Contribución al conocimiento limnológico del Río Paraguay en su tramo inferior

The main limnological feactures of the Paraguay river have been studied in two sampling sites: La Herradura and Puerto Bermejo stations. The former is situated above the confluence with the Bermejo river and the latter is located below the confluence. The phytoplankton community has been dominated by Diatomophyceae (mainly Melosira granulala) and Chlorophyceae (mainly Monoraphídium, Schroederia and Scenedesmus). Crytophyceae (Cryptonomas) and Dinophyceae (Perldlnium) have always been present in low percentage. Cyanophyceae have usually been less than 4% of the total population density. In the low water period of the summer 1978-1979, the maximun phytoplankton density was estimated in 4 000 ind./ml and the production in 750 mg C/m2 d. During the flood period of May through October the lowest phytoplankton density (160 ind./ml) and production (60 mg C/m2 d) were measured. Variations in the suspended solid content and salinity of the water are discussed in relation to the hidrologic regime of the river. The huge amount of sedimenta carried by the Bermejo river to the lower Paraguay produces a drastic decrease in the transparency, phytoplankton density and production of the waters. On the other hand, conductivity, suspended solids and nutrients are highly increased.The main limnological feactures of the Paraguay river have been studied in two sampling sites: La Herradura and Puerto Bermejo stations. The former is situated above the confluence with the Bermejo river and the latter is located below the confluence. The phytoplankton community has been dominated by Diatomophyceae (mainly Melosira granulala) and Chlorophyceae (mainly Monoraphídium, Schroederia and Scenedesmus). Crytophyceae (Cryptonomas) and Dinophyceae (Perldlnium) have always been present in low percentage. Cyanophyceae have usually been less than 4% of the total population density. In the low water period of the summer 1978-1979, the maximun phytoplankton density was estimated in 4 000 ind./ml and the production in 750 mg C/m2 d. During the flood period of May through October the lowest phytoplankton density (160 ind./ml) and production (60 mg C/m2 d) were measured. Variations in the suspended solid content and salinity of the water are discussed in relation to the hidrologic regime of the river. The huge amount of sedimenta carried by the Bermejo river to the lower Paraguay produces a drastic decrease in the transparency, phytoplankton density and production of the waters. On the other hand, conductivity, suspended solids and nutrients are highly increased

Concentración de nitrogeno y fósforo en el agua de lluvia de Corrientes (Argentina)

Inorganic nitrogen, phosphorus, pH and conductivity in rainwater were measured at Corrientes (27°27’S, 58°47’W) during 1984-1985. Mean water pH was 5.97 (4.60 - 7.15) and mean conductivity was 11.5 uS/cm (2.7 - 21 uS/cm) showing good waterquality. Concentration showed positive correlation with the length of time betweensuccessive rains and were inversely correlated with precipitation volume. Both inorganic nitrogen concentrations and fallout, were low (mean conc.: 315 µg Ninorg/1 mean fallout: 190 µg Ninorg/m2 yr) when compared with the reported figures in unpolluted locations. Total phosphorus concentration (36 µg TP/1) and fallout (16.5 µg TP/m2 yr) were relatively high probably because of dust contribution. Fallout rates resulted an order of magnitude lower than those of very polluted areas.lt was shown that nutrient fallout is important in determining trophic status of shallow lakes and ponds profuselly distributed in Corrientes province.Inorganic nitrogen, phosphorus, pH and conductivity in rainwater were measured at Corrientes (27°27’S, 58°47’W) during 1984-1985. Mean water pH was 5.97 (4.60 - 7.15) and mean conductivity was 11.5 uS/cm (2.7 - 21 uS/cm) showing good waterquality. Concentration showed positive correlation with the length of time betweensuccessive rains and were inversely correlated with precipitation volume. Both inorganic nitrogen concentrations and fallout, were low (mean conc.: 315 µg Ninorg/1 mean fallout: 190 µg Ninorg/m2 yr) when compared with the reported figures in unpolluted locations. Total phosphorus concentration (36 µg TP/1) and fallout (16.5 µg TP/m2 yr) were relatively high probably because of dust contribution. Fallout rates resulted an order of magnitude lower than those of very polluted areas.lt was shown that nutrient fallout is important in determining trophic status of shallow lakes and ponds profuselly distributed in Corrientes province

