Xingu River Research Articles

Physicochemical and ecosystem properties of the Middle to Lower Xingu River, Brazil, prior to the operation of the Belo Monte Dam Complex

Physicochemical and ecosystem properties of the Middle to Lower Xingu River, Brazil, prior to the operation of the Belo Monte Dam Complex

A new species of Hypancistrus Isbrücker & Nijssen 1991 (Loricariidae, Siluriformes) from the rapids of the middle Rio Tocantins.

The Hypancistrus genus is recognized in the Río Orinoco basin and Rio Xingu in the Guiana and Brazilian Shields, respectively. Some of its species are important in ornamental fishing. Despite this significance, many other undescribed species are still awaiting to be named. Here we describe a new species of Hypancistrus found on bedrock in the Rio Tocantins, representing an extension of the distribution of the genus. Also, a multigene phylogeny is presented to evaluate the taxonomic position of this species concerning congeners. The new species differs from all congeners by (1) hypertrophied odontodes on cheeks reaching beyond the cleithrum, (2) a supraoccipital crest conspicuously elevated, (3) a supraorbital crest slightly convex, (4) oblique bars on the anterior part of the body, (5) a dark E-shaped mark on the snout, (6) three oblique dark bars on the anterior part of the body and horizontal vermicular bars from the pectoral girdle to the posterior insertion of the dorsal fin, (7) a thin light gray bar on the posterior of the head extending across the branchial opening, (8) a tan background color, (9) a developed suspensorium with a diminished appendix in the metapterygoid, and (10) a dentary plate robust significantly fused with the angulo-articular bone. The molecular phylogenetic results show the new species forming a group with Hypancistrus zebra (Brazilian Shield-Rio Xingu) as a clade, a sister group of a monophyletic group consisting of all congeners from the Río Orinoco.

Geochemical Dynamics and Evolutionary Implications of Sediments at the Xingu–Amazon Rivers’ Confluence: Proxies for Mixing, Mobility and Weathering

This study investigates the geochemical characteristics and evolutionary implications of sediments at the confluence of the Xingu and Amazon Rivers. The main objective is to understand sediment mixing, mobility, and weathering processes through geochemical proxies. Samples were collected from various sections of the lower Xingu River, focusing on its interaction with the Amazon River. Analytical techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP-MS) were employed to analyze major and trace elements. The results reveal significant spatial variations in mineralogical and textural patterns, with sediments forming distinct groupings based on their location. The data suggest that the lower Xingu River is strongly influenced by sediment inputs from the Amazon River, particularly affecting sediment composition and chemical weathering processes. This research highlights the critical interactions between river systems and their implications for the evolution of the Amazon basin, especially regarding sediment contributions from various geological sources. Even though the Xingu River drains cratonic regions at higher elevations, the geochemistry of the bottom sediments confirms that the bedload is derived from heterogeneous sources with primarily intermediate igneous compositions and has undergone substantial recycling during river transport.

Use of long-term underwater camera surveillance to assess the effects of the largest Amazonian hydroelectric dam on fish communities

The increase in the construction of mega dams in tropical basins is considered a threat to freshwater fish diversity. Although difficult to detect in conventional monitoring programs, rheophilic species and those reliant on shallow habitats comprise a large proportion of fish diversity in tropical basins and are among the most sensitive species to hydropower impacts. We used Baited Remote Underwater Video (BRUV), an innovative, non-invasive sampling technique, to record the impacts caused by Belo Monte, the third largest hydropower project in the world, on fishes inhabiting fast waters in the Xingu River. BRUV were set in a river stretch of ~ 240 km for 7 years, 2 before and 5 after the Belo Monte operation. We explored the spatial and temporal variation in fish diversity (α, β, and γ) and abundance (MaxN) using generalized additive models. We also investigated the variation of environmental variables and tested how much information we gained by including them in the diversity and abundance models. Belo Monte altered the flow regime, water characteristics, and fishery yield in the Xingu, resulting in changes in the fish community structure. Temporally, we observed sharp declines in α diversity and abundance, far exceeding those from a previous study conducted with more conventional sampling methods (i.e., catch-based) in the region. γ-diversity was also significantly reduced, but we observed a non-expected increase in β diversity over time. The latter may be associated with a reduction in river connectivity and an increase in environmental heterogeneity among river sectors. Unexpected signs of recovery in diversity metrics were observed in the last years of monitoring, which may be associated with the maintenance of flow levels higher than those previously planned. These results showed that BRUV can be a useful and sensitive tool to monitor the impacts of dams and other enterprises on fish fauna from clear-water rivers. Moreover, this study enhances our comprehension of the temporal variations in freshwater fish diversity metrics and discusses the prevalent assumption that a linear continuum in fish-structure damage associated with dam impoundments may exhibit temporal non-linearity.

