Trophic interactions in shallow lakes of the Pampa plain (Argentina) and their effects on water transparency during two cold seasons of contrasting fish abundance

Trophic interactions in shallow lakes of the Pampa plain (Argentina) and their effects on water transparency during two cold seasons of contrasting fish abundance Trophic cascade interactions in shallow lakes have been studied extensively in the north temperate region mainly during the summer periodo However, fewer studies have examined these interactions in warrner regions during the winter periodo The aim of the present work was to study trophic cascade interactions and their effect on water transparency in small lakes in the Pampean Plain (Argentina) during the cold season. In addition, we examined whether low fish abundance would allow the appearance of key zooplankton genera such as Daphnia. Seven shaIlow lakes were studied during the autumn-winter period in 2000 and 2001. The dominance of the main primary producers varied between lakes. While five lakes were turbid and dominated by phytoplankton, two lakes were cIear and dominated by macrophytes. In the autumn of 2000, fish abundance was reduced from six of these lakes. By the foIlowing year, the fish community had recovered naturaIly. In the phytoplankton dominated lakes, both zooplankton biomass and size were higher during the low fish abundance periodo Moreover, large Daphnia were present, contributing to the decrease in algal biomass per unit of nutrients. Thus, Daphnia has the potential to increase water transparency in these lakes. On the other hand, in the vegetated lakes, zooplankton biomass was low and large Daphnia were scarce, probably because of the presence of macroinvertebrate predators. However, water transparency was stilI high in these ecosystems. From our resuIts, we condude that trophic interactions probably playa fundamental role in the determination of zooplankton structure and biomass in the smalI, temperate warrn lakes of the Pampean Plain, even during the cold season. Moreover, the effects from fish would reach the lowest levels of the trophic chain, affecting water transparency. However, water transparency might be infiuenced by other factors as well. Transparency could be naturaIly elevated in the presence of macrophytes and greatIy affected by the hydrology of the region.Las interacciones tróficas en cascada han sido ampliamente estudiadas en los lagos someros del hemisferio norte, principalmente durante la temporada estival. Sin embargo, su estudio ha sido menos frecuente en los lagos de regiones más cálidas durante la estación fría del año. El objetivo del presente trabajo fue estudiar las interacciones tróficas en cascada de los peces sobre el zooplancton y su posible efecto sobre la transparencia del agua en pequeñas lagunas de la región pampeana (Argentina) durante la estación fría del año. Además, investigamos si una disminución en la abundancia de los peces per-mitiría la presencia de géneros zooplanctónicos claves tales como Daphnia. Para ello se estudiaron siete lagunas durante el otoño e invierno de los años 2000 y 2001. Dos de estas lagunas lagunas fueron nombradas como "claras" pues estuvieron dominadas por la macrófita. En cambio, las otras cinco lagunas fueron nombradas "turbias" pues estuvieron dominadas por el fitoplancton. La abundancia de peces fue reducida en 6 lagunas durante el otoño de 2000. Sin embargo, al año siguiente la comunidad de peces estuvo naturalmente re establecida. En las lagunas dominadas por el fitoplancton, la biomasa y la talla de zooplancton fueron mayores durante el período correspondiente a la baja abundancia de peces. Durante este período, las Daphnia estuvieron presentes y contribuyeron a disminuir la biomasa de fitoplancton por unidad de nutrientes. Por lo tanto estos organismos tendrían la capacidad de incrementar la transparencia del agua de las lagunas. Por otro lado, la biomasa del zooplanctonfue escasa y la abundancia de las Daphniafue baja en las lagunas dominadas por la macrófita, probablemente por el efecto de la predación de organismos invertebrados. A pesar de esto, la transparencia del agua fue elevada en estos ecosistemas. A partir de nuestros resultados, concluimos que las interacciones tróficas determinarían la estructura y la biomasa del zooplancton en las pequeñas lagunas templado cálidas de la región Pampeana, incluso durante la estación mas fría del año. Este efecto en cascada, alcanzaría el eslabón más bajos de la cadena trófica, afectando entonces la transparencia del agua. Sin embargo, la transparencia del agua estaría también influenciada por otros factores. La misma sería naturalmente elevada en presencia de las macrófitas y ademds estaría altamente afectada por la hidrología de la región

