El presente trabajo se realizó en el arroyo El Chacay y en el río Las Albahacas desde la primavera de 1999 hasta la primavera de 2000. El objetivo de esta investigación fue comparar la composición y abundancia de la comunidad diatómica en ríos y arroyos serranos de la cuenca del río Piedra Blanca, durante un ciclo anual. En total, 121 taxa (especies, variedades y formas) fueron registrados a partir del análisis taxonómico. El orden Pennales predominó en número de especies y porcentaje de frecuencia relativa. El género con mayor número de especies fue Navicula. El número de especies osciló entre un mínimo de 21 en invierno de 2000 en el río Las Albahacas (aguas arriba del balneario) y un máximo de 49 en verano de 2000 en el arroyo El Chacay y en primavera de 2000 en el río Las Albahacas (aguas arriba del balneario), respectivamente. El mayor número de especies corresponde a los menores porcentajes de frecuencia. La densidad osciló entre 1 org.ml-1 en otoño de 2000 en el río Las Albahacas, aguas arriba del balneario y 1596,40 org.ml-1 registrados en primavera de 1999 en el arroyo El Chacay. Los parámetros fisicoquímicos y la composición de especies determinaron una mayor afinidad entre los sitios en la estación de primavera.<br>The present work was developed in El Chacay Creek and Las Albahacas River from 1999 spring to 2000 spring. The aim of this investigation was to compare the composition and abundance of the diatom communities of a highland water stream and a river within the Piedra Blanca River basin, during an annual cycle. As a result of a taxonomic analysis a total of 121 taxa (species, varieties and forms) were recorded. The Order Pennales predominated in number of species and relative frequency. The genus with the highest number of species was Navicula. The total number of species varied from a minimum of 21 in 2000 winter season in the Las Albahacas River (upstream riverside resort) to a maximun of 49 in 2000 summer in the El Chacay Creek and during 2000 spring in the Las Albahacas River (upstream riverside resort) respectively. The occurrence of a number of species with low frequency was noticed. The density varied from a minimun of 1 org.ml-1 in 2000 fall in the Las Albahacas River, upstream riverside resort, to a maximum of 1596,4 org.ml-1 in 1999 spring at El Chacay Creek. The physical and chemical factors as well as the species composition, a more similarity was found for the spring season in all studied spots.

The main aim of this study was to analyze the composition and structure of the diatom community (Bacillariophyceae) in the River Vacacaí hydrographic basin, Santa Maria municipal district, state of Rio Grande do Sul, Brazil, and its relation to physical and chemical variables, related to water quality. Monthly field trips were carried out between June 2011 and July 2012 in six sampling stations along the river course, in order to collect epilithic diatoms in natural substrates as well as water samples. Qualitative and quantitative analyses of the communities were performed on permanent glass slides under a light microscope. The relative abundance of diatom species was obtained from the count of at least 600 valves on each slide, as well as identification of taxa to species and variety levels. The following water quality variables were also measured: biochemical oxygen demand (BOD), chemical oxygen demand (COD), pH, suspended solids (SS), conductivity, turbidity, and dissolved oxygen. The results were compared to the water use categories determined by the National Council for the Environment (CONAMA) in a resolution issued in 2005. Multivariate techniques (cluster, canonical correspondence and indicator species analyses) and community structure parameters (species richness, Shannon‟s Diversity Index, determination of abundant and dominant species in each sample) were used in order to describe environmental and biological patterns found. 