Integrative taxonomy reveals a new species of Characidium (Characiformes: Crenuchidae) shared by tributaries of upper Tapajós and Xingu river basins, Brazil

AbstractA new species of Characidium shared by adjacent tributaries of the upper portions of the Tapajós and Xingu river basins is described. Characidium varii, new species, can be distinguished from the congeners by having distinctly speckled pattern of colouration, including dark blotches on cheek and ventral surface of head, by having conspicuous dark marks on fins, along with a single row of dentary teeth, isthmus completely covered by scales, 14 circumpeduncular scales, and swimbladder reduced. Molecular data reinforce the validation of the new species. The distribution of C. varii supports the hypothesis of the existence of a faunistic mixing between Tapajós and Xingu river basins, corresponding to the region of the Serra do Cachimbo and surrounding areas, previously proposed in the literature.

Effect of Stocking Density on the Growth of the Endangered Amazonian Fish Hypancistrus zebra (Siluriformes: Loricariidae)

ABSTRACTStocking density has a significant influence on animal homeostasis, and so is a crucial factor in the management of organisms in captivity and an important role in ex situ conservation of endangered species. Hypancistrus zebra is an endemic fish species from the Xingu River, Brazil—considered Critically Endangered since the early 2000s due to fishing pressure and, more recently, due to habitat changes resulting from the construction of the Belo Monte Hydroelectric Dam. The implementation of appropriate management in captivity is of utmost importance for its conservation, particularly in enhancing ex situ breeding techniques. This study aimed to evaluate the growth of juvenile H. zebra in aquaria with three different stocking density levels. The juveniles were distributed between three treatments, each with three replicates. We found no correlation between biomass and aquarium volume. The highest correlation coefficients were found between growth rates and densities related to the number of individuals per shelter area. Mortality rate was directly related to the initial number of fish in the aquariums, with larger populations showing higher mortality rates. The treatment with lower stocking density displayed the highest growth rate, while the treatment with higher density had the lowest growth rate, with a 23.38% difference between them.

Rainfall analysis in Xingu River Basin based on the 1981-2020 timeframe

It is essential understanding the incidence of hydrometeorological variables in each river basin to help planning actions focused on guaranteeing multiple water uses, environmental preservation and prevention measures taken against extreme events. The aim of the current study is to investigate rainfall trends in Xingu River Hydrographic Basin (XRHB) from 1981 to 2020. Data propensity analysis was carried out based on the Mann-Kendall methods, on five-year moving average graph, as well as on variations in Climatological Normals (CN) recorded from 1981 to 2010 and from 1991 to 2020. Moreover, the Log-Normal theoretical distribution was adjusted to show mean rainfall predictions within 10-to-100-year return time (Rt). It was done by applying the Kolmogorov-Smirnov (KS), Chi-Square (?2), Filliben (Fi) and Anderson-Darling (AD) tests. Results have evidenced historical series with no trend and minimal variation (-0.5%) between the two CN intervals. Estimates within a 10-to-100-year RT scenario have evidenced rainfall rates higher than the historical average (HA) ranging from 10.0% to 20.0%. Thus, XRHB is a promising scenario for water security planning purposes, since it meets the fundamentals of Brazilian environmental and water resources laws, as well as target 6.5 of Sustainable Development Goal 6 (SDG 6 - UN), which deals with implementing integrated water-resources management at global level.

