Trace elements in sediments and plankton from two high-altitude lakes in a volcanic area from North Patagonia, Argentina.

This study analyzes the distribution of nine potentially toxic trace elements (arsenic, antimony, bromine, cobalt, chromium, mercury, rubidium, selenium, and zinc) in sediments and plankton from two small mesotrophic lakes in a non-industrialized area impacted by the Caviahue-Copahue volcanic complex (CCVC). The two lakes have different plankton community structures and received different amounts of pyroclastic material after the last CCVC eruption. Trace element concentrations of surface sediments differed between lakes, according to the composition of the volcanic ashes deposited in the lakes. The size of organisms was the principal factor influencing the accumulation of most trace elements in plankton within each lake, being trace element concentrations generally higher in the microplankton than in the mesozooplankton. The planktonic biomass in the shallower lake was dominated by small algae and copepods, while mixotrophic ciliates and different-sized cladocerans dominated the deeper lake. These differences in the community structure and species composition influenced the trace element bioaccumulation, especially in microplankton, while habitat use and feeding strategies seem more relevant in mesozooplankton bioaccumulation. This work contributes to the scarce records of trace elements and their dynamics in plankton from freshwater ecosystems impacted by volcanic activity.

Landscape factors modulating patterns of salmonid distribution during summer in north Patagonian rivers.

Understanding how ecosystem processes influencing fish distribution operate across spatial scales is important to understand biological invasions. Salmonids, originally from the Northern Hemisphere, have been repeatedly introduced throughout the world, making them an ideal group to test hypotheses about factors driving invasions. We assessed the influence of environmental variables at the watershed scale on the abundance and structure of salmonid assemblages in the breeding streams of the Upper Limay river basin, Rio Negro, Argentina. We combined field captures with digital map data and geographic information systems to examine landscape-level patterns of salmonid abundance in 35 representative sub-basins of the environmental gradient. We employed a hierarchical cluster analysis and classification and regression tree models to relate the abundance of salmonids and types of species assemblages with environmental characteristics at watershed level. We found stream localization, precipitation regime, altitude and air temperature to be important predictors of the abundance and assemblage structure of salmonids. Total catches showed an increasing gradient of catch-per-unit-effort from west to east and from north to south, with Oncorhynchus mykiss being the most abundant species. O. mykiss relative abundance was westward skewed, where smaller catchments with steeper and shaded valleys are drained by less productive streams with more irregular hydrological regimes, like those found in this species' North American native range. In contrast, the abundance of Salmo trutta abundance was eastward skewed, where larger, sunnier and more gently sloped catchments result in more productive streams with stable hydrological regimes, like those found in that species' European native range. Thus, differential salmonid abundance could result from the interplay between the evolutionary fingerprint left by each species' native environment (especially flow and temperature regimes) and the availability of those conditions in new environments to which they have been translocated. By furthering our understanding of how landscape conditioned invasion success, these findings can help guide the management of economically important introduced fish.

Análisis estado trófico de las lagunas pampeanas (Argentina) / Analysis of the trophic state of the pampan lakes (Argentina)

Las lagunas pampeanas son lagos de llanura someros, polimícticos, eutróficos o hipertróficos, con tiempos de permanencia y salinidad variable. Su estructura y funcionamiento son explicados por su geomorfología, clima drenaje en suelos ricos en nutrientes, y por modificaciones antrópicas en el uso de tierra y agua. Estas características explican las elevadas biomasas de sus comunidades bióticas. Un análisis sincrónico durante el pico de la estación de crecimiento permitió discriminar, dentro de las grandes lagunas, dos tipos: a) con relativamente baja biomasa de fitoplancton y abundante desarrollo de la macrofitia acuática arraigada, y b) con abundante desarrollo del fitoplancton pero escaso desarrollo de la macrofitia. El primer tipo coincide con lo que se conoce como lagunas "claras", de aguas relativamente transparentes y alta abundancia relativa de peces piscívoros de alto porte, localizadas principalmente en las zonas de pastizajes naturales. El segundo tipo coincide con lagunas verdes y "turbias", con alta abundancia de peces planctivoros visuales. En las lagunas impactadas por descargas orgánicas se produce un incremento en la abundancia de planctivoros filtradores. Las lagunas estudiadas no se presentaron como totalmente "claras" o plenamente "turbias"; un continuo entre lagunas muy "claras" y muy "turbias" expresa mejor resultados. La abundancia relativa de lagunas "turbias" es mayor en zonas con mayor uso de la tierra. La alta variabilidad anual e interanual del paisaje pampeano se refleja en el funcionamiento del ecosistema lagunar; la interacción de factores climáticos y de uso de la tierra explicaría los cambios aperiódicos en la tipología de una determinada laguna