Low-water Season Research Articles

Seasonally flooded landscape connectivity and implications for fish in the Napo Moist Forest: A high-resolution mapping approach

The Amazon River Basin's fish diversity is shaped by its dynamic flood-pulse system, critical for hydrological and ecological connectivity. This study examines the Napo Moist Forest (NMF) ecoregion, mapping permanent and seasonally flooded areas from 2018 to 2021 using remote sensing and deep learning models. We aimed to map these areas at a high spatial resolution (10-m pixels) and analyse their role in maintaining lateral connectivity essential for fish diversity. Using synthetic aperture radar data from Sentinel-1 combined with deep learning algorithms, we produced high-accuracy flood maps to assess landscape connectivity between rivers and floodplains. Our methodology included creating a ground truth dataset with the Normalized Difference Water Index and integrating high-resolution optical data for model training, overcoming challenges of cloud coverage and dense vegetation. Our predictive model achieved high accuracy (mean pixel accuracy = 97 %) and consistently predicted 4801 km² of surface water, with only 3 % (130 km²) being seasonally flooded areas over four years. The Caquetá, Bajo Marañón, Napo, and Pastaza watersheds accounted for nearly 60 % of the flooded areas, highlighting their ecological importance. Connectivity analysis in three areas of interest within the NMF ecoregion revealed important seasonal and interannual fluctuations in hydrological connectivity due to changes in flooded patch characteristics. Reductions in the number and flooded patch area during low water seasons increased the distance between patches, leading to a disconnection between flooded areas, channels and rivers. Despite hydrological fluctuations, certain patches maintained consistent flooding, critical for lateral connectivity and sustaining aquatic biodiversity. These seasonally flooded areas act as connectors, influencing patch dynamics and connectivity with tributaries. Seasonal and interannual variations in hydrological connectivity are crucial for sustaining fish diversity. Conserving dynamic floodplains supports migratory fish life cycles and biodiversity. This study underscores the importance of high-resolution temporal and spatial data in conservation planning for aquatic ecosystems.

Comparative life-history strategies in three Lebiasinidae (Characiformes) in a Rio Negro tributary, Brazilian Amazon.

Reproductive traits co-evolve and form successful life-history strategies adapted to the biology and environment of a particular taxon, maximizing offspring and species survival chances, therefore studies investigating differences in adaptive traits across different environments can enhance our understanding of the natural selection process and evolution. Herein, we address whether the reproductive strategies of phylogenetically closely related fishes are influenced by habitat predictability, using three species of the Lebiasinidae family as models. The predominance of larger and mature individuals during the flood season, with high waters characterized by smaller immature individuals, suggests a seasonal reproductive strategy for Nannostomus trifasciatus. Copella callolepis, which inhabits both habitats, also showed a single reproductive peak. However, compared to N. trifasciatus, this species displayed late spawning, restricted to the flood season, as indicated by the higher abundance of larger and mature individuals during this period and the presence of smaller (juveniles) and spawned individuals in the following season. The reproductive tactics observed in N. marginatus differed significantly from the single reproductive peak of the other species, as two reproductive peaks were observed: one during the flood season and another during the low water season. In conclusion, our study demonstrates that the environment strongly influences reproductive strategies for lebiasinids. N. marginatus, restricted to small water bodies, exhibited an opportunistic reproductive strategy, whereas the species inhabiting main rivers, N. trifasciatus and C. callolepis, exhibited a more seasonal strategy.

Optimization of mine water discharge with the river hydrograph. Case study Samara River in Western Donbas

The paper deals with modeling salt transport in surface watercourses affected by mine water discharge taking into account the river hydrograph, hydrogeological, and climatic data. The developed model enables optimizing the discharge parameters; thus, minimizing the mineralization of river water throughout the year. As the case study, we considered the section of the Samara River in the Western Donbas where mine water is discharged from three storage ponds located in the ravines of Kosminna, Taranova, and Svidovok. Taking into account the pond capacities, it is proposed to discharge at least 60% of mine water from all ponds in December-April, with more than 88% of the most mineralized waters from the pond in the Svidovok ravine. The increase of the river water mineralization at the exit from the coal mining area does not exceed 0.22 g/dm3 on average per year, with a maximum of 0.36 g/dm3 during the low water season. The model novelty is coupling natural and man-made factors forming the water and salt balance in the surface watercourse throughout the year with the optimization methods. The proposed technique can be used to optimize the mode of mine water discharge.

