International audienceIn this study, we performed a partitioning of evapotranspiration (ET) under fully controlled conditions (climatic chamber) along growth of a tall fescue cover (Festuca arundinacea) into soil evaporation (Ev) and plant transpiration (Tr) by measuring their stable oxygen isotopic compositions (δET, δEv and δTr). We showed that it was possible, under the chamber's particular conditions, to realize the partition without (1) making the hypothesis of steady state transpiration usually done in the field, nor (2) calculating δEv as a function of air relative humidity, soil water and atmospheric vapour isotopic compositions. The contribution of Ev to total ET decreased over the experiment from 100% (bare soil) to 94% [16 days after the seeding (DAS), 83% (28 DAS), 70% (36 DAS) and 5% (43 DAS)]. Soil isotopic profiles calculated using a typical exponential-type expression and measured Ev flux were compared with the bare soil steady state measured profiles. Agreement between modelled and measured values was sensitive to soil tortuosity and kinetic fractionation values. Another significant result was highly enriched isotopic values estimated for soil water at the evaporation front [the surface under our experimental conditions (δsurf)]. The theoretical estimate of δsurf was about 1-6‰ enriched as compared to the values measured in the top 1 cm of the soil, raising important implications for the determination of δEv as a function of δsurf under field conditions. Our work also points out uncertainties related to the determination of partition values and isotopic composition measured in the field, a point that is often ignored in many papers on isotopic biogeochemistry applied to geochemical fluxes, although it can be important. Copyright © 2010 John Wiley & Sons, Ltd

Stable water isotopes such as oxygen 18, are natural tracers of water movement within the soil-vegetation-atmosphere continuum. They provide useful information for a better understanding of evaporation and water vapor transport within soils. This paper presents a novel controlled experimental set up. It is dedicated to detailed measurements of the evaporation fluxes from bare soil columns, as well as to the corresponding isotopic composition of the water vapor, under non steady state conditions. The experiment allowed an accurate determination of these quantities. The formulae encountered in the literature were used to estimate the isotopic composition of the evaporated water vapor. None of them was able to correctly reproduce the measured isotopic composition of water. The data were then used to estimate the value of the isotopic composition of the soil liquid water, which should be used to get the right results for the isotopic composition of the evaporated water vapor. Results suggest that, when liquid transfer is dominant within the soil, the isotopic composition of evaporation was controlled by the isotopic composition of the liquid water within very thin soil surface layers. When there is a peak in the isotopic profile, i.e. when water vapor is dominant close to the surface, the isotopic composition of the evaporated water seems to be governed by the isotopic composition of the soil liquid water at the peak. The data were also used to estimate the kinetic fractionation factor. The results suggest that the latter is not constant in time. The values seem to depend on the shape of the isotopic profile. In both cases, the uncertainty on the results is very large. The estimation of the kinetic fractionation factor is studied more in details using the modeling results presented in Part II of a companion paper where the data set is modeled using the SiSPAT_Isotope model.

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Because of the absence of lighting calculation tools at the initial stage of tunnel design, the lighting systems are usually over-dimensioned, leading to over illumination and increased energy consumption. For this reason, a fine-tuning method for switching lighting stages according to the traffic weighted L20 luminance is proposed at no additional cost. The method was applied in a real –case scenario, where L20 luminance of the access zone at eleven (11) existing tunnels was calculated. The traffic weighted method of CR14380 was used in order to calculate the actual luminance levels for the entrance zone. The new transition zone, which decreases luminance curves, was produced and compared with the existing ones. Thus, a new switching control was proposed and programed for the Supervisory Control and Data Acquisition (SCADA) system of the tunnel. The signals of the corresponding eleven L20 meters for a period of eight days were used and the corresponding annual energy consumptions were calculated using the proposed switching program for each tunnel. The results were compared with a number of scenarios in which the existing lighting system was retrofitted with Lighting Emitting Diodes (LED) luminaires. In these scenarios, the new luminaire arrangement was based not only on the existing luminance demand value for the threshold zone, but also on the newly proposed one with two different control techniques (continuous dimming and 10% step dimming). The fine-tuning method for switching resulted in energy savings between 11% and 54% depending on the tunnel when the scenario of the existing installation at no extra cost was used. Energy savings, when LED luminaires were installed, varied between 57% (for the scenario with existing luminance demand value for the threshold zone and 10% step dimming) and 85% (for the scenario with the new calculated luminance demand and continuous dimming).

Life cycle assessment (LCA) methodology has been used to evaluate the performance of the following lighting systems: compact fluorescent lamps (CFL), light-emitting diode (LED) lamps, and fluorescent tubes (T5 type). This work covers the singularity of the French electricity mix for indoor workplaces lighting and describes the best strategy for lamp replacement. We have defined the light loss factor to integrate the following additional parameters: lumen depreciation, dirt accumulation, and risks of failure. Therefore, we propose a new definition of the functional unit (maintained megalumen hour), and we conduct this assessment to be compliant with the standards of lighting system equipment (NF EN 12464-1). Unlike previous studies, we observed that the manufacturing phase is the most impacting over the whole life cycle, thus making the extension of LED lamps’ lifetime a more effective strategy to reduce the potential environmental impacts than increasing their efficacy. This paper highlights how the light loss factor affects the LCA results and proves that it should be taken into account for subsequent assessments. Finally, this new approach includes the real usage of the lamps in the study and contributes to lay the foundation for life cycle sustainability assessment to also evaluate the economic, social, and human impacts of lighting.

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