Fijación de fosforo en sedimientos de fondo de los Ríos Paraná, Paraguay y Bermejo

Phosphorus sorption'from Solutions containing 0-5 mgP/l was studied in bottom sediments from Paraná, Paraguay and Bermejo rivers. Sorptidh frtted a Langmuir isotherm with phosphate sorption capacities of 96, 87 and 52 MgP/g (dry weight) sediment. Hieltjesand Lijklema (1980) phosphorus fractionation showed that the iron bound phosphate is the mainfraction in the Paraná and Paraguay sediments while the calcium bound phosphorus is the main fraction in the Bermejo sediments. Caleiuhi content was high (32 mg/g) in the Bermejo sediments and low (5.5 and 5;3 mg/g) in the Paraná and Paraguay sediments, respectively, The organic matter composition is also dlfferent in the three rivers being the Paraná and the l^íraguay ríchér in huihic ^ibstánces. Low phosphorus content and sorption capacity in the three sediments are thought to be related with a granulometry dominated by the coarse fractions. Clay size partióles only accounted for 13-23 % of the total sediment weight.Phosphorus sorption'from Solutions containing 0-5 mgP/l was studied in bottom sediments from Paraná, Paraguay and Bermejo rivers. Sorptidh frtted a Langmuir isotherm with phosphate sorption capacities of 96, 87 and 52 MgP/g (dry weight) sediment. Hieltjesand Lijklema (1980) phosphorus fractionation showed that the iron bound phosphate is the mainfraction in the Paraná and Paraguay sediments while the calcium bound phosphorus is the main fraction in the Bermejo sediments. Caleiuhi content was high (32 mg/g) in the Bermejo sediments and low (5.5 and 5;3 mg/g) in the Paraná and Paraguay sediments, respectively, The organic matter composition is also dlfferent in the three rivers being the Paraná and the l^íraguay ríchér in huihic ^ibstánces. Low phosphorus content and sorption capacity in the three sediments are thought to be related with a granulometry dominated by the coarse fractions. Clay size partióles only accounted for 13-23 % of the total sediment weight

Abnormalities in amphibian populations inhabiting agroecosystems in northeastern Buenos Aires Province, Argentina

The occurrence of abnormalities in amphibians has been reported in many populations, and its increase could be related to environmental pollution and habitat degradation. We evaluated the type and prevalence of abnormalities in 5 amphibian populations from agroecosystems with different degrees of agricultural disturbance (cultivated and reference areas). We detected 9 types of abnormalities, of which the most frequent were those occurring in limbs. The observed prevalence of abnormality in assessed populations from cultivated and reference areas was as follows: Rhinella fernandezae (37.1 and 10.2%, respectively), Leptodactylus latrans adults (28.1 and 9.2%) and juveniles (32.9 and 15.3%), and Hypsiboas pulchellus (11.6 and 2.8%). Scinax granulatus populations did not show abnormalities. Pseudis minuta, which was only detected in the reference area, exhibited a prevalence of 13.3%. For R. fernandezae, L. latrans, and H. pulchellus, generalized linear mixed models showed that prevalence of abnormalities was significantly higher (p < 0.05) in cultivated than in reference areas. L. latrans juveniles were more vulnerable to abnormalities than adults (p < 0.05). The presence of abnormalities in some species inhabiting different agroecosystems suggests that environmental stress factors might be responsible for their occurrence. While we detected pesticides (endosulfan, cypermethrin, and chlorpyrifos) and lower dissolved oxygen levels in ponds of the cultivated area, no data are currently available on how other factors, such as injuries from predators and parasite infections, vary by land use. Further research will be necessary to evaluate possible causes of abnormalities detected in the present study mainly in the context of factor interactions.Facultad de Ciencias Naturales y Muse

