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El objetivo de este estudio fue investigar los cambios ocurridos en la estructura y dinámica de la comunidad de zooplancton durante los trabajos de dragado realizados en el sector inferior del río Salado (Buenos Aires, Argentina). Las muestras se tomaron antes y durante la extracción de una restricción de río y la sustitución de un puente en un sitio aguas arriba y otro río abajo de esta modificación hidráulica. Los trabajos de dragado se realizaron durante el período de bajo nivel de agua. Las muestras de zooplancton se obtuvieron filtrando volúmenes de 10 l extraídos en tres puntos de una transecta en el canal del río (en ambas orillas y en la mitad del curso) durante 14 semanas (semanalmente de marzo a junio). Los parámetros físicos y químicos se midieron in situ con un multímetro. La conductividad disminuyó de 12,000 μS/cm (marzo-abril) a 6,000 μS/cm (abril-junio). Las combinaciones de zooplancton se correlacionaron con factores como la conductividad, la turbidez, la temperatura del agua y la densidad del fitoplancton. Los tintínidos (Tintinnidium fluviatile y Codonella cratera) prevalecieron con alta salinidad, mientras que los rotíferos (Brachionus plicatilis y Keratella tropica, entre otros) dominaron más tarde. Los microcrustáceos eran escasos en relación con la conductividad del río. Los sitios analizados mostraron una composición y abundancia similares de zooplancton durante todo el período de muestreo. Podemos suponer que los efectos de los trabajos de dragado en condiciones de poca agua causan perturbaciones mínimas en la corriente de la comunidad del zooplancton.

Dredging works in several sectors of Salado River are probably the most important activity of disturbance in a pampean aquatic ecosystem, with implications in a RAMSAR site (Samborombón Bay). The interventions are taking place in the lower basin and considered as a reference of disturbance for future and major works as the dredging of almost 100 km of the Salado River main channel. Physical and chemical conditions were analysed in two sectors: upstream (El Destino, ED) and downstream (Guerrero, G) of La Postrera. This study was done before and during the extraction of a river restriction and the old bridge replacement. Samples were collected during 18 weeks (3/04-7/04) (2 or 3 times/week). Each sample was the result of the water sample integration on a transversal transect of the stream. The physical and chemical parameters measured «in situ» were: pH, conductivity, turbidity, dissolved oxygen, temperature and salinity. Fractions of phosphorus and suspended solids were analysed. The simulation of different sampling frequencies showed that variables related to physic environment (temperature, conductivity and pH) can be explained by monthly and biweekly sampling. On the other hand, the main variations of total phosphorus, suspended solids and turbidity can be only explained by the daily sampling. Suspended solids concentration was higher upstream (mean: 0.12 g.L -1 ) than downstream (mean: 0.10 g.L -1 ). Maximum mean phosphorus concentration values were reached at ED. Soluble reactive phosphorus concentrations were similar at both river sectors (305.81 and 307.08 μg.L -1 in ED and G, respectively). Conductivity diminished from 6,770to 2,530 μS.cm -1 due to the discharge increase. Total particulate phosphorus, suspended solids and turbidity increased at ED and diminished at G. The dredging works in moments of low waters, and taking care of the extracting material location, as recommended the environmental management techniques, did not affect sediment transport through the river. The phosphorus concentration differences between both river sectors could be by the settlement processes in La Tigra Lake and the availability of this nutrient to the phytoplankton and macrophytes.

Floristic composition of vascular plants and their distribution is reported for growth habits in a low montane rain forest (2600 m and 2500 mm/yr mean annual precipitation) in the northern Andes, based on a plot of 1 ha. The samples collected represented 318 species/morphospecies, 82 families (nine of which were pteridophytes) and 173 genera. 78% of the samples were identified to species. Groups with most species are pteridophytes (sensu lato), Orchidaceae, Asteraceae, Rubiaceae, Melastomataceae and Piperaceae, that represented 44% of all species recorded. The most diverse genera are Peperomia, Elaphoglossum, Mikania, Anthurium, and Miconia. Three species endemic to Antioquia (Brunellia trianae, Meriania antioquiensis and Mikania fragrans) were found. The individuals found in the plot represent 47% of the species, 48% of the genera and 60% of the families found in Arví Park, a reserve of 11400 hectares in which the plot was located. The plot had 108 species, 30 genera and one family not previously reported for Arvi Park. The number of common taxa between the plot and the Arví Park was 144 species, 142 genera and 69 families. Species richness/ family in the plot accounts for 89% of the variation of species richness/family in the Arví Park, and 75% of the generic richness. We conclude that detailed floristic inventory of known area plots provide information representative of the regional flora and permit a rapid approximation of its biodiversity. [ABSTRACT FROM AUTHOR]

El objetivo de este estudio fue determinar la secreción de LH durante la época reproductiva y anestro estacional en cabras Boer, inmunizadas activamente contra inhibina. Se utilizaron 12 cabras de la raza Boer, inmunizadas contra inhibina, y 12 cabras en el grupo testigo. Para cada muestreo intensivo de sangre se colocó un catéter en la vena yugular por seis horas. Durante la época reproductiva los muestreos se realizaron en la fase del cuerpo lúteo (días 10-16 del ciclo) cada segundo ciclo y durante el anestro estacional cada seis semanas. La concentración plasmática de LH se determinó mediante ELISA. En la época de anestro estacional, la secreción de LH fue significativamente menor (P < 0.01) en el grupo inmunizado que en el grupo testigo. En la época reproductiva la secreción de LH resultó poco afectada por la inmunización, sólo la amplitud del pulso fue significativamente menor (P < 0.01). Tanto en animales inmunizados como no inmunizados se encontró una diferencia significativa (P < 0.01) en el número de pulsos entre las épocas reproductiva y de anestro estacional. En conclusión, la concentración plasmática de LH fue menor en la época reproductiva que en la de anestro estacional, y en la época reproductiva la inmunización activa contra inhibina afectó de forma mínima la secreción de LH; mientras que en la época de anestro estacional, la inmunización activa contra inhibina sí la afectó. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the LH secretion during the breeding and the anestrous season in Boer goats actively immunized against inhibin. In this experiment, 12 immunized and 12 non-immunized (control) Boer goat does were used. Permanently indwelling jugular catheters were placed permitting repeated blood collection for 6 h periods. During the breeding season, samples were taken during the luteal phase (days 10 to 16 of the cycle) on every other estrous cycle. During the non-breeding season, samplings were conducted every 6 weeks. Plasma LH concentrations were determined by means of ELISA. During the non-breeding season, immunized animals showed significantly lower LH concentrations than control animals (P < 0.01). During the breeding season, LH secretion was hardly affected by inhibin- immunization with only the pulse amplitude being slightly, though significantly reduced (P < 0.01). In both immunized and non-immunized animals, the pulse rate was significantly enhanced during the non-breeding season as compared to the breeding season (P < 0.01). In conclusion, during the breeding season goats showed lower plasma LH concentrations than during the non-breeding season. During the breeding season LH secretion is only slightly affected by active immunization, whereas during the non-breeding season the LH-suppressive effect of inhibin immunization was more pronounced. [ABSTRACT FROM AUTHOR]