RESUMEN

Lenitic and lotic aquatic environments were studied in the Middle Paraná River basin, one of the largest rivers of the world (basin: 1,510,000 km2, length: 2,570 km). The Paraná River (S 31° 42’ 04"; W 60° 29’ 39"), during El Niño-Southern Oscillation (ENSO) (1997-1998), registered maximum flows of 29,962 m3 s-1(more than twice the mean flow) and also positive pluvial anomalies (A) (from +120 mm to +161 mm). However, concentrations of Escherichia coli remained low, with values similar to the mean (p > 0.05) (1.3802 log10 cfu/100 ml). Only a maximum peak (1.903 log10 cfu/100 ml), significantly higher than the mean (p < 0.0001), was detected during the ascending phase of the flood pulse. During La Niña (September 1999 - March 2000; Q =11,255 m3 s-1; A = -78 mm to -84 mm), concentrations of E. coli were significantly lower than the mean (p< 0.0001). During the post-Niña period, with normal flows (Q = 14,900 m3 s-1) but with strong positive pluvial anomalies (A= +118 mm to +377 mm), the fecal indicator density reached maximum values (up to 2.699 log10 cfu /100 ml, p< 0.0001). The multiple regression model used with all the results obtained in the Paraná River showed that variations in concentrations of E. coli are mainly explained by pluvial precipitations and hydrometric level (p = 0.001). Temporal patterns of concentrations of E. coli in a small, secondary course (Q = 101 m3 s-1) followed those of the Paraná River, but concentrations and peaks of E. coli produced by exceptional rains showed a higher magnitude (maximum: 3.325 log10 cfu /100 ml). In the floodplain lakes, away from urban centers, concentrations of E. coli were not associated to hydroclimatic anomalies, but directly to vegetable cover: maximum concentrations were always registered during periods that lakes remained covered by floating macrophytes (mainly Eichhornia crassipes); on the contrary, minimum concentrations were registered during periods without vegetable cover.

Se estudiaron ambientes acuáticos leníticos y lóticos en la cuenca del río Paraná Medio, uno de los ríos más grandes del mundo (cuenca: 1.510.000 km2, longitud: 2.570 km). El río Paraná (31° 42’ 04"S; 60° 29’39"W), durante El Niño Oscilación Sur (ENOS) (1997-1998), registró caudales máximos de 29.962 m3 s-1(más del doble del caudal medio) y también anomalías pluviales (A) positivas (desde +120mm a +161mm). Sin embargo, la concentración de Escherichia coli se mantuvo baja, con valores similares (p > 0,05) a la media (1,3802 log10ufc/100ml). Solamente se detectó un pico máximo (1,903 log10ufc/100ml) significativamente mayor a la media (p < 0,0001) durante la fase ascendente del pulso de la creciente. Durante La Niña (sept. 1999 - marzo 2000; Q =11.255 m3 s-1 ;A = -78mm a -84mm), las concentraciones de E. coli resultaron inferiores a la media (p<0,0001). Durante el período post-Niña, con caudales normales (Q = 14.900 m3 s-1) pero con fuertes anomalías pluviales positivas (A= +118 mm a +377mm), la densidad del indicador fecal alcanzó valores máximos (hasta 2,699 log10ufc /100ml, p< 0,0001).La aplicación de un modelo de regresión múltiple al conjunto de los resultados obtenidos en el río Paraná, muestra que las variaciones en la concentración de E. coli son principalmente explicadas por las precipitaciones pluviales y el nivel hidrométrico (p = 0,001). Los patrones temporales de las concentraciones de E. coli en un pequeño cauce secundario (Q = 101 m3s-1) siguieron a las del río Paraná, pero las concentraciones y los picos de E. coli producidos por lluvias excepcionales fueron de mayor magnitud (máximo: 3,325 log10ufc /100ml). Enlas lagunas de la llanura de inundación, lejos de centros urbanos, la concentración de E. coli no estuvo asociada con anomalías hidroclimáticas, sino directamente con la cobertura vegetal: las concentraciones máximas se registraron siempre durante los períodos que permanecían cubiertas con macrófitas flotantes (principalmente Eichhornia crassipes). Durante los períodos sin cobertura vegetal, por el contrario, se registraron las concentraciones mínimas de E. coli.

