Vulnerabilidade à erosão hídrica do solo, bacia hidrográfica do rio Araguaia

O entendimento dos efeitos climáticos e do uso do solo em conjunto é crucial para análise ambiental e prevenções de desastres naturais. O objetivo deste trabalho é analisar a vulnerabilidade à erosão hídrica do solo na bacia hidrográfica do rio Araguaia. Usou-se dados de precipitação (Agência Nacional das Águas); uso e ocupação da terra (Projeto MapBiomas); declividade (Instituto Nacional de Pesquisas Espaciais) e de solo (Empresa Brasileira de Pesquisas Agropecuária) no cálculo de mapas através do geoprocessamento para obter-se a representação da erosão hídrica do solo. A bacia hidrográfica do rio Araguaia caracteriza-se na maior parte por zonas de transição de estabilidade e vulnerabilidade, porém destaca-se as áreas estáveis nas proximidades da foz, regiões críticas á sudoeste (Rio das Mortes), nos limites (leste) do Alto Araguaia, nas partes sudeste e sudoeste do Baixo Araguaia. Na escala climática, a precipitação não apresenta riscos significativos. No entanto, o intenso uso e ocupação da terra na região foi a forçante que maior agravou a vulnerabilidade, principalmente em áreas (declives e solo) naturalmente instáveis. Assim, algumas cidades precisam estar em alerta para possíveis eventos erosivos. Vulnerability to soil water erosion, Araguaia basin riverA B S T R A C TThe Understanding climate effects and land use together is crucial for environmental analysis and natural disaster prevention. The objective of this work is to analyze the vulnerability to soil water erosion in the hydrographic basin of the Araguaia river. Rainfall data (National Water Agency) was used; land use and occupation (MapBiomas Project); slope (National Institute for Space Research) and soil (Brazilian Agricultural Research Corporation) in the calculation of maps through geoprocessing to obtain the representation of soil water erosion. The hydrographic basin of the Araguaia river is characterized in the most part by transition zones of stability and vulnerability, however the stable areas in the vicinity of the mouth stand out, critical regions to the southwest (Rio das Mortes), on the (eastern) limits of the Alto Araguaia, in the southeast and southwest parts of the Lower Araguaia. On the climate scale, the rainfall does not present significant risks. However, the intense use and occupation of land in the region was the forcing that increased the risk, mainly in naturally unstable areas (slopes and soil). Thus, some cities need to be alert to possible erosive events.

The biosonar of the boto: evidence of differences among species of river dolphins (Inia spp.) from the Amazon

Echolocation clicks can reflect the anatomy of the vocalizing animal, enabling the distinction of species. River dolphins from the family Iniidae are formally represented by one species and two subspecies (Inia geoffrensis geoffrensis and I. g. humboldtiana). Additionally, two other species have been proposed (I. boliviensis and I. araguaiaensis) regarding its level of restricted distribution and morph-genetics differences. For the Committee on Taxonomy of the Society for Marine Mammalogy, the specific status of the proposed species relies on further knowledge on morphology, ecology, and genetics. Given that species-specific status is required for conservation efforts, we described and compared the echolocation clicks of Inia spp., searching for specific differences on their vocalizations. The sounds were captured with a Cetacean Research ™ C54XRS (+3/−20 dB, −185 dB re: 1V/μPa) in Guaviare River (Orinoco basin), Madeira River (Madeira basin), Xingu River (Amazon Basin), and Araguaia River (Tocantins-Araguaia basin). We found significant differences in all analyzed parameters (peak frequency, 3 dB bandwidth, 10 dB bandwidth and inter-click interval) for all species and subspecies. Differences in acoustical parameters of clicks are mainly related to the animal’s internal morphology, thus this study may potentially support with information for the species-level classification mostly of I. araguaiaensis (the Araguaian boto). Classifying the Araguaian boto separately from I. geoffrensis has important implications for the species in terms of conservation status, since it is restricted to a highly impacted river system.