171 species were identified in total. Multivariate analyses resulted in grouping of the sampling stations rather than sampling dates, with the upstream sections separated from the downstream zones. The latter were characterized by higher values of BOD, COD and conductivity, as well as the dominance of diatoms species typical of pollutes sites such as Sellaphora pupula, Nitzschia palea, Gomphonema parvulum and Cocconeis placentula. At the most polluted site, species richness and diversity indices were significantly lower than at the remaining sampling stations. Human activities, markedly sewage effluents are pointed as the main causes of water quality degradation. | Coordenação de Aperfeiçoamento de Pessoal de Nível Superior | Este trabalho teve como objetivo analisar a composição e estrutura das comunidades de algas diatomáceas (Bacillariophyceae) na Bacia hidrográfica do Vacacaí, município de Santa Maria RS, Brasil e sua relação com alguns parâmetros físicos e químicos, inferindo sobre a qualidade d‟água. Foram realizadas coletas mensais de diatomáceas epilíticas e de água no período de junho de 2011 a junho de 2012, em seis pontos de amostragem. Para estipular a percentagem relativa foram contadas 600 valvas em cada lâmina. Efetuou-se também análises da demanda bioquímica de oxigênio (DBO), demanda química de oxigênio (DQO), pH, sólidos suspensos (SS), condutividade, turbidez e oxigênio dissolvido. Os parâmetros foram comparados com as classes de uso da água prevista na resolução do Conselho Nacional de Meio Ambiente (CONAMA 357/2005). No processamento da informação, empregou-se uma análise de componentes principais (PCA), análise de agrupamento, análise de correspondência canônica (CCA), análise de espécies indicadoras, análises de diversidade, riqueza e foram também determinadas as espécies abundantes e dominantes de acordo com o critériode Lobo & Leighton (1986). Ao todo 171 espécies foram identificadas. A análise estatística utilizada se complementa, podendo observar-se uma separação espacial, onde pontos a montante foram separados de pontos a jusante, sendo que os pontos a jusante foram correlacionados com maiores valores de DBO, DQO e condutividade e caracterizaram-se pela dominância de espécies de diatomáceas típicas de locais poluídos como Sellaphora pupula, Nitzschia palea, Gomphonema parvulum e Cocconeis placentula. No ponto considerado o mais poluído a riqueza específica e diversidade é significativamente menor que nos demais pontos. As atividades humanas, especialmente o lançamento de esgotos são responsáveis pela alteração da qualidade d‟água.

Con la finalidad de determinar la influencia del evento El Niño 2009-2010 que se dsarrolló en elas regiones Niño 1+2 y 3.4, en base a los organismos indicadores de masas de aguas para determinar la intensidad y efectos en la costa ecuatoriana, se utilizaron cinco grupos de organismos planctónicos: Diatomeas, Dinoflagelados, Quetognatos, Pterópodos, Heterópodos y las concentraciones de clorofila a antes, durante y después del evento El Niño 2009-2010. En el primer trimestre del 2009 se registró una alta producción primaria, mientras que desde septiembre a noviembre se observó la más baja productividad del mar, en las estaciones fijas La Libertad como en Manta.En la estación fija de La Libertad, durante todo el 2009 predominaron especies de fitoplancton que se relacionan con masas de aguas frías como Leptocylindrus danicus y Rhizosolenia stolterfothii, pero también se presentaron dinoflagelados que indican la presencia de aguas cálidas como Proboscia alata y Ceratium macroceros, que desde mayo a agosto aumentaron su porcentaje, originando aguas de mezcla. Las especies de zooplancton de aguas frías como Sagitta peruviana, se presentaron durante El Niño 2009-2010, pero siempre su porcentaje fue menor en Manta, otra especie que ha predominado es Sagitta bedoti, indicadora de aguas de mezcla, estuvo dominante el segundo semestre con mayor porcentaje en Manta. De las 10 especies de Pterópodos y heterópodos identificadas, se observaron desde septiembre del 2009 a marzo del 2010, estadías juveniles de Hyalocylis striata indicando la presencia de Aguas Subtropicales y Tropicales cerca de la costa Ecuatoriana, relacionadas con el evento cálido que se encontraba en la región Niño 3.4. El evento de El Niño desarrollado en la región Niño 3.4 en el Pacífico Central tuvo una influencia débil a moderada en la costa Ecuatoriana porque en la región Niño 1+2 del Pacífico Oriental existía un episodio neutral, que minimizaba la influencia del evento cálido que se encontraba en el Pacífico Central. | With the purpose of determining the influence of the event El Niño 2009-2010 who was developed in regions Niño 1+2 and 3.4, on the basis of the indicators organisms of water masses to determine the intensity and effects