Asunto(s)

RESUMEN

Lenitic and lotic aquatic environments were studied in the Middle Paraná River basin, one of the largest rivers of the world (basin: 1,510,000 km2, length: 2,570 km). The Paraná River (S 31 degrees 42' 04"; W 60 degrees 29' 39"), during El Niño-Southern Oscillation (ENSO) (1997-1998), registered maximum flows of 29,962 m3 s(-1) (more than twice the mean flow) and also positive pluvial anomalies (A) (from +120 mm to +161 mm). However, concentrations of Escherichia coli remained low, with values similar to the mean (p > 0.05) (1.3802 log10cfu/100 ml). Only a maximum peak (1.903 log10cfu/100 ml), significantly higher than the mean (p < 0.0001), was detected during the ascending phase of the flood pulse. During La Niña (September 1999-March 2000; Q = 11,255 m3 s(-1); A = -78 mm to -84 mm), concentrations of E. coli were significantly lower than the mean (p < 0.0001). During the post-Niña period, with normal flows (Q = 14,900 m3 s(-1)) but with strong positive pluvial anomalies (A = +118 mm to +377 mm), the fecal indicator density reached maximum values (up to 2.699 log10cfu/100 ml, p < 0.0001). The multiple regression model used with all the results obtained in the Paraná River showed that variations in concentrations of E. coli are mainly explained by pluvial precipitations and hydrometric level (p = 0.001). Temporal patterns of concentrations of E. coli in a small, secondary course (Q = 101 m3 s(-1)) followed those of the Paraná River, but concentrations and peaks of E. coli produced by exceptional rains showed a higher magnitude (maximum: 3.325 log10cfu/100 ml). In the floodplain lakes, away from urban centers, concentrations of E. coli were not associated to hydroclimatic anomalies, but directly to vegetable cover: maximum concentrations were always registered during periods that lakes remained covered by floating macrophytes (mainly Eichhornia crassipes); on the contrary, minimum concentrations were registered during periods without vegetable cover.

Asunto(s)

RESUMEN

Lenitic and lotic aquatic environments were studied in the Middle Paraná River basin, one of the largest rivers of the world (basin: 1,510,000 km2, length: 2,570 km). The Paraná River (S 31 degrees 42 04[quot ]; W 60 degrees 29 39[quot ]), during El Niño-Southern Oscillation (ENSO) (1997-1998), registered maximum flows of 29,962 m3 s(-1) (more than twice the mean flow) and also positive pluvial anomalies (A) (from +120 mm to +161 mm). However, concentrations of Escherichia coli remained low, with values similar to the mean (p > 0.05) (1.3802 log10cfu/100 ml). Only a maximum peak (1.903 log10cfu/100 ml), significantly higher than the mean (p < 0.0001), was detected during the ascending phase of the flood pulse. During La Niña (September 1999-March 2000; Q = 11,255 m3 s(-1); A = -78 mm to -84 mm), concentrations of E. coli were significantly lower than the mean (p < 0.0001). During the post-Niña period, with normal flows (Q = 14,900 m3 s(-1)) but with strong positive pluvial anomalies (A = +118 mm to +377 mm), the fecal indicator density reached maximum values (up to 2.699 log10cfu/100 ml, p < 0.0001). The multiple regression model used with all the results obtained in the Paraná River showed that variations in concentrations of E. coli are mainly explained by pluvial precipitations and hydrometric level (p = 0.001). Temporal patterns of concentrations of E. coli in a small, secondary course (Q = 101 m3 s(-1)) followed those of the Paraná River, but concentrations and peaks of E. coli produced by exceptional rains showed a higher magnitude (maximum: 3.325 log10cfu/100 ml). In the floodplain lakes, away from urban centers, concentrations of E. coli were not associated to hydroclimatic anomalies, but directly to vegetable cover: maximum concentrations were always registered during periods that lakes remained covered by floating macrophytes (mainly Eichhornia crassipes); on the contrary, minimum concentrations were registered during periods without vegetable cover.

