Araguaia Research Articles

A snapshot of the limnological features in tropical floodplain lakes: the relative influence of climate and land use

Abstract Aim This study aimed to investigate the relative influence of climate (temperature and precipitation) and land use on limnological features of 30 floodplain lakes in the Araguaia River, in Central Brazil, an important river that drains in the Brazilian Cerrado. Methods The lakes were sampled in one same period, at a large spatial scale (900 km along the river) covering climate and landscape variability. For decomposing the relative importance of land use and climate, we used the RDA and partitioning variance techniques. Results The lakes presented limnological gradient along the floodplain; in general, the lakes presented low transparency, nutrients concentrations (total nitrogen and total phosphorus) and oxygen saturation. The water pH was considered weakly acidic. Considering land use in Araguaia river basin, lakes in downstream presented more remnant vegetation and lakes in upstream presented more livestock and agriculture soil use. The climate conditions were the most important in explaining the variation in limnological characteristics of the lakes, while the individual analysis of limnological variables showed that land use was important to explain to the pH and transparency of the water. Conclusions Finally, this study showed the importance of investigating regional climatic attributes and land use information to explain the limnological characterization of floodplain lakes. Thus, it highlights the importance of the possible impacts of global climate change on limnological conditions.

On the millipede genus Heteropyge: description of the adults of H. araguayensis and revalidation of H. bidens (Diplopoda: Spirostreptida: Spirostreptidae)

ABSTRACT The South American genus Heteropyge Silvestri, 1897 is revised, accommodating now six accepted species. Adults of the poorly known species Heteropyge araguayensis (Schubart, 1947) are described for the first time from near-topotypic material collected near the Araguaia River, state of Mato Grosso, Brazil. In addition, based on recent samplings and on material from Schubart’s collection, H. bidens (Schubart, 1945) is removed from the synonymy of H. cayennophilus (Silvestri, 1897) and revalidated. Both species show significant differences concerning the gonopods and male leg-pair 1. New records and additional data for H. bidens and H. cayennophilus are provided, as well as an updated checklist of the species belonging to Heteropyge.

Entre o Sublime e o Belo: As Representações Estéticas Sobre o Rio Araguaia

O objetivo deste artigo é analisar as representações estéticas sobre o Rio Araguaia. A hipótese é que as narrativas de cunho estético sobre o rio, vigentes no século XIX até a primeira metade do século XX, valiam-se da estética do sublime; após a segunda metade do século XX, quando a natureza tornou-se, para utilizar uma expressão de Anthony Giddens, humanizada, os relatos estéticos sobre o rio realçaram a beleza bucólica. A reflexão sobre o belo e o sublime apoiou-se nos textos de Edmund Burke e Emmanuel Kant; sobre a representação da natureza, utilizou textos de Georg Simmel e Keith Thomas. As fontes para a análise das representações foram relatos (como os de Conde de Castelnau, Couto de Magalhães, Jacintho Lacomme e Hermano Ribeiro da Silva) e canções sobre o rio Araguaia (compostas por Tião Carreiro e Pardinho, Irmãs Freitas, Marcelo Barra e Amauri Garcia).

Ser (Tão) Imaginado: História e Natureza na Ocupação da Região de Aragarças (GO)/Barra do Garças (MT)

Este artigo tem como objetivo discorrer sobre como o processo de ocupação de Barra do Garças (MT) e Aragarças (GO) teve na natureza um condicionante regulador e um chamariz nos seus diferentes processos migratórios. Os dois municípios, limítrofes entre os estados de Goiás e Mato Grosso, possuem a confluência dos rios Garças e Araguaia como fronteira natural, o que forma uma paisagem singular e evidencia as características geomorfológicas do Cerrado: o vale fica entre planaltos e depressões, e é banhado por águas termais. Tais características naturais imprimiram à região uma dinâmica migratória particular. Neste sentido, a formação dos núcleos urbanos do Vale do Araguaia pode ser observada a partir da perspectiva das possibilidades de transmutação entre migrantes e natureza, que nos processos de modificação, exploração e integração com a paisagem local reorganizaram o viver às margens do Garças/Araguaia.

Remarkable Geographic Structuring of Rheophilic Fishes of the Lower Araguaia River.

