s for the Siberian rivers have been analyzed. Long periods (phases) of increased and decreased water flow have been identified. The boundaries of contrast phases are determined with cumulative deviation curves in combination with Student’s test. The duration of the phases varies from 20–25 years to many decades (for runoff in low-water seasons of the Volga and Don). For the Volga and Don, the phases of decreased runoff are generally longer than increased flow phases (this is especially true for low-water seasons). The identified contrast phases show a statistically significant difference between the annual and seasonal runoffs, which varies from 10 to 65%. In the phases of increased flow, high-water years occur much more often than low-water years, and vice versa. In the period of current climate warming (since 1981), the changes in annual runoff relative to the calculated runoff of the reference period (from the 1930s to 1980) are opposing, i.e., the runoff decreased in the Don and increased in the Volga, Yenisei, and Lena. In this case, the changes are most significant in the Don. In the period of current climate warming, both the winter and snow-melt flood runoff has increased only for the Lena. At the same time, the contributions of climatic and anthropogenic factors to the changes in runoff differ significantly for each of the rivers under study.