Contribution à l’étude de l’impact d’un site minier abandonné dans la haute Moulouya sur la qualité de l’Oued Moulouya, Maroc

Dans le but d’évaluer le degré de contamination chimique des eaux et des sédiments superficiels de l’oued Moulouya (Maroc) qui draine les centres miniers d’Aouli, de Mibladen et de Zaida, abandonnés sans réhabilitation dans haute Moulouya et d’estimer l’extension possible des éléments traces métalliques (ETM) au niveau du secteur aval, des échantillons d’eau et de sédiments ont été prélevés le long de l’oued Moulouya, en vue d’en déterminer les teneurs en ETM : Plomb (Pb), Arsenic (As), Zinc (Zn), Cuivre (Cu) et Cadmium (Cd) en période sèche et en période de pluie, et établir un diagnostic de l’état actuel de la pollution. Dans les sédiments superficiels de l’oued Moulouya, les analyses ont permis de mettre en relief le degré élevé de pollution par le Zn et le Pb dans la station S3 en aval de ces sites miniers dans la haute Moulouya, avec des valeurs maximales respectives de 191,62 et 156,72ppm, dépassant les normes internationales des sédiments des rivières (88ppm pour le Zn) et (22ppm pou le Pb). Par ailleurs, dans les stations situées plus en aval (S8, S10, S11 et S13), les rejets urbains des agglomérations avoisinantes de l’oued Moulouya contribuent aussi à cette contamination par un apport  anthropique qui se traduit par une augmentation des teneurs en ETM. Or, la mise en place du barrage Hassan II sur l’oued Moulouya a toute fois limité les apports en eaux fluviales et par conséquent diminué son pouvoir d’évacuation des polluants émanant des sites miniers de la haute Moulouya vers l’aval de l’oued. En effet, la comparaison des teneurs en As, Pb, Zn, Cu et Cd avec les normes Marocaines, montre que les eaux superficielles de l’oued Moulouya sont de qualité moyenne à excellente. Mais, l’accumulation des ETM dans les sédiments superficiels en teneurs excessives, dont le pourcentage élevé, pourrait être lié aux années qui ont précédé l’édification du barrage, ce qui représente un risque potentiel pour l’écosystème aquatique par relargage de ces éléments, au moindre changement des conditions physico-chimiques du milieu.Mots-clés : Maroc, Oued Moulouya, éléments traces métalliques, contamination, sédiments, eaux, mines, résidus miniers

Towards an integrated management of water resource issues in the Dyle catchment (Scheldt basin, Belgium): the European MULINO project (MULti-sectoral, INtegrated and Operational decision support system for sustainable use of water resources at the catchment scale)

The pressure on water resources is continuously increasing in Europe. If a great deal of scientific knowledge is available in many fields, this knowledge is often treated in isolation. To support the scientific basis for integrated water management, the MULINO project, an acronym for MULti-sectoral, Integrated and Operational decision support system (DSS) for the sustainable use of water resources at the catchment scale, funded by the European Union, is currently executed. The purpose of the MULINO project is to provide a tool to improve the integrated management of water resources at the catchment scale, following the requirements of the EU Water Framework Directive (WFD, J.O.CE, 2000). The DSS developed is a computer system based on hydrological modelling, multi-disciplinary indicators and multi-criteria evaluation procedures. The underlying design of the DSS is based on the Driving Forces-Pressures-State-Impact-Responses framework for reporting on environmental issues (EEA, 1999; OECD, 1993). One case study is the 700 km² Dyle catchment situated in the centre of Belgium (50°38N 4°45E) and part of the Scheldt basin. A coupling of an integrated hydrological model (SWAT: Soil and Water Assessment Tool, Arnold et al., 1993) with land use change modelling (SFARMMOD, Audsley et al., 1979) is developed in close collaboration with local end users and stakeholders. This work will provide a useful tool to analyse water resources management alternatives and to assist local managers in complex problems such as flooding, nitrate and pesticides contamination of waters, as to identify solutions for the implementation of the WFD at the catchment scale

Calibration of WAVE in irrigated maize: fallow vs. cover crops.

Nitrate leaching decreases crop available N and increases water contamination. Replacing fallow by cover crops (CC) is an alternative to reduce nitrate contamination, because it reduces overall drainage and soil mineral N accumulation. A study of the soil N and nitrate leaching was conducted during 5 years in a semi-arid irrigated agricultural area of Central Spain. Three treatments were studied during the intercropping period of maize (Zea mays L.): barley (Hordeum vulgare L.), vetch (Vicia villosa L.), and fallow. Cover crops, sown in October, were killed by glyphosate application in March, allowing direct seeding of maize in April. All treatments were irrigated and fertilised following the same procedure. Soil water content was measured using capacity probes. Soil Nmin accumulation was determined along the soil profile before sowing and after harvesting maize. Soil analysis was conducted at six depths every 0.20m in each plot in samples from 0 to 1.2-m depth. The mechanistic water balance model WAVE was applied in order to calculate drainage and plant growth of the different treatments, and apply them to the N balance. We evaluated the water balance of this model using the daily soil water content measurements of this field trial. A new Matlab version of the model was evaluated as well. In this new version improvements were made in the solute transport module and crop module. In addition, this new version is more compatible with external modules for data processing, inverse calibration and uncertainty analysis than the previous Fortran version. The model showed that drainage during the irrigated period was minimized in all treatments, because irrigation water was adjusted to crop needs, leading to nitrate accumulation on the upper layers after maize harvest. Then, during the intercrop period, most of the nitrate leaching occurred. Cover crops usually led to a shorter drainage period, lower drainage water amount and lower nitrate leaching than the treatment with fallow. These effects resulted in larger nitrate accumulation in the upper layers of the soil after CC treatments

