Low-water Season Research Articles

Plastic contamination in fish digestive tracts in Amazonian rivers during a period of extreme low water.

Microplastics (MPs) are frequently detected in the gastrointestinal tracts of aquatic organisms worldwide. We studied the contamination with plastic in an aquatic environment and in the gastrointestinal tracts of fish in two Amazonian rivers waters, Rio Negro and Rio Solimões. The research was conducted in November/December 2023 during the low water season in a year of drastically decreased water level. We evaluated the abundance, shape, type, size as well as polymer type of the MPs and compared the contamination between fish species and feeding types. The amounts of MPs in the water were 0.25 ± 0.05 and 0.78 ± 0.19 pcs/L in the Prato canal and Vila do Janauacá, respectively. In total, 128 fish individuals belonging to different feeding types (piscivorous, planktivorous, herbivorous, invertivorous, detritivorous, omnivorous) were analysed in this study, with 84.0% and 87.4% of fish containing MPs caught from the Prato canal and Vila do Janauacá, respectively. We found no statistical relationship between the length/weight of the fish and the amount of MPs or the sizes of the plastic parts. MPs with dimensions of 0.04-5.0 mm were found in the digestive tracts of fish. There was an average of 3.3 ± 2.9 and 2.8 ± 2.1 plastic particles per fish in the study sites of the Prato canal and Vila do Janauacá, respectively. There was a statistical difference in the size of the MPs between the river sites that was correspondingly reflected in fish. In the digestive tracts of Solimões fish, plastics were on average larger than in the Rio Negro study site. At the Vila do Janauacá study site, predatory fish had the most MPs in their digestive system, while in the Prato canal, plankton-eating fish had the most MPs. Regarding the shape of MPs ingested by fishes, most were filaments, followed by fragments. The majority of the fibres were determined to be polyamide (nylon), polyethylene terephthalate and polypropylene. Our results indicate that even the remote aquatic environments may be impacted with intensive MP infestation. At the same time, with higher rainfall and higher water levels, a higher concentration of MPs is expected and this, in turn, can lead to greater contamination of fish with MPs. It has been observed that when water has a higher plastic content, more MPs end up in fish, especially in visual foragers.

Exploring the Bacteriome Diversity and Use as a Proxy for Climate Change and Human Impacts on Groundwater in Temperate and Tropical Countries

This research investigates bacterial communities in various cave pool water and substrates from Brazil and Romania for their use as indicators of environmental impacts on groundwater. Regional and seasonal differences were observed even if, at the phylum level, common bacteria for both countries were found. Distinct patterns emerged at the genus level due to the different climates (tropical vs. temperate) and ecosystems. Chemoautotrophic conditions define an utterly different groundwater bacteriome than oligotrophic conditions independent of the temperature. Bacteria as a proxy for climate change were explored using seasonal changes in Romanian caves; specific genera become dominant in summer months, such as Acinetobacter, Paeniglutamicibacter, Polaromonas, and Saccharimonadales, indicating processes that occur during the low-water season. Climate change, particularly dryness, is expected to exacerbate these variations, threatening the stability of groundwater ecosystems. The research also identified anthropic pollution indicators (Vogesella, Cutibacterium) and potential decontaminants (Bacillus) in Brazilian cave waters. Anthropic pollution indicators, like Pseudoarthrobacter. were also found in Romanian caves. Other key bacteria genera, such as Flavobacterium, Pseudomonas, and Acinetobacter, are chemolithotrophs or involved in the nitrogen cycle, which is critical in supplying nutrients for the cave food web. Marked differences between water and substrate microbiomes within the same pools suggested that substrates may play a crucial, underexplored role in groundwater ecosystem processes. Our study found unassigned taxa, 3 phyla, 2 families, and 832 genera (> 40%) in the studied pools. The results underscore the need to further explore groundwater microbiomes as potentially crucial yet fragile ecosystems in the face of climate change and human impacts.

How do extreme fluctuations in water level affect fish condition in Amazonian Floodplain Lakes?

