Araguaia Research Articles

A new species of Astyanax Baird & Girard (Characiformes: Characidae) from the upper rio Araguaia, Central Brazil

We describe a new species of Astyanax from the upper rio Araguaia basin, Mato Grosso State, Brazil. The new species presents a combination of characters that indicates its allocation within the A. scabripinnis species complex. The new species differs from congeners belonging to the A. scabripinnis species complex by a combination of the following characters: lateral dark stripe beginning immediately behind the upper margin of the opercle; a single vertical humeral dark blotch; a scattered pattern of dark chromatophores below lateral line, at the abdominal region; 15 to 20 branched anal-fin rays; lateral line with 33 to 36 perforated scales; dentary teeth decreasing abruptly in size from the fourth or fifth tooth onwards; and 13 or 14 circumpeduncular scales.

Stand dynamics of the drought-affected floodplain forests of Araguaia River, Brazilian Amazon

BackgroundThe floodplain forests of Araguaia River, a clear-water river in the southeastern Amazon (Tocantins State, Brazil), are characterized by seasonal flooding up to 3.5 m height, low nutrient levels in the water, and seasonal drought periods of 4–5 months.MethodsWe studied the forest dynamics (tree diameter growth, tree mortality and recruitment) of this unique forest ecosystem over a 5-year period by repeated censuses in 12 permanent plots established along a flooding gradient.ResultsThe cumulative basal area in the plots increased by 0.84 (±0.45) m2∙ha–1∙yr–1 (mean ±SD) in the annually-flooded (AF) plots in lower terrain and by 0.69 (±1.00) m2∙ha–1∙yr–1 in the higher non-annually flooded (NAF) plots, corresponding to an aboveground biomass increase of 0.81 (±0.57) and 0.69 (±1.58) Mg∙ha–1∙yr–1 in the AF and NAF plots, indicating a recent carbon sink in the biomass. Mean diameter growth rate was 1.8 (±0.44) mm∙yr–1 in the AF and 2.0 (±0.56) mm∙yr–1 in the NAF plots (corresponding to a coarse wood production of 1.53 (±1.29) and 2.02 (±0.52) Mg∙ha–1∙yr–1), indicating no flooding effect on radial growth. Mean mortality rates in the 5-year period were 1.9 (±0.37)%∙yr–1 in the AF plots and 1.8 (±0.87)%∙yr–1 in the NAF plots with no differences along the flooding gradient. Highest mortalities were registered in the AF plots for the 10–20 cm dbh class (2.4%∙yr–1), likely as a consequence of flooding, and in the NAF plots for the 40–50 cm dbh class (3.0%∙yr–1), probably mainly caused by ENSO-related droughts.ConclusionsWe conclude that these drought-affected tropical floodplain forests have a lower standing biomass and aboveground productivity than central Amazonian floodplain forests in more humid climates, and the imprint of the flooding gradient on stand dynamics is relatively weak, which may result from the lower flooding height and the interaction of flooding with low nutrient supply and periodic drought.

Biodiversity of ostracod communities (Crustacea, Ostracoda) in a tropical floodplain

Neotropical floodplains harbour both floating and rooted plants and are associated with rich ostracod communities. After dry seasons, flooding causes recruitment in 2 ways: floods bring in allochthonous macrophytes with associated pleuston communities, and these rising water levels rehydrate plants and attached (ostracod) eggs that dried at the onset of the dry season. We analysed the ostracods communities in the Araguaia River floodplain (Brazil) during 2 hydrological periods (dry and rainy) and evaluated the species distribution in relation to abiotic and biotic factors. We compared the ostracod fauna of 6 lakes in the dry and rainy period and 17 lakes in the rainy period. We tested the hypothesis that the highest values of ostracod community attributes (richness, density, and evenness) occur in the rainy season owing to the influx of allochthonous individuals and the rehydration of the dried autochthonous macrophytes. We indeed observed the highest richness and diversity of ostracods in the rainy season; the homogenizing effect of the flood pulse at the onset of the rainy season caused a more homogeneous fauna (lower beta diversity) during that hydrological period. The distribution of species showed a significant effect of both abiotic factors (local) and hydrological period (regional).

