Limnology in Argentina: An historical account

This short review includes major books, articles and episodes concerned with studies on inland waters that have affected the development of limnology in Argentina. It is divided into three periods; (1) an early period of protolimnologists; (2) a period previous to the present times, subdivided into a first stage from 1900 to 1938 and a second stage from 1938 to 1962; and (3) a period of integrated research

Consumo bacteriano heterotrófico sobre glucosa y glicolato en una laguna eutrófica (Chascomús, Argentina)

El presente trabajo se realizó en la Laguna de Chascomús (Prov. Bs, As., Argentina),cuerpo eutrófico, poco profundo, de gran productividad y capacidad biogenética. La metodología aplicada fue la propuesta por Wright & Hobbie (1965), efectuándose las correcciones por la tasa de expiración de CO2 (Hobbie & Crawford, 1969). Los parámetros cinéticos del consumo de glicolato muestran una marcada fluctuación estacional y con la productividad. Vmax y Kt + Sn se incrementaron durante el verano en superficie (12,8 µg.-1h-1 y 588 µg.l-1 respectivamente), y disminuyen en la muestra cercana al fondo en invierno, hasta valores no detectables con esta metodología. El Tt aumentó en agosto a 76 hs. Estos parámetros, para glucosa, no variaron ni estacional ni verticalmente tanto como los del glicolato; siendo sus valores máximos: 5,6 µg.l-1h-1 (Vmax); 49,5 µg.l-1 (Kt + Sn) y 57,27 hs. (Tt) durante enero-febrero de 1986. Las elevadas tasas de consumo, asimilación y excreción halladas durante la primavera y el verano, son producto de la presencia de una comunidad bacteriana heterotrófica adaptada a consumir los productos de excreción. El máximo porcentaje de mineralización observado, para él glicolato (85%) fue hallado en superficie durante enero de 1986; por el contrario el porcentaje de excreción de 14CO2 proveniente de la glucosa no superó el 36% en igual época del año, siendo por lo tanto su rendimiento mucho mayor.El presente trabajo se realizó en la Laguna de Chascomús (Prov. Bs, As., Argentina),cuerpo eutrófico, poco profundo, de gran productividad y capacidad biogenética. La metodología aplicada fue la propuesta por Wright & Hobbie (1965), efectuándose las correcciones por la tasa de expiración de CO2 (Hobbie & Crawford, 1969). Los parámetros cinéticos del consumo de glicolato muestran una marcada fluctuación estacional y con la productividad. Vmax y Kt + Sn se incrementaron durante el verano en superficie (12,8 µg.-1h-1 y 588 µg.l-1 respectivamente), y disminuyen en la muestra cercana al fondo en invierno, hasta valores no detectables con esta metodología. El Tt aumentó en agosto a 76 hs. Estos parámetros, para glucosa, no variaron ni estacional ni verticalmente tanto como los del glicolato; siendo sus valores máximos: 5,6 µg.l-1h-1 (Vmax); 49,5 µg.l-1 (Kt + Sn) y 57,27 hs. (Tt) durante enero-febrero de 1986. Las elevadas tasas de consumo, asimilación y excreción halladas durante la primavera y el verano, son producto de la presencia de una comunidad bacteriana heterotrófica adaptada a consumir los productos de excreción. El máximo porcentaje de mineralización observado, para él glicolato (85%) fue hallado en superficie durante enero de 1986; por el contrario el porcentaje de excreción de 14CO2 proveniente de la glucosa no superó el 36% en igual época del año, siendo por lo tanto su rendimiento mucho mayor

Limnology in Argentina: an historical account

This short review includes major books, articles and episodes concernedwith studies on inland waters that have affected the development oflimnology in Argentina. Earlier accounts of the history of limnology,though based on various other criteria, are by Popovici & Righi (1948);Olivier (1961a); Marini et al. (1963); Di Persia & Neiff (1973); Schnack(1984); Lopez (1988); Drago (1990); Gabellone & Casco (1992). In thisaccount we adopt the proposal of Di Persia & Neiff (1973) who dividedtheir historical analysis into three periods: (1) an early period ofprotolimnologists; (2) a period previous to the present times, subdividedinto a first stage from 1900 to 1938 and a second stage from 1938 to1962; (3) a period of integrated research

Cuantificación, frecuencia de división celular y producción de bacterias planctónicas en el Embalse del Río III - variables relacionadas

