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ResumenLas 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.

Abstract The tolerance of ten diatom species (Bacillariophyceae) to water's physico-chemical factors in the Sarapiqui River, Costa Rica. 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. Rev. Biol. Trop. 64 (1): 105-115. Epub 2016 March 01.

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The aim of this work was to study the physicochemical parameters of water quality collected from 12 sampling stations from Topputhurai to Muthupet in Vedaranyam located on the southeast coast of India from January to December 2008. Results showed that the DO and nutrients were the maximum in the Bay of Bengal during the monsoon period. High concentration of the nutrients in summer season was obtained near the Muthupet mangroves compared to the Palk Strait, which showed that this acted as a source of nutrients to the adjacent coastal waters. Low concentrations of the nutrients observed in the monsoon could be attributed to the terrestrial runoff from Muthupet lagoon. The physicochemical characteristics of coastal waters between the Point Calimere and Muthupet could be used as a baseline data for the monitoring, conservation and management of Point Calimere Wildlife and Bird sanctuary, Great Vedaranyam swamp and Muthupet mangrove ecosystem.

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Well-drained Oxisols are named Latossolos in the Brazilian Soil Classification System. These soils cover extensive areas in Brazil and are essential to food production and environmental quality maintenance. Both roles rely on the existence of stable, small aggregates. Although several studies have been published about it, there is no agreement on the factors and mechanisms involved in the genesis and stability of such aggregates. The reasoning used to explain such mechanisms in other soils cannot be used in Latossolos without difficulty because they do not have aggregate hierarchy. The main goal of this review is to gather information about mineralogical characteristics of pedogenic minerals and their association with organic colloids and relate it to aggregation and dispersion of Latossolos.

Latossolos cobrem extensas áreas no Brasil e são essenciais para a produção agrícola e a qualidade ambiental. As funções ambientais destes solos se baseiam na existência de pequenos agregados bastante estáveis. Ainda não há consenso sobre os mecanismos formadores e reguladores da estabilidade dos agregados em Latossolos e os processos de agregação propostos para outros tipos de solos não podem ser extrapolados para os Latossolos sem alguma dificuldade, pois estes não possuem hierarquia de agregados. O objetivo desta revisão é apresentar informações sobre características de partículas minerais presentes na maioria dos Latossolos e como suas propriedades e sua associação com colóides orgânicos podem influenciar a agregação e a dispersão.

RESUMEN

Well-drained Oxisols are named Latossolos in the Brazilian Soil Classification System. These soils cover extensive areas in Brazil and are essential to food production and environmental quality maintenance. Both roles rely on the existence of stable, small aggregates. Although several studies have been published about it, there is no agreement on the factors and mechanisms involved in the genesis and stability of such aggregates. The reasoning used to explain such mechanisms in other soils cannot be used in Latossolos without difficulty because they do not have aggregate hierarchy. The main goal of this review is to gather information about mineralogical characteristics of pedogenic minerals and their association with organic colloids and relate it to aggregation and dispersion of Latossolos.

Latossolos cobrem extensas áreas no Brasil e são essenciais para a produção agrícola e a qualidade ambiental. As funções ambientais destes solos se baseiam na existência de pequenos agregados bastante estáveis. Ainda não há consenso sobre os mecanismos formadores e reguladores da estabilidade dos agregados em Latossolos e os processos de agregação propostos para outros tipos de solos não podem ser extrapolados para os Latossolos sem alguma dificuldade, pois estes não possuem hierarquia de agregados. O objetivo desta revisão é apresentar informações sobre características de partículas minerais presentes na maioria dos Latossolos e como suas propriedades e sua associação com colóides orgânicos podem influenciar a agregação e a dispersão.