La presencia de fósforo y nitrógeno en proporciones elevadas puede afectar negativamente la calidad de cualquier ecosistema. Hasta la fecha no ha sido publicado un estudio bibliométrico de fósforo y nitrógeno en ecosistemas acuáticos ecuatorianos. Nuestro objetivo es analizar y presentar marcadores bibliométricos de la producción científica de fósforo y nitrógeno en ecosistemas acuáticos ecuatorianos. Para la recolección de datos se utilizó la base de datos Scopus. Se hallaron un total de 823 documentos, de los cuales solo se validaron 49. Las publicaciones aumentaron considerablemente a partir del año 2013, y llegaron a un máximo de 16 en el año 2018. De estos los ríos fueron los ecosistemas más estudiados a lo largo del periodo, la mayor parte de las publicaciones fueron en el idioma inglés y la revista con más artículos fue Water. La mayor parte de los artículos se publicaron en revistas prestigiosas de biología, limnología, agua e hidrobiología. Las universidades lideres en esta temática son: la Universidad de Cuenca y la Escuela Superior Politécnica del Litoral.

This paper presents an evaluation of the elaboration of compost as an educational methodology in teaching the subject of natural sciences. The experiment was carried out for two types of compost to recognize which offers better soil fertility from the different materials used in its elaboration. Two groups of students were used to evaluate the performance presented with the practical and traditional theoretical methods. The main results show that teaching from experimentation offers better alternatives to recognize concepts and their applications, to retain knowledge effectively.

The objective of the present study was to determine the general combinatorial aptitude (GCA), specific combinatorial aptitude (SCA) and heterosis in inbred lines of yellow maize and its crosses for, the yield of grain, height of plant and ear and days to male and female flowering. Six inbred lines from CIMMYT, their direct crosses and four controls were evaluated at UNALM during 2016-2018, under a 5 x 5 lattice design with four repetitions. The effects of GCA and SCA were calculated using method II, model I of Griffing. Heterosis was measured based on the mean and best parent. Heterosis was measured based on the mean and best parent. The combined analysis of years showed significance (p ≤ 0.01) in: genotypes by years for days to male and female flowering; GCA for years for days to male flowering and SCA for years for days to female flowering. The effects of ACG for grain yield were significant in lines CML 229 and CML 428, for plant height, precocity, ear and precocity CML 487 line highlighted. The effect of ACE was superior in the cross CML 453 x CML 486 for the grain yield character. Heterosis was higher for the grain yield in the CML 229 x CML 453 and CML 453 x CML 487 crosses. The GCA / SCA relationship evidenced effects of additive genes on plant height, days to male and female flowering, therefore, for grain yield and ear height, non-additive effects governed.

Se presenta la evaluación del procedimiento de extracción secuencial aprobado por la BCR (BCR, por sus siglas en inglés, Community Bureau of Reference) para determinar metales en muestras de sedimentos del río Catatumbo, Venezuela. Las fracciones consistieron en 4 etapas: en la primera, llamada intercambiable, se extrajo utilizando ácido acético; la segunda, o reducible, con hidroxicloruro de amonio; la tercera, u oxidable, con peróxido de hidrógeno y acetato de amonio y la residual, que es la etapa remanente, se digirió con agua regia. El análisis se realizó por espectrometría de absorción atómica con llama (FAAS), horno de grafito (ETAAS) y espectrometría de emisión atómica con plasma inductivamente acoplado (ICP-AES). Los metales determinados fueron Pb y V. Las determinaciones por FAAS, ETAAS e ICP-AES indicaron que no hubo diferencias estadísticamente significativas (p < 0,05) cuando se compararon los resultados de 24 muestras de sedimentos del río Catatumbo realizadas por triplicado. La exactitud encontrada sumando las cuatro etapas de la BCR para Pb y V fueron comparables a los resultados obtenidos por digestión ácida, lo cual indica que el procedimiento es adecuado para la cuantificación de los metales estudiados. El Pb y V se encontró mayormente (55-97 %) en la etapa residual lo que los hace no disponibles. Palabras clave: digestión ácida, extracción BCR, sedimento, plomo, vanadio  Abstract: The aim of the present work is the evaluation of the procedure of sequential extraction approved by the BCR and used to determine metals in samples of sediments from Catatumbo River in Venezuela. The fractions consisted in four (4) stages: the first one or interchangeable was extracted using acetic acid, the second one or reducible with ammonia hydroxi-chloride, the third one or oxidable with hydrogen peroxide and ammonium acetate and the residual which is the remnant stage was digested with aqua regia. The analysis was made by Flame Atomic Absorption Spectrometry (FAAS), Electrothermal Atomisation Atomic Absorption Spectrometry (ETA-AAS) and Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The metals evaluated were Pb and V. The evaluations for FAAS, ETA-AS and ICP-AES indicated that there were not statistically significant differences (p <0.05) when the results of 24 samples of sediments from the Catatumbo River carried out in triplicate were compared. The exact result found by adding the four stages of the BCR for Pb and V were comparable to the results obtained by acid digestion. The Pb and V were found mainly (55-97 %) in the residual stage which makes them not available and these results are comparable to other studies published. Key words: Acid Digestion, Extraction of BCR, sediment, Pb, V

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