Физико-географический контроль определения границ рек, их водоохранных зон, зон затопления и подтопления в Томской области (Российская Федерация)

Purpose: to develop the methodology of physical and geographical control of the validity of determining the boundaries of rivers and their special zones in the territory of Tomsk region. Materials and methods. The initial materials were the materials of the regime hydrological (Roshydromet) and hydrogeological (Gidrospetzgeology) observations, the results of engineering surveys and examinations. The main objects are the Tom river at Tomsk city, the Vasyugan river at New Vasyugan settlement, the Iksa river at Plotnikovo village, the Klyutch river at Polynyanka village. Additionally, data on the Ob and Parabel rivers and other tributaries of the Ob river were used. Results. The calculations of the position of the coastline and the boundaries of flood and underflooding zones of a number of river valleys in Tomsk region were carried out. A comparison of the characteristic levels of river waters with the hydrogeological, geomorphological and geobotanical conditions of river valleys (also underflooding conditions with the prevailing channel process types) was carried out. The physicogeographical methodology of validity control of estimating the coastline, protection, flooding and underflooding zones boundaries are proposed. Conclusions. It is shown that estimating the position of the river coastal line in Tomsk region can be carried out according to the data not only on the average daily water levels for the period of the free channel, but also the average monthly levels of river waters of the spring-summer flood and summer-autumn low water season. It was established that the average maximum level and the maximum level of 1 % occurrence relate to the relief, groundwater levels and the vegetation cover of the river valleys. It was revealed that the probability of the river valley underflooding increases in the case of floodplain anabranching and free meandering and decreases with the pre-dominance of limit meandering.

Subsistence strategies in the Inner Congo Basin since the 14th century AD: the faunal remains from Nkile and Bolondo (DR Congo)

The faunal remains are described from Nkile and Bolondo, two archaeological sites in the equatorial rainforest of the Democratic Republic of Congo. Both river-side settlements, located in the Ruki-Tshuapa basin and dating to between the 14th century to the second half of the 20th century, show a heavy reliance on aquatic food resources. The animal remains show that fishing was a major subsistence activity, whereas hunting, slaughtering of domestic stock and harvesting of molluscs were less frequent activities. The contribution to the diet of the different animal taxa suggested by the zooarchaeological data is in line with recently published stable isotope results obtained on humans and animals from Bolondo. The type of fish, and in particular their reconstructed sizes, show that the major exploited fishing grounds were shallow waters that became accessible during the low water seasons (nowadays July-August and a minor season in March at both sites). The proportions of the exploited fish taxa are comparable to those marketed nowadays in larger urban centres. Juvenile fish, and to some extent, small crocodiles, were heavily exploited but it is argued that at the time this was still a sustainable activity that did not deplete the fauna as much as today since human populations were smaller and the fishing gear less effective.

Detecting free-ranging river dolphin using deep learning based algorithms

Indus river dolphin is an endangered freshwater river dolphin and is included in IUCN red list of endangered species. Canal-strandings is one of the major issues that results in high mortality of the dolphin because the dolphins that are stranded into canals during flood season cannot return to the river during low-water season. As the dolphin uses high frequency echolocation clicks for navigation in muddy river waters, passive acoustic monitoring can be used for detection and localization of the dolphin and can assist in conservation efforts. In this context, we compare performance of variants of deep learning (LSTM) based event detection algorithms for dolphin click detection with conventional algorithms (such as the Teager Energy based click detection and Envelope Derivative Operator based click detection) and analyze the possible scenarios where machine learning based methods may assist in better performance by automatic detection of reflected clicks.

Evaluation of sediment phosphorus dynamics in cascade reservoir systems: A case study of Weiyuan River, China