Mercury Dynamics and Bioaccumulation Risk Assessment in Three Gold Mining-Impacted Amazon River Basins.

Mercury contamination from gold mining in the Amazon poses significant environmental and health threats to the biome and its local populations. The recent expansion of non-industrial mining areas has severely impacted territories occupied by traditional communities. To address the lack of sampling data in the region and better understand mercury dynamics, this study used the probabilistic model SERAFM to estimate the mercury distribution and bioaccumulation in fish. The analysis covered 8,259 sub-basins across three major Amazonian basins: the Branco, Tapajós and Xingu rivers. The findings revealed increasing downstream mercury levels, with notable accumulations in the main watercourses influenced by methylation processes and mining releases. The projected concentrations showed that an average of 27.47% of the sub-basins might not comply with Brazilian regulations, rising to 52.38% in the Branco and Tapajós river basins separately. The risk assessment of fish consumption based on the projections highlighted high mercury exposure levels among traditional communities, particularly indigenous populations, with an average of 49.79% facing an extremely high risk in the Branco and Tapajós river basins. This study demonstrated SERAFM's capacity to fill information gaps in the Amazon while underscoring the need for enhanced data collection, culturally sensitive interventions and regulatory updates to mitigate mercury contamination in gold mining-affected areas.

Study of the Risk Associated with Fish Ingestion in the Volta Grande of the Xingu River - Brazilian Amazon Region

Study of the Risk Associated with Fish Ingestion in the Volta Grande of the Xingu River - Brazilian Amazon Region

The role of the environment and connectivity on multiple facets of local fish diversity in tropical headwater streams

Abstract The identification of multiple facets of biodiversity (e.g., phylogenetic and functional) can help to understand how evolutionary and ecological mechanisms shape the assembly of biological communities. Here, we employed multiple regressions and variance partitions to investigate the effects of environmental conditions, connectivity and space on aspects of the functional and phylogenetic facets of fish fauna in tropical headwater streams of the Xingu River basin, in Eastern Amazonia. We found that the functional and phylogenetic diversities of fish communities are related to local environmental conditions and stream connectivity in the drainage network, with marked differences occurring between the rainy and dry periods. Furthermore, we discovered that functional uniqueness was influenced mainly by environmental factors, whereas phylogenetic uniqueness had a more complex relationship with the influence of local environmental factors and connectivity. Our findings indicate that the fish assemblages of small headwater streams of the Xingu River basin share a close phylogenetic history. This is probably because of the climatic and environmental stability experienced by Amazonian ichthyofauna over evolutionary time. Our findings emphasise the role of niche‐based processes in shaping the unique functional composition of fish assemblages in headwater streams, and highlight the importance of environmental heterogeneity in maintaining the ecological integrity of these freshwater ecosystems.

Operational effects on aquatic carbon dioxide and methane emissions from the Belo Monte hydropower plant in the Xingu River, eastern Amazonia

