Trichomycterus venulosus (Steindachner, 1915): posible especie extinta del páramo de Cruz Verde (Cundinamarca, Colombia)

The investigation was carried out between November 2004 and August 2005, and was based on the rivers Teusaca, Idaza, La Laguna (Quebrada Blanca), del Salteador creek, Marlene creek (affluent of the del Salteador creek), Blanca creek (Mataredonda-Reserve) and El Charco creek (affluent of Santa Barbara creek). All the rivers, with exception of the river Teusaca (Magdalena river basin), are part of the El Palmar river basin (Orinoco river basin). The waters are characterized by low conductivity (<52 μS cm-1), low temperature (11-14 °C), acid pH (5,5–6,3) and a high oxygen concentration (>90%). According to our field observations, some small forested areas still exist, and the soil is mainly used for agriculture (potato culture) and livestock farming

Effects of aquatic vegetation on the spatial distribution of grundulus bogotensis, humboldt 1821 (characiformes: characidae)

G. bogotensis has a geographic distribution restricted to the Colombian Cundiboyacenseplateau, it is listed as near threatened, and research on its autoecology is scarce. Threecollections were made in 2006 in the Fúquene Lake, Cundinamarca, Colombia (5°27’ 55’’ N, 75° 46’ 19’’ W) to describe the habitats occupied by G. bogotensis and todetermine its vertical and horizontal distribution. Three sampling zones were selectedaccording to the type of dominant macrophyte (Eichornia crassipes, Schoenoplectussp. and Egeria densa). In each sampling zone two different cylindrical sampling traps(cloth and PVC) were placed at three depths: surface, mid-depth and bottom. Threereplicates were used for each depth and type of trap. Traps were exposed for 24 hoursand checked every 6 hours. In addition to the traps, sampling by electrofishing wasconducted in each sampling zone during every month. To characterize the study area,physical and chemical variables were analyzed and the structure of phytoplankton,zooplankton, periphyton, and macroinvertebrate communities was studied. Resultsshowed spatial differences on G. bogotensis habitat occupation and differences incaptures at each depth, which depend on the dominant type of aquatic vegetationand size of individual. We conclude that only cylindrical cloth traps are suitable toconduct population studies of G. bogotensi

New excavations at the HWK EE site: Archaeology, paleoenvironment and site formation processes during late Oldowan times at Olduvai Gorge, Tanzania

This paper reports the results of renewed fieldwork at the HWK EEsite(Olduvai Gorge, Tanzania). HWK EEis positioned across the boundary between Lower andMiddle Bed II, a crucialinterval for studyingthe emergence of the Acheulean at Olduvai Gorge. Our excavations at HWK EEhave produced one of the largest collections of fossils and artefacts from any Oldowan site, distributed across several archaeological units and a large excavation surface in four separate trenches thatcan be stratigraphically correlated. Here we present the main stratigraphic and archaeological units and discuss site formation processes.Results show a great density of fossils and stone tools vertically through two stratigraphic intervals (Lemuta and Lower Augitic Sandstone)and laterally across an area of around 300 m2, and highlight the confluence of biotic and abiotic agents in the formation of the assemblage. The large size and diversityof the assemblage, as well as its good preservation, qualify HWK EEas a reference sitefor the study of the late Oldowan at Olduvai Gorge and elsewhere in Africa. In addition, thedescriptionof the stratigraphic and archaeological sequenceof HWK EE presented in this paper constitutesthe foundation for further studies on hominin behaviour and palaeoecologyin Lower and Middle Bed II

Diatom-based reconstruction of Late Glacial and Early Holocene environment in the Pyrenees = Reconstrucción ambiental del Tardiglaciar y el Holoceno Temprano en los Pirineos utilizando el registro sedimentario de diatomeas

