Wood decomposition in Amazonian hydropower reservoirs : an additional source of greenhouse gases

Amazonian hydroelectric reservoirs produce abundant carbon dioxide and methane from large quantities of flooded biomass that decompose anaerobically underwater. Emissions are extreme the first years after impounding and progressively decrease with time. To date, only water-to-air fluxes have been considered in these estimates. Here, we investigate in two Amazonian reservoirs (Balbina and Petit Saut) the fate of above water standing dead trees, by combining a qualitative analysis of wood state and density through time and a quantitative analysis of the biomass initially flooded. Dead wood was much more decomposed in the Balbina reservoir 23 years after flooding than in the Petit Saut reservoir 10 years after flooding. Termites apparently played a major role in wood decomposition, occurring mainly above water, and resulting in a complete conversion of this carbon biomass into CO2 and CH4 at a timescale much shorter than reservoir operation. The analysis of pre-impounding wood biomass reveals that above-water decomposition in Amazonian reservoirs is a large, previously unrecognized source of carbon emissions to the atmosphere, representing 26-45% of the total reservoir flux integrated over 100 years. Accounting for both below-and above-water fluxes, we could estimate that each km(2) of Amazonian forest converted to reservoir would emit over 140 Gg CO2-eq in 100 years. Hydropower plants in the Amazon should thus generate 0.25-0.4 MW h per km(2) flooded area to produce lower greenhouse gas emissions than gas power plants. They also have the disadvantage to emit most of their greenhouse gases the earliest years of operation

Well-ordered patterning of multi-functional ZnO by templated growth and self-organization technique

International audienc

Impregnation of Chitosan Microspheres with the Natural Dye Curcuma

The purpose of this study was to investigate the impregnation of chitosan microspheres with the natural dye curcuma. The impregnation with curcuma dye was investigated in aqueous medium at pH 9.0, 9.5 and 10.0. The process of impregnation was monitored using capillary electrophoresis analysis which was carried out to observe the presence of dye in the impregnated microspheres. The microspheres loaded with dye at pH 10.0 were evaluated by infrared spectroscopy, optical microscopy, scanning electron microscopy and thermal analysis. The dye was impregnated in the chitosan microspheres through an adsorption process and was released when placed in contact with acidic solutions at pH 1.0-5.0. The dye was released from the chitosan in less than 3 h, regardless of the pH, although most of the microspheres dissolved within 1 h. The release mechanism followed the Super Case II transport release model.Colegio de Farmacéuticos de la Provincia de Buenos Aire

Aggregation behavior of self-assembled nanoparticles made from carboxymethyl-hexanoyl chitosan and sodium dodecyl sulphate surfactant in water

Biopolymers can be used to produce nano-objects in solution and they are generally of low cost and biocompatible. However, they commonly have low kinetic stability and form aggregates with a broad particle size distribution, characteristics that hinder their use in drug delivery systems. Herein, we report the thermodynamics and mechanisms underlying the formation of nanostructures through the self-assembly of carboxymethyl-hexanoyl chitosan (ONCHC) and the effect of the presence of the surfactant sodium dodecyl sulfate (SDS). The pre- and post-aggregation regimes were monitored using several techniques and indicated that self-assembly is thermodynamically favorable. The presence of SDS decreased the hydrodynamic radius and surface charge of the SDS-ONCHC nanoaggregates and increased the kinetic stability in aqueous solution over a period of 150 days. The SDS-ONCHC interaction is driven mainly by a hydrophobic effect and the addition of SDS increases the number and strength of the hydrophobic domains, where the integral enthalpy change for the aggregate formation is −2.11 kJ mol−1