Operational demands and the natural inflow of water actively drive biweekly fluctuations in water levels in hydropower reservoirs. These daily to weekly fluctuations could have major effects on methane (CH4) and carbon dioxide (CO2) emissions via release of bubbles from reservoir bottom sediments (ebullition) or organic matter inputs, respectively. The impact of transient fluctuations in water levels on GHG emissions is poorly understood and particularly so in tropical run-of-the-river reservoirs. These reservoirs, characterized by high temperatures and availability of labile organic matter, are usually associated with extensive CH4 generation within bottom sediments. The aim of this study is to determine how water level fluctuations resulting from the operation of the Belo Monte hydropower plant on the Xingu River, eastern Amazon River Basin, affect local CO2 and CH4 emissions. Between February and December 2022, we monitored weekly fluxes and water concentrations of CO2 and CH4 in a site on the margin of the Xingu reservoir. Throughout the study period, fluxes of CO2 and CH4 were 118 ± 137 and 3.62 ± 8.47 mmol m−2 d−1 (average ± 1SD) while concentrations were 59 ± 29.77 and 0.30 ± 0.12 μM, respectively. The fluxes and water concentrations of CO2 were clearly correlated with the upstream discharge, and the variation observed was more closely associated with a seasonal pattern than with biweekly fluctuations in water level. However, CH4 fluxes were significantly correlated with biweekly water level fluctuations. The variations observed in CH4 fluxes occurred especially during the high-water season (February–April), when biweekly water level fluctuations were frequent and had higher amplitude, which increased CH4 ebullition. Reducing water level fluctuations during the high-water season could decrease ebullitive pulses and, consequently, total flux of CH4 (TFCH4) in the reservoir margins. This study underscores the critical role of water level fluctuations in near-shore CH4 emissions within tropical reservoirs and highlights significant temporal variability. However, additional research is necessary to understand how these findings can be applied across different spatial scales.

Temporal evolution of deforestation in the Xingu River Watershed between 2008 to 2020

Anthropic activities that alter land cover patterns in Watersheds, such as deforestation, affect the food and sanitary security of the population. Thus, the objective of this study was to develop a quantitative analysis of the temporal evolution of deforestation in the Xingu River Watershed between the years 2008 and 2020. To achieve this, the methodology was organized into the following steps: Database construction (Xingu River Watershed boundaries, deforested areas, and Land Use and Land Cover); Data preprocessing; Analysis of the temporal evolution of deforestation; and Quantitative analysis of land cover change in the deforested areas. It became evident that deforestation did not exhibit a standardized behavior, due to the large proportion of deforested areas in 2008 and the abrupt reduction in 2012. Furthermore, the deforestation in 2012, 2016, and 2020 resulted in greater conversion of native forests into pasture than the regeneration of these areas. Therefore, it can be concluded that 2008 had the highest deforestation rate, due to the increase in soybean prices, and that 2012 had the lowest rates due to the implementation of environmental policies, highlighting the relationship between environmental policies and the seasonality of commodity prices with deforestation rates. It was also concluded that the main destination for the deforested areas has been pastureland for livestock, and a viable solution to identify and punish offenders, as well as support small-scale producers and recover areas devastated by deforestation, is land regularization.

Dewatering the Xingu River: hydrological alterations and biocultural connections among the Arara Indigenous People in the Volta Grande region, Brazilian Amazon

Dewatering the Xingu River: hydrological alterations and biocultural connections among the Arara Indigenous People in the Volta Grande region, Brazilian Amazon

Two decades of clear-cutting threats in the Brazilian Amazonian protected areas around the Jirau, Santo Antônio, and Belo Monte large dams

Deforestation rates in the Amazon have markedly increased in the last few years, affecting non-protected and protected areas (PAs). Brazil is a hotspot of Protected Area Downgrading, Downsizing, and Degazettement (PADDD) events, with most events associated with infrastructure projects. Despite the threats dams impose on PAs, there is a knowledge gap in assessing deforestation in PAs around large dams in the Amazon. This study investigates how deforestation affects Biodiversity Protection Areas (BioPAs) and Indigenous Lands around the Jirau and Santo Antônio (JSA) dams (Madeira River, Rondônia) and Belo Monte dam (Xingu River, Pará) in the Brazilian Amazon. We compared clear-cutting between PAs and control areas and the annual rates of forest change between pre-dam and post-dam periods. We discussed deforestation-related factors (e.g., PADDD events and the presence of management plans or councils). Our results show an increase in deforestation after the operation of the dams when environmental control from licensing agencies decreases and other political and economic factors are in practice. Indigenous Lands experienced a significant increase in deforestation around the Belo Monte dam, which is associated with the demarcation process and land conflicts. Surrounding the JSA dams, sustainable use BioPAs showed high deforestation rates, and 27 PADDD events were reported, four directly related to dams. In addition to dams, deforestation was associated with the crisis of Brazilian democracy and the weakening of environmental policies. In conclusion, the weak environmental control from environmental licensing agencies during dam operation and PADDD events have contributed to increased deforestation rates and additional stresses in the Amazon.