Patterns in fish species composition and assemblage structure in the upper Salado River lakes, Pampa Plain, Argentina

The Pampa Plain, in the central region of Argentina, is mostly drained by the Salado River. The fish fauna of this river is mostly known from field collections in lower reach lakes. Consequently, we aimed to explore the composition and structure of the fish assemblages in the upper Salado River lakes. Patterns in dominance and persistence of species and assemblage level attributes were correlated with environmental and human activity-derived (NO 3 :NH 4 ) variables. Overall, 19,913 individuals of 17 species included in 5 orders and 11 families were collected. Several species are first records for the upper Salado River lakes. There was a marked proliferation of species in the family Characidae. Conversely, the remainder 10 families were only represented by one or two species. The species composition along the study lakes changed slightly but their relative contribution to the total fish collected (dominance) varied greatly. Rather few species were present in all collections suggesting an important interannual variability in assemblage stability. The gradient in water conductivity was an important factor for the persistence of particular species in the lakes. The gradients in water conductivity and NO 3 :NH 4 ratio were associated with particular fish communities dominated by different groups of species. These results suggest that even when broad management and conservation strategies should encompass the system as a whole, lake-specific approaches must also be addressed. Overall, our results highlight that human impacts on surface waters may interact with environmental factors to influence the dynamics of fish species and the structure of their communities. A planície pampeana, na região central da Argentina, é em grande parte drenada pelo rio Salado. A ictiofauna desse rio é conhecida principalmente pelos estudos conduzidos nos lagos dos segmentos inferiores do rio. Em consequência, procuramos examinar a composição e a estrutura das assembleias de peixes dos lagos do alto rio Salado. Os padrões na dominância e persistência das espécies e os atributos das assembleias de peixes foram correlacionados com variáveis ambientais e variáveis indicadoras de perturbações antropogênicas (NO 3 :NH 4 ). Foram coletados 19913 indivíduos de 17 espécies pertencentes a 5 ordens e 11 famílias. Várias espécies foram registradas pela primeira vez para as lagoas do alto rio Salado. Houve uma marcada proliferação de espécies da família Characidae. Em contraste, as 10 famílias de peixes restantes foram representadas por uma ou duas espécies. A composição de espécies variou pouco ao longo dessas lagoas mas sua contribuição ao total de peixes coletados (dominância) foi muito variável. Poucas espécies estiveram presentes em todas as coletas, sugerindo uma importante variação interanual na estabilidade da assembleia de peixes. O gradiente na condutividade elétrica da água foi importante fator para a persistência de algumas espécies nessas lagoas. A condutividade elétrica da água e o gradiente na relação NO 3 :NH 4 estiveram associados com assembleias de peixes particulares dominadas por diferentes grupos de espécies. Nossos resultados sugerem que, embora as estratégias de conservação e manejo deveriam considerar o sistema por completo, questões particulares a cada lagoa devem também ser consideradas. Em geral, nossos resultados ressaltam que os impactos humanos nas águas superficiais podem interagir com fatores ambientais para influenciar a dinâmica das espécies de peixes e a estrutura de suas comunidades