RESUMEN

At the moment of examination, the bacteriological quality of water is not, to a large extent, more than an a posteriori evaluation: the population is advised afterwards that it had been exposed to a sanitary risk. The ideal situation for managing aquatic environments or recreational use would be to be able to predict at any moment their bacteriological quality. An approach would be to develop predictive models to relate the exceedance (number of days during which the bacteriological indicator exceeds the standards) with environmental variables. Studies were carried out at two beaches with different limnological characteristics, a fluvial beach and a lacustrine beach, from the beginning of 1998 to the end of 2000, so that it was possible to obtain information on the impact of very different hydroclimatic situations on microorganisms of sanitary interest (Escherichia coli and cyanobacteria). Three variables, maximum concentration of E. coli, rains and water level, justified 92.6% of the exceedance variance in the multiple regression model at the fluvial beach. Other abiotic variables (temperature, pH, conductivity, transparency and dissolved oxygen) showed collinearity problems or did not make statistically significant contributions to the model. During the El Niño event (gauge heights > 5 m) there were no exceedances after the rains, even with precipitations of 200 mm. Moreover, cyanobacteria density remained low (x = 1.191 +/- 0.703 log10 cian./ml). During the negative pluvial anomalies, although the exceedances of E. coli were not very frequent at both beaches due to the scarce rains, a massive development of cyanobacteria was produced (x = 4.657 +/- 0.578 log10 cian./ml) at the lacustrine beach. At this beach, the mean decay coefficient (K) for E. coli was significantly (p < 0.05) lower than that estimated for the fluvial beach (K = -0.682 +/- 0.32 versus K = -0.387 +/- 0.16, respectively), possibly due to the unfavourable environment created by the higher development of photosynthetic organisms. Analizing separately the anomalous period, variables that better explained (98.6%) the exceedances were (in addition to the maximum concentration of E. coli) pH, temperature and days without rains (DWR) before the sampling. The longest exceedances (6 to 8 days) were produced at the end of the negative pluvial anomalies, after prolonged periods (> 30 days) of droughts. Regression models obtained to predict the exceedance of E. coli were simplified using only three abiotic variables (water level, rains and DWR). Although, in this way, the percentage of explanation of the exceedance is lower (78.5%), the information needed for the model is obtained quickly and preventive measures can be carried out immediately while waiting for more information.

Asunto(s)

RESUMEN

Actualmente, la calidad bacteriológica del agua no es, en gran parte, más que una evaluación a posteriori: la población es advertida después de que estuvo expuesta al riesgo sanitario. La situación ideal, en materia de gestión de los ambientes acuáticos de uso recreativo, sería poder prever en cualquier momento su calidad bacteriológica. Una aproximación es desarrollar modelos predictivos que relacionen la excedencia (número de días durante los cuales el indicador bacteriológico excede los estándares) con variables ambientales. Los estudios se llevaron a cabo en dos balnearios con características limnológicas diferentes: uno fluvial y otro lacustre, durante principios de 1998 hasta fines del año 2000, en cuyo transcurso se pudo obtener información del impacto de situaciones hidro-climáticas muy disímiles sobre microorganismos de interés sanitario (Escherichia coli y cianobacterias). Las variables concentración máxima de E.coli, lluvias y nivel hidrométrico (Nh) explicaron el 92,6 por ciento de la varianza de la excedencia en el modelo de regresión múltiple en el balneario fluvial. Otras variables abióticas (temperatura, pH, conductividad, transparencia, oxígeno disuelto) presentaron problemas de colinearidad o no realizaron aportes estadísticamente significativos al modelo (p>0,05). Durante el fenómeno de El Niño (Nh>5m) no se produjeron excedencias después de las lluvias, incluso con precipitaciones de 200 mm. Además, la densidad media (x) de cianobacterias se mantuvo baja (x=1,191ñ0,703 log sub10 cian./ml). Durante las anomalías pluviales negativas si bien las excedencias de E.coli fueron poco frecuentes en ambos balnearios (debido a las escasas lluvias), se produjo un masivo desarrollo de cianobaterias (x=4,657ñ0,578 log sub10 cian./ml) en el balneario lacustre. En este balneario, la media del coeficiente de decaimiento (K) para E.coli resultó inferior al estimado para el balneario fluvial (K=-0,682ñ0,32 versus K=-0,387ñ0,16, respectivamente). Estas diferencias (p<0,05), posiblemente fueron debidas al ambiente desfavorable creado por el mayor desarrollo de microorganismos fotosintéticos. Analizando separadamente el período anómalo, las variables que mejor explicaron (98,6 por ciento) las excedencias fueron (además de la concentración máxima de E.coli) el pH, temperatura y días sin lluvias (DSL) previos al muestreo. (AU)