Unravelling a specialised diet of an Amazonian catfish in a controlled flood-pulse area by combining stomach-content and stable-isotope analyses

Context Hydrological dynamics are crucial in fish ecology. Aims To evaluate the effect of the flood pulse on the feeding ecology of Doras higuchii in the reduced-flow section of the Belo Monte dam, Xingu River, Brazil. Methods Collections were conducted between December 2020 and November 2021. The fish were measured and had their stomachs removed. Muscle tissue was also extracted for stable-isotope analysis. Stomach contents were inspected to assess diet, testing the influence of hydrological periods by using GLM. In addition, we evaluated the effect of the flood pulse on the δ13C and isotopic ratios of individuals Results In total, 362 specimens of D. higuchii were analysed, highlighting a diet mainly on the basis of sediment (74.9%) and aquatic insects (24.8%), not varying between periods characterising the species as a specialist for having detritivorous habit, as well as the extension of the trophic niche. There was variation in food intensity, with higher average food consumption in the flood period. The isotopic composition (δ13C and δ15N) also did not differ between periods. Finally, δ15N did not vary by length class. Conclusions This information helps understand the interface between environmental and biological factors in an environment affected by a hydroelectric dam. Implications Our results may help fill gaps in knowledge about the diet of doradid fishes.

A systematic assessment of Leporinus tigrinus (Characiformes: Anostomidae) using morphological and molecular data

Leporinus tigrinus was described based on specimens collected in the rio Tocantins basin, and was only recently recorded at the rio Xingu, rio Tapajós and upper rio Paraná basins. So far, no study has compared specimens of all these distinct drainages focusing on understanding whether all these populations truly belong to a single species or may consist instead in a species complex. Our study focused on investigating the intraspecific variation within Leporinus tigrinus using morphological and molecular data. Both morphology and molecular analyses support that all samples belong to a single species widespread in the rio Araguaia, rio Tocantins, rio Xingu and rio Tapajós. In addition, the population occurring at upper rio Paraná is considered to be allochthonous, originating from the rio Araguaia/Tocantins. A comprehensive morphological description of the species, including osteological illustrations and descriptions are provided, as well as a comparative diagnosis with similar-looking species.

Waterscapes meet socio‐ecological models: A relational framework to examine water insecurity and human health and well‐being

Abstract Water insecurity, the inability to benefit from affordable, adequate, reliable and safe water, is one of the greatest contemporary threats facing humans. While ‘water insecurity’, as a concept, is globally recognized and serves an essential function in policymaking, it does not capture the multiple, relational connections between Indigenous peoples and local communities (IPLCs) and water systems. We contend that studies of water insecurity and health among IPLCs can be improved by applying a systematic approach to the concept of waterscapes. The term waterscape describes the socio‐natural relations between humans and water. To make examining waterscapes more systematic and to draw attention to the importance of health within waterscapes, we use a four‐tiered socio–ecological approach to describe the multi‐level interactions between IPLCs and local water systems in the Amazonian watershed. We then apply this four‐tiered model to the case of the Belo Monte dam in the Brazilian Amazon to identify the specific health impacts of disrupting the Xingu River waterscape. Applying the four‐tiered socio‐ecological approach to the Belo Monte case study showed that this dam led to flooding and compromised water quality that local people associated with an increased risk for chronic health conditions, such as kidney and renal diseases, and vector‐borne diseases, such as dengue. Displacement due to the dam threatened food security, economic security, community cohesion and the cultural survival of multiple IPLCs along the Xingu river. Our approach uncovers not only the direct consequences of the dam on water insecurity but also the broader implications for community well‐being and cultural integrity, addressing the diverse challenges arising from human‐water interactions. The four‐tiered approach for assessing waterscapes offers a framework that enables a comprehensive examination of the intricate relations between water and humans. While there are overlaps among the levels, this framework is applicable to other situations where mining, oil extraction and the construction of hydrovías are substantially altering local waterscapes. Tools such as this one can promote more meaningful engagement between researchers, policymakers, and IPLCs in defining the range of outcomes to be considered in social and environmental impact assessments. Read the free Plain Language Summary for this article on the Journal blog.

