Meta River Research Articles

Habitat connectivity of threatened ungulate species in a native savanna landscape of northern South America

AbstractThe native savanna ecosystem of the Orinoquia region is the habitat of 50% of the wild ungulate species reported for Colombia. Over the last 20 years, this high species diversity has been strongly threatened by the human transformation of the natural land cover causing connectivity loss of the habitats. The Orinoquia region lacks a biological connectivity analysis with a multi-species approach involving species groups that are representative of the savanna ecosystem such as the ungulates. Understanding the spatial distributions of suitable areas and the main habitats that act as primary habitats for ungulate species in these landscapes is fundamental for the design of conservation strategies. We use an occurrence dataset for lowland tapir (Tapirus terrestris), white-tailed deer (Odocoileus virginianus), and white-lipped peccary (Tayassu pecari) in the development of species’ potential distribution models, binarization process, and morphological spatial pattern analysis. This information was used for the modeling of dispersal corridors connecting the core habitats of the ungulate focal species using the randomized shortest path algorithm and quantifying the weighted global connectivity metrics. Our results suggest an integral corridor with potential least-cost dispersal routes between the native savanna landscape on the middle basins of the savanna rivers and the Meta River. These areas associated with the fluvial dendritic systems are connected, while the core habitats in the eastern part of the savanna landscape are disconnected. We discuss how the application of such knowledge on the spatial ecology of ungulate focal species might improve the management of the metapopulations in the Orinoquia region.

Predictive Assessment of Climate Change Impact on Water Yield in the Meta River Basin, Colombia: An InVEST Model Application

This paper presents a hydrological assessment of the 113,981 km2 Meta River basin in Colombia using 13 global climate models to predict water yield for 2050 under two CMIP6 scenarios, SSP 4.5 and SSP 8.5. Despite mixed performance across subbasins, the model was notably effective in the upper Meta River subbasin. This study predicts an overall increase in the basin’s annual water yield due to increased precipitation, especially in flatter regions. Under the SSP 4.5, the Meta River basin’s water flow is expected to rise from 5141.6 m3/s to 6397.5 m3/s, and to 6101.5 m3/s under the SSP 8.5 scenario, marking 24% and 19% increases in water yield, respectively. Conversely, the upper Meta River subbasin may experience a slight decrease in water yield, while the upper Casanare River subbasin is predicted to see significant increases. The South Cravo River subbasin, however, is expected to face a considerable decline in water yield, indicating potential water scarcity. This study represents a pioneering large-scale application of the InVEST–AWY model in Colombia using CMIP6 global climate models with an integrated approach to produce predictions of future water yields.

Fish diversity of a tributary of the Meta River, in the flat highlands of the colombian Orinoquia

The distribution and abundance of fish for the Orinoco River basin drainages are influenced by hydrometric seasonality and the structural complexity of the habitat, so understanding how fish assemblages are structured on a temporal and spatial scale is essential for biological conservation. Therefore, the purpose of this study was to describe the fish assemblage for the Mitimiti stream and test the hypothesis of spatial and temporal variation. To do this, collections were made at four sampling stations on the Mitimiti stream, during three contrasting rainfall seasons, with the help of a 10 m x 1.5 m trawl net and a 2 mm mesh eye. The diversity of fish assemblages was analyzed using Hill numbers, abundance-based dissimilarity, and a Canonical Correspondence Analysis (CCA). In total, 2493 individuals and 115 species were recorded, where the orders with the highest dominance were Characiformes and Blenniiformes. Regarding the diversity of order q = 0, no significant differences were found between the hydrological periods and the sampling stations, however, the low water period and St3 exhibited the highest species richness. The most dissimilar hydrological period was the high water season and the variables that significantly influenced fish assemblage were water temperature (p = 0.02) and dissolved oxygen (p = 0.05).

