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Le Bourget-du-Lac, France

Deshmukh C.,CNRS Laboratory for Aerology | Deshmukh C.,TERI University | Serca D.,CNRS Laboratory for Aerology | Delon C.,CNRS Laboratory for Aerology | And 9 more authors.

In the present study, we measured independently CH4 ebullition and diffusion in the footprint of an eddy covariance system (EC) measuring CH4 emissions in the Nam Theun 2 Reservoir, a recently impounded (2008) subtropical hydroelectric reservoir located in the Lao People's Democratic Republic (PDR), Southeast Asia. The EC fluxes were very consistent with the sum of the two terms measured independently (diffusive fluxes + ebullition Combining double low line EC fluxes), indicating that the EC system picked up both diffusive fluxes and ebullition from the reservoir. We showed a diurnal bimodal pattern of CH4 emissions anti-correlated with atmospheric pressure. During daytime, a large atmospheric pressure drop triggers CH4 ebullition (up to 100 mmol mg-2 d-1), whereas at night, a more moderate peak of CH4 emissions was recorded. As a consequence, fluxes during daytime were twice as high as during nighttime. Additionally, more than 4800 discrete measurements of CH4 ebullition were performed at a weekly/fortnightly frequency, covering water depths ranging from 0.4 to 16 m and various types of flooded ecosystems. Methane ebullition varies significantly seasonally and depends mostly on water level change during the warm dry season, whereas no relationship was observed during the cold dry season. On average, ebullition was 8.5 ± 10.5 mmol mg-2 d -1 and ranged from 0 to 201.7 mmol mg-2 d-1. An artificial neural network (ANN) model could explain up to 46% of seasonal variability of ebullition by considering total static pressure (the sum of hydrostatic and atmospheric pressure), variations in the total static pressure, and bottom temperature as controlling factors. This model allowed extrapolation of CH4 ebullition on the reservoir scale and performance of gap filling over four years. Our results clearly showed a very high seasonality: 50% of the yearly CH4 ebullition occurs within four months of the warm dry season. Overall, ebullition contributed 60-80% of total emissions from the surface of the reservoir (disregarding downstream emissions), suggesting that ebullition is a major pathway in young hydroelectric reservoirs in the tropics. © Author(s) 2014. Source

Descloux S.,Hydro Engineering Center | Chanudet V.,Hydro Engineering Center | Poilve H.,Infoterra France | Gregoire A.,Environmental Expert
Environmental Monitoring and Assessment

An assessment of the organic carbon stock present in living or dead vegetation and in the soil on the 450 km 2 of the future Nam Theun 2 hydroelectric reservoir in Lao People's Democratic Republic was made. Nine land cover types were defined on the studied area: dense, medium, light, degraded, and riparian forests; agricultural soil; swamps; water; and others (roads, construction sites, and so on). Their geographical distribution was assessed by remote sensing using two 2008 SPOT 5 images. The area is mainly covered by dense and light forests (59%), while agricultural soil and swamps account for 11% and 2%, respectively. For each of these cover types, except water, organic carbon density was measured in the five pools defined by the Intergovernmental Panel on Climate Change: aboveground biomass, litter, deadwood, belowground biomass, and soil organic carbon. The area-weighted mean carbon densities for these pools were estimated at 45.4, 2.0, 2.2, 3.4, and 62.2 tC/ha, respectively, i.e.; a total of about 115 ± 15 tC/ha for a soil thickness of 30 cm, corresponding to a total flooded organic carbon stock of 5.1 ± 0.7 MtC. This value is much lower than the carbon density for some South American reservoirs for example where total organic carbon stocks range from 251 to 326 tC/ha. It can be mainly explained by (1) the higher biomass density of South American tropical primary rainforest than of forests in this study and (2) the high proportion of areas with low carbon density, such as agricultural or slash-and-burn zones, in the studied area. © 2010 Springer Science+Business Media B.V. Source

Maruzewski P.,Hydro Engineering Center | Rogeaux C.,Hydro Engineering Center | Laurier P.,Hydro Engineering Center
IOP Conference Series: Earth and Environmental Science

In developing countries with great and unexploited renewable energy potential, Governments can exploit local resources for electricity supply, substantial energy savings and sustainable socio-economic development of these own countries. The decision-making process regarding the choice of renewable energy sources for energy supply in these countries is multidimensional, made up of a number of aspects at different levels such as economic, technical, environmental, and social. Therefore, reaching clear and unambiguous solutions may be very difficult. It is from this difficulty that the need arises to develop a tool for the design of hydro energy sources for electricity. The work involved in seeking a compromise solution requires an adequate technical assessment based on multiple criteria methods. One of the criteria is the assessment of the appropriate size of the hydropower plant. This paper presents the state-of-art of preliminary sizing of hydropower plant for the given renewable energy potential. The main step consists of carefully selecting and sizing the innovative hydraulic units based upon the suitability of the flow and head range. Since the flow and head data have now been confirmed, the potential annual energy generation can be properly assessed. © Published under licence by IOP Publishing Ltd. Source

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