Impacto de agroquímicos sobre los ensambles de macroinvertebrados en arroyos rurales

La creciente adopción de sistemas productivos basados en la siembra directa, junto con el uso de agroquímicos y la introducción de semillas modificadas genéticamente permitió extender la superficie sembrada de los cultivos, principalmente de soja. Es en el sur de América Latina donde este cambio tecnológico se ha implementado con mayor velocidad e intensidad. En Argentina, el área sembrada del cultivo de soja aumentó de 4,9 a 20,5 millones de hectáreas desde la campaña 90/91 hasta el presente; en Brasil, el área cultivada con soja se incrementó en 126% durante el período 1995/2011 y en Paraguay, aumentó de 1,3 a 3,5 millones de hectáreas entre el 2000 y el 2015. La misma tendencia se observa con el consumo de agrotóxicos y fertilizantes para las tres regiones. Los biocidas más utilizados en nuestra región son el herbicida glifosato y los insecticidas cipermetrina, clorpirifos y endosulfán. El organoclorado endosulfán fue prohibido en Argentina, a partir de 2013. El objetivo del presente trabajo de tesis es estudiar el impacto de la práctica agrícola sobre los ensambles de macroinvertebrados acuáticos de cuencas rurales, poniendo especial énfasis en el efecto producido por los agroquímicos. Se compararon los ensambles de macroinvertebrados, las características físicas y químicas del agua, las concentraciones de agrotóxicos en sedimentos y la calidad del hábitat en arroyos que atraviesan zonas con uso intensivo del suelo y arroyos de características similares, en cuyas cuencas no se realiza agricultura intensiva y/o poseen franjas de atenuación cubiertas por vegetación. En el laboratorio se realizaron ensayos de toxicidad para determinar la concentración letal (LC50) de los agrotóxicos más utilizados (cipermetrina, lambda-cialotrina, endosulfán, clorpirifos) en el anfípodo Hyalella curvispina en agua y sedimento. La sensibilidad de H. curvispina fue comparada con la de otras especies por medio de la curva de distribución de sensibilidad de especies (SSDs). El piretroide lambda-cialotrina registró los valores de LC50 más bajos, seguido de cipermetrina, clorpirifos y endosulfán. Se observó que la sensibilidad de H. curvispina es similar a la de H. azteca, comúnmente utilizado como organismo indicador de contaminación en America del Norte, y que ambos organismos son más sensibles que la mayoría de los taxones de invertebrados de agua dulce. Los arroyos estudiados se encuentran en áreas agrícolas de Argentina, Paraguay y Brasil. Los muestreos se realizaron durante el período de crecimiento de la soja, correspondiente a los meses de noviembre a abril. En Argentina se llevó a cabo el estudio durante un período de tres años y se monitorearon 23 arroyos ubicados en dos regiones de La Pampa argentina, incluyendo una región de producción intensiva de soja, en Arrecifes, y una región mixta: agrícola y ganadera, en La Plata. En el año 2013 se estudiaron dos regiones de la Selva Paranaense: 17 arroyos en Paraguay ubicados sobre la cuenca del río Pirapó, departamento de Itapúa y 18 arroyos en Brasil en Toledo, estado de Paraná. Ambas regiones poseen producción intensiva de soja y una legislación que exige a los productores dejar una franja sin cultivar entre el cultivo y los arroyos. En la región Pampeana se determinó que los ensambles de macroinvertebrados registraron diferencias significativas entre arroyos con distinto uso del suelo en sus cuencas (agrícolas, ganaderos y reserva). Las mayores concentraciones de nutrientes y la presencia de agrotóxicos se registraron en los arroyos de cuencas donde la agricultura fue la actividad dominante. Asimismo, en los arroyos agrícolas se registraron los mayores valores de Unidad Tóxica total (UT) alcanzando, en algunos sitios, valores extremos mayores a la unidad. Se observó que en los sitios menos disturbados la dominancia correspondió a Hyalellidae (Amphipoda), Palaemonidae (Decapoda) y Caenidae (Ephemeroptera), considerados sensibles a los agrotóxicos, mientras que en los sitios más disturbados Gastropoda, Oligochaeta e Hirudinea, considerados tolerantes, fueron los taxones mejor representados. En la Selva Paranaense se observó que la mayor riqueza taxonómica y abundancia correspondió a los arroyos estudiados de Paraguay, como así también los índices de diversidad y equitatividad. Los