Asunto(s)

RESUMEN

Actualmente, la calidad bacteriológica del agua no es, en gran parte, más que una evaluación a posteriori: la población es advertida después de que estuvo expuesta al riesgo sanitario. La situación ideal, en materia de gestión de los ambientes acuáticos de uso recreativo, sería poder prever en cualquier momento su calidad bacteriológica. Una aproximación es desarrollar modelos predictivos que relacionen la excedencia (número de días durante los cuales el indicador bacteriológico excede los estándares) con variables ambientales. Los estudios se llevaron a cabo en dos balnearios con características limnológicas diferentes: uno fluvial y otro lacustre, durante principios de 1998 hasta fines del año 2000, en cuyo transcurso se pudo obtener información del impacto de situaciones hidro-climáticas muy disímiles sobre microorganismos de interés sanitario (Escherichia coli y cianobacterias). Las variables concentración máxima de E.coli, lluvias y nivel hidrométrico (Nh) explicaron el 92,6 por ciento de la varianza de la excedencia en el modelo de regresión múltiple en el balneario fluvial. Otras variables abióticas (temperatura, pH, conductividad, transparencia, oxígeno disuelto) presentaron problemas de colinearidad o no realizaron aportes estadísticamente significativos al modelo (p>0,05). Durante el fenómeno de El Niño (Nh>5m) no se produjeron excedencias después de las lluvias, incluso con precipitaciones de 200 mm. Además, la densidad media (x) de cianobacterias se mantuvo baja (x=1,191ñ0,703 log sub10 cian./ml). Durante las anomalías pluviales negativas si bien las excedencias de E.coli fueron poco frecuentes en ambos balnearios (debido a las escasas lluvias), se produjo un masivo desarrollo de cianobaterias (x=4,657ñ0,578 log sub10 cian./ml) en el balneario lacustre. En este balneario, la media del coeficiente de decaimiento (K) para E.coli resultó inferior al estimado para el balneario fluvial (K=-0,682ñ0,32 versus K=-0,387ñ0,16, respectivamente). Estas diferencias (p<0,05), posiblemente fueron debidas al ambiente desfavorable creado por el mayor desarrollo de microorganismos fotosintéticos. Analizando separadamente el período anómalo, las variables que mejor explicaron (98,6 por ciento) las excedencias fueron (además de la concentración máxima de E.coli) el pH, temperatura y días sin lluvias (DSL) previos al muestreo.

Asunto(s)

RESUMEN

At the moment of examination, the bacteriological quality of water is not, to a large extent, more than an a posteriori evaluation: the population is advised afterwards that it had been exposed to a sanitary risk. The ideal situation for managing aquatic environments or recreational use would be to be able to predict at any moment their bacteriological quality. An approach would be to develop predictive models to relate the exceedance (number of days during which the bacteriological indicator exceeds the standards) with environmental variables. Studies were carried out at two beaches with different limnological characteristics, a fluvial beach and a lacustrine beach, from the beginning of 1998 to the end of 2000, so that it was possible to obtain information on the impact of very different hydroclimatic situations on microorganisms of sanitary interest (Escherichia coli and cyanobacteria). Three variables, maximum concentration of E. coli, rains and water level, justified 92.6

of the exceedance variance in the multiple regression model at the fluvial beach. Other abiotic variables (temperature, pH, conductivity, transparency and dissolved oxygen) showed collinearity problems or did not make statistically significant contributions to the model. During the El Niño event (gauge heights > 5 m) there were no exceedances after the rains, even with precipitations of 200 mm. Moreover, cyanobacteria density remained low (x = 1.191 +/- 0.703 log10 cian./ml). During the negative pluvial anomalies, although the exceedances of E. coli were not very frequent at both beaches due to the scarce rains, a massive development of cyanobacteria was produced (x = 4.657 +/- 0.578 log10 cian./ml) at the lacustrine beach. At this beach, the mean decay coefficient (K) for E. coli was significantly (p < 0.05) lower than that estimated for the fluvial beach (K = -0.682 +/- 0.32 versus K = -0.387 +/- 0.16, respectively), possibly due to the unfavourable environment created by the higher development of photosynthetic organisms. Analizing separately the anomalous period, variables that better explained (98.6