On the Fluctuation Relation for Nose-Hoover Boundary Thermostated Systems

We discuss the transient and steady state fluctuation relation for a mechanical system in contact with two deterministic thermostats at different temperatures. The system is a modified Lorentz gas in which the fixed scatterers exchange energy with the gas of particles, and the thermostats are modelled by two Nos\'e-Hoover thermostats applied at the boundaries of the system. The transient fluctuation relation, which holds only for a precise choice of the initial ensemble, is verified at all times, as expected. Times longer than the mesoscopic scale, needed for local equilibrium to be settled, are required if a different initial ensemble is considered. This shows how the transient fluctuation relation asymptotically leads to the steady state relation when, as explicitly checked in our systems, the condition found in [D.J. Searles, {\em et al.}, J. Stat. Phys. 128, 1337 (2007)], for the validity of the steady state fluctuation relation, is verified. For the steady state fluctuations of the phase space contraction rate \zL and of the dissipation function \zW, a similar relaxation regime at shorter averaging times is found. The quantity \zW satisfies with good accuracy the fluctuation relation for times larger than the mesoscopic time scale; the quantity \zL appears to begin a monotonic convergence after such times. This is consistent with the fact that \zW and \zL differ by a total time derivative, and that the tails of the probability distribution function of \zL are Gaussian.Comment: Major revision. Fig.10 was added. Version to appear in Journal of Statistical Physic

Depuración del efluente de una empresa metalúrgica utilizando un wetland construido

Los humedales o wetlands han demostrado ser altamente eficientes en la remoción de contaminantes, son de bajo costo de instalación y mantenimiento, operables por mano de obra no especializada e integrables funcionalmente con el entorno. El objetivo de este trabajo fue evaluar la eficiencia de un wetland construido para la depuración en forma conjunta del efluente industrial y el cloacal de una industria metalúrgica. Las dimensiones del mismo son de 50 m de largo por 40 m de ancho y profundidad de 80 cm, con un tabique central de manera que la relación largo-ancho sea 5:1. Está impermeabilizado con bentonita, y las plantas se arraigan sobre una capa de 1 m de suelo. Se transplantaron macrófitas de la zona del Río Paraná Medio: Eichhornia crassipes (jacinto de agua), Typha domingensis (totora) y Pontederia cordata (aguapey), entre otras. La eficiencia del humedal se determinó analizando la composición química del efluente a la entrada y salida. En sedimentos y vegetales se determinó P, Cr, Ni y Zn. El muestreo se realizó quincenalmente durante 2 años. El wetland eficientemente disminuyó las concentraciones medias y la variabilidad de los parámetros analizados, salvo en el caso de fosfato y amonio debido a la anoxia. Las remociones medias fueron de 86% para Cr, 67% para Ni, 95% para Fe, 70% para nitrato, 60% para nitrito, 78% para DQO, 77% para DBO. Las concentraciones de Zn en el afluente estuvieron por debajo de los 50 μg.l-1 en la mayoría de los muestreos. La concentración de metales no aumentó significativamente en el sedimento de fondo después de 2 años de operación. Un aumento en la concentración de metales y nutrientes en los tejidos de las macrófitas, así como también el aumento de la biomasa, representó el principal mecanismo de remoción de contaminantes. La ventaja de las macrófitas es la posibilidad de ser cosechadas, lo que conduce a importantes tasas de remoción en corto tiempo. La superficie del wetland se cubrió en un 80% de E. crassipes, lo que probablemente contribuyó a la disminución de oxígeno en agua. Disminuir el nivel de agua contribuiría a favorecer la dominancia de las macrófitas enraizadas y a aumentar la concentración de oxígeno en agua. La calidad del efluente se mejoró diseñándose la salida del mismo a nivel superficial.Facultad de Ciencias Naturales y Muse

Depuración del efluente de una empresa metalúrgica utilizando un wetland construido

