Le débat international sur la gestion des forêts

Cet article décrit, au niveau mondial, une perception nouvelle des questions forestières. Il illustre ce débat par plusieurs exemples : l'affaire de la chouette tachetée aux USA, la polémique sur la déforestation en Amazonie, les pluies acides. Il résume le «rapport Bruntland», puis pose cinq grands défis pour les forestiers européens, susceptibles de rénover radicalement le contexte forestier

Simulation and implementation of a piezoelectric sensor for harmonic in-situ strain monitoring

To monitor the strain in a multilayer steel/adhesive/ceramic beam structure, a 9-µmthick piezoelectric PVDF film is inserted in the adhesive joint. Two 2D finite element models of the structure with and without the film were developed using a sub-structuring procedure to reduce computational time and to refine the mesh in the thickness of the film. The models provide the harmonic displacement of the beam and the voltage across the film which is related to the strain. A prototype of the analyzed structure has been developed as well. Simulation and experimental analysis was performed and obtained results were compared. It was demonstrated that the influence of the presence of the film on the stress distribution is negligible, thus the implementation of an embedded PVDF film is a well-suited technique to monitor the strain transfer in a bonded assembl

Co-composting: An Opportunity to Produce Compost with Designated Tailor-Made Properties

AbstractCo-composting is a technique that allows the aerobic degradation of organic waste mixtures, primarily aiming at obtaining compost that can be used as fertiliser or soil amendment. As compared to the typical composting activity, the main difference is not merely the use of more than one feedstock to start and sustain the biodegradation process, but also the possibility of combining various kinds of waste to obtain 'tailored' products with designed properties, or to reclaim and valorise natural resources, such as degraded soils or polluted soils and sediments. Set up of appropriate co-composting protocols can be a way to optimise the management of waste produced by different sectors of agriculture and industry and also from human settlements. Different formulations can not only optimise the biodegradation process through the adjustment of nutrient ratios, but also lead to the formation of products with innovative properties. Moreover, co-composting can be a technique of choice for the reclamation of soils degraded by intensive agriculture or contaminated soils and sediments. In fact, an appropriate mix of organic waste and soils can restore the soil structure and induce fertility in nutrient-depleted soils, and also remediate polluted soils and sediments through degradation of organic pollutants and stabilisation of heavy metals. While the selection of different mixes of organic waste may lead to the design of composts with specific properties and the potential valorisation of selected waste materials, there are still several factors that hamper the development of co-composting platforms, mainly insufficient knowledge of some chemical and microbiological processes, but also some legislative aspects. This chapter illustrates the progress achieved in co-composting technology worldwide, some key legislative aspects related to the co-composting process, the main scientific and technical aspects that deserve research attention to further develop co-composting technology, and successful applications of co-composting for the reclamation of soils and sediments, allowing their use for cultivation or as growing media in plant nurseries. A specific case study of the production of fertile plant-growing media from sediment co-composting with green waste is also illustrated

A review of source tracking techniques for fine sediment within a catchment

Excessive transport of fine sediment, and its associated pollutants, can cause detrimental impacts in aquatic environments. It is therefore important to perform accurate sediment source apportionment to identify hot spots of soil erosion. Various tracers have been adopted, often in combination, to identify sediment source type and its spatial origin; these include fallout radionuclides, geochemical tracers, mineral magnetic properties and bulk and compound-specific stable isotopes. In this review, the applicability of these techniques to particular settings and their advantages and limitations are reviewed. By synthesizing existing approaches, that make use of multiple tracers in combination with measured changes of channel geomorphological attributes, an integrated analysis of tracer profiles in deposited sediments in lakes and reservoirs can be made. Through a multi-scale approach for fine sediment tracking, temporal changes in soil erosion and sediment load can be reconstructed and the consequences of changing catchment practices evaluated. We recommend that long-term, as well as short-term, monitoring of riverine fine sediment and corresponding surface and subsurface sources at nested sites within a catchment are essential. Such monitoring will inform the development and validation of models for predicting dynamics of fine sediment transport as a function of hydro-climatic and geomorphological controls. We highlight that the need for monitoring is particularly important for hilly catchments with complex and changing land use. We recommend that research should be prioritized for sloping farmland-dominated catchments

A review of source tracking techniques for fine sediment within a catchment

Excessive transport of fine sediment, and its associated pollutants, can cause detrimental impacts in aquatic environments. It is therefore important to perform accurate sediment source apportionment to identify hot spots of soil erosion. Various tracers have been adopted, often in combination, to identify sediment source type and its spatial origin; these include fallout radionuclides, geochemical tracers, mineral magnetic properties and bulk and compound-specific stable isotopes. In this review, the applicability of these techniques to particular settings and their advantages and limitations are reviewed. By synthesizing existing approaches, that make use of multiple tracers in combination with measured changes of channel geomorphological attributes, an integrated analysis of tracer profiles in deposited sediments in lakes and reservoirs can be made. Through a multi-scale approach for fine sediment tracking, temporal changes in soil erosion and sediment load can be reconstructed and the consequences of changing catchment practices evaluated. We recommend that long-term, as well as short-term, monitoring of riverine fine sediment and corresponding surface and subsurface sources at nested sites within a catchment are essential. Such monitoring will inform the development and validation of models for predicting dynamics of fine sediment transport as a function of hydro-climatic and geomorphological controls. We highlight that the need for monitoring is particularly important for hilly catchments with complex and changing land use. We recommend that research should be prioritized for sloping farmland-dominated catchments

A deconvolutional Bayesian mixing model approach for river basin sediment source apportionment

Increasing complexity in human-environment interactions at multiple watershed scales presents major challenges to sediment source apportionment data acquisition and analysis. Herein, we present a step-change in the application of Bayesian mixing models: Deconvolutional-MixSIAR (D-MIXSIAR) to underpin sustainable management of soil and sediment. This new mixing model approach allows users to directly account for the 'structural hierarchy' of a river basin in terms of sub-watershed distribution. It works by deconvoluting apportionment data derived for multiple nodes along the stream-river network where sources are stratified by sub-watershed. Source and mixture samples were collected from two watersheds that represented (i) a longitudinal mixed agricultural watershed in the south west of England which had a distinct upper and lower zone related to topography and (ii) a distributed mixed agricultural and forested watershed in the mid-hills of Nepal with two distinct sub-watersheds. In the former, geochemical fingerprints were based upon weathering profiles and anthropogenic soil amendments. In the latter compound-specific stable isotope markers based on soil vegetation cover were applied. Mixing model posterior distributions of proportional sediment source contributions differed when sources were pooled across the watersheds (pooled-MixSIAR) compared to those where source terms were stratified by sub-watershed and the outputs deconvoluted (D-MixSIAR). In the first example, the stratified source data and the deconvolutional approach provided greater distinction between pasture and cultivated topsoil source signatures resulting in a different posterior distribution to non-deconvolutional model (conventional approaches over-estimated the contribution of cultivated land to downstream sediment by 2 to 5 times). In the second example, the deconvolutional model elucidated a large input of sediment delivered from a small tributary resulting in differences in the reported contribution of a discrete mixed forest source. Overall D-MixSIAR model posterior distributions had lower (by ca 25-50%) uncertainty and quicker model run times. In both cases, the structured, deconvoluted output cohered more closely with field observations and local knowledge underpinning the need for closer attention to hierarchy in source and mixture terms in river basin source apportionment. Soil erosion and siltation challenge the energy-food-water-environment nexus. This new tool for source apportionment offers wider application across complex environmental systems affected by natural and human-induced change and the lessons learned are relevant to source apportionment applications in other disciplines

Effect of decomposition products produced in the presence or absence of epigeic earthworms and minerals on soil carbon stabilization

International audienceMicrobial use efficiency is thought to greatly influence organic carbon storage in soils through the formation of decomposition products and their stabilization as organo-mineral complexes. Earthworm activity may play a significant role in these processes. Of the three ecological earthworm groups only two (endogeic and anecic species) are thought to be involved in soil organic carbon (SOC) stabilization as they are living in mineral soil. The aim of this study was to investigate the role of decomposition products produced, with and without minerals, by epigeic earthworms living at the litter-soil interphase for carbon stabilization. We investigated the impact of eight different types of decomposition products on CO2 emissions, microbial biomass, watersoluble C, mineral N and SOC pool allocation of an arenic cambisol during 79 days under laboratory conditions. Our results indicated that the nature of decomposition products affected their impact on SOC mineralization and soil physico-chemical parameters. In general, the presence of epigeic earthworms during OM decomposition decreased CO2 emissions after soil addition of decomposition products and increased microbial carbon use efficiency when compared to those produced without earthworms. Mineral-containing decomposition products increased CO2 emissions after their addition to soil when compared to their mineral free counterparts. They also changed carbon allocation to physico-chemically protected pools, decreasing the contribution of particulate organic matter when compared to mineral free decomposition products. Extrapolation of the data showed that these short-term effects were not necessarily long-term in nature, but they also indicated that microbial products produced in the presence of epigeic earthworms and minerals may increase SOC sequestration in the amended soil. We therefore conclude that the nature of decomposition products is crucial for their fate in soil and that in contrast to the general paradigm, epigeic earthworms could have an important role to play in SOC sequestration through the formation of material susceptible to be protected, when incorporated into mineral soil

Interface forces measurement in laminated composites

In laminated composites, interfaces are the transfer spots of mechanical charges, mechanical over-stresses adaptations and energy dissipations. We have realised an experiment in order to observe the visco-elastic interface behaviour of a laminated composite. Between two composite plies of a multilayer cantilever beam, piezoelectric PVDF thin films are bonded. The voltage signals generated by the piezoelectric elements are dependant of the expected interlaminar stresses. The data acquisition system program of the signals is written with LabVIEW^{\fontsize{6}{8}\selectfont{\hbox{\textregistered}}}. The results of the experiment validate the parameters of finite element simulations realised on the dynamic behaviour of the cantilever beam