Rapids and waterfalls, and their associated fauna and flora are in peril. With the construction of each new hydroelectric dam, more rapids and waterfalls are destroyed, leading to the disappearance of associated fauna and flora. Areas of rapids harbor distinct, highly endemic rheophilic fauna and flora adapted to an extreme environment. Rheophilic habitats also have disjunct distribution both within and across rivers. Rheophilic habitats thus represent islands of suitable habitat separated by stretches of unsuitable habitat. In this study, we investigated to what extent, if any, species of cichlid and anostomid fishes associated with rheophilic habitats were structured among the rapids of Araguaia River in the Brazilian Amazon. We tested both for population structuring as well as non-random distribution of lineages among rapids. Eight of the nine species had multiple lineages, five of these nine species were structured, and three of the eight species with multiple lineages showed non-random distribution of lineages among rapids. These results demonstrate that in addition to high levels of endemicism of rheophilic fishes, different rapids even within the same river are occupied by different lineages. Rheophilic species and communities occupying different rapids are, therefore, not interchangeable, and this realization must be taken into account when proposing mitigatory/compensatory measures in hydroelectric projects, and in conservation planning.

A new miniature cryptic species of the seasonal killifish genus Spectrolebias from the Tocantins River basin, central Brazil (Cyprinodontiformes, Aplocheilidae)

The miniature seasonal killifishSpectrolebiascostae, first described for the middle Araguaia River basin, has been also recorded from two areas in the middle Tocantins River basin, from where male specimens exhibit some differences in their colour pattern. Analyses directed to species delineation (GMYC and bPTP), using a fragment of the mitochondrial gene COI, strongly support two species,S.costaefrom the Araguaia River basin and a new species from the Tocantins River basin.Spectrolebiasgracilissp. n.is described on the basis of specimens collected from two localities separated by about 530 km, Canabrava River floodplains near Alvorada do Tocantins and Tocantins River floodplains near Palmeirante. Field inventories were unsuccessful in finding additional populations in the region, which is attributed to the high environmental degradation, including several large dams that have permanently inundated typical killifish habitats.Spectrolebiasgracilisis member of a clade also includingS.costae,S.inaequipinnatus, andS.semiocellatus, diagnosed by having the dorsal and anal fins in males with iridescent dots restricted to their basal portion, caudal fin in males hyaline, and caudal-fin base with two pairs of neuromasts. Within this clade, a single miniaturisation event is supported for the most recent common ancestor of the subclade comprisingS.costaeandS.gracilis, which differ from other congeners by reaching only about 20 mm standard length as maximum adult size.

Reversibility of the Hardening Process of Plinthite and Petroplinthite in Soils of the Araguaia River Floodplain under Different Treatments

ABSTRACT Although ferruginous materials occur frequently in soils of tropical regions, information about the reversal of the hardening process of these materials is scarce. This study assessed the influence of different chemical treatments and periods of immersion on the reversibility of the hardening process of plinthite and petroplinthite in soils of the Araguaia River plain. Soil samples were collected from the plinthic horizons in 0.10 m high and 0.15 m diameter PVC cylinders and divided into subsamples with a rock [...]

Hardening and Stability of Plinthic Materials of the Araguaia River Floodplain under Different Drying Treatments

ABSTRACT Plinthite and petroplinthite occur frequently in Brazilian soils, but there is little information on the behavior of these materials. The aim of the present study was to assess the effect of different drying periods on the hardening and stability of plinthic materials of soils in the floodplain of the Araguaia River and the Joao Leite stream in Goias. Soil samples were collected, with the aid of 0.10 m high and 0.15 m diameter PVC cylinders, directly from the plinthic [...]

Unrecognized biodiversity in a world’s hotspot: three new species of Melanorivulus (Cyprinodontiformes: Rivulidae) from tributaries of the right bank of the Rio Paraná basin, Brazilian Cerrado

The genusMelanorivuluspresents a wide geographical distribution in the Neotropical region. AmongMelanorivulus, theM.pictusspecies group has currently 18 species distributed in the Brazilian Cerrado, mainly in the upper Rio Paraná basin, with some species occurrences in the upper Rio Araguaia and Tocantins. In the present study, we describe three newMelanorivulusspecies, belonging to theM.pictusspecies group from different drainages of the right bank of the Rio Paraná basin in Mato Grosso do Sul state, Brazil. These new species are easily distinguished from the others by their unique colour patterns.Melanorivulusinterruptusis distinguished from all species of theM.pictusgroup by the presence of oblique chevron-like red bars interrupted, mainly on the midline of the flank in males; whileM.ivinhemensisby the yellow colouration of the caudal fin with thin red bars arranged only in the median region of the fin in males.Melanorivulusamambaiensisis distinguished from all species of theM.pictusspecies group by having an orange anal fin or sometimes more reddish-orange with distal margin grey or dark grey and chevron-like bars along the body, distinctly branched ventrally forming an inverted Y-shape in males. The high diversity of theMelanorivulusspecies with high levels of endemism demands the development of conservation strategies to avoid the loss of their vulnerable habitats in the Cerrado biome. We expect presence of more species of theM.pictusspecies group also along the lower reaches of the tributaries of the Rio Paraná. Additionally a dichotomic identification key of theM.pictusspecies group is provided.