Assessing the Effectiveness of the Use of the InVEST Annual Water Yield Model for the Rivers of Colombia: A Case Study of the Meta River Basin

This paper presents the results of one of the hydrological models, the InVEST “Annual Water Yield” (InVEST–AWY), applied to the Meta River basin in Colombia, which covers an area of 113,981 km². The study evaluates the performance of the model in different subbasins of the Meta River basin. The model’s accuracy was assessed using different statistical measures, including Nash–Sutcliffe Efficiency (NSE) coefficient, Root Mean Square Error (RMSE), correlation coefficients for the calibration (rcal) and validation (rval) periods. The overall performance of the model in the Meta River basin is relatively poor as indicated by the low NSE value of 0.07 and high RMSE value of 1071.61. In addition, the model explains only a 7% of the variance in the observed data. The sensitivity analysis revealed that a 30% reduction in crop coefficient (Kc) values would result in a 10.7% decrease in water yield. The model estimated, for example, the annual average water yield of the river in 2018 as 1.98 × 1011 m3/year or 6273.4 m3/s, which is 1.3% lower than the reported value. The upper Meta River subbasin shows the highest NSE value (0.49), indicating a good result between observed and simulated water discharge. In contrast, the South Cravo River subbasin shows a negative NSE value of −1.29, indicating poor model performance. The Yucao River subbasin and the upper Casanare River subbasin also show lower NSE values compared to the upper Meta River subbasin, indicating less accurate model performance in these subbasins. The correlation coefficients in calibration (rcal) and validation (rval) for the upper Meta River, Yucao River, South Cravo River, and upper Casanare River subbasins were 0.79 and 0.83, 0.4 and 0.22, 0.5 and −0.25, and 0 and 0.18, respectively. These results provide useful insights into the limitations for the proper use of the InVEST–AWY model in Colombia. This study is the first to use the InVEST–AWY model on a large scale in the territory of Colombia, allowing to evaluate its effectiveness in hydrological modeling for water management.

Mitochondrial Genetic Diversity, Population Structure and Detection of Antillean and Amazonian Manatees in Colombia: New Areas and New Techniques.

The Antillean manatee (Trichechus manatus) and the Amazonian manatee (Trichechus inunguis) are distributed in rivers in the Caribbean and Amazonian region of Colombia respectively. For 30 years, genetic information has been obtained from these populations in order to inform conservation programs for these endangered species and decide on the location to release them back to the wild. However, in previous studies, samples from rivers in some areas of the country were not included, given the difficulties to access these regions due to either logistic or safety issues. In this study, we analyzed mitochondrial DNA (mtDNA) control region (CR) sequences of from samples of T. manatus (n = 37) and T. inunguis (n = 4) (410 and 361 bp, respectively), obtained in new and previously unexplored rivers and bays in the country, including Santa Marta, Urabá Gulf, Ayapel Marsh (San Jorge River Basin), Meta River and Magdalena Medio and the low Magdalena River (Cesar Province and Canal del Dique) as well as additional samples from Puerto Nariño in the Colombian Amazon. Our results included the discovery of two newly described mtDNA CR haplotypes for T. manatus. In addition, we confirmed significant population differentiation at the mitochondrial level between the Magdalena and Sinú rivers and differentiation among areas of the same river, including the middle and low Magdalena River. This differentiation may be related to anthropic changes in the river since construction of the Canal del Dique in the XVI century. We also tested environmental DNA sampling and analyses techniques to evaluate its potential use for manatee detection and monitoring in bodies of water in Colombia, in order to evaluate new areas for future manatee conservation initiatives. We emphasize the need to continue using genetic information to provide evidence on the potential best locations to undertake animal release to prevent outbreeding depression.