taxones Coleoptera, Ephemeroptera y Trichoptera resultaron ser más abundantes en Paraguay y registraron una correlación inversa con la concentración de los biocidas. Por el contrario, los taxones Diptera y Bivalvia fueron más abundantes en Brasil y registraron correlación positiva con la concentración de algunos agrotóxicos. Cabe destacar, que el ancho de la franja de atenuación en Paraguay fue mayor y menos variable que en los arroyos estudiados de Brasil. En los sedimentos analizados de los arroyos de Argentina, en cuencas con producción intensiva de soja, Brasil y Paraguay se detectó la presencia de todos los biocidas utilizados con mayor frecuencia en los cultivos regionales. Sin embargo, el impacto de los mismos sobre los taxones sensibles estaba más claramente correlacionado en los arroyos pampeanos. Una posible razón de esta discrepancia puede ser que las franjas de atenuación de los arroyos de Argentina son mucho más pequeñas y no están forestadas, por lo que las comunidades de invertebrados no serían tan resilientes. Estos resultados confirmarían el efecto protector de las franjas de atenuación y ponderan su utilidad como norma de manejo para mitigar el impacto agrícola. En la presente tesis se observaron reiteradamente correlaciones positivas entre la concentración de PRS y la concentración de agrotóxicos y negativas entre el PRS y la abundancia de algunos grupos taxonómicos. Su correlacion no significa una relación causa efecto sino la simultaneidad de su aplicación con los agrotóxicos y su similar comportamiento ambiental, por lo cual, resulta un buen indicador del impacto agrícola. Asimismo, se determinaron las variables ambientales que tienen mayor influencia en la composición de los ensambles de macroinvertebrados, entre ellos se encuentran la materia orgánica y textura de los sedimentos. En este estudio se concluye que la exposición a los agrotóxicos contribuye a las diferencias observadas en la composición del ensamble de macroinvertebrados en arroyos con distinto uso del suelo en sus cuencas. Aquellos arroyos que atraviesan zonas con uso intensivo del suelo sin franja de atenuación poseen una fauna con mayor abundancia de taxones tolerantes a los agrotóxicos y una disminución o ausencia de taxones sensibles. Se concluye también que los ensambles de macroinvertebrados son una herramienta eficaz para evaluar ecosistemas acuáticos y sus respuestas a los cambios en el uso del suelo de la cuenca.The increasing adoption of productive systems based on direct sowing, together with the use of agrochemicals and the introduction of genetically modified seeds increased the sown area of the crops, mainly soybean. It is in southern Latin America where this technological change has been implemented with greater speed and intensity. In Argentina, the area planted with soybean increased from 4.9 to 20.5 million hectares form 90/91 up to the present; in Brazil, the area cultivated with soybeans increased by 126% during the period 1995/2011 and in Paraguay, increased from 1.3 to 3.5 million hectares between 2000 and 2015. The same trend is observed with the consumption of pesticides and fertilizers for the three regions. The most used biocides in our region are the glyphosate herbicide and the cypermethrin, chlorpyrifos and endosulfan insecticides. The organochlorine endosulfan has been prohibited in Argentina, since 2013. The objective of this thesis is to study the impact of the agricultural practice on the assemblage of aquatic macroinvertebrates of rural basins, with special emphasis on the effect produced by agrochemicals. The assemblage of macroinvertebrates, the physical and chemical characteristics of the water, the concentrations of agrochemicals in sediments and the quality of the habitat in streams adjacent to plots with different land use were compared. Laboratory toxicity tests were performed to determine the lethal concentration (LC50) of the most commonly used agrotoxics (cypermethrin, lambda-cyhalothrin, endosulfan, chlorpyrifos) for the amphipod Hyalella curvispina in water and sediment. The sensitivity of H. curvispina was compared with the sensitivity of other species by means of the species sensitivity distribution curve (SSDs). The pyrethroid lambdacyhalothrin registered the lowest LC50 values, followed by cypermethrin, chlorpyrifos and endosulfan. It was observed that the