Reservoirs tend to accumulate phosphorus (P) originating from agriculture, industry, and other upstream sources in sediment, with this stored P later released. However, the spatiotemporal dynamics of sediment P release in reservoirs remains unclear. This study investigated the spatiotemporal dynamics in P of the sediment and water of three cascade reservoirs in the Weiyuan River (Tuojiang tributary). The results showed elevated P in sediment [total P (TP): 1208.93 mg kg−1] and water (TP: 0.23 mg L−1) during the low-water season (LWS), which could be attributed to notably higher organic matter content (9.65%), finer particle size (20.95 μm), and extended hydraulic retention time (HRT: 13.13 days) downstream of the cascade reservoirs. Further study employing static in-situ diffusive gradient in thin films (DGT) and dynamic ex-situ adsorption kinetic experiments confirmed that the downstream release of P from sediments [diffusion flux (Fd): 1.67 mg m−2 d−1, equilibrium P concentrations (EPC0): 0.22 ± 0.10 mg L−1] greatly exceeded those upstream (−0.66 ± 0.17 mg m−2 d−1, 0.07 ± 0.001 mg L−1), Fe (II) was a critical factor in regulating sedimentary P release. The combined effects of high P in overlying water and sediment significantly stimulated downstream phytoplankton growth, particularly among cyanobacteria (26.48%) and green algae (8.33%). Further regulatory steps are needed to regulate LWS algal blooms downstream of cascade reservoirs.

Flood pulses and fish species coexistence in tropical rivers - a theoretical food web model

AbstractFreshwater fish diversity reaches its zenith in large tropical rivers. Although the origins of this diversity have been relatively well studied, the mechanisms that maintain high fish diversity in tropical rivers remain largely unknown. It has been hypothesized that the annual flood pulse, a perennial feature of many lowland rivers in the tropics, reduces competitive exclusion and consequently promotes species coexistence. During the high-water season, superabundant allochthonous resources and relatively low fish density may reduce intra- and interspecific competition. During the low-water season on the other hand, resource availability is low and predation pressure high, offsetting competitive differences between species and controlling fish population sizes. Here, we tested the potential role of these mechanisms for species coexistence using a food web model where fish species exhibit strong differences in competition strength and compete for finite resources. We simulated fish interactions when a regular flood pulse was either present or absent. We found that extinction rates in the simulations without an annual flood pulse were consistently higher when compared to those with a flood pulse, indicating more species could coexist when a regular annual flood pulse is present. If the flood pulse is a relevant mechanism for fish species coexistence, as our model results suggest, then flood pulse changes could result in species extinctions and lower fish diversity. Deforestation, climate change, and the construction of large hydropower dams are current drivers of hydrological change across the tropics, increasing the urgency to understand the role of natural flooding regimes for the maintenance of tropical freshwater fish diversity.

Anthropogenic factors do not affect male or female jaguar habitat use in an Amazonian Sustainable Reserve

Conservation actions should account for species natural history and behavior related to differences between sexes. However, most studies have not taken into consideration non-independence of observations from the same individual. We used data from camera-trap surveys undertaken over six consecutive years to investigate habitat use by jaguar (Panthera onca) in varzea seasonally flooded forest. We used hierarchical modeling to assess sex differences in occurrence probability related to environmental factors, while accounting for individual and spatial autocorrelation. Specifically, we tested whether male and female jaguars responded differently to habitat type and anthropogenic influence. Our results do not support previous conclusions related to differences between sexes and indicate that, in the studied area, jaguars are habitat generalists, exploring all environments with similar probability during the low-water season. Human settlements also apparently have little effect on habitat use by jaguars in this area. The lack of avoidance of settlements might be due to the low levels of anthropogenic pressure in the area, which adds support to the effectiveness of sustainable-development reserves. The difference between our results and previous studies may be due to the fact that we took into account individual differences, or may be related to the unique environmental characteristics of the varzea of Mamirauá Sustainable Development Reserve in Central Amazonia.

Water Flow Changes In The Don River (European Russia) During 1891–2019

The Don River Long near Razdorskaya Village had long phases (lasting 33–86 years) of increased/decreased naturalized annual and seasonal water flow, and their properties for 1891–2019 were identified. Long-term changes in the annual and snow-melt flood flow occurred in the opposite phase relative to changes in the winter and summer-autumn flow. Annual hydrographs in the phase of decreased flow were characterized by an increase in water discharge during the low-water seasons of the year, but a noticeable decrease in daily flood water discharge and maximum water discharge. The share of high-water years (years with a flow exceedance probability equal to or less than 25%) in the phase of increased flow is significantly higher than the share of low-water years (years with a flow exceedance probability equal to or more than 75%). And on the contrary. At the same time the cumulative share of low- and high-water years remains relatively stable. The total changes in the annual and seasonal flow, caused by both anthropogenic and climatic factors, throughout the entire period of modern global warming (since 1989) consisted in a decrease of the annual and snow-melt flood flow and an increase of flow values during low-water seasons.