Recent uplift and the origin of hydrodynamic traps in the Llanos Basin of Colombia

More than 1.4 Bbls of heavy oil (11–15° API) have been discovered to date in hydrodynamic traps in the southeastern Llanos Basin of Colombia, of which the largest is the Rubiales Field. All these are stratigraphic traps defined by the intersection of the top seal (usually the Miocene Carbonera C6 Unit) with an inclined oil-water contact (OWC) (dipping 0.3° towards the NW). In many cases the accumulations occur where there are minor inflections in the top seal, controlled by the underlying paleo-relief of the Paleozoic.The area of stratigraphic traps coincides with the forebulge of the Llanos Basin. A very striking feature is that the area of the stratigraphic traps, which is found south east of the Meta River is being actively uplifted. This is clearly shown in the different levels of terraces that are present south of the Meta River. The highest present-day terrace has an elevation of near 287 m, (vs. approx. 140 m of the Meta River). All of this is indication that this zone is actively being uplifted (at least 200 m) and eroded in contrast to the rest of the basin that is a zone of deposition.It has been proposed that the tilted oil-water contact is related to hydrodynamic flow from the margin of the basin, or from areas with a higher hydraulic head. However, the orientation of the tilted OWC trend (NE-SW) is almost perpendicular to the hydraulic head contours for the basin but coincides with the present-day trend of active inversion related to right lateral movement along the Algeciras/Rio Meta lineament and the location of the Llanos Basin forebulge. It is proposed that the tilting of the OWC is related to recent uplift in areas where the oil is biodegraded due bacterial activity and did not yet have time to equilibrate.

Analysis of Streamflow Variability and Trends in the Meta River, Colombia

The aim of this research is the detection and analysis of existing trends in the Meta River, Colombia, based on the streamflow records from seven gauging stations in its main course, for the period between June 1983 to July 2019. The Meta River is one of the principal branches of the Orinoco River, and it has a high environmental and economic value for this South American country. The methods employed for the trend detection and quantification were the Mann–Kendall (MK) test, the modified MK (MMK) test, and the Sen’s slope (SS) estimator. Statistically significant trends (at a 95% level of confidence) were detected in more than 30% of the 105 evaluated datasets. The results from the MK test indicate the presence of statistically significant downward trends in the upstream stations and upward trends in the downstream stations, with the latter presenting steep positive slopes. The findings of this study are valuable assets for water resources management and sustainable planning in the Meta River Basin.

Population estimate and identification of major conservation threats for the river dolphin (Inia geoffrensis humboldtiana) at the Colombian Orinoquia

South American sub-continent, housed the largest diversity of river dolphins on the planet, here there are two species in the genus Sotalia and three species in the genus Inia. Tonina, present on the Orinoco basin, are expose to many different anthropogenic threats, such as: the fragmentation and loss of aquatic ecosystems; acoustic contamination; risk of collision with boats; entanglement; deaths by retaliation, resulting from biological and operational interactions with artisanal and industrial fisheries; biomagnification of heavy metals such as mercury in the aquatic trophic web; capture of individuals for their usage as bait for the fishery of Calophysus macropterus, primarily on borderline localities between Colombia and Venezuela; and finally, the negative effects of climate change. We conducted a study to determine population sizes and anthropogenic threats affecting river dolphins populations during the beginning of high-water season, between November 2018 and February of 2019, along 1,402 km. We calculated the degradation index for streams of continental waters and density of the river dolphins. Water quality, habitat transformation, species exploitation, and the increment in number of human settlements were identified as the main conservation stressor in the analyzed area. We obtained density values by habitat type for different aquatic environments and population sizes for river dolphins and the value in the index of degradation, with a potential increment in value through time. River confluences were identified as priority areas for the conservation of the species. Water quality, habitat modification, and species exploitation were particularly intense. Our results highlight a potential transformation of the ideal conditions that allow for the establishment of the species, explaining its distribution with predicted values between 46.6 % and 70.1 % for the evaluated timeframe due to the effects of climate change on aquatic ecosystems. The Meta River, has the highest value for the index of freshwater ecosystems degradation followed by the Orinoco basin, water quality and species exploitation appear to be the major stressors for dolphins in these areas. Finally, river confluences were identified as conservation hot spots for dolphin populations. We point out on the importance of river dolphins as bioindicator, sentinel species, and one of the most susceptible to the negative effects of climate change.