Sudden death associated with Niedenzuella stannea (Malpighiaceae) in cattle in the State of Mato Grosso, Brazil: importance and epidemiological aspects

ABSTRACT: The aim of this study was to investigate the importance of an acute disease that was characterized by sudden death associated with exercise that affected cattle in the region of the Araguaia River, especially in the municipality of Torixoréu, southeastern Mato Grosso, Brazil. Between August and September 2013, eighty farms in the municipality were visited and the pastures of these farms were inspected. Epidemiological questionnaires were completed from 65 farms. A plant identified as Niedenzuella stannea (N. stannea) of the Malpighiaceae family was attributed to the cause of sudden death in cattle, what causes major economic losses. Sudden death reports have occurred since 1970, when livestock was introduced into the region, and sudden death reports still occur. Outbreaks were reported to occur from May to October, but mainly during the dry season between June and August. N. stannea was identified at 41 farms and was always found in near to rivers. The most effective plant control methods included plowing the pastures and fields followed by manual application of Tordon® (Picloram and 2.4D). The administration of 5g/kg of young leaves which were collected from a farm with a sudden death history in cattle also caused sudden death in a sheep. Thus, it is concluded that the sudden death of cattle in the region of the Araguaia River is caused by the consumption of N. stannea.

Às margens do Rio Araguaia... o Presídio Militar de Santa Leopoldina (Província de Goyaz, 1850-1959)

Neste texto analisamos a implantação dos presídios militares às margens do rio Araguaia por meio dos Relatórios da Presidência da Província de Goiás que datam da segunda metade do século XIX. Buscamos entender como a construção do presídio Santa Leopoldina influenciou o povoamento a beira-rio Araguaia contribuindo, em especial, para o surgimento da cidade Aruanã.

A formação de cidades ribeirinhas no Araguaia a partir de presídios militares — século XIX

O presente artigo aborda o Rio Araguaia como o caminho, a estrada para o desenvolvimento do comércio, na segunda metade do século XIX. A navegação fluvial brasileira apresenta-se, nesse período, como meio de propiciar condições de vida aos moradores das cidades mais afastadas dos principais centros comerciais e próximas dos rios, fundamentadas no intercâmbio comercial mais efetivo com o exterior. Na primeira metade do século XIX, os receios de invasão externa através dos rios levaram o príncipe D. João VI, em 1809, a viabilizar a política de defesa e proteção do Território Imperial através da implantação de Presídios Militares nos principais rios brasileiros. No vasto sertão do Araguaia, essas tentativas foram frustradas em vista da não permissão dos povos indígenas — Xavantes, Caiapós, Karajás, Javaés, Xambioás e outros, que viviam agrupados em aldeias, avessos à entrada de outros povos de culturas distintas. Na segunda metade do referido século, o governo Imperial, ciente da impossibilidade de desenvolver o comércio via fluvial, optou por adotar a política de Implantação de Presídios Militares com a pretensão de criar os Portos de Embarques e Entrepostos Comerciais para garantir a navegação comercial e a formação de cidades beiras. Uma saída em duplo sentido, para possibilitar uma ligação com o litoral e salvar a Província do marasmo em que se encontrava.

Sampling sufficiency for estimating zooplankton diversity in neotropical floodplain lakes

AbstractThis study focuses on determining how many samples are needed to effectively assess the species richness of a community. Zooplankton samples at 40 sampling sites distributed among four lakes in the floodplain of the middle Araguaia River (Central‐West region of Brazil) were evaluated to determine the effect of the accumulation of collecting points by lake on species richness estimates. The results indicated the zooplankton community has high spatial heterogeneity. Thus, using a single sampling unit per lake would not be sufficient to accurately estimate their diversity (i.e. the zooplankton composition in these cases would be represented mainly by abundant species). Sampling designs that include a minimum of seven sampling sites in each lake are needed to record 70% of the total species richness. It is recommended, therefore, that researchers use a larger number of sampling sites per lake or, alternatively, that the water obtained and filtered through plankton nets is extracted from a wide area and in different lake compartments, rather than from a single site.