sensitivity of H. curvispina is similar to H. azteca, a commonly used test organism in North America, and that both organisms are more sensitive than most freshwater invertebrate taxa. The streams studied are found in agricultural areas of Argentina, Paraguay and Brazil. The samplings were made during the period of soybean growth, corresponding 10 to the months of November to April. In Argentina, the study was conducted over a three years period and 23 streams were monitored in two regions of the Argentine Pampa, including a region of intensive soy production, in Arrecifes, and a mixed region: agricultural and livestock, in La Plata. Two regions of the Paranaense Forest were studied in 2013: 17 streams in Paraguay located on the Pirapó river basin, Itapúa department and 18 streams in Brazil in Toledo, Paraná state. Both regions have intensive soy production and legislation that requires farmers to leave a strip of uncultivated land between the crop and the streams. In the Pampean region it was shown that the assemblage of macroinvertebrates registered significant differences between streams with different land use in their basins (agricultural, livestock and reserve). The highest concentrations of nutrients and the presence of agrotoxics were recorded in the streams of basins where agriculture was the dominant activity. Likewise, in the agricultural streams the highest values of Total Toxic Unit (TU) were recorded, reaching, in some places, extreme values greater than unity. It was observed that in the least disturbed sites the dominance corresponded to Hyalellidae (Amphipoda), Palaemonidae (Decapoda) and Caenidae (Ephemeroptera), considered sensitive to the agrotoxics, while in the most disturbed site Gastropoda, Oligochaeta and Hirudinea, considered tolerant, were the taxa best represented. In the Paranaense Forest it was observed that the highest taxonomic richness and abundance corresponded to the studied streams of Paraguay, as well as diversity and equitability indexes. Coleoptera, Ephemeroptera and Trichoptera were found to be more abundant in Paraguay and showed an inverse correlation with the concentration of the biocides. On the contrary, Diptera and Bivalvia were more abundant in Brazil and showed a positive correlation with the concentration of some agrotoxics. It is noteworthy that the width of the attenuation strip in Paraguay was greater and less variable than in the streams studied in Brazil. In the analyzed sediments of the streams of Argentina, in basins with intensive soybean production, Brazil and Paraguay, the presence of all the biocides most frequently used in regional crops was detected. However, the impact of them on sensitive taxa was more clearly correlated in the Pampean streams. One possible reason for this discrepancy may be that the attenuation strips of stream in Argentina are much smaller and are not forested, so that invertebrate communities would not be so resilient. 11 These results confirm the protective effect of the attenuation strips and their usefulness as a management practice to mitigate the agricultural impact. In the present thesis, positive correlations were observed between the PRS concentration and the concentration of agrotoxics and negatives between the PRS and the abundance of some taxonomic groups. Its correlation does not mean a cause-effect relationship but the simultaneity of its application with agrotoxics and its similar environmental behavior, which is a good indicator of agricultural impact. The environmental variables that have the greatest influence on the composition of the macroinvertebrate assemblage were determined; among them are the organic matter content and texture of the sediments. In this study it is concluded that the exposure to agrotoxics contribute to the observed differences in the composition of the macroinvertebrate assemblage in streams with different land use in their basins. Draining basins with intensive land use without attenuation strips possess a fauna with greater abundance of taxa tolerant to the agrotóxicos and a decreased or absence of sensible taxa. It is also concluded that the assemblage of macroinvertebrates is an effective tool to evaluate aquatic ecosystems and their responses to changes in the land use from the adjacent fields.Fil: Marrochi, María Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentin

Do Riparian Buffers Protect Stream Invertebrate Communities in South American Atlantic Forest Agricultural Areas?

We investigated the influence and relative importance of insecticides and other agricultural stressors in determining variability in invertebrate communities in small streams in intensive soy-production regions of Brazil and Paraguay. In Paraguay we sampled 17 sites on tributaries of the Pirapó River in the state of Itapúa and in Brazil we sampled 18 sites on tributaries of the San Francisco River in the state of Paraná. The riparian buffer zones generally contained native Atlantic forest remnants and/or introduced tree species at various stages of growth. In Brazil the stream buffer width was negatively correlated with sediment insecticide concentrations and buffer width was found to have moderate importance in mitigating effects on some sensitive taxa such as mayflies. However, in both regions insecticides had low relative importance in explaining variability in invertebrate communities, while various habitat parameters were more important. In Brazil, the percent coverage of soft depositional sediment in streams was the most important agriculture-related explanatory variable, and the overall stream-habitat score was the most important variable in Paraguay streams. Paraguay and Brazil both have laws requiring forested riparian buffers. The ample forested riparian buffer zones typical of streams in these regions are likely to have mitigated the effects of pesticides on stream invertebrate communities. This study provides evidence that riparian buffer regulations in the Atlantic Forest region are protecting stream ecosystems from pesticides and other agricultural stressors. Further studies are needed to determine the minimum buffer widths necessary to achieve optimal protection.Instituto de Limnología "Dr. Raúl A. Ringuelet

Species at Risk (SPEAR) index indicates effects of insecticides on stream invertebrate communities in soy production regions of the Argentine Pampas

We investigated relationships among insecticides and aquatic invertebrate communities in 22 streams of two soy production regions of the Argentine Pampas over three growing seasons. Chlorpyrifos, endosulfan, cypermethrin, and lambda-cyhalothrin were the insecticides most frequently detected in stream sediments. The Species at Risk (SPEAR) pesticide bioassessment index (SPEARpesticides) was adapted and applied to evaluate relationships between sediment insecticide toxic units (TUs) and invertebrate communities associated with both benthic habitats and emergent vegetation habitats. SPEARpesticides was the only response metric that was significantly correlated with total insecticide TU values for all three averaged data sets, consistently showing a trend of decreasing values with increasing TU values (r2 = 0.35 to 0.42, p-value = 0.001 to 0.03). Although pyrethroids were the insecticides that contributed the highest TU values, toxicity calculated based on all insecticides was better at predicting changes in invertebrate communities than toxicity of pyrethroids alone. Crustaceans, particularly the amphipod Hyalella spp., which are relatively sensitive to pesticides, played a large role in the performance of SPEARpesticides, and the relative abundance of all crustaceans also showed a significant decreasing trend with increasing insecticide TUs for two of three data sets (r2 = 0.30 to 0.57, p-value = 0.003 to 0.04) examined. For all data sets, total insecticide TU was the most important variable in explaining variance in the SPEARpesticides index. The present study was the first application of the SPEAR index in South America, and the first one to use it to evaluate effects of pesticides on invertebrate communities associated with aquatic vegetation. Although the SPEAR index was developed in Europe, it performed well in the Argentine Pampas with only minor modifications, and would likely improve in performance as more data are obtained on traits of South American taxa, such as pesticide sensitivity and generation time.Instituto de Limnología "Dr. Raúl A. Ringuelet

Land use effect on invertebrate assemblages in Pampasic streams (Buenos Aires, Argentina)