During a whole year (1987-1988), monthly variations of biomass, frequency of dividing cells and production of bacterioplankton were studied in the Embalse del Río III Reservoir (Córdoba, Argentina). Algal biomass and production were measuredsimultaneously. A significant relationship between bacterial and algal production was observed, being temperature an important regulator factor. Bacterial biomass valúes did not correlate with their production rates. Low valúes and variability in the frequency of dividing cells were probably due to methodological difficulties for detecting división in very little cells. These data suggest that the frequency of dividing cells is not a reliableindicator of total active bacteria. Annually bacteria cycled nearly 60% of organic matter produced by phytoplankton in the water column.During a whole year (1987-1988), monthly variations of biomass, frequency of dividing cells and production of bacterioplankton were studied in the Embalse del Río III Reservoir (Córdoba, Argentina). Algal biomass and production were measuredsimultaneously. A significant relationship between bacterial and algal production was observed, being temperature an important regulator factor. Bacterial biomass valúes did not correlate with their production rates. Low valúes and variability in the frequency of dividing cells were probably due to methodological difficulties for detecting división in very little cells. These data suggest that the frequency of dividing cells is not a reliableindicator of total active bacteria. Annually bacteria cycled nearly 60% of organic matter produced by phytoplankton in the water column

Relación entre la actividad heterotrófica bacteriana y la actividad autotrófica algal en el Embalse del Río III (Córdoba, Argentina)

La actividad autotrófica del fitoplancton se estimó mediante la técnica de Steemann Nielsen (1952) y la actividad heterotróflca del bacterioplancton mediante el cálculo de los parámetros cinéticos para ,4C-glucosa (Wright & Hobbie, 1965) y el consumo anaplerótico de CO, según Overbeck (1981). La máxima actividad heterotróflca fue observada en la zona eufótica (833 µg C 1-1 h-1) en coincidencia con la mayor tasa de producciónprimaria (338,7 mg C m-2 d-1) y numerosidad de Peridinium ga túnense (fin de verano). El potencial heterotrófleo calculado en base al consumo de glucosa, comprende solo una pequeña parte del proceso de degradación total de la materia orgánica disuelta. El 11% del carbono Ajado fotosintéticamente fue descompuesto por las bacterias como C-glucosa. Durante el verano se observó una mayor afinidad de las bacterias heterotrófleas por la glucosa en la zona eufótica, mientras que en los meses de invierno so detectó una comunidad fisiológicamente diferente, con mayor afinidad por otros compuestos orgánicos, siendo la relación C-glucosa/O-CO2, inferior a la unidad. En la composición fitoplanctónica se observa dominancia estival de dinoflagelados c invernal de diatomeas.La actividad autotrófica del fitoplancton se estimó mediante la técnica de Steemann Nielsen (1952) y la actividad heterotróflca del bacterioplancton mediante el cálculo de los parámetros cinéticos para ,4C-glucosa (Wright & Hobbie, 1965) y el consumo anaplerótico de CO, según Overbeck (1981). La máxima actividad heterotróflca fue observada en la zona eufótica (833 µg C 1-1 h-1) en coincidencia con la mayor tasa de producciónprimaria (338,7 mg C m-2 d-1) y numerosidad de Peridinium ga túnense (fin de verano). El potencial heterotrófleo calculado en base al consumo de glucosa, comprende solo una pequeña parte del proceso de degradación total de la materia orgánica disuelta. El 11% del carbono Ajado fotosintéticamente fue descompuesto por las bacterias como C-glucosa. Durante el verano se observó una mayor afinidad de las bacterias heterotrófleas por la glucosa en la zona eufótica, mientras que en los meses de invierno so detectó una comunidad fisiológicamente diferente, con mayor afinidad por otros compuestos orgánicos, siendo la relación C-glucosa/O-CO2, inferior a la unidad. En la composición fitoplanctónica se observa dominancia estival de dinoflagelados c invernal de diatomeas

Ritmo diario de la fotosintesis, respiración, pigmentos y bacterias heterotróficas (Embalse del Río III, C´órdoba, Argentina)

The results of the variante analysis obtaíned show us the relevando of the diel and day-to-day viriations of the photosyndiesís, ehlorophylba and phaeopigments, specially during summer months, The, short-term variation observed is expiain by displacement of water masses with diffferent amoumts of phytoplankton. In winter, vertical circulation occurs, and the variability of those parameters decrease, Heterotrophic bacteria deosity was the variable with greatest change throughout the observaron period. The establishment of nocturnal eirculaticm and diumal stratification were not observed, being these changes seasonal depend.The results of the variante analysis obtaíned show us the relevando of the diel and day-to-day viriations of the photosyndiesís, ehlorophylba and phaeopigments, specially during summer months, The, short-term variation observed is expiain by displacement of water masses with diffferent amoumts of phytoplankton. In winter, vertical circulation occurs, and the variability of those parameters decrease, Heterotrophic bacteria deosity was the variable with greatest change throughout the observaron period. The establishment of nocturnal eirculaticm and diumal stratification were not observed, being these changes seasonal depend