Los humedales o wetlands han demostrado ser altamente eficientes en la remoción de contaminantes, son de bajo costo de instalación y mantenimiento, operables por mano de obra no especializada e integrables funcionalmente con el entorno. El objetivo de este trabajo fue evaluar la eficiencia de un wetland construido para la depuración en forma conjunta del efluente industrial y el cloacal de una industria metalúrgica. Las dimensiones del mismo son de 50 m de largo por 40 m de ancho y profundidad de 80 cm, con un tabique central de manera que la relación largo-ancho sea 5:1. Está impermeabilizado con bentonita, y las plantas se arraigan sobre una capa de 1 m de suelo. Se transplantaron macrófitas de la zona del Río Paraná Medio: Eichhornia crassipes (jacinto de agua), Typha domingensis (totora) y Pontederia cordata (aguapey), entre otras. La eficiencia del humedal se determinó analizando la composición química del efluente a la entrada y salida. En sedimentos y vegetales se determinó P, Cr, Ni y Zn. El muestreo se realizó quincenalmente durante 2 años. El wetland eficientemente disminuyó las concentraciones medias y la variabilidad de los parámetros analizados, salvo en el caso de fosfato y amonio debido a la anoxia. Las remociones medias fueron de 86% para Cr, 67% para Ni, 95% para Fe, 70% para nitrato, 60% para nitrito, 78% para DQO, 77% para DBO. Las concentraciones de Zn en el afluente estuvieron por debajo de los 50 μg.l-1 en la mayoría de los muestreos. La concentración de metales no aumentó significativamente en el sedimento de fondo después de 2 años de operación. Un aumento en la concentración de metales y nutrientes en los tejidos de las macrófitas, así como también el aumento de la biomasa, representó el principal mecanismo de remoción de contaminantes. La ventaja de las macrófitas es la posibilidad de ser cosechadas, lo que conduce a importantes tasas de remoción en corto tiempo. La superficie del wetland se cubrió en un 80% de E. crassipes, lo que probablemente contribuyó a la disminución de oxígeno en agua. Disminuir el nivel de agua contribuiría a favorecer la dominancia de las macrófitas enraizadas y a aumentar la concentración de oxígeno en agua. La calidad del efluente se mejoró diseñándose la salida del mismo a nivel superficial.Facultad de Ciencias Naturales y Muse

Depuración del efluente de una empresa metalúrgica utilizando un wetland construido

Los humedales o wetlands han demostrado ser altamente eficientes en la remoción de contaminantes, son de bajo costo de instalación y mantenimiento, operables por mano de obra no especializada e integrables funcionalmente con el entorno. El objetivo de este trabajo fue evaluar la eficiencia de un wetland construido para la depuración en forma conjunta del efluente industrial y el cloacal de una industria metalúrgica. Las dimensiones del mismo son de 50 m de largo por 40 m de ancho y profundidad de 80 cm, con un tabique central de manera que la relación largo-ancho sea 5:1. Está impermeabilizado con bentonita, y las plantas se arraigan sobre una capa de 1 m de suelo. Se transplantaron macrófitas de la zona del Río Paraná Medio: Eichhornia crassipes (jacinto de agua), Typha domingensis (totora) y Pontederia cordata (aguapey), entre otras. La eficiencia del humedal se determinó analizando la composición química del efluente a la entrada y salida. En sedimentos y vegetales se determinó P, Cr, Ni y Zn. El muestreo se realizó quincenalmente durante 2 años. El wetland eficientemente disminuyó las concentraciones medias y la variabilidad de los parámetros analizados, salvo en el caso de fosfato y amonio debido a la anoxia. Las remociones medias fueron de 86% para Cr, 67% para Ni, 95% para Fe, 70% para nitrato, 60% para nitrito, 78% para DQO, 77% para DBO. Las concentraciones de Zn en el afluente estuvieron por debajo de los 50 μg.l-1 en la mayoría de los muestreos. La concentración de metales no aumentó significativamente en el sedimento de fondo después de 2 años de operación. Un aumento en la concentración de metales y nutrientes en los tejidos de las macrófitas, así como también el aumento de la biomasa, representó el principal mecanismo de remoción de contaminantes. La ventaja de las macrófitas es la posibilidad de ser cosechadas, lo que conduce a importantes tasas de remoción en corto tiempo. La superficie del wetland se cubrió en un 80% de E. crassipes, lo que probablemente contribuyó a la disminución de oxígeno en agua. Disminuir el nivel de agua contribuiría a favorecer la dominancia de las macrófitas enraizadas y a aumentar la concentración de oxígeno en agua. La calidad del efluente se mejoró diseñándose la salida del mismo a nivel superficial.Facultad de Ciencias Naturales y Muse

