Inorganic mercury (Hg2+) uptake by different plankton fractions of Andean Patagonian lakes (Argentina)

The species composition and the size structure of natural planktonic food webs may provide essential information to understand the fate of mercury and, in particular, the bioaccumulation pattern of Hg2+ in the water column of lake ecosystems. Heterotrophic and autotrophic picoplankton and phytoplankton are the most important entry points for Hg in aquatic ecosystems since they concentrate Hg2+ and MeHg from ambient water, making them available to planktonic consumers at higher trophic levels of lake food webs. In this investigation we studied the uptake of 197Hg2+ in natural plankton assemblages from four Andean lakes (Nahuel Huapi National Park, Patagonia, Argentina), comprised in the size fractions 0.2-2.7 μm (picoplankton), 0.2-20 μm (pico and nanoplankton) and 20-50 μm (microplankton) through experiments using Hg2+ labeled with 197Hg2+. The experimental results showed that the uptake of Hg2+ was highest in the smallest plankton fractions (0.2-2.7 μm and 0.2-20 μm) compared to the larger fraction comprising microplankton (20-50 um). This pattern was consistent in all lakes, reinforcing the idea that among pelagic organisms, heterotrophic and autotrophic bacteria with the contribution of nanoflagellates and dinoflagellates constitute the main entry point of Hg2+ to the pelagic food web. Moreover, a significant direct relationship was found between the Hg2+ uptake and surface index of the planktonic fractions (SIf). Thus, the smaller planktonic fractions which bore the higher SI were the major contributors to the Hg2+ passing from the abiotic to the biotic pelagic compartments of these Andean lakes

Inorganic mercury (Hg

The species composition and the size structure of natural planktonic food webs may provide essential information to understand the fate of mercury and, in particular, the bioaccumulation pattern of Hg2+ in the water column of lake ecosystems. Heterotrophic and autotrophic picoplankton and phytoplankton are the most important entry points for Hg in aquatic ecosystems since they concentrate Hg2+ and MeHg from ambient water, making them available to planktonic consumers at higher trophic levels of lake food webs. In this investigation we studied the uptake of 197Hg2+ in natural plankton assemblages from four Andean lakes (Nahuel Huapi National Park, Patagonia, Argentina), comprised in the size fractions 0.2-2.7 μm (picoplankton), 0.2-20 μm (pico and nanoplankton) and 20-50 μm (microplankton) through experiments using Hg2+ labeled with 197Hg2+. The experimental results showed that the uptake of Hg2+ was highest in the smallest plankton fractions (0.2-2.7 μm and 0.2-20 μm) compared to the larger fraction comprising microplankton (20-50 um). This pattern was consistent in all lakes, reinforcing the idea that among pelagic organisms, heterotrophic and autotrophic bacteria with the contribution of nanoflagellates and dinoflagellates constitute the main entry point of Hg2+ to the pelagic food web. Moreover, a significant direct relationship was found between the Hg2+ uptake and surface index of the planktonic fractions (SIf). Thus, the smaller planktonic fractions which bore the higher SI were the major contributors to the Hg2+ passing from the abiotic to the biotic pelagic compartments of these Andean lakes

Superconducting Critical State of Bi2Sr2CaCu2O8Two-Dimensional Effects At Low Temperatures

The critical current in the c direction of Bi 2 Sr 2 CaCu 2 O 8 is shown to increase with temperature in low temperature ZFC measurements. The results are consistent with a loss of the c direction long range phase correlation, induced by the temperature dependent critical current flowing in the ab planes. As a result of this and the loss of the long range correlation induced by thermal disorder, the low temperature electrical resistance of the ZFC critical state is finite at low temperatures, becomes zero and is finite again at higher temperature

Critical State of the Weakly Coupled Two-Dimensional Superconductor Bi2Sr2CaCu2O8

Transport measurements show that the critical current in the c direction, Jcc of Bi2Sr2CaCu2O8 single crystals increases with temperature for low temperature zero field cooled (ZFC) measurements. As a consequence, the c direction electrical resistance of the ZFC critical state, at a given dc current, is finite, goes to zero with increasing temperature, and becomes finite again at higher temperatures. The results are consistent with a loss of the c axis long range correlation induced by the critical current flowing in the ab planes, Jcab, and an increase of that correlation with temperature, as a consequence of the corresponding decrease of Jcab

Determinación de selenio en muestras de concentrados de níquel más cobalto empleando el análisis por activación con neutrones epitérmicos

La determinación de Se en los concentrados de sulfuros de níquel más cobalto obtenidos en la industria niquelífera cubana, se requiere como parte del control de la calidad de estos productos. En este trabajo se determina la concentración de Se y otros elementos en 17 muestras de sulfuros de níquel más cobalto empleando el EAAN. Mediante este método fue posible analizar el Se hasta el orden de los ppm sin destruir la muestra a pesar de la existencia de altos contenidos de Co, Fe, Ni y Cr en las mismas

Determinación de selenio en muestras de concentrados de níquel más cobalto empleando el análisis por activación con neutrones epitérmicos

La determinación de Se en los concentrados de sulfuros de níquel más cobalto obtenidos en la industria niquelífera cubana, se requiere como parte del control de la calidad de estos productos. En este trabajo se determina la concentración de Se y otros elementos en 17 muestras de sulfuros de níquel más cobalto empleando el EAAN. Mediante este método fue posible analizar el Se hasta el orden de los ppm sin destruir la muestra a pesar de la existencia de altos contenidos de Co, Fe, Ni y Cr en las mismas