New occurrence of a non-native ornamental cichlid in the Paranapanema River, southern Brazil

Fish introductions are common practices due to intentionally or unintentionally translocations of species between watersheds. Herein we report the spread of the non-native cichlid Laetacara araguaiae Ottoni & Costa 2009 in the Paranapanema River basin, southern Brazil. Native from the Araguaia River (Central Brazil), this species was probably introduced by releases made by aquarists. Its new area of occurrence is characterized as natural nursery and important for the life cycle of native fish. Due to its biological characteristics, the species has the ability to cause a negative impact on the aquatic biota through possible interactions, such as predation of eggs, larvae and juveniles of native fish, and spread of parasites.Keywords: biological invasion, Cichlinae, fish, exotic species, Upper Paraná River basin.

MGB-IPH model for hydrological and hydraulic simulation of large floodplain river systems coupled with open source GIS

Large-scale hydrological models are useful tools for water resources studies, however, river network flow routing is generally represented using simplified methods, which may lead to simulation errors in flat regions. We present recent improvements to the large-scale hydrological model MGB-IPH to improve its capability of simulating large river basins with extensive floodplains. We also describe the coupling of MGB-IPH to an open source GIS and a large set of developed pre-processing tools with a user-friendly interface for remote sensing data preparation and output visualization. The new features implemented are demonstrated applying the model to the whole Araguaia river basin (380,000 km2). Results are compared to the previous MGB-IPH routing method, observed flow and water level data and remote sensing imagery, showing improvement in the representation of floodplain inundation dynamics. The test case also shows that the proposed model software framework amplifies possibilities of large-scale simulation of ungauged basins.

Environmental Vulnerability by Floods and Occupation of Permanent Preservation Area: An Approach about Three Cities of Midwest of Brazil

The purpose of this article is to identify the areas of environmental vulnerability by flooding in urban areas of the municipalities of Barra dos Garças - MT, Pontal do Araguaia - MT and Aragarças - GO; and demarcate the occupations in permanent preservation areas (PPAs) in the study area. The methodology uses variables such as time series of maximum quotas of the Araguaia River, from 1968 to 2014, the frequency of those floods, as well as the local level curves. From the junction of these data, it was stipulated the levels of environmental vulnerability by floods in five levels: very high, high, medium, low and very low. The results indicate that areas with very high vulnerability correspond to approximately 1,58 square kilometers which equals to 0.5% of the total area studied; the high vulnerability areas, have only 3.19 square kilometers, corresponding to 1% of the area; the medium vulnerability areas have 7.66 square kilometers, which corresponds to 2.41% of the area; low vulnerability areas, have 11.18 square kilometers of extension relating to 3.52% of the area; and finally the remainder of the study area was characterized as very low vulnerability. After this mapping, it was found by satellite imaging from Google earth software dated 2014, the main occupations in PPAs. The main uses and occupations refer to human activities related to tourism, as well as commercial, residential and industrial buildings. It was found that it is of salutary importance that the Government enforces the fulfillment of the restrictions set out in the Forest Code, preventing that more occupations occur in PPAs and areas subject to flooding. Moreover, the mapping of areas of flooding is also a tool for future public policies that aim to guide the recommended areas to urban expansion, as well as ordering the use and occupation of land by developing zoning.

Cyphocharax boiadeiro, a new species from the upper rio Araguaia, Amazon basin, Brazil (Characiformes: Curimatidae).

Cyphocharax boiadeiro, new species, is described from the upper rio Araguaia, a tributary of the Amazon basin in central Brazil. The new species is readily distinguished from its congeners by the presence of a distinct longitudinal dark stripe from supracleithrum to the caudal peduncle and by a combination of morphometric, meristic, and pigmentation features. Morphological characters supporting putative subunits of Cyphocharax are also discussed.