A new species of driftwood catfish Centromochlus Kner, 1858 (Siluriformes, Auchenipteridae, Centromochlinae) from Tocantins-Araguaia River drainage

The genus Centromochlus includes eight catfish species in the Amazon and Orinoco river systems: C. schultzi from Xingu and Tocantins-Araguaia rivers; C. melanoleucus from Tapajós and Teles Pires rivers; C. macracanthus from Negro River; C. orca from Nhamundá River; C. heckelii and C. existimatus from Amazon and additionally at the Essequibo rivers; C. carolae and C. musaica from Orinoco River system. Recent field expeditions and collection examination revealed an undescribed species of Centromochlinae that has compatible features with Centromochlus. We herein describe a new species of Centromochlus from the Tocantins-Araguaia River drainage, diagnosed among most Centromochlinae by having a vermiculated color pattern on the dorsum and included in Centromochlus by sharing the derived features: ventrolateral position of eye socket; sphenotic notched for the exit of infraorbital canal; and posterior serrations along pectoral-fin spine numerous. The new species is diagnosed from congeners by having the pectoral-fin spine with dark bars, alternating with light bars (vs. pectoral-fin spine with light and uniform color in all Centromochlus); and it is further distinguished from its congeners (except C. carolae) by the ventral surface of head moderate to largely pigmented (vs. ventral surface of head unpigmented in C. heckelii, C. existimatus, C. orca, C. musaicus, C. schultzi, with few scattered dark chromatophores in C. macracanthus and C. melanoleucus; see diagnosis). A discussion about the systematics of the genus, plus the conservation status of the new species, and an identification key to species of Centromochlus, are also provided.

Long known, brand new, and possibly threatened: a new species of watersnake of the genus Helicops Wagler, 1828 (Serpentes; Xenodontinae) from the Tocantins-Araguaia River Basin, Brazil

We describe a new species of watersnake of the genus Helicops from the Tocantins-Araguaia River Basin based on characters of coloration and hemipenial morphology, also corroborated by a molecular phylogenetic analysis including 18 terminals of 10 additional congeners. The new species superficially resembles the spotted-patterned He. leopardinus, but differs from it in exhibiting dorsal spots fused into irregular bands, and a unique hemipenial structure with two pairs of distinctly enlarged basal spines. In addition, despite the superficial resemblance of color pattern, our genetic evidence indicates that the new species does not belong to the He. leopardinus radiation, representing the sister group of a component including terminals of this species, He. modestus, and He. infrataeniatus. Finally, we discuss the apparent restriction of the new species to the Tocantins-Araguaia Basin with focus on vicariant processes that may have promoted its differentiation, as well as on the conservation challenges in an area severely affected by anthropic impacts associated with the rapid expansion of hydroelectric and agricultural sectors in the Brazilian Cerrado.

Streams fish from Upper Araguaia and Middle Rio da Mortes basin, Brazil: generating subsidies for preservation and conservation of this critical natural resource

The Araguaia River basin has the highest fish biodiversity within the Cerrado biome (Brazilian savannah), with many endemic and threatened species by human activities. Despite growing efforts to catalog Neotropical freshwater fish biodiversity, many regions are still undersampled. Our objective is to complement the information about stream fish in two hydrographic basins in the Cerrado. We sampled 72 streams with 50 m stretch in the Upper Araguaia (n = 32) and Middle Rio das Mortes (n = 40) basins. We collected 14,887 individuals distributed in 137 species, 81 genera, 30 families, and six orders. Characidae, Loricariidae, and Cichlidae were the families richer in species. We found a high diversity of rare fish species in the streams sampled, ca. 71.5% of the species had at least five individuals collected, and 18 species had only one collected specimen. The most frequent species were Astyanax cf. goyacensis, Knodus cf. breviceps, and Characidium cf. zebra. Both basins shared around 43% of the species. We caught 76 species in Upper Araguaia and 120 species in Middle Rio das Mortes. Seventeen exclusive fish species occurred in Upper Araguaia, whereas 61 were found in the Middle Rio das Mortes basin. Our analysis showed lower diversity of fish in Upper Araguaia than in the Middle Rio das Mortes basin. Considering the exclusive fish species of both basins, the human threats in those regions, and the few existent protected areas, we need a better look at the aquatic biodiversity conservation of this ecosystem.