River Model Calibration Based on Design of Experiments Theory. A Case Study: Meta River, Colombia

Numerical models are important tools for analyzing and solving water resources problems; however, a model’s reliability heavily depends on its calibration. This paper presents a method based on Design of Experiments theory for calibrating numerical models of rivers by considering the interaction between different calibration parameters, identifying the most sensitive parameters and finding a value or a range of values for which the calibration parameters produces an adequate performance of the model in terms of accuracy. The method consists of a systematic process for assessing the qualitative and quantitative performance of a hydromorphological numeric model. A 75 km reach of the Meta River, in Colombia, was used as case study for validating the method. The modeling was conducted by using the software package MIKE-21C, a two-dimensional flow model. The calibration is assessed by means of an Overall Weighted Indicator, based on the coefficient of determination of the calibration parameters and within a range from 0 to 1. For the case study, the most significant calibration parameters were the sediment transport equation, the riverbed load factor and the suspended load factor. The optimal calibration produced an Overall Weighted Indicator equal to 0.857. The method can be applied to any type of morphological models.

Assessing Orinoco river sediment discharge trend using MODIS satellite images

The aim of this study was to derive the Surface Suspended Sediment Concentration (SSSC) and river sediment discharge (for the period 2000-2016) along the Orinoco River reaches using MODIS remote sensing data. A single SSC retrieval algorithm was calibrated using HYBAM long term monitoring program data (n = 183). The comparison of satellite and field measurements showed a RMSE of 32%, corresponding to a mean absolute error of 21 mg l−1. These results supported the use of MODIS sensors to monitor the SSSC at six virtual stations in the middle and lower reaches of the Orinoco River. The highest mean SSSC were found downstream of the Meta River (101 mg l−1) and of the Apure River (99 mg l−1), which provide the major sediment input to the Orinoco main stream. The lowest mean SSSC was found upstream of the Meta River (42 mg l−1). In the lower reach, at Ciudad Bolivar station we assessed a mean SSSC of 88 mg l−1.MODIS-derived and ground-derived assessments of the annual sediment discharge show very fine agreement, within −2%. Coupling satellite-derived SSSC estimates and river discharge monitoring data, we calculated the Orinoco River sediment discharge at Ciudad Bolivar station between 2001 and 2016. For a mean Orinoco River discharge of 33,320 m3.s−1, the sediment loads varied from 75 to 103 Mt.yr−1, with a mean value of 89 Mt.yr−1 (RSD of 9%) corresponding to a sediment yield of 91–125 t.km−2yr−1 with no positive or negative trends over the observed period.

Health composite indicator: risk of transmission of rabies virus

To design a composite health indicator on the risk of rabies virus transmission in the department of Meta, Colombia. Ecological, exploratory study. Data from secondary sources were collected from the databases of the Meta Department of Health and the Colombian Agricultural Institute (ICA) for the period 2009 - 2014. The composite health indicator was created based on the normalization (logX) of the data and the selection of measures for the elaboration of three thematic indexes in the 29 municipalities of the department. They were integrated by means of the aggregation method, and their distribution was reflected in a geographical mapping with the zoning of the risk for rabies virus transmission in the department. In the classification of the composite health indicator on the risk of rabies transmission, the high level corresponds to 34% of the municipalities of the department, the middle level involves 17%, the low level, 28%. The municipalities without risk are La Macarena, Mapiripán, Vistahermosa, Villavicencio, Puerto Concordia, Granada and Puerto Rico, representing 21%. The high level of the composite health indicator on the risk of rabies virus transmission is found in municipalities of the Meta River sub-region, the Cordillera sub-region and the upper Ariari sub-region. These areas are characterized by high concentrations of animals, decreased coverage of rabies vaccination and circulating confirmation of the virus.