A new long-snouted Corydoras (Siluriformes: Callichthyidae) from the rio Xingu and rio Tapajós basins, Brazilian Amazon

Abstract A new species of Corydoras is described from the rio Xingu and rio Tapajós basins, Pará State, Brazil. The new species can be promptly distinguished from its congeners by the combination of the following features: (I) temporal sensory canal at sphenotic with two pores; (II) upper tooth plate of branchial arch with three or four series of teeth; (III) area at the corner of the mouth, ventral to the maxillary barbel, with a small, roughly triangular fleshy flap, not forming an elongated barbel-like structure; (IV) contact between posterior process of the parieto-supraoccipital and nuchal plate; (V) dark stripe transversally crossing the orbit, forming a mask-like blotch; (VI) absence of a distinct color pattern along midline of flank; (VII) dorsolateral body plates only with small, irregular, rounded or vertically elongated dark brown or black blotches; ground color of plates typically dusky but not forming large, conspicuous black patches; and (VIII) absence of a relatively large, conspicuous dark patch on anterior portion of dorsal fin.

Karyotypic characterization of Centromochlus schultzi Rössel 1962 (Auchenipteridae, Centromochlinae) from the Xingu River basin: New inferences on chromosomal evolution in Centromochlus.

Centromochlinae is a widely diverse subfamily with more than 50 species and several taxonomic conflicts due to morphological similarity between Tatia and Centromochlus species. However, cytogenetic studies on this group have been limited to only four species so far. Therefore, here we present the karyotype of Centromochlus schultzi from the Xingu River in Brazil using classic cytogenetic techniques, physical mapping of the 5S and 18S rDNAs, and telomeric sequences (TTAGGG)n. The species had 58 chromosomes, simple NORs and 18S rDNA sites. Heterochromatic regions were detected on the terminal position of most chromosomes, including pericentromeric and centromeric blocks that correspond to interstitial telomeric sites. The 5S rDNA had multiple sites, including a synteny with the 18S rDNA in the pair 24st, which is an ancestral feature for Doradidae, sister group of Auchenipteridae, but appears to be a homoplastic trait in this species. So far, C. schultzi is only the second species within Centromochlus to be karyotyped, but it has already presented characteristics with great potential to assist in future discussions on taxonomic issues in the subfamily Centromochlinae, including the first synteny between rDNAs in Auchenipteridae and also the presence of heterochromatic ITSs that could represent remnants of ancient chromosomal fusions.

New species of Pseudacanthicus (Siluriformes: Loricariidae) from the rio Xingu, Amazon, Brazil

Abstract The genus Pseudacanthicus encompasses eight recognized species so far: P. histrix, P. serratus, P. spinosus, P. fordii, P. leopardus, P. pitanga, P. pirarara, P. major. Only P. pirarara has been formally described from the rio Xingu basin. To address this gap in taxonomic knowledge of the region, a new species of the Pseudacanthicus is described here, aimed at enhancing our understanding of the genus within the rio Xingu basin and contributing to conservation efforts. The new species is primarily found downstream the impact zone of the Belo Monte Hydroelectric Power Plant. It can be promptly diagnosed from congeners by the color pattern of the body dark brown to black with light gray vermicular spots on the dorsal and ventral surfaces, and fins; lower maximum number of teeth in premaxilla and dentary; and other osteological characters. It’s worth noting that the ichthyofauna of the Amazonian drainages lacks comprehensive taxonomic and biological information regarding Pseudacanthicus. In this context, unchecked anthropogenic activities are leading to changes in the ecosystem, often resulting in the extinction of species even before they are scientifically addressed.