) the exceedances were (in addition to the maximum concentration of E. coli) pH, temperature and days without rains (DWR) before the sampling. The longest exceedances (6 to 8 days) were produced at the end of the negative pluvial anomalies, after prolonged periods (> 30 days) of droughts. Regression models obtained to predict the exceedance of E. coli were simplified using only three abiotic variables (water level, rains and DWR). Although, in this way, the percentage of explanation of the exceedance is lower (78.5

), the information needed for the model is obtained quickly and preventive measures can be carried out immediately while waiting for more information.

RESUMEN

During certain environmental conditions, the floating aquatic vegetation, mainly represented by Eichhornia crassipes (water hyacinth) invade and even cover water courses assigned to recreational activities or to the supply of drinkable water. The rhizosphere of these plants constitutes an unknown biotope of bacteria of sanitary interest, possibly different from waters without vegetation and of the sediment of the same aquatic system. To verify such possibility, 206 isolated strains in MacConkey Agar (Difco) were typified and identified (78 from water, 65 from sediment and 63 from rhizosphere) using the API 20 E system (v. 4.0) and Apilab plus software (v 3.3.3), both of bioMérieux (Marcy-l'Etoile, France, 1998). Nineteen different biochemical phenotypes from E. coli were found. The 79% of the population belonged to only 7 phenotypes; the 21% remaining, to the other 12 phenotypes. Twelve phenotypes did not share the biotopes, while only 4 were in the three. These results (and those obtained by other authors who used the API 20 E system in other biotopes) suggest that it would be possible to characterize the rhizosphere using those phenotypes that are found in smaller proportion. The greatest index of diversity (H) and evenness (E) were found in the rhizosphere (H = 2.903; E = 0.874). The dendrogram (average distances and UPGMA method) reaffirms the dissimilarity in biochemical phenotypes of E. coli populations of the rhizosphere with regard to the other biotopes. The most abundant bacterial species in the three biotopes were E. coli, Klebsiella terrigena and K. pneumoniae, corresponding to 75.2% of the community. The rhizosphere differed from Serratia odorifera and from Klebsiella spp. because of its higher rate of isolation.

Asunto(s)

RESUMEN

During certain environmental conditions, the floating aquatic vegetation, mainly represented by Eichhornia crassipes (water hyacinth) invade and even cover water courses assigned to recreational activities or to the supply of drinkable water. The rhizosphere of these plants constitutes an unknown biotope of bacteria of sanitary interest, possibly different from waters without vegetation and of the sediment of the same aquatic system. To verify such possibility, 206 isolated strains in MacConkey Agar (Difco) were typified and identified (78 from water, 65 from sediment and 63 from rhizosphere) using the API 20 E system (v. 4.0) and Apilab plus software (v 3.3.3), both of bioMUrieux (Marcy-lEtoile, France, 1998). Nineteen different biochemical phenotypes from E. coli were found. The 79 of the population belonged to only 7 phenotypes; the 21 remaining, to the other 12 phenotypes. Twelve phenotypes did not share the biotopes, while only 4 were in the three. These results (and those obtained by other authors who used the API 20 E system in other biotopes) suggest that it would be possible to characterize the rhizosphere using those phenotypes that are found in smaller proportion. The greatest index of diversity (H) and evenness (E) were found in the rhizosphere (H = 2.903; E = 0.874). The dendrogram (average distances and UPGMA method) reaffirms the dissimilarity in biochemical phenotypes of E. coli populations of the rhizosphere with regard to the other biotopes. The most abundant bacterial species in the three biotopes were E. coli, Klebsiella terrigena and K. pneumoniae, corresponding to 75.2 of the community. The rhizosphere differed from Serratia odorifera and from Klebsiella spp. because of its higher rate of isolation.(AU)

Asunto(s)