Extreme Low Flow during Long-Lasting Phases of River Runoff in the Central Part of the East European Plain

In the rivers of the central part of the East European Plain (the Volga at Staritsa, the Oka at Kaluga, and the Don at Stanitsa Kazanskaya), long phases (10–15 years or more) of increased/decreased annual and seasonal runoff have occurred, as well as differences in the frequencies of extremely low flow conditions from the late 19th century to 2020. Phase boundaries were identified by cumulative deviation curves and statistical homogeneity. The frequencies of specific water flow values were estimated using the empirical curves of the exceedance probability of annual and seasonal water flows based on their long-term time series. In the century-long changes of rivers considered, two long contrasting phases were revealed. These phases are characterized by increased and decreased runoff of hydrological seasons. Near simultaneously, a phase of increased runoff was first observed for the freshet season. On the contrary, phases of decreased runoff were first observed for low-water seasons. The runoff phases differ significantly in duration and differences in flow. Significant differences were revealed in the frequency of low-water years for a low runoff with an exceedance probability above or equal to 75% and above or equal to 95%.

Food web structure in the Xingu River rapids prior to operation of the Amazon’s largest hydropower plant

The results of recent theoretical studies suggest that food webs are size-structured, with top predators coupling across different energy sources. However, evidence supporting this hypothesis is still scarce, especially in highly diverse tropical rivers. In the present study, we explored the association between body size, trophic position, and the use of allochthonous and autochthonous basal production sources in the Volta Grande rapids of the Xingu River, a major clearwater tributary of the Amazon River, during the period prior to operation of the Belo Monte Hydropower Plant (BMHP). This section of the river contains a maze of channels with rocky shoals that support dozens of endemic fishes, mollusks and other aquatic taxa that may be impacted by flow regulation by the Pimental Dam located upstream. During the low-water season, we surveyed fish, crustaceans, mollusks, sponges, aquatic and terrestrial insects, zooplankton, and basal production sources to obtain tissue samples for analysis of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N). The results indicated that the biomass of most aquatic organisms appears to be largely supported by riparian vegetation, highlighting the importance of the lateral connectivity between aquatic and terrestrial habitats. In contrast to expectation, we did not observe a gradual increase in the coupling of energy pathways with increasing body size and trophic position. These findings provide a baseline for the trophic ecology of this river under the natural flow regime that can be used for future impact assessments, and they also indicate that more complex food web models, potentially including additional functional traits (e.g., gut length) are needed to describe resource and habitat use in highly diverse tropical ecosystems.

Distribution and encounter rates of the river dolphin (Inia geoffrensis boliviensis) in the central Bolivian Amazon

The ecology and conservation status of river dolphins (Inia sp.) distributed in the lowland rivers of Bolivia are poorly understood and only recently have basic studies been conducted to investigate their population size, taxonomic status, distribution, behaviour, environmental threats and ecology in this region. This paper examines the distribution and encounter rates of the bufeo (Inia sp.) in the middle reach of the Bolivian Amazon and was conducted in the Mamoré River and four of its tributaries during the low water season. Methods were employed which can be replicated during future surveys of Bolivian river dolphins and the results can be compared with those from surveys of Inia throughout its range. Sixty-two hours were spent surveying for dolphins, with 68% of the effort in Mamoré River and 32% in its tributaries. The Inia encounter rates reported here (1.6-5.8 dolphins km21) are the highest recorded anywhere in its broad geographic range; and indicate the importance of continuing and expanding surveys in this area. The mean group size was greatest in the Tijamuchi River (3.3±2.96) and smallest in the Yacuma River (1.8±0.75) and the maximum group size was 14. The high bufeo encounter rates in the central Bolivian Amazon can be taken as a reflection of the general environmental status of the region; however, a growing human population, associated with an increase in boat traffic and fishing activity, poses a future threat to bufeos and their aquatic habitats.