Adrenal function testing in patients with septic shock

INTRODUCTION: Adrenal failure (AF) is associated with increased mortality in septic patients. Nonetheless, there is no agreement regarding the best diagnostic criteria for AF. We compared the diagnosis of AF considering different baseline total cortisol cutoff values and Δmax values after low (1 μg) and high (249 μg) doses of corticotropin, we analyzed the impact of serum albumin on AF identification and we correlated laboratorial AF with norepinephrine removal. METHODS: A prospective noninterventional study was performed in an intensive care unit from May 2002 to May 2005, including septic shock patients over 18 years old without previous steroid usage. After measurement of serum albumin and baseline total cortisol, the patients were sequentially submitted to 1 μg and 249 μg corticotropin tests with a 60-minute interval between doses. Post-stimuli cortisol levels were drawn 60 minutes after each test (cortisol 60 and cortisol 120). The cortisol 60 and cortisol 120 values minus baseline were called Δmax(1 )and Δmax(249), respectively. Adrenal failure was defined as Δmax(249 )≤ 9 μg/dl or baseline cortisol ≤ 10 μg/dl. Other baseline cortisol cutoff values referred to as AF in other studies (≤15, ≤20, ≤25 and ≤34 μg/dl) were compared with Δmax(249 )≤ 9 μg/dl and serum albumin influence. Norepinephrine removal was compared with the baseline cortisol values and Δmax(249 )values. RESULTS: We enrolled 102 patients (43 male). AF was diagnosed in 22.5% (23/102). Patients with albumin ≤2.5 g/dl presented a lower baseline total cortisol level (15.5 μg/dl vs 22.4 μg/dl, P = 0.04) and a higher frequency of baseline cortisol ≤25 μg/dl (84% vs 58.3%, P = 0.05) than those with albumin > 2.5 g/dl. The Δmax(249 )levels and Δmax(249 )≤ 9, however, were not affected by serum albumin (14.5 μg/dl vs 18.8 μg/dl, P = 0.48 and 24% vs 25%, P = 1.0). Baseline cortisol ≤ 23.6 μg/dl was the most accurate diagnostic threshold to determine norepinephrine removal according to the receiver operating characteristic curve. CONCLUSION: AF was identified in 22.5% of the studied population. Since Δmax(249 )≤ 9 μg/dl results were not affected by serum albumin and since the baseline serum total cortisol varied directly with albumin levels, we propose that Δmax(249 )≤ 9 μg/dl, which means Δmax after high corticotropin dose may be a better option for AF diagnosis whenever measurement of free cortisol is not available. Baseline cortisol ≤23.6 μg/dl was the best value for predicting norepinephrine removal in patients without corticosteroid treatment

Revisión de los temas del taller

En esta sección, se analizan las presentaciones realizadas por los participantes del taller. Sobre la base de sus contenidos se elabora una discusión en la cual se identifican los puntos coincidentes en lo referente a problemáticas, críticas e interpretaciones acerca de la situación actual del manejo de los recursos pesqueros de la pampasia. Luego de este planteo, se evalúan nuevas propuestas de manejo desde los enfoques adaptativo y ecosistémico, que se considera podrían ajustarse mejor a la dinámica de los ecosistemas acuáticos pampeanos y sus pesquerías.In this section, the presentations made by the workshop participants are analyzed. Based on its contents the matching points in terms of problems, reviews and interpretations about the current situation of the management of fisheries resources of Pampa Plain are identified and discussed. After this pose, new management proposals are evaluated from the adaptive and ecosystem approaches, considering that they could suit to the dynamics of these aquatic ecosystems and their fisheries.El taller al que se refiere el trabajo es el Taller de normas y criterios actuales para el manejo de recursos pesqueros pampeanos, dictado en el marco del VIII EMEAP.Instituto de Limnología "Dr. Raúl A. Ringuelet

Taller de normas y criterios actuales para el manejo de recursos pesqueros pampeanos : Revisión de los temas del taller

Fil: Colautti, Darío César. Instituto de Limnología Dr. Raúl A. Ringuelet (ILPLA). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Rosso, Juan José. Grupo de Biotaxonomía Morfológica y Molecular de Peces. Instituto de Investigaciones Marinas y Costeras (IIMyC-CONICET). Universidad Nacional de Mar del Plata; Argentin

Level of leverage and business financial stability: Case of firms from Colombia and Argentina

This paper aims to explain the effect of financial instability on the capital structure of firms in two emerging markets: Colombia and Argentina. For the analysis, the study uses an unbalanced panel dataset with 167 companies, with quarterly data between 2005 and 2015, and regressions with the random-effects method. The results show that lower liquidity level and losses during two or more consecutive quarters increase the level of leverage in companies; therefore, signs of financial insolvency lead firms to become over-indebted and to reproduce the same conditions that lead to the emergence of a financial crisisEste artículo busca explicar el efecto de la inestabilidad financiera en las firmas y su estructura de capital, en dos mercados emergentes: Colombia y Argentina. Para el análisis se construye un panel desbalanceado con 167 empresas, con datos trimestrales entre 2005 y 2015, y se realizan regresiones con el método de efectos aleatorios. Los resultados evidencian que el menor nivel de liquidez y las pérdidas durante dos o más trimestres consecutivos elevan el nivel de apalancamiento de las empresas; por tanto, síntomas de insolvencia financiera conducen a que las firmas se sobre en deuden y propaguen las condiciones que lleven a la aparición de una crisis financiera