Measuring the free fall of antihydrogen

After the first production of cold antihydrogen by the ATHENA and ATRAP experiments ten years ago, new second-generation experiments are aimed at measuring the fundamental properties of this anti-atom. The goal of AEGIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is to test the weak equivalence principle by studying the gravitational interaction between matter and antimatter with a pulsed, cold antihydrogen beam. The experiment is currently being assembled at CERN's Antiproton Decelerator. In AEGIS, antihydrogen will be produced by charge exchange of cold antiprotons with positronium excited to a high Rydberg state (n > 20). An antihydrogen beam will be produced by controlled acceleration in an electric-field gradient (Stark acceleration). The deflection of the horizontal beam due to its free fall in the gravitational field of the earth will be measured with a moire deflectometer. Initially, the gravitational acceleration will be determined to a precision of 1%, requiring the detection of about 105 antihydrogen atoms. In this paper, after a general description, the present status of the experiment will be reviewed

Cinética de consumo de sustratos orgánicos de bacterias aisladas de la Laguna de Chascomus

Eight bacterial strains were isolated from Chascomús Pond (Buenos Aires Province) and their capacity to growth at low concentrations of glycolate and glucose, as a solé source of organic carbón was evaluated.Substrate affinities (Kt valúes) and other kinetic parameters were measured by Wright & Hobbie methodology with 14C-labelled glycollate and MC-labelled glucose as substrates. Four o f the eight puré culture studied followed Michaelis-Menten uptakekinetics giving good straight lines after the Lineweaver-Burke transfonnation.Vmax valúes o f natural popuiations and the experimental ones were similar for glycollate; for glucose the experimental valúes were a little higher. This suggest the possibility o f applying the experimental Kt valúes to natural popuiations as a way of evaluation o f the natural substrate concentration.Eight bacterial strains were isolated from Chascomús Pond (Buenos Aires Province) and their capacity to growth at low concentrations of glycolate and glucose, as a solé source of organic carbón was evaluated.Substrate affinities (Kt valúes) and other kinetic parameters were measured by Wright & Hobbie methodology with 14C-labelled glycollate and MC-labelled glucose as substrates. Four o f the eight puré culture studied followed Michaelis-Menten uptakekinetics giving good straight lines after the Lineweaver-Burke transfonnation.Vmax valúes o f natural popuiations and the experimental ones were similar for glycollate; for glucose the experimental valúes were a little higher. This suggest the possibility o f applying the experimental Kt valúes to natural popuiations as a way of evaluation o f the natural substrate concentration

Condiciones de luz subacuática como factores determinantes de la eficiencia fotosintética fitoplanctónica. l. Embalse de Rio Tercero (Córdoba, Argentina)*

Underwater light conditions as a key factor for phytoplankton photosynthetic etliciency. The Secchi disc depth, the energy of photosynthetic available radiation (PAR) in the water column, the primary production rate and the concentration of photosynthetic pigments were measured in Rio Tercero reservoir (Argentina). The compensation point, the relative intensities of such point and Secchi disc, the photosynthetically stored radiation, and the respective photosynthetic efficiencies were calculated. The percentage of transmitt d light fluctuated according to the suspended amount of particulated material (winter) or the presence of high algal concentration (spring-summer). The euphotic stratum in summer (1:1 m to 3 m) r ached 5.5 m in winter (August). The mean extinction coefficient up to the euphotic stratum was very highly variable. The photosynthetic efficiency was lower than 1 in surface during spring and summer. The values obtained in the euphotic stratum were intermediate. Other significantly high values were found at deeper levels. The relevant fluctuations of all variables including the extinction coefficient, the relative depth and intensity of Secchi disc, the euphotic stratum depth and the compensation point confirm the eutrophic characteristics of the ecosystem. Eutrophication levels of reservoir are clear from values of other parameters such as the primary production rate, pigment concentration, photosynthetic efficiencies and the seasonal appearance of algal blooms.Underwater light conditions as a key factor for phytoplankton photosynthetic etliciency. The Secchi disc depth, the energy of photosynthetic available radiation (PAR) in the water column, the primary production rate and the concentration of photosynthetic pigments were measured in Rio Tercero reservoir (Argentina). The compensation point, the relative intensities of such point and Secchi disc, the photosynthetically stored radiation, and the respective photosynthetic efficiencies were calculated. The percentage of transmitt d light fluctuated according to the suspended amount of particulated material (winter) or the presence of high algal concentration (spring-summer). The euphotic stratum in summer (1:1 m to 3 m) r ached 5.5 m in winter (August). The mean extinction coefficient up to the euphotic stratum was very highly variable. The photosynthetic efficiency was lower than 1 in surface during spring and summer. The values obtained in the euphotic stratum were intermediate. Other significantly high values were found at deeper levels. The relevant fluctuations of all variables including the extinction coefficient, the relative depth and intensity of Secchi disc, the euphotic stratum depth and the compensation point confirm the eutrophic characteristics of the ecosystem. Eutrophication levels of reservoir are clear from values of other parameters such as the primary production rate, pigment concentration, photosynthetic efficiencies and the seasonal appearance of algal blooms