Isotope geochemistry as a natural tag of fish in Patagonian freshwater environments: The invasive Chinook salmon case

Patagonian aquatic environments have been invaded since the end of the last century by different species of salmonids. Knowing the natal origin and homing/straying rate of the salmonids in colonised environments is essential to understanding the dispersal mechanisms and developing management plans. In the last two decades, Chinook salmon Oncorhynchus tshawytscha showed the greatest natural dispersal capacity in Patagonia. The main goal of this study was to evaluate the environmental strontium isotope ratio (87Sr/86Sr) as a potential natural tag to infer the natal origin and ontogenetic habitat use of salmonids in Patagonia, specifically Chinook salmon. 87Sr/86Sr ratio was determined in water samples from 26 sites distributed in 14 Atlantic and Pacific basins in low and high water seasons. Environmental 87Sr/86Sr showed greater spatial than temporal variation, revealing great potential as a tool to infer the natal origin and life history of several migratory fish species in Patagonia. Otolith core-to-edge 87Sr/86Sr profiles were also analysed in 108 Chinook salmon from six basins. A cluster analysis based on the Unweighted Pair Group method (UPGMA) and Euclidean distances without prior classification grouped the sampled rivers into five main groups with significantly different (p < 0.05) isotopic ratios, sometimes integrated basins with different slopes (Atlantic or Pacific). The cluster analysis based on the natal 87Sr/86Sr period in otolith (∼natal origin) showed clear segregation between the Atlantic and Pacific samples. A mismatch between water and otolith natal 87Sr/86Sr ratio was detected in some Atlantic basins (e.g. De las Vueltas River in Santa Cruz Basin) and Pacific (e.g. Liquiñe Basin) and, which could be explained either by straying behaviours or by large geochemical variability between tributaries, within river systems. Our results showed that 87Sr/86Sr is a useful natural tag to trace the life history of migratory fishes in Patagonia, especially for invasive species such as Chinook salmon.

Seasonal flooding decreases fruit-feeding butterfly species dominance and increases spatial turnover in floodplain forests of central Amazonia.

The seasonal flood pulse in Amazonia can be considered a primary driver of community structure in floodplain environments. Although this natural periodic disturbance is part of the landscape dynamics, the seasonal inundation presents a considerable challenge to organisms that inhabit floodplain forests. The present study investigated the effect of seasonal flooding on fruit-feeding butterfly assemblages in different forest types and strata in central Amazonia. We sampled fruit-feeding butterflies in the canopy and the understory using baited traps in adjacent upland (unflooded forests-terra firme), white and blackwater floodplain forests (várzea and igapó, respectively) during the low- and high-water seasons. Butterfly abundance decreased in the high-water season, especially of dominant species in várzea, but the number of species was similar between seasons in the three forest types. Species composition differed between strata in all forest types. However, the flood pulse only affected butterfly assemblages in várzea forest. The β-diversity components also differed only in várzea. Species replacement (turnover) dominated the spatial β-diversity in igapó and terra firme in both seasons and várzea in the high-water season. Nonetheless, nestedness was relatively higher in várzea forests during the low-water season, mainly due to the effect of dominant species. These results emphasize the importance of seasonal flooding to structure butterfly assemblages in floodplain forests and reveal the idiosyncrasy of butterfly community responses to flooding in different forest types. Our results also suggest that any major and rapid changes to the hydrological regime could severely affect floodplain communities adapted to this natural seasonal hydrological cycle, threatening the existence of these unique environments.

Current State of Flooding and Water Quality of Nokoue Lake in Benin (Ouest Africa)

A thorough literature review was conducted in order to discover the previous studies that have been done in relation to the problems of flooding and water pollution of Nokoue lake (Benin, West Africa), to identify the limitations of these previous studies, to draw lessons in order to propose how to overcome them. This bibliographic synthesis has shown that previous studies related to the flooding issue have focused on the dynamics of understanding the genesis of flooding. These studies range from the oldest conducted in 1979 to the most recent conducted in 2016. The major results of these studies in relation to floods are hydrodynamic techniques allowing to evaluate in a punctual way the hydrological regime of the Nokoue lake. In other words, they are solutions allowing to reconstitute the floods generated by the river waters. It appeared that these results of flood reconstitution are difficult to generalize because of the complexity of the hydrographic network of Nokoue lake. The hydrodynamics of Nokoue lake is influenced differently by its main water tributaries (the Sô River, the Ouémé River, the Porto Novo Lagoon and the Atlantic Ocean). Therefore, a decision-making issue on planning and flood management must be motivated by a decision support tool. It is moreover recommended in these studies the resumption of the process of hydraulic techniques periodically during the period of high water in order to take advantage of the hydrological behavior of Nokoue lake in terms of overflow which are at the origin of the floods. The need for innovative decision-making solutions on flood planning and management in order to reduce disasters is still a priority for decision-makers. These innovative solutions are undoubtedly the flood forecasting. On the water quality of Nokoue lake, the oldest study conducted dates back to 1987 and the most recent one in 2018. In these studies, water quality is evaluated in two seasons: the low water season (December to mid-May) and the high-water season. It was found that the salinity of the lake increased significantly with an average of 16 ppt during the low water period while during the high-water period, freshwater inflows from the tributaries invaded the lake and prevented water from the Atlantic Ocean from entering. The concentrations of inorganic nutrients in the lake increase from low water to high water. However, the quantification to date of nutrient loads from external sources as well as internal sources to the lake have not been quantified. This implies that further research on the water quality of the lake could be conducted. Prevention actions should consider a predictive monitoring of the water quality index of Nokoue lake.