Abnormalities in amphibian populations inhabiting agroecosystems in northeastern Buenos Aires Province, Argentina

The occurrence of abnormalities in amphibians has been reported in many populations, and its increase could be related to environmental pollution and habitat degradation. We evaluated the type and prevalence of abnormalities in 5 amphibian populations from agroecosystems with different degrees of agricultural disturbance (cultivated and reference areas). We detected 9 types of abnormalities, of which the most frequent were those occurring in limbs. The observed prevalence of abnormality in assessed populations from cultivated and reference areas was as follows: Rhinella fernandezae (37.1 and 10.2%, respectively), Leptodactylus latrans adults (28.1 and 9.2%) and juveniles (32.9 and 15.3%), and Hypsiboas pulchellus (11.6 and 2.8%). Scinax granulatus populations did not show abnormalities. Pseudis minuta, which was only detected in the reference area, exhibited a prevalence of 13.3%. For R. fernandezae, L. latrans, and H. pulchellus, generalized linear mixed models showed that prevalence of abnormalities was significantly higher (p < 0.05) in cultivated than in reference areas. L. latrans juveniles were more vulnerable to abnormalities than adults (p < 0.05). The presence of abnormalities in some species inhabiting different agroecosystems suggests that environmental stress factors might be responsible for their occurrence. While we detected pesticides (endosulfan, cypermethrin, and chlorpyrifos) and lower dissolved oxygen levels in ponds of the cultivated area, no data are currently available on how other factors, such as injuries from predators and parasite infections, vary by land use. Further research will be necessary to evaluate possible causes of abnormalities detected in the present study mainly in the context of factor interactions.Facultad de Ciencias Naturales y Muse

Effects of the herbicide Roundup on freshwater microbial communities: a mesocosm study

The impact of the widely used herbicide glyphosate has been mainly studied in terrestrial weed control, laboratory bioassays, and field studies focusing on invertebrates, amphibians, and fishes. Despite the importance of phytoplankton and periphyton communities at the base of the aquatic food webs, fewer studies have investigated the effects of glyphosate on freshwater microbial assemblages. We assessed the effect of the commercial formulation Roundup using artificial earthen mesocosms. The herbicide was added at three doses: a control (without Roundup) and two treatments of 6 and 12 mg/L of the active ingredient (glyphosate). Estimates of the dissipation rate (k) were similar in the two treatments (half-lives of 5.77 and 7.37 d, respectively). The only two physicochemical parameters showing statistically significant differences between treatments and controls were the downward vertical spectral attenuation coefficient kd(k), where k is wavelength, and total phosphorus concentration (TP). At the end of the experiment, the treated mesocosms showed a significant increase in the ratio kd(490 nm)/kd(550 nm) and an eightfold increase in TP. Roundup affected the structure of phytoplankton and periphyton assemblages. Total micro- and nanophytoplankton decreased in abundance in treated mesocosms. In contrast, the abundance of picocyanobacteria increased by a factor of about 40. Primary production also increased in treated mesocosms (roughly by a factor of two). Similar patterns were observed in the periphytic assemblages, which showed an increased proportion of dead : live individuals and increased abundances of cyanobacteria (about 4.5-fold). Interestingly, the observed changes in the microbial assemblages were captured by the analysis of the pigment composition of the phytoplankton, the phytoplankton absorption spectra, and the analysis of the optical properties of the water. The observed changes in the structure of the microbial assemblages are more consistent with a direct toxicological effect of glyphosate rather than an indirect effect mediated by phosphorus enrichment.Facultad de Ciencias Naturales y Muse