in the Ecuadorian coast, five groups of planktonics organisms were used: The Diatoms, Dinoflagellates, Chaetognatha, Pterópods, heterópods and concentrations of chlorophyll a, before, during and after the event El Niño 2009-2010. In the first trimester of the 2009 a high primary production was registered, whereas from september to november the lowest productivity of the sea in the fixed station of La Libertad like as much in Manta was observed. In the fixed station of La Libertad during the year 2009 predominated species of phytoplankton that are related to cold water masses like Leptocylindrus danicus and hizosolenia stolterfothii, but also they appeared dinoflagellates that indicates the presence of warm water like Proboscia alata and Ceratium macroceros, which from may to august they increased his percentage, originating mixture waters. The species of zooplankton of cold waters like Sagitta peruviana, they appeared during El Niño 2009-2010, but always its percentage was smaller in Manta, another species that has predominated is Sagitta bedoti, indicator of mixture water, was dominant the second semester with greater percentage in Manta. of 10 species of Pterópods and heterópods, identified they were observed from september of 2009 to march of 2010, juveniles stages of Hyalocylis striata indicating the presence of subtropical and tropical water near the Ecuadorian coast, related to the warm event that was in region Niño 3.4. The event the El Niño developed in region Niño 3,4 in the Central Pacific had a weak to moderate influence in the Ecuadorian coast because in region Niño 1+2 of the Eastern Pacific a neutral episode existed, that diminished the influence of the warm event that was in the Central Pacific. | Published

Diatoms are useful ecological indicators because they are found in abundance in most lotic ecosystems. The use of diatoms as indicators of the quality of river waters is widely accepted based on the fact that all diatom species have optima with respect to their tolerance for environmental conditions such as nutrients, organic pollution, pH, etc. Moreover diatoms are indicators of pollution in short term compared with other groups eg. macroinvertebrates. The rivers and streams of the Pampean plain, in Buenos Aires Province, are subjected to different human impacts. The most important stresses on rivers and streams in the Pampean plain are organic enrichments (discharge of insufficiently treated sewage), nutrients, heavy metals, pathogenic agents, pesticides, herbicides and physical changes produced by dredging and canalisation. The bottom substrate is mostly composed of slime-clay with low proportions of gravel and sand; in consequence, the epipelon is the most represented benthic community and suitable for biomonitoring purposes because it allows for comparing similar substrates along the rivers and streams. The aim of this study is to summarise the most common methodologies used in biomonitoring with diatoms and the application of biotic indices (diversity and pollution indices) in the evaluation of water quality of rivers and streams from the Pampean plain. | Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA)

The study of the different biotic and abiotic processes involved in the current formation of Fe-stromatolites in rivers affected by acid mine drainage (AMD) is essential not only to understand this unique and extreme environment, but also to achieve a better understanding of the past iron formation on the Earth and on Mars. The Fe-stromatolites studied in the highly polluted AMD in Tharsis, SW Spain, revealed a unique mineral assemblage with jarosite and rostite as the most unexpected Fe and Al phases and goethite and schwertmannite as the main constituents. Seasonal variations in this region greatly affected the composition of the precipitates and the distribution of diatoms within the Fe-stromatolites. Drought and flood events were also recognized in the sedimentary textures and in the mineral assemblages observed of particular layers within the Fe-stromatolites. The characterization of the chemical and mineralogical composition of Fe-stromatolites in Tharsis as well as the different formation mechanisms proposed complement the existing literature on newly-formed Fe-stromatolites and provides new observations to increase our understanding of those extreme environments.