[spa] Los lagos son ecosistemas expuestos a la influencia combinada del clima y la entrada de materiales y nutrientes desde la cuenca. La información de estos procesos y de la dinámica interna del sistema suele archivarse en los sedimentos mediante la acumulación de los materiales externos y los producidos por el sistema. Dentro de los materiales acumulados en los sedimentos, las valvas de diatomeas pueden aportar información limnológica que es difícil de obtener con otros indicadores. El objetivo principal de esta tesis fue explorar el potencial de las diatomeas para realizar reconstrucciones ambientales multivariadas del pasado, con una aplicación a la secuencia sedimentaria del Holoceno Temprano y el Tardiglaciar del lago Burg (Pirineos). La variabilidad regional de la distribución de diatomeas en zonas alpinas y templadas es generalmente explicada por el gradiente de pH y alcalinidad. Sin embargo, existe una gran variabilidad que está relacionada con otros factores ambientales y que podría también ser utilizada en el desarrollo de la reconstrucción del ambiente acuático. Algunos autores ponen en duda la viabilidad de realizar reconstrucciones independientes, utilizando un único registro de diatomeas, argumentando que la correlación entre las variables puede alterar las señales que son reconstruidas. Sin embargo, otros autores sostienen que es posible realizar reconstrucciones, si existen conjuntos de especies con respuestas distintas. De acuerdo con esto, inicialmente se realizó un estudio taxonómico y ecológico de las diatomeas de 80 lagos de montaña de los Pirineos. Se exploraron los factores ambientales que, además del pH, explican la distribución de diatomeas en los lagos pirenaicos, incluyendo factores próximos al lago y descriptores generales de la cuenca. Este análisis se realizó siguiendo la aproximación de especies indicadoras. Así mismo, se desarrollaron funciones de transferencia para reconstruir diferentes variables independientes a partir de un mismo conjunto de datos de diatomeas. Posteriormente, se aplicaron los resultados las especies indicadoras y las funciones de transferencia en la secuencia sedimentaria del lago Burg cubriendo el Tardiglaciar y el Holoceno Temprano. Finalmente, se analizan los resultados encontrados en términos de los procesos internos del lago y su eventual vinculación con procesos relacionados con el clima y la cuenca.[eng] Lakes are ecosystems exposed to the combined influence of climate and catchment processes. Lakes collect and archive evidence of these forcings in their sediments through of a complex interaction with internal processes. Deciphering and extracting information from the sediments is a challenging task because, in addition to the inter-dependence between the forcing agents, the lake ontogeny affects the way in which the system responds to them. Among the sub-fossil material, diatoms occupy an outstanding position. The remains can be identified to the species level, due to the siliceous composition of their valves. This fact, added to the rich community that at any instant exists in the lake, make diatoms an excellent proxy for environmental reconstructions. In this study, the focus is placed on the diatom assemblages of the lakes of the Pyrenees and their potential as indicators of environmental conditions. The findings are applied to the sedimentary sequence of the former Burg Lake to reconstruct the lake conditions during Late Glacial and early Holocene periods. The regional variability of diatom distributions is usually explained by pH or acid neutralising capacity gradients in alpine and temperate areas. However, there is a large remaining unexplained variability, which is related to other environmental factors, and could be also used in environmental reconstructions. Some researchers question the feasibility of independent reconstructions of several variables from a single diatom record; they argue that the high temporal autocorrelation of the local assemblages might obscure secondary influences. However, some others sustain that it is possible to perform reconstructions, even of particularly dependent variables if they present contrasting trends at some sites. Accordingly, it was carried out an extensive taxonomical study of diatom of the mountain lakes of the Pyrenees. After this, were explored the environmental factors that, besides pH, explains the diatom distribution in the lakes of the Pyrenees, including in-lake proximal factors as well as general descriptors of catchment characteristics and using indicator analysis approach. In order to demonstrate that it is possible to reconstruct different independent variables from a unique diatom data set were developed transfer functions for selects variables and analysed the reliability and the independence of models performed. The analysis was carried out by comparing the performance of two sample data-sets (bottom surface sediment and epilithon samples). The ratio between Chrysophycean cysts and diatoms was analysed as a potential environmental indicator. Indicator species and the transfer functions were applied to the diatoms of the sedimentary sequence of Burg Lake covering Late Glacial and Early Holocene. The reconstructed variables were analysed in terms of in-lake processes and their eventual link with climate and catchment processes. An interpretation of the reconstruction of climate during Late Glacial and Early Holocene in the Pyrenees is shown