Ichthyofauna of piedmont and savannah environments in the Casanare River drainage, Orinoco Basin, Colombia 

Currently, only 20 fish species have been recorded from the Casanare River, which is one of the main tributaries of the Meta River drainage. To characterize the fish assemblages of this river, samplings were carried out at 35 collecting stations in low and high water seasons of 2015. The results obtained, raised the number of fish species of the Casanare River drainage to 180, of which 41 are exclusive to the piedmont, 83 to the savannah and 56 are shared between both units; 19 species are endemic, 11 are migratory, and three are classified in one of the national threat categories. Three species were found to be undescribed and one represents a new record for the Orinoco River Basin in Colombia. This study fills the lack of information for the Casanare River drainage, highlights its importance as a potential area for biodiversity conservation and facilitates the decision-making process related to the management planning and conservation of the hydrographic basin

Fishes of the Cusiana River (Meta River basin, Colombia), with an identification key to its species.

The Cusiana River sub-basin has been identified as a priority conservation area in the Orinoco region in Colombia due to its high species diversity. This study presents an updated checklist and identification key for fishes of the Cusiana River sub-basin. The checklist was assembled through direct examination of specimens deposited in the main Colombian ichthyological collections. A total of 2020 lots from 167 different localities from the Cusiana River sub-basin were examined and ranged from 153 to 2970 m in elevation. The highest number of records were from the piedmont region (1091, 54.0 %), followed by the Llanos (878, 43.5 %) and Andean (51, 2.5 %). 241 species distributed in 9 orders, 40 families, and 158 genera were found. The fish species richness observed (241), represents 77.7 % of the 314 estimated species (95 % CI=276.1–394.8). The use of databases to develop lists of fish species is not entirely reliable; therefore taxonomic verification of specimens in collections is essential. The results will facilitate comparisons with other sub-basins of the Orinoquia, which are not categorized as areas of importance for conservation in Colombia.

El Río como Infraestructura: Paisaje y navegación en el río Meta, Colombia

A comienzos del siglo XXI, los ríos se entienden en Colombia ya no como elementos ‘naturales’ de la geografía y del paisaje, sino como un tipo particular de artefacto. Han pasado a ser entendidos como infraestructura, como elementos del ensamblaje de un nuevo sistema de producción. El río se convierte así en eje de un régimen de intervención, es decir, en el eje de un conjunto de prácticas instrumentales y discursivas, que constituyen un cierto tipo de espacialidad y de organización social; respondiendo a la lógica y prioridades de expansión del capitalismo. Y este régimen deja huellas en el paisaje. Este trabajo se propone así, primero, discutir el concepto de ‘regímenes de intervención’ y los debates teóricos a los que hace referencia; segundo, proponer una reflexión sobre la forma que estos regímenes se configuran y leen en el paisaje; y tercero, explorar el caso del río Meta desde esta perspectiva.

First record of Amatitlania nigrofasciata (Günther, 1867) (Cichliformes: Cichlidae) as introduced species in natural freshwaters of Colombia

Amatitlania nigrofasciata is a small fresh­water fish species native to Central America. Is a popular ornamental fish that has been traded and cultivated for the aquarium industry, introduced into temperate and tropical regions across the world. Two specimens of A. nigrofasciata were collected from two small creeks draining into the Guavio River, upper Meta River in Mambita, Ubalá, Cundinamarca, Colombia in the Piedmont Orinoco ecoregion. This is the first record of A. nigrofasciata in natural freshwaters of Colombia and the Orinoco River basin. Diagnostic characters of species and updated distribution at country level are provided.

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The Meta River is full of hopes and dreams that have been built from the early conquerors and missionaries who plied its waters to the large infrastructure projects of the 21st century. From the Colonial times, the Plains region, through which the Meta River runs, was established as a boundary because of hot weather, the “wild” dwellers, as well as the Andes range as a geographical barrier that pulled away from the administrative center; however, the river was always thought and imagined as an integrating axis to include a vast territory into civilization, progress and development. This article aims to analyze different views and projects for the integration of Colombia’s Eastern Plains, whose axis is the Meta River, and whose objective was to change the border situation of the region. Although none of the projects fully achieved its goal, their execution makes evident that the region has always been planned and operated from the outside; and without considering its peculiarities or those of its inhabitants; and that situation has generated profound changes in the landscape. Keywords: Colombia, Orinoquia, Llanos Orientales, Border.