Growth and nutrient contents in lowland rice due to phosphorus and potassium fertilization

ABSTRACT In order to reach an optimum and sustainable production, growers must know the fertilizing potassium (K) and phosphorous (P) application rates. The present study aimed to determine the rice development in response to combined rates of P and K, on Plinthaquults (380-400 g kg-1 of clay), under high and low fertility conditions, in the tropical lowland plain of the Araguaia river, Brazil. Three field experiments were performed, each one consisting of a completely randomized factorial block design, with three replications. Treatments included a combination of six K2O rates (0 kg ha-1, 30 kg ha-1, 60 kg ha-1, 90 kg ha-1, 120 kg ha-1 and 150 kg ha-1) with six P2O5 rates (0 kg ha-1, 30 kg ha-1, 60 kg ha-1, 90 kg ha-1, 120 kg ha-1 and 150 kg ha-1). No interaction effect between P and K rates was observed for the evaluated variables in any fertility level/year. Phosphorous application under low fertility conditions, as well as K under high fertility conditions, affect overall crop nutrition, tillering capacity, yield components and grain yield of lowland rice, though no effects were observed due to the P application in high fertility soils and K in low fertility soils. Under high fertility conditions, the grain yield increment rate due to the K application was 4.04 kg ha-1, whereas in the low fertility areas, such as recently cleared fields, a maximum yield of 7,161 kg ha-1 was achieved by applying 140 kg ha-1 of P.

The non-monotypic status of the neotropical fish genus Hemiodontichthys (Siluriformes, Loricariidae) evidenced by genetic approaches

The combination of cytogenetic and molecular data with those traditionally obtained in areas like systematics and taxonomy created interesting perspectives for the analysis of natural populations under different aspects. In this context, this study aimed to evaluate the genetic differentiation among populations of the genus Hemiodontichthys Bleeker, 1862, through combined genetic techniques and included the analysis of populations sampled in the Araguaia River, Guamá River, Madeira River and two populations from the Purus River. Hemiodontichthys samples from the two localities in Purus River were also karyotyped in order to address the degree of chromosomal variation between populations. Through GMYC analysis of the COI tree, the patterns of genetic variation among local populations revealed to be higher than the ones found among distinct species from other genera of the subfamily Loricariinae, suggesting the existence of probable four cryptic species in this genus. The possible existence of a species complex in the genus is corroborated by the different cytogenetic patterns between Hemiodontichthys sp. 1 and sp. 2, revealing the necessity of a deep taxonomic review of the group.

New species of the genus Spectracanthicus (Loricariidae, Hypostominae, Ancistrini) from the Rio Javaés (Rio Araguaia basin), with a description of gross brain morphology.

A new species of Spectracanthicus is described from the Rio Javaés, Rio Araguaia basin. The new species is distinguished from its congeners (except Spectracanthicus immaculatus) by colour pattern: body dark grey to dark brown without dots or blotches (v. body colour with yellowish small dots in Spectracanthicus murinus, Spectracanthicus punctatissimus and Spectracanthicus tocantinensis and large white dots in Spectracanthicus zuanoni). It can be further distinguished from S. immaculatus by having thicker and less numerous teeth, with up to eight premaxillary and 20 dentary teeth (v. teeth thinner and more numerous with up to 22 premaxillary and 30 dentary teeth); dorsal and caudal fins without curved spines (v. dorsal and caudal fins with curved spines). Other osteological characters can also diagnose the new species from its congeners. In addition, a gross brain description and brief comments on the new species' ecological habitat are given.

IMPACTS OF THE HYDROELECTRIC POWER GENERATION OVER THE FISH FAUNA OF THE TOCANTINS RIVER, BRAZIL: MARABÁ DAM, THE FINAL BLOW

As the eyes of environmentalist's focused on the Madeira, Xingu and Tapajos rivers dams, one unknown project to bystanders will negatively affect an entire watershed, causing impacts far greater than any other megadam constructed in Brazil. Despite the environmental modifications, little is known about the UHE Maraba dam and its impacts over such a splendid cellar of species: the Araguaia- Tocantins basin. Historically the Tocantins River is the most impacted amazon tributary, with several already built dams, though the Araguaia River is free of dams. Building the UHE Maraba dam will affect both rivers, and probably extinguish many species increasing the already high number of Amazonian endangered fish species. Due to its unique evolutionary history among Amazonian tributaries, the endemicity found in the basin is probably higher than any other amazon tributary, inasmuch as some authors consider it as a different watershed, separated from the Amazon. Describing and foreseen the impacts locally and globally are the main goals of the present study.As the eyes of environmentalists and researchers focused on the Madeira, Xingu and Tapajos rivers dams, one unknown project to bystanders will negatively affect an entire watershed, causing impacts far greater than any other megadam constructed in Brazil. Despite the environmental modifications, little is known about the UHE Maraba dam and its impacts over such a splendid cellar of species: the Araguaia- Tocantins basin. Historically the Tocantins River is the most impacted amazon tributary, with several already built dams, though the Araguaia River is free of dams. Building the UHE Maraba dam will affect both rivers, and probably extinguish many species increasing the already high number of Amazonian endangered fish species. Due to its unique evolutionary history among Amazonian tributaries, the endemicity found in the basin is probably higher than any other Amazon tributary, as some authors consider it as a different watershed, separated from the Amazon. Describing and foreseeing the impacts locally and globally are the main goals of the present study.