GRANDES TAXONES DE FITOBENTOS Y SU RELACIÓN CON LA HIDROLOGÍA, FÍSICA Y QUÍMICA DE PEQUEÑOS RÍOS ANDINOS

In 16 sampling points, which were located in 14 streams of the middle and high basin of the Bogotá River (2.617 - 2.988 m), we analyzed some physical, chemical and hydrological variables and the benthic algae community (taxonomic classes). By means of Principal Component Analysis, we concluded that the rivers respond to a basin area gradient and mineralization gradient. The streams are of the acidic order 1-4, and their flow rates are lower than 3.7 m3 s-1. The total nitrogen and total  phosphorus concentrations are lower than 7 mg l-1 and 1.4 mg l-1,  respectively. The benthic community is dominated by diatoms,  cyanobacteria and green algae. The basin area and mineralization gradients determine the dominant and co-dominant benthic algae class per stream

Diatomeas de pequeños ríos andinos y su utilización como indicadoras de condiciones ambientales

En veinte ríos de la cuenca alta y media del Río Bogotá (Cundinamarca, Colombia)se estudió la relación entre algunas variables físicas, químicas e hidrológicas con lacomunidad de diatomeas perifíticas. A partir de un Análisis de ComponentesPrincipales se estableció que la conductividad, el pH, el amonio, la turbidez, elfósforo total, el dióxido de carbono y la velocidad de la corriente fueron las variablesque determinaron los patrones físicos y químicos de los ríos. Mediante un Análisisde Correspondencia Canónica se estableció que el pH, el fósforo reactivo soluble,el nitrógeno total y la conductividad fueron las variables que determinaron lacomunidad de diatomeas. Finalmente, se propone un modelo de regresión ycalibración para inferir los valores de las variables significativas a partir de laestructura de la comunidad

GRANDES TAXONES DE FITOBENTOS Y SU RELACIÓN CON LA HIDROLOGÍA, FÍSICA Y QUÍMICA DE PEQUEÑOS RÍOS ANDINOS

In 16 sampling points, which were located in 14 streams of the middle and high basin of the Bogotá River (2.617 - 2.988 m), we analyzed some physical, chemical and hydrological variables and the benthic algae community (taxonomic classes). By means of Principal Component Analysis, we concluded that the rivers respond to a basin area gradient and mineralization gradient. The streams are of the acidic order 1-4, and their flow rates are lower than 3.7 m3 s-1. The total nitrogen and total  phosphorus concentrations are lower than 7 mg l-1 and 1.4 mg l-1,  respectively. The benthic community is dominated by diatoms,  cyanobacteria and green algae. The basin area and mineralization gradients determine the dominant and co-dominant benthic algae class per stream

ESTUDIO MORFOMÉTRICO DEL LAGO GUATAVITA (COLOMBIA)

En el lago Guatavita se estudiaron sus características morfométricas con el objeto de analizar implicaciones de la morfología sobre su funcionamiento y discutir algunas hipótesis que existen sobre el origen del lago. El lago presenta una cubeta con una forma cónica, bajo desarrollo del perímetro, profundidad máxima de 30m y profundidad relativa de 7.9%. La curva hipsográfica indica que el lago presenta un aumento constante del área de la sección con respecto a la profundidad. La forma del lago promueve una estratificación térmica que se mantiene durante ocho meses del año, con un hipolimnio hipóxico y un fuerte gradiente en la conductividad y en la concentración de amonio. Estos resultados indican un papel muy importante de la profundidad sobre las características físicas y químicas del lago que a su vez determinan la dinámica de las comunidades biológicas y una baja productividad primaria del sistema

<em>Trichomycterus venulosus<em> (Steindachner, 1915): posible especie extinta del páramo de Cruz Verde (Cundinamarca, Colombia)

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