Ednaldo Oliveira dos Santos

Greenhouse gases and initial findings on the carbon circulation in two reservoirs and their watersheds

the overlying water. Bubbles containing mainly CO2, and CH4 also rise from this fresh sediment layer. We draw the lower boundary at the surface below which all carbon is permanent (i.e. not susceptible to mobilization and on its way to fossilization). We estimate that this boundary is somewhere between 5‐20 cm below the water-sediment interface. At this depth humic substances are already resistant to further carbon decomposition, as can be seen from the constant C/Si ratio starting at about this depth. In fact, the lower boundary could be described as lying in the two-dimensional region where this ratio is constant from this point down. Reservoir carbon inputs into the black box come through rivers, underground water, rainfall, and occasional diffusive absorption. Carbon outputs are effluent outflow, permanent sedimentation, and diffusive and bubbling emissions such as CH4 and CO2.

Gross Greenhouse Gas Emissions from Brazilian Hydro Reservoirs

This paper presents the results of gross carbon dioxide and methane emission measurements in several Brazilian hydro reservoirs. The term ‘gross emissions’ means gas flux measurements from the reservoir surface without correcting for natural pre-impoundment emissions by natural bodies such as the river channel, seasonal flooding and terrestrial ecosystems. The net emissions result from estimating pre-existing emissions by the reservoir. Measurements were carried in the Miranda, Barra Bonita, Segredo, Tres Marias, Xingo, Samuel and Tucurui reservoirs, located in two different climatological regimes. Additional data were used here from measurements taken at the Itaipu and Serra da Mesa reservoirs. Emissions of carbon dioxide and methane in each of the reservoirs selected, whether through bubbles or diffusive exchange between water and atmosphere, were assessed by sampling, with subsequent extrapolation of results to obtain a value for the reservoir. A great variability was found in the emissions, linked to the influence of various factors, including temperature, depth at the point of measurement, wind regime, sunlight, physical and chemical parameters of water, the composition of the local vegetation and the operational regime of the reservoir.

Effect of heat treatment on ethylene and CO2 emissions rates during papaya (Carica papaya L.) fruit ripening

Ripening studies of nontreated and treated papaya (papaya L) are accomplished by monitoring the ethylene and CO2 emission rates of that climacteric fruit, to evaluate its shelf life. The treatments simulate the commercial Phitosanitarian process used to avoid the fly infestation. Ethylene emission was measured using a commercial CO2 laser driven photoacoustic setup and CO2, using a commercial gas analysis also based on the photothermal effect. The results show a marked change in ethylene and CO2 emission rate pattern for treated fruits when compared to the ones obtained for nontreated fruits and a displacement of the climacteric pick shown that the treatment causes a decrease of shelf life of fruit.

Estimate of degassing greenhouse gas emissions of the turbined water at tropical hydroelectric reservoirs

Biogenic gases generated underwater in hydroelectric reservoirs come from organic matter decomposition by microorganisms. There are 3 different pathways of emitting greenhouse gases (GHG). Gas emissions by impoundments are mainly methane (CH4), carbon dioxide (C02) and nitrous oxide (N20) transported through bubbles formed by decomposing organic matter on the lake bottom, as well as rising up the lake gradient through molecular diffusion. Another gas emission pathway is the degassing of these gases at turbined water sites and along the river below the dam. These different gases (C02, CH4, and N20) have distinct warming effects in the atmosphere; their instantaneous radiative forcing are different and so are their atmospheric life spans. This is particularly true in the case of power generation. The use of fossil fuels in thermal power plants and bacterial decomposition of biomass in hydroelectric reservoirs produce greenhouse gases. Debate continues regarding the amount of GHG emitted from freshwater reservoirs, especially the question of effects of impoundment on degassing emissions downstream of the power house. These emissions were observed for the first time by French researchers at Petit Saut reservoir in French Guiana in 1995 (GALY-LACAUX et al. 1997). The water coming out of the turbine was anoxic (O% o f oxygen); to allow the survival o f fish in the ri v er between the dam and the estu-