Agriculture and livestock may contribute to water quality degradation in adjacent waterbodies and produce changes in the resident invertebrate composition. The objective of the present study was to assess land use effects on the stream invertebrate assemblages in rural areas of the Argentine Pampa. The four sampling events were performed at six sites in four streams of the Pampa plain; two streams were sampled inside a biosphere reserve, and another one was surrounded by extensive livestock fields. The fourth stream was sampled at three sites; the upstream site was adjacent to agricultural plots, the following site was adjacent to an intensive livestock plot and the downstream site was adjacent to extensive breeding cattle plots. Higher pesticide concentrations were found at the site adjacent to agricultural plots and higher nutrient concentrations at the sites adjacent to agricultural and intensive breeding cattle plots. The invertebrate fauna were also different at these sites. Multivariate analysis showed a relationship between nutrient concentrations and taxonomic composition. Amphipoda (Hyalella curvispina) was the dominant group in the reserve and extensive breeding cattle sites, but was not present in the agricultural site. Also, Chironomidae were absent from the agricultural site while present at other sites. Gasteropoda (Biomphalaria peregrina), Zygoptera, and Hirudinea were dominant at the most impacted agricultural and intensive breeding cattle sites.Instituto de Limnología "Dr. Raúl A. Ringuelet

Insecticide concentrations in stream sediments of soy production regions of South America

Concentrations of 17 insecticides were measured in sediments collected from 53 streams in soy production regions of South America (Argentina in 2011-2014, Paraguay and Brazil in 2013) during peak application periods. Although environmental regulations are quite different in each country, commonly used insecticides were detected at high frequencies in all regions. Maximum concentrations (and detection frequencies) for each sampling event ranged from: 1.2–7.4 ng/g dw chlorpyrifos (56-100%); 0.9–8.3 ng/g dw cypermethrin (20-100%); 0.42–16.6 ng/g dw lambda-cyhalothrin (60-100%); and 0.49– 2.1 ng/g dw endosulfan (13-100%). Other pyrethroids were detected less frequently. Banned organochlorines were most frequently detected in Brazil. In all countries, cypermethrin and/or lambda-cyhalothrin toxic units (TUs), based on Hyalella azteca LC50 bioassays, were occasionally >0.5 (indicating likely acute toxicity), while TUs for other insecticides were <0.5. All samples with total insecticide TU > 1 were collected from streams with riparian buffer width < 20 m. A multiple regression analysis that included five landscape and habitat predictor variables for the Brazilian streams examined indicated that buffer width was the most important predictor variable in explaining total insecticide TU values. While Brazil and Paraguay require forested stream buffers, there were no such regulations in the Argentine pampas, where buffer widths were smaller. Multiple insecticides were found in almost all stream sediment samples in intensive soy production regions, with pyrethroids most often occurring at acutely toxic concentrations, and the greatest potential for insecticide toxicity occurring in streams with minimum buffer width < 20m.Instituto de Limnología "Dr. Raúl A. Ringuelet

Fish Assemblages in Pampean Streams (Buenos Aires, Argentina): Relationship to Abiotic and Anthropic Variables

The present study reported the effect of natural and anthropic environmental variables on the fish assemblages in the pampean streams, in the coastal strip along the Río de la Plata, Buenos Aires province, Argentina. Five streams were sampled at 12 sites surrounded by land devoted to different uses. A correspondence analysis sorted the streams into two groups: a less impacted group formed by sites surrounded by livestock- raising pastures and a more impacted one passing through urban sites and including a stream adjacent to a modest rural urbanization with a dairy in the stream’s basin. The nutrient concentrations were significantly higher in the more impacted group; with species richness, diversity, abundance, and biomass being significantly lower. A canonical-correspondence analysis linked the more impacted sites to high concentrations of soluble reactive phosphorus and impoverished fish assemblages, composed of species tolerant to environmental pollution. On the other hand, sites with higher oxygen concentrations and pH were related to richer assemblages pointing to good environmental conditions at the sites surrounded by livestock-raising pastures. The downstream sites on the less impacted streams contained fish assemblages in which the juvenile stages of species corresponding to the Río de la Plata were dominant.Instituto de Limnología "Dr. Raúl A. Ringuelet