RESUMEN

During certain environmental conditions, the floating aquatic vegetation, mainly represented by Eichhornia crassipes (water hyacinth) invade and even cover water courses assigned to recreational activities or to the supply of drinkable water. The rhizosphere of these plants constitutes an unknown biotope of bacteria of sanitary interest, possibly different from waters without vegetation and of the sediment of the same aquatic system. To verify such possibility, 206 isolated strains in MacConkey Agar (Difco) were typified and identified (78 from water, 65 from sediment and 63 from rhizosphere) using the API 20 E system (v. 4.0) and Apilab plus software (v 3.3.3), both of bioMÚrieux (Marcy-l'Etoile, France, 1998). Nineteen different biochemical phenotypes from E. coli were found. The 79 of the population belonged to only 7 phenotypes; the 21 remaining, to the other 12 phenotypes. Twelve phenotypes did not share the biotopes, while only 4 were in the three. These results (and those obtained by other authors who used the API 20 E system in other biotopes) suggest that it would be possible to characterize the rhizosphere using those phenotypes that are found in smaller proportion. The greatest index of diversity (H) and evenness (E) were found in the rhizosphere (H = 2.903; E = 0.874). The dendrogram (average distances and UPGMA method) reaffirms the dissimilarity in biochemical phenotypes of E. coli populations of the rhizosphere with regard to the other biotopes. The most abundant bacterial species in the three biotopes were E. coli, Klebsiella terrigena and K. pneumoniae, corresponding to 75.2 of the community. The rhizosphere differed from Serratia odorifera and from Klebsiella spp. because of its higher rate of isolation.

Asunto(s)

RESUMEN

During certain environmental conditions, the floating aquatic vegetation, mainly represented by Eichhornia crassipes (water hyacinth) invade and even cover water courses assigned to recreational activities or to the supply of drinkable water. The rhizosphere of these plants constitutes an unknown biotope of bacteria of sanitary interest, possibly different from waters without vegetation and of the sediment of the same aquatic system. To verify such possibility, 206 isolated strains in MacConkey Agar (Difco) were typified and identified (78 from water, 65 from sediment and 63 from rhizosphere) using the API 20 E system (v. 4.0) and Apilab plus software (v 3.3.3), both of bioMérieux (Marcy-lEtoile, France, 1998). Nineteen different biochemical phenotypes from E. coli were found. The 79

of the population belonged to only 7 phenotypes; the 21

remaining, to the other 12 phenotypes. Twelve phenotypes did not share the biotopes, while only 4 were in the three. These results (and those obtained by other authors who used the API 20 E system in other biotopes) suggest that it would be possible to characterize the rhizosphere using those phenotypes that are found in smaller proportion. The greatest index of diversity (H) and evenness (E) were found in the rhizosphere (H = 2.903; E = 0.874). The dendrogram (average distances and UPGMA method) reaffirms the dissimilarity in biochemical phenotypes of E. coli populations of the rhizosphere with regard to the other biotopes. The most abundant bacterial species in the three biotopes were E. coli, Klebsiella terrigena and K. pneumoniae, corresponding to 75.2

of the community. The rhizosphere differed from Serratia odorifera and from Klebsiella spp. because of its higher rate of isolation.

RESUMEN

There are no standards accepted by all the countries to fix top concentrations of microbiological indicators in recreational waters. Even now there is still a considerable discussion either in USA as in Europe. The universal application of a bacteriological quality criterion is hard due to several environmental factors that affect the relation between the indicator, the exposition and the health risks. Our purpose was to present a case study as an example of the influence of the climatic conditions in the application of the most known standards (Environmental Protection Agency of USA, Council of European Communities, World Organization of Health, and others from Canada, South Africa and Hong Kong). The pluvial rainfall increased the number of E. coli, thermotolerant coliforms (C Te), and total coliforms (CT) 6-10 fold, in comparison to the number registered during the steady-state conditions of the system. However, not all the standards included that factor. In Summer, hourly, daily and weekly variations were proved, therefore the standards that suggest fortnightly sampling frequencies would not be convenient in that system. Although the main source of variation was time, spatial variability was also detected. The percentage of E. coli among the C Te was very variable, but the average resulted low (26%) compared to the levels in temperate regions of other countries (> 90%). According to the directives proposed by the Commission of European Communities, the parameter has been changed (C Te for E. coli), but the standard has remained (2000/100 ml). Thus, the directive would be more permissive.