El Museo Municipal de El Puerto o las tribulaciones de un museo local

La conmemoración del centésimo quincuagésimo aniversario de la creación del Museo Arqueológico Nacional, institución a la que felicitamos por su perdurabilidad y buen hacer, nos ofrece la oportunidad de reflexionar sobre la trayectoria del modesto Museo Municipal de El Puerto de Santa María, caso que pone de manifiesto la debilidad de la gestión del patrimonio arqueológico mueble en Andalucía

Efectos de la exclusión de ganado sobre la calidad ambiental de un arroyo pampeano

Durante dos años, se hicieron registros de la morfología del canal y la calidad de la ribera en una sección de un arroyo dado que se excluyó la ganadería en una sección de 500 metros de largo cerca de la orilla y 10 metros en cada orilla. También se registraron cambios en la vegetación acuática y algunos parámetros físico-químicos. El muestreo de peces se realizó anualmente para observar la presencia de especies y su  abundancia relativa. Se detectó una rápida mejora en la calidad de las orillas y un aumento de la riqueza de peces en cada muestra. Contrariamente a lo esperado, la riqueza de macrófitos se redujo y la heterogeneidad morfológica del canal no aumentó. Sin embargo, el arroyo dejó de estar interrumpido y comenzó a tener más agua en todo el tramo. Esto fue como resultado de la remodelación de las riberas. Aunque este registro debe validarse con estudios futuros, los resultados sugieren que la recuperación de las riberas es muy rápida y que el lecho del arroyo y la colonización de peces están escalonadas. A pesar de esto, hubo una clara recuperación en el sector estudiado con exclusión del ganado en el área como la única práctica de manejo única.For two years, records of channel morphology and quality of the bank on a section of a stream were made because the cattle farming have been excluded at a section of 500 meters of long near the bank and 10 meters at each bank. There were registered also changes in the aquatic  vegetation and some physico-chemical parameters. Fish sampling was conducted annually to observe species presence and their relative abundance. It was detected a rapid improvement in the quality of banks and an increase of the richness of fishes in each sample. Contrary to expectations macrophyte richness was reduced and morphological heterogeneity of the channel is not increased. However, the stream ceased to be interrupted and started having more water in the entire stretch. This was as a result of reshaping the banks. Although this register should be validated with future surveys, the results suggest that the recovery of the banks is very fast and the runway and the fish colonization are staggered. Despite this, there was a clear recovery at the studied reach, with the exclusion of cattle in the area as the unique management practice

Ictiólogos de la Argentina: Rolando Quirós

This series will include all those people who, by means of their contributions, great and small, played a part in the consolidation of ichthyology in Argentina. The general plan of this work consists of individual factsheets containing a list of works by each author, along with reference bibliography and, whenever possible, personal pictures and additional material. The datasheets will be published primarily in chronological order, although this is subject to change by the availability of materials for successive editions. This work represents another approach for the recovery and revalorization of those who set the foundations of Argentine ichthyology while in diverse historical circumstances. I expect this to be the beginning of a major work that achieves the description of such a significant part of the history of natural sciences in Argentina

Efectos de la exclusión de ganado sobre la calidad ambiental de un arroyo pampeano

For two years, records of channel morphology and quality of the bank on a section of a stream were made because the cattle farming have been excluded at a section of 500 meters of long near the bank and 10 meters at each bank. There were registered also changes in the aquatic vegetation and some physico-chemical parameters. Fish sampling was conducted annually to observe species presence and their relative abundance. It was detected a rapid improvement in the quality of banks and an increase of the richness of fishes in each sample. Contrary to expectations macrophyte richness was reduced and morphological heterogeneity of the channel is not increased. However, the stream ceased to be interrupted and started having more water in the entire stretch. This was as a result of reshaping the banks. Although this register should be validated with future surveys, the results suggest that the recovery of the banks is very fast and the runway and the fish colonization are staggered. Despite this, there was a clear recovery at the studied reach, with the exclusion of cattle in the area as the unique management practice.Facultad de Ciencias Naturales y Muse