Consecuencias de la actividad agrícola sobre la fauna de los arroyos pampeanos

Si observamos las zonas adyacentes a los cursos de agua que atraviesan la llanura pampeana podemos apreciar distintos usos del suelo, entre ellos los más comunes son la ganadería y la agricultura. Esta última emplea diferentes productos para aumentar la producción, como plaguicidas fertilizantes y ,que pueden producir un impacto negativo en la fauna que habita en estos arroyos.Instituto de Limnología "Dr. Raúl A. Ringuelet

Efectos de agroquímicos en arroyos de cuencas agrícolas y hortícolas

En las últimas décadas las áreas periurbanas de la región del gran La Plata fueron cambiando el uso del suelo. Comenzaron con una ganadería extensiva sobre pasturas naturales, luego agricultura y, más recientemente, horticultura. La incorporación del invernadero permitió el desarrollo de cultivos en épocas en las cuales resultaría imposible su producción, pero trajo consigo un incremento en el uso de insecticidas, fungicidas y herbicidas. Los productores necesitan agregar agroquímicos al cultivo para aumentar el rendimiento de sus cosechas. El problema es que, mucho de lo que se aplica en los cultivos llega a los cuerpos de agua, como por ejemplo a los humedales de la zona. Los humedales son áreas cubiertas de agua y vegetación adaptada al anegamiento, que suelen encontrarse en las zonas bajas del relieve.Instituto de Limnología "Dr. Raúl A. Ringuelet

Cypermethrin, Chlorpyrifos and Endosulfan Toxicity to Two Non-Target Freshwater Organisms

Pesticide consumption has increased considerably over the last decades in the Argentine Pampa. The persistence of toxicity of three commonly used insecticides to two regionally abundant organisms was assayed at environmentally realistic conditions. To simulate a runoff event, insecticides were added to aquariums containing water and sediment collected from a representative stream. The toxicity of insecticides formulations containing cypermethrin, chlorpyrifos and endosulfan to the amphipod Hyallela curvispina and the fish Cnesterodon decemmaculatus was assessed with laboratory bioassays conducted on water taken from the aquariums immediately after pesticide addition and every 2 to 3 days thereafter until toxicity ceased. Endosulfan did not cause mortality to H. curvispina at a nominal concentration of 1 µg/L. Cypermethrin and chlorpyrifos caused 100% mortality immediately after application at this concentration. Toxicity ceased 4 days after addition of chlorpyrifos, and 9 days after addition of cypermethrin, resulting in a 50% lethal time of 3 and 4 days, respectively. C. decemmaculatus demonstrated no mortality at 1 µg/L nominal concentration of the formulated insecticides assayed. At a dose of 5µ/L, no mortality was exhibited for cypermethrin and chlorpyrifos, while endosulfan produced 100% mortality immediately after application, but no significant toxicity 2 days after application. Present results suggest short persistence of toxicity of the commonly used insecticide formulations in Pampasic surface waters.Fil: Mugni, Hernan Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Paracampo, Ariel Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Marrochi, María Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Bonetto, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentin

Acute toxicity of cypermethrin to the non target organism Hyalella curvispina

The acute toxicity of cypermethrin to the amphipod Hyalella curvispina was evaluated by means of a toxicity test under laboratory conditions. Cypermethrin is one of the most widely used insecticides in Argentina. H. curvispina is a widely distributed and commonly abundant component of the invertebrate assemblages in shallow waters of southern South America. The experiments were repeated three times. The mean 48-h LC50 value for H. curvispina was estimated at 0.066 μg/l. H. curvispina represents a good model for exotoxicological risk assessment.Fil: Mugni, Hernan Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raul A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Paracampo, Ariel Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raul A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Marrochi, María Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raul A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Bonetto, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raul A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentin