Salinisation des eaux et des sols en zone littorale méditerranéenne : état, pratiques et trajectoires d’évolution

National audienc

The Chlordecone crisis in the French West Indies : Its fate in soils and water

International audienceIn the French West Indies, chlordecone (CLD), an organochlorine pesticide, which is highly persistent in the environment, was applied in banana plantations from 1972 to 1993 against the banana weevil Cosmopolites sordidus. Pollution surveys conducted in 2001 by the French Department of Health revealed the presence of chlordecone in soils, rivers, springs over large areas in Guadeloupe and Martinique islands. Contamination of drinking water, food crops, aquatic species by CLD has been observed as well as its presence in blood of men, pregnant women and newborns. There is therefore a large social concern about the extent and evolution of CLD pollution in the French West Indies and its impact on human health and ecosystems. From 2008 to 2012 a multidisciplinary project CHLORDEXCO took place to study the CLD fate in water, soils and the contamination characteristics of aquatic species and food crops. Here, we summarize results obtained on the processes controlling the spatial and temporal patterns of soil and water contamination at the scale of the banana cropping area in Guadeloupe and of the Perou catchment. The main soils in the contaminated areas are andosols and nitisols and formed from the weathering of volcanic ashes. They have a high organic carbon content and high content of secondary minerals, allophane for andosols and halloysite for nitisols. An analysis of the spatial distribution of CLD in soil over 1045 field plots showed that the soil type had a strong impact. Andosols, with a high sorption capacity (Koc 20 000 L/kg), had the highest CLD concentrations and stocks, unlike Nitisols, which had 10-fold lower sorption capacities. A significant « farm effect », due to between-farm variations of application times and amounts, was also noticed. The observed stocks of CLD clearly correspond to the accumulation in soil of successive treatments and thereby confirm the high persistence of CLD in soil also observed in incubation studies in soil microcosms. Soil column studies of the transport of aged CLD however showed that CLD concentration in percolation water varied little (5 to 10 μg/L) and were of same magnitude for both soils although their sorption properties and hydrodynamic behaviours differed with larger macropore flow in the andosols. At catchment scale, contamination of surface waters was permanent with CLD concentrations one order of magnitude less than in percolation water. Temporal variations of contamination were due to dilution effects caused by water from uncontaminated uphill areas. CLD concentrations were highest in base flow indicating that the main pathway of applied CLD to surface waters is by percolation and groundwater flow. In conclusion, contamination of soil and water in the banana cropped areas of the French West Indies is general and permanent. If no soil remediation strategies can be elaborated this severe environmental contamination will last over centuries as estimated by Cabidoche et al. (2009, Environ. Poll., 57, 1697-1705). Since CLD propagates mainly by subsurface flow, buffer strips, usually recommended in many regions to limit the pollution of water by pesticides, will not be useful

Case studies

The objective of this chapter is to let a representative cross-section of practitioners, drawn from several regions of the world, reflect on their experiences through short illustrations of the approaches they have adopted to address a PUB problem. The chosen case studies cover the full range of runoff predictions in ungauged basins, using a wide range of methods, in places across broad climatic and geographic gradients. We then undertook a limited assessment of PUB practice seen in the case studies from two perspectives: (i) what lessons can be learned from the experiences of the case studies towards strengthening the outcomes of the synthesis?, and (ii) how can the outcomes of the synthesis help advance the practice of PUB globally

Managing ditches for agroecological engineering of landscape. A review

International audienceAbstractAgriculture must now feed the planet with the lowest environmental impact. Landscape management is a means to protect natural resources from the adverse impacts. In particular, the adequate management of ditches could improve crop quality. Here, we review ditch design and maintenance. We found the following major points: (1) ditch networks have been primarily designed for waterlogging control and erosion prevention. Nonetheless, when properly managed, farm ditches provide other important ecosystem services, namely groundwater recharge, flood attenuation, water purification, or biodiversity conservation. (2) All ditch ecosystem services depend on many geochemical, geophysical, and biological processes, whose occurrence and intensity vary largely with ditch characteristics. (3) The major ruling characteristics are vegetative cover; ditch morphology; slope orientation; reach connections such as piped sections and weirs, soil, sediment and litter properties, biota, and biofilms; and network topology. (4) Ditch maintenance is an efficient engineering tool to optimize ecosystem services because several ditch characteristics change widely with ditch maintenance. For instance, maintenance operations, dredging, chemical weeding, and burning improve waterlogging and soil erosion control, but they are negative for biodiversity conservation. Mowing has low adverse effects on biodiversity conservation and water purification when mowing is performed at an adequate season. The effects of burning have been poorly investigated