Asunto(s)

RESUMEN

There are no standards accepted by all the countries to fix top concentrations of microbiological indicators in recreational waters. Even now there is still a considerable discussion either in USA as in Europe. The universal application of a bacteriological quality criterion is hard due to several environmental factors that affect the relation between the indicator, the exposition and the health risks. Our purpose was to present a case study as an example of the influence of the climatic conditions in the application of the most known standards (Environmental Protection Agency of USA, Council of European Communities, World Organization of Health, and others from Canada, South Africa and Hong Kong). The pluvial rainfall increased the number of E. coli, thermotolerant coliforms (C Te), and total coliforms (CT) 6-10 fold, in comparison to the number registered during the steady-state conditions of the system. However, not all the standards included that factor. In Summer, hourly, daily and weekly variations were proved, therefore the standards that suggest fortnightly sampling frequencies would not be convenient in that system. Although the main source of variation was time, spatial variability was also detected. The percentage of E. coli among the C Te was very variable, but the average resulted low (26) compared to the levels in temperate regions of other countries (> 90). According to the directives proposed by the Commission of European Communities, the parameter has been changed (C Te for E. coli), but the standard has remained (2000/100 ml). Thus, the directive would be more permissive.(AU)

Asunto(s)

RESUMEN

There are no standards accepted by all the countries to fix top concentrations of microbiological indicators in recreational waters. Even now there is still a considerable discussion either in USA as in Europe. The universal application of a bacteriological quality criterion is hard due to several environmental factors that affect the relation between the indicator, the exposition and the health risks. Our purpose was to present a case study as an example of the influence of the climatic conditions in the application of the most known standards (Environmental Protection Agency of USA, Council of European Communities, World Organization of Health, and others from Canada, South Africa and Hong Kong). The pluvial rainfall increased the number of E. coli, thermotolerant coliforms (C Te), and total coliforms (CT) 6-10 fold, in comparison to the number registered during the steady-state conditions of the system. However, not all the standards included that factor. In Summer, hourly, daily and weekly variations were proved, therefore the standards that suggest fortnightly sampling frequencies would not be convenient in that system. Although the main source of variation was time, spatial variability was also detected. The percentage of E. coli among the C Te was very variable, but the average resulted low (26) compared to the levels in temperate regions of other countries (> 90). According to the directives proposed by the Commission of European Communities, the parameter has been changed (C Te for E. coli), but the standard has remained (2000/100 ml). Thus, the directive would be more permissive.

Asunto(s)

RESUMEN

There are no standards accepted by all the countries to fix top concentrations of microbiological indicators in recreational waters. Even now there is still a considerable discussion either in USA as in Europe. The universal application of a bacteriological quality criterion is hard due to several environmental factors that affect the relation between the indicator, the exposition and the health risks. Our purpose was to present a case study as an example of the influence of the climatic conditions in the application of the most known standards (Environmental Protection Agency of USA, Council of European Communities, World Organization of Health, and others from Canada, South Africa and Hong Kong). The pluvial rainfall increased the number of E. coli, thermotolerant coliforms (C Te), and total coliforms (CT) 6-10 fold, in comparison to the number registered during the steady-state conditions of the system. However, not all the standards included that factor. In Summer, hourly, daily and weekly variations were proved, therefore the standards that suggest fortnightly sampling frequencies would not be convenient in that system. Although the main source of variation was time, spatial variability was also detected. The percentage of E. coli among the C Te was very variable, but the average resulted low (26

) compared to the levels in temperate regions of other countries (> 90

). According to the directives proposed by the Commission of European Communities, the parameter has been changed (C Te for E. coli), but the standard has remained (2000/100 ml). Thus, the directive would be more permissive.

RESUMEN

The main objective was to determine the bacteriological quality of a shallow lake in the lower Salado River Basin (Bedetti, 31 degrees 40' S and 60 degrees 45' W). Seventy samples were tested by the most probable number (MPN) method, throughout three years. The number of thermotolerant coliforms was very variable: from 20 MPN/100 ml to 130,000 MPN/100 ml. These variations were mainly associated to the local rains (rs = 0.4853, p = 0.0001) and to the hydrometric level-h-(rs = 0.3835, p = 0.008). Statistically significant correlations between coliform bacteria and other variables (temperature, oxygen, pH, conductivity and transparency) were not found. The increase of coliforms associated to the increase of the hydrometric level indicates the presence of diffuse contamination sources. It was found that the rains affected the bacteriological quality, specially during the low water periods (h < 3.60). During the high water periods (h > 4.70) one of the main coliform contributor was represented by the incoming floating islans and aquatic macrophyte, from allochthonous fluvial systems. The coliform concentrations between the Bedetti lake and the Salado river were compared. The results show a better bacteriological quality of the lake (geometric average = 1,990/100 ml vs. 420/100 ml, n = 56) so that, connecting them by the construction of an artificial channel is not advisable.

Asunto(s)

RESUMEN

Con el objeto de estimar la calidad bacteriológica de la laguna Bedetti (31º 40S y 60º 45O) se analizaron 70 muestras recolectadas a través de tres años. El número de coliformes termotolerantes resultó muy variable: desde 20 NMP/100 ml hasta 130.000 NMP/100 ml. Las variaciones estuvieron asociadas principalmente a las lluvias l

Asunto(s)

RESUMEN

Con el objeto de estimar la calidad bacteriológica de la laguna Bedetti (31§ 40'S y 60§ 45'O) se analizaron 70 muestras recolectadas a través de tres años. El número de coliformes termotolerantes resultó muy variable: desde 20 NMP/100 ml hasta 130.000 NMP/100 ml. Las variaciones estuvieron asociadas principalmente a las lluvias locales (rs=0,4853, p= 0,0001) y al nivel hidrométrico -Nh- (rs=0,3835, p=0,008). No se comprobaron relaciones estadísticamente significativas con otras variables (temperatura, oxígeno, pH, conductividad y transparencia). El aumento de coliformes asociado al aumento del nivel hidrométrico, indicó la presencia de fuentes dispersas de contaminación. Las lluvias afectaron la calidad bacteriológica, especialmente durante los períodos de aguas bajas (Nh < 3,60). Durante los períodos de aguas altas (Nh > 4,70) uno de los principales aportes de coliformes estuvo representado por la entrada de islas flotantes y de macrófitas acuáticas, provenientes de sistemas fluviales alóctonos. Se compararon las concentraciones de coliformes entre la laguna Bedetti y el río Salado (56 muestras). Los resultados indicaron una mejor calidad bacteriológica de la laguna (promedio geométrico = 1990/100 ml vs. 420/100 ml). Por lo tanto, no es bacteriológicamente aconsejable conectarlos mediante la construcción de un proyectado canal artificial

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RESUMEN

Durante enero 1993 - diciembre 1996 se recolectaron 85 muestras de agua y 40 de plancton en la cuenca inferior del río Salado. En el 69,4 o/o de las muestras de agua en el 75 o/o de las muestras de plancton se detectó Vibrio cholerae. Ninguna de las cepas de V. cholerae aisladas pertenecieron a los subgrupos O1 y O139. No se comprobó estacionalidad en la frecuencia de los aislamientos de V. cholerae aplicando la prueba de comparación de proporciones múltiples (p>0,05). Se registraron diferencias significativas (p<0,05) entre la frecuencia de aislamiento de V. cholerae en el río Salado (85 muestras, 69,4 o/o) y la hallada en ambientes del río Paraná (16 muestras, 25 o/o) y en efluentes municipales (18 muestras, 33,3 o/o) (AU)

Asunto(s)

RESUMEN

Durante enero 1993 - diciembre 1996 se recolectaron 85 muestras de agua y 40 de plancton en la cuenca inferior del río Salado. En el 69,4 o/o de las muestras de agua en el 75 o/o de las muestras de plancton se detectó Vibrio cholerae. Ninguna de las cepas de V. cholerae aisladas pertenecieron a los subgrupos O1 y O139. No se comprobó estacionalidad en la frecuencia de los aislamientos de V. cholerae aplicando la prueba de comparación de proporciones múltiples (p>0,05). Se registraron diferencias significativas (p<0,05) entre la frecuencia de aislamiento de V. cholerae en el río Salado (85 muestras, 69,4 o/o) y la hallada en ambientes del río Paraná (16 muestras, 25 o/o) y en efluentes municipales (18 muestras, 33,3 o/o)

Asunto(s)