Tallas de captura de Prochilodus mariae en la parte alta del río Meta, Orinoquia colombiana

A partir del análisis del comportamiento histórico (1980 a 2011) de las tallas de captura y tallas de madurez de hembras y machos de Prochilodus mariae, se pretendió establecer si sobre la población de la parte alta del río Meta, se presentaba algún tipo de afectación evidenciable en las tallas medias de captura anual (TMCA) y tallas de madurez (TMG). La información fue colectada mediante muestreos a los desembarcos en Puerto López, Meta. Cada ejemplar fue medido, pesado y sexado y a partir de 13444 registros, se estimaron la TMCA y las tallas de captura mensuales (TMCM); estos estimativos se compararon entre años; se hicieron análisis de correlación con los niveles del río Metica y las anomalías ENSO. Se estimó la TMG al 25%, 50% y 75% por año. El rango de las tallas de captura comercial de P. marie fue de 14 a 45 cm longitud estándar (LE), con diferencia entre machos y hembras. La mayor TMCA de hembras (32,6 cm LE) y machos (32 cm LE) se presentó en el año 1980, en los años siguientes este parámetro oscilo entre 30 y 26,4 cm LE en hembras y entre 26 y 29 cm LE en machos. En el ciclo anual las mayores TMCM de hembras se presentaron de abril a junio y de machos en mayo y junio. La TMGL50 de hembras, fue significativamente mayor en el año 1980 (33,5 cm LE), en los años siguientes osciló entre 27,1 y 31,8 cm LE en hembras; en machos durante todo el periodo de estudio vario entre 25,8 y 29,5 cm LE. La población de P. marie bajo presión de pesca en la zona de estudio, no se encuentra afectada por sobrepesca al crecimiento ni al reclutamiento.

Valoración estacional de las amenazas contra la conservación de Inia geoffrensis humboldltiana (Cetartiodactyla Iniidae) en la cuenca del Río Meta, Colombia

Introduction: As a consequence of population isolation by the presence of geomorphological barriers, dolphins from northern South America are subdivided into three species: I. geoffrensis (Amazon and Orinoco Rivers), I. boliviensis (Madeira River in Bolivia), and the recently described I. araguaiaensis inhabiting the hydrologic complex of the Araguaia –Tocantins Rivers in the northeastern Brazilian Amazon. The importance of pink dolphins at the ecosystems they inhabit is supported by: 1) its position as top predators in the food chain; 2) bioindicators for ecosystem health; 3) its cultural and mythological meaning for the local ethnic groups, such as Sikuanis from the Orinoco, and Ticuna for the Amazon; and 4) their economic value, mainly as a touristic attraction. The conservation status of Orinoquian populations of river dolphins ( i. g. humboldtiana ), has not been fully established. However, we know their populations are threatened by a series of human activities on both aquatic and terrestrial environments, affecting their occurrence across the basin. This research is part of an inter-institutional effort conducted between the Corporacion para el Desarrollo Sostenible del Area de Manejo Especial de la Macarena (CORMACARENA) and Fundacion Omacha, to monitor pink dolphin populations inhabiting the rivers: Meta, Manacacias, Yucao, and Cusiana, in order to identify conservation tensors affecting the species in the study area. Methods: We conducted a multitemporal study to determine anthropogenic threats affecting dolphin populations during two hydrologic periods along 317.2 km -1 across the middle Meta River basin. We calculated the degradation index for streams of continental waters and density of the river dolphins, developed by Gomez-Salazar et al. (2012). Water quality, habitat transformation, species exploitation, and the increment in number of human settlements were identified as the main conservation tensors in the analyzed area. Results: We obtained a high value in the index of degradation, with a potential increment in value through time. River confluences were identified as priority areas for the conservation of the species. The development of infrastructure projects on the main streams was identified as a future threat on freshwater ecosystems in the basin. Differences in hydrologic periods were identified as an important variable, not only affecting the ecological dynamic of the species, but also determining the anthropogenic tensors through time. Water quality, habitat modification, and species exploitation were particularly intense at low water level periods, while boat traffic, and fishing activities are more frequent at periods of high water levels in the region. Discussion and conclusions: For the Meta River, water quality and species exploitation appear to be the major tensors for dolphins and they may explain the low densities recorded for the area in comparison with densities reported for the Amazon basin. Even though, we consider this analysis is not definite and more samplings are necessary to confirm this hypothesis. Finally, river confluences were identified as conservation hot spots for dolphin populations. We point out on the importance of river dolphins as umbrella species, ideal to develop conservation strategies in the region. Key words: Degradation index, Meta River, threats and conservation, Tonina.