Woody plant community structure in “Dense Cerrado” fragments in the Upper Basin of the Araguaia River (Central Brazil): relationship with habitat loss and geographical distance

Habitat loss and fragmentation are severe threats to biodiversity but have been little explored in studies of the woody vegetation of the Cerrado. The present study addressed the community structure of woody plants in 17 “Dense Cerrado” fragments in the Upper Basin of the Araguaia River (GO and MT), standardizing variables such as fragment size (>50 ha), shape, disturbance and matrix. The phytosociological structure was assessed with an inclusion criterion of D30 ≥ 5 cm in three plots, 50 × 20 m each, per fragment. A total of 131 species were recorded. Pielou’s equitability index was equal to 0.82, and Shannon’s diversity index (H′) was equal to 4.03 nats/ind.−1. Basal area and density were equal to 18.13 m2 ha−1 and 1715.49 ind. ha−1, respectively. The estimated richness (Jackknife 1) was superior to the observed richness. The assessment whether density, observed diversity and Shannon’s diversity index for each fragment explained either fragment size or habitat lost in 28 years revealed that these parameters did not explain either the woody community structure or the species diversity. The assumption that the fragments with the greatest area loss throughout this time period would have less diverse communities was not corroborated. The results of the Mantel test did not demonstrate any relationship between geographical distance and floristic similarity in “Dense Cerrado” fragments; therefore, it was not possible to corroborate the hypothesis that fragments located closer to each other are more floristically similar. As suggested by some authors, the floristic similarity in Cerrado areas can be better explained by other factors than geographical distance among sampled sites.

Three new species of the killifish genus Melanorivulus from the central Brazilian Cerrado savanna (Cyprinodontiformes, Aplocheilidae).

Three new species are described from the Neotropical region comprising the Cerrado savannas of the central Brazilian plateaus, which is among the most important biodiversity centres in the world. These species are considered closely related to Melanorivulus dapazi from the same region, with which they share the presence of a rudimentary interarcual cartilage and a dark reddish brown distal margin on the male anal fin. The group comprising Melanorivulus dapazi and the three new species is here named as the Melanorivulus dapazi species group. Melanorivulus ignescens sp. n., from the upper Rio Araguaia basin, is distinguished from all other species of the Melanorivulus dapazi group by the anal-fin colour pattern in males; Melanorivulus flavipinnis sp. n. and Melanorivulus regularis sp. n. from the Rio Paraguai basin are distinguished from all other congeners of the Melanorivulus dapazi group by the colour pattern of the caudal fin and number of scales in the longitudinal series, respectively. All the new species are further unambiguously diagnosed by unique combinations of morphological characters, including meristic and morphometric data, and colour patterns. This study reinforces the importance of using live colour patterns to diagnose species and species groups of the genus Melanorivulus, but also indicates that osteological characters may be informative for species diagnosis. This study confirms the high diversity of species of Melanorivulus in the central Brazilian Cerrado plateaus already reported in previous studies, indicating that endemic species are often restricted to short segments of a single river drainage.

Mixing the waters: a linear hybrid zone between two riverine Neotropical cardinals (Paroaria baeri and P. gularis)

ABSTRACTAmazonian rivers have been more frequently conceptualised as barriers rather than as habitats for birds with their own ecological and biogeographic histories. However, many river-restricted bird species have differentiated within the formidable network formed by the Amazon and its tributaries. Here we demonstrate that the riverine-distributed Crimson-fronted Cardinal (Paroaria baeri) is narrowly distributed along the middle Rio Araguaia basin, where it comes into contact and hybridises with the geographically widespread Red-capped Cardinal (P. gularis). This one-dimensional hybrid zone, which is situated over ca.160 km along the Araguaia and Javaés Rivers, appears to be of recent origin. Admixed individuals between the non-sister P. baeri and P. gularis are phenotypically intermediate between the parental species, and superficially resemble the geographically disjunct and phylogenetically distant Masked Cardinal (P. nigrogenis). Two phenotypically admixed specimens were confirmed as such based on sequences of the mitochondrial Cytb and the Z-linked MUSK gene. Field observations and genetic data indicate that P. baeri × P. gularis hybrids are capable of producing viable offspring, but more data are necessary to confirm hybrid viability and fertility. The non-sister hybridising species P. baeri and P. gularis last shared a common ancestor 1.8–2.8 mya (uncorrected genetic p-distance of 4%), which corresponds closely to when the Araguaia/Tocantins river basin last discharged directly into the Amazon.