Sedimentation and Erosion Patterns of the Lena River Anabranching Channel

Lena River is one of the largest “pristine” undammed river systems in the World. In the middle and low (including delta) 1500 km course of the Lena main stem river forms complex anabranching patterns which are affected by continuous permafrost, degradation of the frozen ground and changes in vegetation (taiga and tundra). This study provides a high-resolution assessment of sediment behavior along this reach. Comprehensive hydrological field studies along the anabranching channel located in the middle, low and delta courses of the Lena River were performed from 2016 to 2022 including acoustic Doppler current profiler (ADCP) discharge measurements and sediment transport estimates by gravimetric analyses of sediment concentration data and surrogate measurements (optical by turbidity meters and acoustic by ADCP techniques). These data were used to construct regional relationships between suspended sediment concentrations (SSC, mg/L), turbidity (T, NTU) and backscatter intensity (BI, dB) values applicable for the conditions of the Lena River. Further, field data sets were used to calibrate the seasonal relationships between Landsat reflectance intensities and field surface sediment concentration data. Robust empirical models were derived between the field surface sediment concentration and surface reflectance data for various hydrological seasons. Based on the integration of in situ monitoring and remote sensing data we revealed significant discrepancies in the spatial and seasonal patterns of the suspended sediment transport between various anabranching reaches of the river system. In the middle course of the Lena River, due to inundation of vegetated banks and islands, a downward decrease in sediment concentrations is observed along the anabranching channel during peak flows. Bed and lateral scour during low water seasons effects average increase in sediment load along the anabranching channels, even though a significant (up to 30%) decline in SSC occurs within the particular reaches of the main channel. Deposition patterns are typical for the secondary channels. The anabranching channel that was influenced by the largest tributaries (Aldan and Viluy) is characterized by the sediment plumes which dominate the spatial and temporal sediment distribution. Finally, in the distributary system of the Lena delta, sediment transport is mostly increased downwards, predominantly under higher discharges and along main distributary channels due to permafrost-dominated bank degradation.

Detection and genetic analysis of Escherichia coli from Tonle Sap Lake and its tributaries in Cambodia: Spatial distribution, seasonal variation, pathogenicity, and antimicrobial resistance

As an indicator of fecal contamination, Escherichia coli was monitored in Tonle Sap Lake, Cambodia, and its tributaries during low- and high-water seasons, focusing on the impacts on floating villagers inhabiting boathouses. E. coli concentrations in the floating villages (3.6 × 103 and 5.7 × 103 CFU/100 mL during the low- and high-water seasons, respectively) were significantly higher than those in other lake sites (4.0 × 101 and 7.0 × 100 CFU/100 mL during the low- and high-water seasons, respectively) and rivers (3.3 × 102 and 8.9 × 102 CFU/100 mL during the low- and high-water seasons, respectively), most likely because fecal materials from the boathouses were discharged without treatment. At most of the lake sampling sites remote from the boathouses, the E. coli concentration was lower during the high-water season than that during the low-water season, due to dilution by lake water. E. coli colonies detected during monitoring were isolated for pathotyping, antimicrobial susceptibility testing, beta-lactamase gene detection, and multilocus sequencing typing (MLST). Of the 659 E. coli isolates, 101 (15.3%) were diarrheagenic E. coli (DEC). The prevalence of DEC (52.2%) in the floating villages during the low-water season was higher than that during the high-water season (4.2%) and that in other sites during both seasons (10.6–21.3%). The DEC isolates from the floating villages during the low-water season showed high antimicrobial resistance, including ampicillin (83.4%) and ciprofloxacin (83.4%), and frequently possessed a beta-lactamase gene (blaTEM) (83.4%). MLST analysis indicated that the predominant sequence type (ST) of DEC isolates from the floating villages possibly originated from humans, whereas more diverse STs were detected in isolates from other sites. We revealed the wide presence of diarrheagenic and antimicrobial-resistant E. coli in Tonle Sap Lake and identified a considerable infection risk in floating villages, especially during the low-water season.