Sediment yield along the Andes: continental budget, regional variations, and comparisons with other basins from orogenic mountain belts

We assess the sediment yield at 119 gauging stations distributed from Colombia to Patagonia, covering the different morphotectonic and morphoclimatic settings of the Andes. The most productive areas are the Meta River basin within the northern Andes and the Bolivian and northern Argentina-Chaco systems, which produce an average of 3345, 4909 and 2654tkm2 y−1 of sediment, respectively. The rivers of the northern and central Andes (excluding the Pacific watersheds of Peru, northern Chile, and central Argentina) have a weighted mean sediment yield of 2045tkm−2 y−1 and produce 2.25 GTy−1 of total sediment. A major constraint estimating the Andean continental budget of sediment yield lies in the lack of gauging data for the Peruvian region. Using the available gauge stations, the regional sediment yield appears underestimated. Assuming a higher value of sediment yield for the Peruvian Andes, the total budget for the whole central Andes could range between 2.57 GT y−1 and 3.44 GT y−1. A minimum of~0.55 GT y−1 and a probable maximum of~1.74 GT y−1 of sediment are deposited in the intramontane and surrounding proximal sedimentary basins. The magnitude of sediment yield in the Andes is comparable to other rivers draining orogenic belts around the world.

Una nueva especie de pez del género Hemibrycon (Characiformes: Characidae)

Hemibrycon pautensis (Characiformes, Characidae), a new fish species from Paute River, eastern Ecuador is described. Diagnostic characteristics: eight to nine branched rays in the dorsal fin (vs. six to seven), and 27 - 28 in the anal fin (vs. 16 - 26, except in H. dariensis which presents 22 - 27, in H. metae 26 - 31 and H. jabonero 23 - 28); a no occurrence of dorsal pharyngeal plate (vs. occurrence); a cartilaginous and divided-in-two basihial (vs. an osseous base and a cartilaginous upper part). Hemibrycon pautensis resembles H. metae by its oblique external edge of the pelvic fins. They can be distinguished by the position of the pectoral fins in relation to the snout (38.24-41.6% in H. pautensis vs. 21.21-25.87) and by the position of the pectoral fins in relation to the origin of the dorsal fin (20.95-24.30 in Hemibrycon pautensis vs. 35.89-42.63), and by the number of proximate radials in the pectoral girdle (five in Hemibrycon pautensis vs. three to four). In addition, the geographic distribution of H. metae is restricted to the upper part of the Meta River in Colombia and can be distinguished of H. boquiae by: the number of scales between the lateral-line and the origin of the dorsal fin (eight in H. pautensis vs. 5-7); the distance between the snout and the pelvic fins (38.00-42.90 % in H. pautensis vs. 42.9-46.19%); the pelvic fins length (13.77-17.96% in H. pautensis vs. 10.72-13.21%); and the snout length (21.34-27.88 in H. pautensis vs. 26.92-33.66%).