Arthropod-borne agents in wild Orinoco geese (Neochen jubata) in Brazil.

Although Orinoco goose (Neochen jubata) is an anatid species widely distributed in South America, scarce are the reports on the occurrence of arthropod-borne pathogens in this avian species. The present work aimed to verify, by serological and molecular methods, the occurrence of haemosporida piroplasmids and Anaplasmataceae agents in wild Orinoco geese captured in Brazil. Between 2010 and 2014, 62 blood samples were collected from free-living geese captured in the Araguaia River, Goiás State, Brazil. Six geese (10%) were seropositive for Anaplasma phagocytophilum, showing titers ranging from 40 and 80. Twenty out of 62 blood samples (32.25%) were positive in nested PCR for hemosporidia (cytochrome b gene). Fifteen and five sequences shared identity with Haemoproteus and Plasmodium, respectively. Six out of 62 blood samples (9.68%) were positive in nested PCR for Babesia spp. (18S rRNA gene); one sequence showed to be closely related to Babesia vogeli. Thirty (48.38%) out of 62 Orinoco geese blood samples were positive in nested cPCR assays for Anaplasmataceae agents (16S rRNA gene): three for Anaplasma spp. and 27 for Ehrlichia. Six geese were simultaneously positive to Haemoproteus and Ehrlichia; three animals were co-positive to different Ehrlichia species/genotypes; and one goose sample was positive for both Anaplasma and Ehrlichia. The present work showed the occurrence of Ehrlichia, Anaplasma, Babesia, Plasmodium, and Haemoproteus species in free-living N. jubata in Brazil. The threat of these arthropod-borne pathogens in Orinoco goose's fitness, especially during the breading season, should be assessed in the future.

Assessing the spatial variation of functional diversity estimates based on dendrograms in phytoplankton communities

ABSTRACT Variation in phytoplankton functional diversity is partioned and mapped using several indices and linkage methods based on dendrograms. The relationships between diversity metrics and major environmental predictors, including zooplankton density, were assessed in 29 phytoplankton communities of floodplain lakes distributed along the Middle Araguaia River in central Brazil. The dendrogram-based functional diversity indices were Functional Group Richness, Functional Diversity, Mean Pairwise Distance and Mean Nearest Taxon Distance, whereas seven different hierarchical agglomerative linkage methods we used. The performance of indices were compared using ANOVA and their spatial variation in response to major environmental predictors evaluated. The results indicate that variation in functional diversity values is primarily a product of the type of index chosen. This variation was statistically significant in 90 % of the floodplain lakes studied; however, a spatial pattern of variation in index values along the river was not detected. Furthermore, environmental constraints, including zooplankton density, were weak predictors of functional diversity indices. Therefore, the mathematical characteristics of indices are of primary importance in explaining variation among functional diversity values.

Hydrological characterization of the Araguaia River through reference flows

This study examined the hydrological behavior of the Araguaia River through reference flow, analyzing the capacity of granting the river segments in three different fluviometric stations. The study exposed the comparison of monthly and annual reference flow, considering a hydrological series of 33 years. Consequently, it was proposed seasonal flow comparing to the methodology of annual reference flow for water grants in national rivers. The adoption of the annual reference flow restricts the grants of water use in most of the time, because the proposal of monthly and seasonal Q95% in the rainy period for grants processes showed much higher values. The proposal of monthly and seasonal reference flows to grant the multiple right of use of water may be the most adequate for power generation, because it presents the inherent characteristics of the flows of each month and per period, respectively. However, the use of seasonality for grants must be analyzed along with the environmental aspect of the river basin concerning to the damage of aquatic life of the Araguaia River.

Occurrence of Boto-do-Araguaia (Inia araguaiaensis) in a Region of the Araguaia River, Brazil, Documented for an Environmental Impact Study for a Hydroelectric Dam

Occurrence of Boto-do-Araguaia (Inia araguaiaensis) in a Region of the Araguaia River, Brazil, Documented for an Environmental Impact Study for a Hydroelectric Dam

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).