Pesca Amadora e Turismo no Médio Rio Araguaia, Brasil Central

O rio Araguaia, principal tributário do rio Tocantins, apresenta a sua região média inserida numa planície de inundação, a qual durante o período de estiagem constitui um atrativo para a pesca amadora e o turismo. Este estudo visa avaliar a pesca amadora realizada pelos turistas instalados em 103 acampamentos no trecho entre as cidades de Aragarças e Luis Alves, estado de Goiás. Trinta e sete espécies de peixes são apreciadas e consumidas pelos turistas havendo preferência pelos peixes-de-couro. Em geral, os peixes são capturados utilizando-se anzóis com diferentes iscas, entre as quais predominam: espécies nativas ou não de peixes, vegetais e minhocas (nativas ou não). A pesca dos peixes é realizada principalmente no canal principal do rio Araguaia.

Landscape changes in a neotropical forest-savanna ecotone zone in central Brazil: The role of protected areas in the maintenance of native vegetation

In the Amazon-savanna ecotone in northwest Brazil, the understudied Araguaia River Basin contains high biodiversity and seasonal wetlands. The region is representative of tropical humid-dry ecotone zones, which have experienced intense land use and land cover (LULC) conversions. Here we assessed the LULC changes for the last four decades in the central portion of the Araguaia River Basin to understand the temporal changes in the landscape composition and configuration outside and inside protected areas. We conducted these analyzes by LULC mapping and landscape metrics based on patch classes. During this period, native vegetation was reduced by 26%. Forests were the most threatened physiognomy, with significant areal reduction and fragmentation. Native vegetation cover was mainly replaced by croplands and pastures. Such replacement followed spatial and temporal trends related to the implementation of protected areas and increases in population cattle herds. The creation of most protected areas took place between 1996 and 2007, the same period during which the conversion of the landscape matrix from natural vegetation to agriculture occurred. We observed that protected areas mitigate fragmentation, but their roles differ according to their location and level of protection. Still, we argue that landscape characteristics, such as suitability for agriculture, also influence landscape conversions and should be considered when establishing protected areas. The information provided in this study can guide new research on species conservation and landscape planning, as well as improve the understanding of the impacts of landscape composition and configuration changes.

Araguaia River Floodplain: Size, Age, and Mineral Composition of a Large Tropical Savanna Wetland

The Araguaia River floodplain is a large wetland in the tropical savanna belt (cerrado) in the southern Amazon basin. Studies using multitemporal satellite Landsat 5 TM images with a spatial resolution of 30 m indicate a surface area at maximum flood level of 88,119 km2. During the low-water period, only 3.3 % of the area is covered by water. Flooding is the result of the annual rise in the water level of the Araguaia River and of local rainfall and insufficient drainage during the rainy season. Sedimentology studies have distinguished between an active recent and sub-recent floodplain, which covers ~20 % of the area, and a paleo-floodplain probably several hundreds of thousand years in age. Paleo-floodplain sediments are strongly weathered and marked by the clay mineral association of kaolinite, gibbsite, goethite, and Al-chlorite, predominantly formed from feldspars and micas. The active paleo-floodplain participates in the hydrological cycle but does not receive recent sediments from the river. Higher-lying, not flooded areas (inactive paleo-floodplain) are probably the remnants of paleo-levees, now in an advanced stage of erosion. A hypothesis to explain the genesis of the floodplain is proposed herein.

Potamotrygon rex, a new species of Neotropical freshwater stingray(Chondrichthyes: Potamotrygonidae) from the middle and upper rio Tocantins, Brazil, closely allied to Potamotrygon henlei (Castelnau, 1855).