Benthic diatoms are the periphyton component most studied in Costa Rican rivers, yet there is still much to be known about their ecology. This study aims to contribute to this knowledge. Periphyton samples from six locations along the middle reach of Sarapiquí river and some of its tributaries were taken and analyzed from 2010 to 2012. A total count of 400 frustules was performed in each sample to obtain relative abundances of each species. Ten species, which were easily recognized at the light microscope, were analyzed here: Achnanthidium exiguum, Coconneis placentula, Cymbella tumida, Luticola goeppertiana, Luticola ventricosa, Navicula symmetrica, Nitzchia clausii, Nupela praecipua, Reimeria sinuata and Synedra goulardi. Their abundance was related to physico chemical data at each site for every sampling date (dissolved oxygen, temperature, conductivity, total suspended solids, turbidity, pH and alkalinity) with a canonical correspondence analysis (CCA) that allowed distinguishing three sectors along the river according to altitude. These sectors differed by substrate, riparian vegetation cover, and physic-chemical parameters, all of which resulted in differences in diatom species composition among them. Optimum values and tolerances form each environmental parameter were calculated for each species. Our results showed that A. exiguum, R. sinuata, L. ventricosa and C. tumida, were dominant in clean and well oxygenated waters with low temperatures. The species N. praecipua, S. goulardi, C. placentula, L. goeppertiana, N. clausii and N. symmetrica inhabited warm waters with high turbidity and low oxygen. The species A. exiguum, R. sinuata were dominant in sites with low alkalinity and conductivity, whereas species like N. symmetrica, C. tumida and L. ventricosa showed a positive relationship with conductivity and pH. The studied species showed good characteristics of their value as water quality indicators, yet due to different interpretations by several authors, it is necessary to perform further studies at more river basins in the country. | Las diatomeas del bentos son el componente más estudiado del perifiton en los ríos de Costa Rica, sin embargo aún queda mucho por conocer sobre su ecología. Por eso en el presente estudio se analizó el perifiton en seis diferentes sitios en la cuenca medio del Río Sarapiquí en el 2010, 2011 y 2012. En cada uno de los muestreos se realizó el conteo de 400 frústulas, de las cuales se obtuvo la abundancia relativa de las especies: Achnanthidium exiguum, Coconneis placentula, Cymbella tumida, Luticola goeppertiana, Luticola ventricosa, Navicula symmetrica, Nitzchia clausii, Nupela praecipua, Reimeria sinuata y Synedra goulardi. Esta información fue relacionada con los datos físico químicos (oxígeno disuelto, temperatura, conductividad, total de sedimentos en suspensión, turbidez, pH y alcalinidad) medidos en cada uno de los sitios. Con el propósito de observar las relaciones entre los diferentes sitios dentro de la cuenca, se utilizó un análisis de correspondencia canónica (ACC), lo que permitió distinguir tres sectores de acuerdo a la altitud. Estos sectores se diferencian en el tipo de sustrato, cobertura riparia vegetal y parámetros físico-químicos, lo que propicia diferencias en la composición de especies de diatomeas entre ellos. Se obtuvieron los valores óptimos calculados y tolerancia calculada para cada una de las especies. Los resultados obtenidos indican que las especies: A. exiguum, R. sinuata, L. ventricosa y C. tumida, dominan en aguas limpias, oxigenadas y baja temperatura. Las especies N. praecipua, S. goulardi, C. placentula, L. goeppertiana, N. clausii y N. symmetrica se encuentran en aguas cálidas, alta turbidez y poco oxigenadas. Las especies A. exiguum, R. sinuata, prevalecen en sitios con agua alcalina y baja conductividad y las especies N. symmetrica, C. tumida y L. ventricosa presentan una relación positiva con la conductividad y el pH de las aguas. Las especies estudiadas mostraron buenos indicios de su valor como indicadores de calidad del agua, sin embargo, debido a diferencias de interpretación por varios autores, es necesario realizar más estudios en otras cuencas hidrográficas en el país.