Initial recovery of fish faunas following the implementation of pen-culture and fishing bans in floodplain lakes along the Yangtze River

Given the decline of natural fish abundance and diversity, a ban on pen-culture and fishing has been imposed on floodplain lakes along the Yangtze River. In order to examine the recovery efficiency of fish faunas, we compared the changes in multidimensional (α and β) diversity in the Shengjin Lake between pen-culture stage (PS) and recovery stage (RS). Our results demonstrated significant variations in fish community composition, with distinct populational restoration in wild species of high trophic level and river-lake migratory species. The higher abundance of wild and migratory species in RS implied the enhanced dispersal and exchange process of fish individuals with the elimination of net pens. Despite significant variations of community composition, the α and β diversity indices exhibited non-significant change between PS and RS. However, our study still revealed the recovery of natural seasonal community dynamics, since there were significant variations of both α and β diversity between high-water (HW) and low-water (LW) seasons in RS. The significant higher α diversity (S, d, H′) in HW indicated flooding induced fish supplements in floodplain lakes, due to the well-developed breeding sites, nurseries and refuges provided by floodplain lakes. Meanwhile, the significant lower βSOR and βSIM in HW implied the homogenized communities during flooding seasons, which can be ascribed to better hydrological connectivity of various habitats and more even distribution of fish faunas triggered by flood pulses. The reappearance of natural seasonal variations in multidimensional (α and β) diversity indicate the initial recovery of fish faunas. There is a pressing need for prolonged surveillance to explore the recovery mechanism of fish assemblage. Meanwhile, our results also highlight the importance of conserving the lacustrine connectivity and seasonal flooding for the recovery of fishery resources in the floodplain lakes.

Лесопригодность экотопов Волго-Ахтубинской поймы для культур сосны

In the south of European Russia, the largest sand massifs are found in the zone of dry steppes and semi-deserts. Effective utilization of such lands requires creation of protective forest planting of drought-resistant coniferous species like Scots pine and Crimean pine. The productivity and longevity of such stands vary widely over the territory and depends on the presence of additional to atmospheric precipitation water supply and the root layer mineral supply. In this regard, sand massifs of steppificated river valleys composed of multiphase or single-phase polymineral rocks are of particular interest for afforestation. One of the most important objects of afforestation is the Northern (within the Volgograd region) highest and most drained part of the Volga-Akhtuba floodplain. Volga River damming by the Volga Hydroelectric Station (Volga GES) led to a restructuring of surface and ground water regimes, formation of new conditions of water and mineral nutrition and changes in other important factors of forest ecosystems in the area. The research aims at developing a classification of the Volga-Akhtuba floodplain ecotopes by water-mineral nutrition conditions, cultivation, expected productivity and longevity of pine plantings. We studied relationships of growth parameters of Pinus silvestris L. stands with soil-ground and hydrological conditions in different ecotopes of the large hilly and transitional floodplains after the Volga River damming by the Volga GES. Dynamics patterns of this relationship were revealed. It was found that in the northern part of the Volga-Akhtuba valley (approximately up to the Kapustin Yar – Kamenny Yar line) with increasing stratification, heavier granulometric composition of the root layer to sandy loam layer, lowering the surface level at a small distance from the drainage channel moisture supply and growth of Scots pine plantations improve, forest suitability of ecotopes increases. There is a risk of early decay and death of high-density pine forests in periods of low water and dry years on soils underlain by thick loams. Three groups of ecotope forest suitability were identified according to these indicators, as well as the conditions for the creation of forest plantations, productivity and longevity of plantings. The least favorable ecotopes are in the highlands of the hilly and transitional floodplains with minor soils of different composition on single-phase open-textured sands with deep (more than 4–5 m) groundwater table during low-water season. The most favorable are welldrained areas of the transitional floodplain with light soils on thick stratified predominantly sandy loam sediments, as well as on sands with close to the surface groundwater occurrence. Average ecotopes in terms of conditions are poorly drained areas of the transitional floodplain with minor sandy loam and loamy soils on deep loams.