The space and time resolutions used for the input variables of a distributed hydrological model have a sufficient impact on the model results. This resolution depends on the required accuracy, experimental site and the processes and variables taken into account in the hydrological model. The influence of space and time resolution is studied here for the case of TOPMODEL, a model based on the variable contributing area concept, applied to an experimental 12 km2 catchment (Coet-Dan, Brittany, France) during a two month winter period. A sensitivity analysis to space and time resolution is performed first for input variables derived from the digital elevation data, secondly for the optimized values of the TOPMODEL parameters and finally for modelling efficiency. This analysis clearly shows that a relevant domain of space and time resolutions where efficiency is fairly constant can be defined for the input topographic variables, as opposed to another domain of larger resolutions that induces a strong decrease of modelling effciency. It also shows that the use of a single set of parameters, defined as mean values of parameters on this relevant domain of resolution, does not modify the accuracy of modelling. The sensitivity of the parameters to space and time resolution allows the physical significance of the parameter values to be discussed.

No abstract

During composting of livestock manure, transformations of organic matter result in gaseous emissions, which can harm the environment. Two experiments were done in enclosures to measure the fluxes of NH3, N2O, CO2, CH4 and H2O emitted by 8 heaps of compost representing the range of biodegradability of nitrogen and carbon in the livestock manure. The heaps were monitored for the first 2 months, corresponding to the thermophilic phase during which nearly all-mass losses occur. Four parameters describe the NH3 emission kinetics and the main influential factors were noted: (1) the response time to reach maximum intensity is affected mainly by the initial micro-flora; (2) the amplitude depends mainly on C biodegradability and also on micro-flora; (3) the emission duration depends mainly on N biodegradability; and (4) the cumulative emission, which varied from 16.5 to 48.9% of the nitrogen initially present in the heap, depends both on C and N biodegradability. A predictive model for NH3 and CO2 emissions for the thermophilic phase of the composting of livestock manure is proposed. The variability in cumulative emissions of CO2 and of NH3 is well explained by the contents of soluble elements and hemicellulose in the dry matter (Van Soest fractioning), and soluble nitrogen (12 h extraction at 4 °C in water). In our conditions of favourable aeration and humidity, N2O and CH4 emissions were low. The role of the biodegradable carbon in reducing NH3 emission is highlighted

A model has been developed to predict pig manure evolution (mass, dry and organic matter, N, P, K, Cu and Zn contents) and related gaseous emissions (methane (CH 4 ), nitrous oxide (N 2 O) and ammonia (NH 3 )) from pig excreta up to manure stored before spreading. This model forms part of a more comprehensive model including the prediction of pig excretion. The model simulates contrasted management systems, including different options for housing (slatted floor or deep litter), outside storage of manure and treatment (anaerobic digestion, biological N removal processes, slurry composting (SC) with straw and solid manure composting). Farmer practices and climatic conditions, which have significant effects on gaseous emissions within each option, have also been identified. The quantification of their effects was based on expert judgement from literature and local experiments, relations from mechanistic models or simple emission factors, depending on existing knowledge. The model helps to identify relative advantages and weaknesses for each system. For example, deep-litter with standard management practices is associated with high-greenhouse gas (GHG) production (1125% compared to slatted floor) and SC on straw is associated with high NH 3 emission (115% compared to slatted floor). Another important result from model building and first simulations is that farmer practices and the climate induce an intra-system (for a given infrastructure) variability of NH 3 and GHG emissions nearly as high as inter-system variability. For example, in deep-litter housing systems, NH 3 and N 2 O emissions from animal housing may vary between 6% and 53%, and between 1% and 19% of total N excreted, respectively. Thus, the model could be useful to identify and quantify improvement margins on farms, more precisely or more easily than current methodologies.

Poultry production has been identified as a major producer of NH 3 and, to a lesser extent, of greenhouse gases (GHGs) mainly by national emissions inventories. However, since most national inventories are based on average emission factors for each type of animal ('tier 1' approach), the factors that influence these emissions (through breeding and manure-management practices) are not taken into account. The first step to improve inventories and propose mitigation options (e.g. best management practices, innovative systems) is a better understanding of the drivers of gaseous emissions and the identification of key factors for the mitigation of NH 3 and GHG emissions. This paper presents a literature review of NH 3 and GHG emissions from poultry housing, with a focus on the influence of practices and rearing conditions. It appears that flockmanagement practices (e.g. dietary practices, slaughtering age) and manure management (e.g. manure removal frequency, chemical treatment of litter) are presented as efficient ways to reduce emissions. Environmental conditions (e.g. ventilation rates, temperature) influence emissions; however, it was not possible to assess the effects of different combinations of these factors (compensatory or synergistic). Some factors, such as stocking density, which may play a significant role, were not studied. Modelling approaches that integrate these key factors with climate factors can be used to update emission factors in emissions inventories, consider national variability and uncertainties in mitigation scenarios, test synergistic and compensatory effects and avoid pollution swapping. Further research must be carried out to check the validity of emission factors and modelling parameters at a national scale.

No abstract

ABSTRACT. Atmospheric reduced nitrogen (NH x ) mainly originates from hot spots, which can be considered as intensive area or point sources. A large fraction of the emitted NH x may be recaptured by the surrounding vegetation, hence reducing the contribution of these hot spots to long-range transport of NH x . This paper reviews the processes leading to local recapture of NH x near hot spots as well as existing models and monitoring methods. The existing models range from research models to more operational models that can be coupled with long-range transport model provided the necessary information on emissions is available. Local recapture of NH 3 ranges from 2% to 60% within 2 km of a hot-spot and it is sensitive to source height, atmospheric stability, wind speed, structure of the surrounding canopies, as well as stomatal absorption, which mainly depends on green leaf area index and stomatal NH 3 compensation point of vegetation, and finally, cuticular deposition, which depends primarily on vegetation wetness. The main uncertainties and limitations on NH x recapture models and monitoring techniques are discussed.

Rural sewage treatment is now paid more and more attention in China. Vermifiltration technology could be one of the practical options under the review of previous studies. It showed good removal rates of contaminants on small to pilot scales for short-term tests. However, the impacts of season, temperature or other unknown factors are usually not taken into account. In this study, a larger vermifilter was designed to treat the sewage on village scale for long-term operation. Filter material composition was optimized by a half year experimentation. The treatment effects of vermifiltration were also compared with traditional activated sludge process for the same influent sewage. The results showed that the designed vermifiltration system could continuously treat the sewage produced by more than 100 inhabitants per day. COD, BOD5 and SS concentration in outflow were rather stable despite the fluctuation of hydraulic loading rate and organic input during one year test. It can also remove N and P to some extent. A suspending design of vermifilter bed cause adequate oxygen content in outflow of vermifilter. The comparative test showed that the treatment efficacy of vermifiltration was similar as activated sludge process. Generally, this vermifiltration system has practical application value for village sewage treatment.