Improving soil moisture profile reconstruction from ground-penetrating radar data: a maximum likelihood ensemble filter approach

The vertical profile of shallow unsaturated zone soil moisture plays a key role in many hydro-meteorological and agricultural applications. We propose a closed-loop data assimilation procedure based on the maximum likelihood ensemble filter algorithm to update the vertical soil moisture profile from time-lapse ground-penetrating radar (GPR) data. A hydrodynamic model is used to propagate the system state in time and a radar electromagnetic model and petrophysical relationships to link the state variable with the observation data, which enables us to directly assimilate the GPR data. Instead of using the surface soil moisture only, the approach allows to use the information of the whole soil moisture profile for the assimilation. We validated our approach through a synthetic study. We constructed a synthetic soil column with a depth of 80 cm and analyzed the effects of the soil type on the data assimilation by considering 3 soil types, namely, loamy sand, silt and clay. The assimilation of GPR data was performed to solve the problem of unknown initial conditions. The numerical soil moisture profiles generated by the Hydrus-1D model were used by the GPR model to produce the "observed" GPR data. The results show that the soil moisture profile obtained by assimilating the GPR data is much better than that of an open-loop forecast. Compared to the loamy sand and silt, the updated soil moisture profile of the clay soil converges to the true state much more slowly. Decreasing the update interval from 60 down to 10 h only slightly improves the effectiveness of the GPR data assimilation for the loamy sand but significantly for the clay soil. The proposed approach appears to be promising to improve real-time prediction of the soil moisture profiles as well as to provide effective estimates of the unsaturated hydraulic properties at the field scale from time-lapse GPR measurements

SAFE - a Tool for Assessing the Sustainability of Agricultural Systems: an Illustration

SAFE (Framework for Assessing Sustainability levels) is a tool for evaluating the sustainability of agricultural systems and uses a hierarchical framework populated with indicators objectively selected by multicriteria evaluation. Indicators are measured at field, farm and landscape scales and progressively integrated into a global sustainability index (SI). SAFE is illustrated below with results on a field scale from a farm site

SAFE: A Framework for Assessing Sustainability Levels in Agricultural Systems

Evaluating the sustainability of agricultural systems is a major challenge for scientists, policy makers and farmers. Numerous sets of indicators have recently been designed, both at national and international levels. However, most of these initiatives focus only on environmental aspects of sustainability, indicators are often selected arbitrarily and usually do not fit in a consistent, comprehensive and universally applicable framework. This paper presents an original framework for integrating the information contained by indicators into a single quantitative measure of agricultural sustainability in order to facilitate comparison and diagnosis

Estimation of root water uptake parameters by inverse modeling with soil water content data

In this paper we have tested the feasibility of the inverse modeling approach to derive root water uptake parameters (RWUP) from soil water content data using numerical experiments for three differently textured soils and for an optimal drying period. The RWUP of interest are the rooting depth and the bottom root length density. In a first step, a thorough sensitivity analysis was performed. This showed that soil water content dynamics is relatively insensitive to RWUP and that the sensitivity depends on the texture of the considered soil. For medium-fine textured soil, the sensitivity is particularly low due to relatively high unsaturated hydraulic conductivity values. These ones allow a “compensating effect” to occur, i.e., vertical unsaturated water fluxes overshadowing in some way the root water uptake. In a second step, we analyzed the well-posedness of the solution (stability and nonuniqueness) when only RWUP are optimized. For this case, the inverse problem is clearly ill-posed except for the estimation of the rooting depth parameter for coarse and the very fine textured soils. In a third step, we addressed the case where RWUP are estimated simultaneously with additional parameters of the system (i.e., with soil hydraulic parameters). For this case, our study showed that the inverse problem is well-posed for the coarse and very fine textured soils, allowing for the estimation of both RWUP of interest provided that a powerful global optimization algorithm is used. On the contrary, the estimation of RWUP is unfeasible for medium-fine textured soil due to the “compensating effect” of the vertical unsaturated water flows. In conclusion, we can state that the inverse modeling approach can be applied to derive RWUP for some soils (coarse and very fine textured) and that the feasibility is strongly improved if the RWUP are simultaneously optimized with additional parameters. Nevertheless, more detailed research is needed to apply the inverse modeling approach to real cases for which additional issues are likely to be encountered such as soil heterogeneity and root dynamics

Retrieving hydrological connectivity from empirical causality in karst systems

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Retrieving hydrological connectivity from empirical causality in karst systems

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