The annual flood pulse is a defining feature of Amazonian floodplain lakes, creating a highly variable environment that influences resource availability, such as food and habitat. These cyclical changes necessitate a high degree of adaptability among fish species, many of which have evolved specialized strategies to cope with the fluctuating conditions. In 2023, the Amazon basin experienced a record-breaking drought event, leading to mass mortality of Amazonian fish and other wildlife. This study examines the effect of this extreme event on fish condition in white-water (Rio Solimões basin) and black-water (Rio Negro basin) floodplain lakes. These contrasting environments provide a unique opportunity to study how different water qualities and extreme water-level fluctuations impact fish condition. Research was conducted during the normal low-water period in November 2019 and the drastically decreased water levels in November 2023. The main objective was to understand how extreme water-level fluctuations affect fish health and nutritional status. A total of 585 fishes were analyzed, with 294 from white-water and 291 from black-water, representing different feeding types to provide a comprehensive picture of changes in fish condition. Water-level changes had a statistically significant impact on fish condition in both areas. Comparing low-water and extreme low-water levels, fish condition was consistently higher during the normal low-water period. The linear mixed-effects model revealed that the intensity of the low-water season had a significant effect on fish length-adjusted mass, suggesting that the decrease in water level is associated with an overall decrease in fish length-adjusted mass. When comparing the mean water-level effect (Glass's Δ) between low-water and extreme low-water levels, we found a bigger effect in the black-water system than in the white-water system. This difference may be attributed to the lower nutrient content and higher levels of humic acids and refractory dissolved organic matter in black-water, which can further limit primary productivity and food availability for fishes.

Geoenvironmental specifics in the microtidal mouths of small rivers with deltas in the Russian Arctic Zone during the summer-fall low water season by the example of the Kad River mouth, the White Sea

The hydrological, hydrochemical and hydrobiological conditions of the Kad River mouth are considered that flows to the Sukhoe More lagoon, the Dvina Bay, the White Sea. It is revealed that suspension sedimentation is most developed in the river delta and on its shallow estuarine seashore. Extensive thickets of halophytes are formed in these areas, and the maximum accumulation of heavy metals is noted in bottom sediments. Manganese, zinc and nickel show the highest concentrations in the bottom sediments within the Kadi River mouth. A similar pattern is observed for the snow cover pollution in the considered area (the southwestern part of the Belomorsko-Kuloiskoe plateau). This indicates a significant contribution of snow to the heavy metal accumulation in the estuary area of the Kadi River and the adjacent section of the Sukhoe More lagoon. Perhaps this situation is typical for the river mouths in the Arctic zone. Under the observed climate warming, the processes noted in the Kadi River mouth suggest that they will lead to waterlogging and a reducing the lagoon area in the micro-tidal estuaries of the rivers of the Arctic seas. They will accumulate suspended material carried out with river runoff during the destruction of permafrost soils. It can contain both biogenic substances that contribute to an increase in the trophic capacity of estuarine ecosystems, and toxic substances that limit their development. At the same time, marginal filters of the estuaries of the rivers in the Arctic islands will increase their spatial extent within the lagoons, primarily due to coagulation-sorption and biological stages.

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

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

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.

Spatial Distribution of Nutrients and Risk of Eutrophication of Lake Tengrela In the Municipality of Banfora In Burkina Faso

The study characterises the spatial distribution of a selection of nutrients from the literature review. A relationship is also established between the selected nutrients and chlorophyll a, which is characteristic of the trophic level of a water body. We used data from water withdrawals during the high and low water seasons, linked to specific coordinates, but also surveys of 36 producers around the shores of the lake. Our results show different levels of nutrients in the water body, modelled according to the lake's right of way. The spatial distribution of aquatic species is also disparate, as they are strongly correlated with these nutrients, and the distribution of nutrients in the water body depends on seasonality and parameters and the presence of macrophytes according to the presence of nutrients. As for the farmers, 100% of them use chemical fertilisers and organic manure in their production. These practices increase the presence of nutrients in the water body. Our results confirm the fact that the spatial analysis of the distribution of nutrients in the water body is, on the one hand, strongly linked to the agricultural activities around the shores of the lake and that they have an impact on the health of the lake. This analysis will make it possible to understand and know the most influential and problematic nutrient for the proper management of this water body.

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

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

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

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

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

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

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.