A systematic revision of the rio Tocantins stingrays has confirmed the occurrence of a new species of Potamotrygon first discovered more than two decades ago but which lacked material for a thorough description. Field surveys since undertaken in the middle and upper rio Tocantins have assembled significant material that forms the basis of an ongoing revision of the diverse Tocantins potamotrygonid assemblage. Potamotrygon rex, sp. nov., is a very large, "black stingray" species from the mid and upper rio Tocantins that is closely related to P. henlei (Castelnau), which occurs in the lower Tocantins basin and in rio Araguaia; both species do not co-occur. Potamotrygon rex, sp. nov., has a unique blackish to dark brown dorsal color with numerous small, yellow to orange irregular spots usually forming distinct clusters on dorsal disc, with ocelli in center of clusters on posterior and outer disc, dorsal tail also with clusters but lateral tail with ocelli, and a dark brownish to gray color covering most of ventral surface except nasoral region, gill slits and anterior snout in some specimens, with small whitish spots on ventral disc, pelvic fins and tail. Potamotrygon rex, sp. nov., can be further distinguished by its broad pelvic-fin apices, lack of labial grooves, irregular double row of dorsal tail thorns, and in having two angular cartilages associated with each hyomandibula. Potamotrygon rex, sp. nov., P. henlei, P. leopoldi Castex & Castello, and another new Potamotrygon species from the rio Tapajós (in description) form a species-group (the "black stingrays") occurring in rivers draining the central Brazilian shield, characterized by their black to dark brown but highly ornate dorsal color, wide pelvic fins with broadly convex apices, among other features. Potamotrygon rex, sp. nov., is the 25^th species of Potamotrygon, and highlights that very large new species of fishes still await discovery and description in the Neotropical region.

Comparative Cytogenetics of Hoplerythrinus unitaeniatus (Agassiz, 1829) (Characiformes, Erythrinidae) Species Complex from Different Brazilian Hydrographic Basins

Chromosomal characteristics of Hoplerythrinus unitaeniatus populations from 5 Brazilian river basins, namely Arinos (Amazonas basin), Araguaia, Paraguai, Alto Paraná, and São Francisco were analyzed by conventional Giemsa staining, C-banding, silver nitrate impregnation, and fluorescence in situ hybridization (FISH) with 18S and 5S rDNA and telomeric sequence (TTAGGG)_n probes. The diploid chromosome number was 2n = 48 in representatives of the populations from Paraguai and Alto Paraná River basins and 2n = 52 for those from the Arinos and Araguaia River basins. The São Francisco population had individuals with 2n = 50 and 52 occurring in sympatry. C-banding showed heterochromatic blocks mainly located at interstitial and pericentromeric positions in most of the chromosomes. Silver nitrate impregnation demonstrated simple NORs for representatives from Arinos and Araguaia River populations and multiple NORs for specimens from Paraguai, Alto Paraná, and São Francisco River populations. FISH with 18S and 5S rDNA probes revealed many chromosomes carrying these cistrons, with up to 21 chromosomes bearing 18S rDNA sites (Alto Rio Paraná basin) and up to 12 chromosomes with 5S rDNA sites (Paraguai basin), besides the occurrence of colocalization in all populations. FISH with telomeric sequence (TTAGGG)_n detected sites in the terminal portion of the chromosomes in all populations. These data reinforce the idea that H. unitaeniatus is a species complex. Evolutionary and biogeographical aspects of the group in the Neotropical region are discussed.

FLUXO DE CH4 EM ÁREA DE FLORESTA ÁS MARGENS DO RIO ARAGUAIA - MT

The aim of this study was to estimate the methane flux in an area of upland forest on the Araguaia River margin, in Santa Terezinha - MT, 15 km far from the LBA project flux measurement tower on the Bananal island - TO. For this a micrometeorological tower was installed on the river margin, with climatic variables sensors, eddy covariance and methane concentration by open optical path and closed in days of the rainy season in the region. Estimates of CH4 concentration showed good correlation between the sensors, with the highest concentrations at night and lower concentrations during the day, likely effect of differences between CLN and CLC, and averages around 1.8 ppm, near to that found in other sites upland forest. Both the river and the forest are sources of methane to the atmosphere. with a higher methane flux from river directions, being double the average of the direction from forest, but the daytime maximum of the forest direction are larger and can reach up to 30 nmol m-2 s-1.