No abstract

Chlordecone, applied on soils until 1993 to control banana weevil, has polluted waters resources in the French West Indies for more than 40 years. At the watershed scale, chlordecone applications were not homogenous, generating a spatial heterogeneity of the pollution. The roles of climate, hydrology, soil, agronomy and geology on watershed functioning generate a temporal heterogeneity of the pollution. This study question the interactions between practices and the environment that induce such variability. We analyzed hydrological and water pollution datasets from a two years monitoring program on the Galion watershed in Martinique (French West Indies). We conjointly analyzed: i) weekly CLD concentration monitored on 3 river sampling sites, ii) aquifer piezometric dynamics and pollutions, and iii) agricultural practices on polluted soils. Our results showed that chlordecone pollution in surface waters are characterized by annual trends and infra-annual variations. Aquifers showed CLD concentration 10 times higher than surface water, with CLD concentration peaks during recharge events. We showed strong interactions between rainfall events and practices on CLD pollution requiring a systemic management approach, in particular during post cyclonic periods. Small sub-watershed with high CLD pollution, appeared to be substantial contributor to CLD mass transfers to the marine environment via rivers, and should therefore receive priority management. We suggest increasing stable organic matter return to soil as well as external input of organic matter to reduce CLD transfers to water. We identified hydrological conditionsnotably drying periodsand tillage as the most influential factors on CLD leaching. In particular, tillage acts on 3 processes that increases CLD leaching: organic matter degradation, modification of water paths in soil and allophane clay degradation.

Abstract. In this study, we investigated the management of long-term environmental pollution by organic pollutants such as organochlorine pesticides. We set out to identify conditions that are conducive to reducing pollution levels for these persistent molecules and then propose a conceptual model of organochlorine fate in water. Our approach looked at spatio-temporal changes in pollutant contents in surface water (SW) and groundwater (GW) on a large scale, in order to decipher the respective roles of soil, geology, hydrology and past treatment practices. The case of chlordecone (CLD) on the island of Martinique (1100 km2) was selected given the sampling campaigns carried out since 2007 over more than 150 sites. CLD, its metabolite chlordecone-5b-hydro (5bCLD) and the metabolite-to-parent-compound ratio were compared. As regards the spatial variability of water contamination, our results showed that banana cropping areas explained the location of contaminated SW and GW, whereas the combination of soil and geology factors explained the main spatial variability in the 5bCLD∕CLD ratio. For temporal variability, these conditions defined a high diversity of situations in terms of the duration of pollution, highlighting two groups: water draining old geological formations and ferralsols or vertisols vs. recent geology and andosols. A conceptual leaching model provided some key information to help interpret downward trends in CLD and 5bCLD observed in water. Lastly, a conceptual model of organochlorine fate is proposed to explain the diversity of the 5bCLD∕CLD ratio in water. Our conclusions highlight the combined role of soil and groundwater residence time for differentiating between conditions that are more conducive, or not, to the disappearance of CLD from the environment. This paper presents a model that provides an overall perception of organochlorine pesticide fate in the environment.

To assist in the sustainable management of water resources, a groundwater model of the shallow groundwater in the Plaine du Nord–Massacre transboundary aquifer system was developed. The Plaine du Nord–Massacre Aquifer is one of the largest aquifer systems of Haiti, supposedly bearing a high potential for water supply and irrigation. The shallower part is already tapped by hundreds of domestic wells and hand-pumped public and private boreholes. In the framework of the AVANSE project (Appui à la Valorisation du Potentiel Agricole du Nord, pour la Sécurité Économique et Environnementale), a USAID funded project aiming at developing sustainable agriculture in the region, a groundwater model was built to assist in decision making. The finite-difference-based MARTHE software was used for the model. Due to the lack of monitoring data, the calibration of the model could only be carried out under steady-state hydraulic conditions. It should thus be considered as a first step towards a better characterisation of the aquifer’s potential. However, the model computed a groundwater balance at the scale of the aquifer showing that significant water resources can be easily mobilized if one carefully manages to rule out local operational difficulties. The simulated groundwater drawdowns using transient simulation of irrigation scenarios are pluri-metric, reaching 6–7 m. New irrigation wells must be deeper than the current average depth of wells to support agricultural development projects.

This chapter presents a review of methods an tools used in France to assess groundwater abstraction limits in unconfined aquifers. The experience gained from over 30 studies shows that the estimation of Maximum Permissible Volume (MPV) is complicated by numerous uncertainties. The first prerequisite is a good knowledge of the dynamics of the hydrosystems and abstraction volumes, but unfortunately this is rarely achieved. Moreover, both the calculation methods and modelling tools that aim to conceptualize these complex systems have limitations due to the simplifying assumptions required for their application. Technical recommendations are proposed for a proper assessment of such uncertainties. In many cases, the calculated maximum permissible volumes were much lower than the previously authorized volumes. Therefore, many of the results were contested by affected users. Such disputes concerned not only the economic consequences of reduced abstraction, but also the scientific basis of the studies in view of the known uncertainties and limitations. The last section of this chapter discusses this phase of negotiations, specifically based on examples from the Adour-Garonne water basin in southwest France.