Le projet européen AgriBMPWater a pour objectif de réaliser une comparaison de différentes modifications de pratiques agricoles élaborées pour améliorer la qualité de l`eau. Cette comparaison est réalisée sur le coût des modifications, leur efficacité attendue, et leur acceptabilité potentielle. Un des résultats novateurs de ce projet est que différencier les politiques de restauration de la qualité de l`eau selon les types d`agriculteurs permet d`accroître l`efficacité de ces politiques tout en diminuant leur coût et en augmentant leur acceptabilité. La traduction sur le terrain de ce résultat de recherche pose cependant de nombreuses questions. C`est cette traduction, sur le bassin versant du Don, qui est exposée ici.

L`intensification de l`agriculture en Bretagne ces 20 dernières années a notamment généré une augmentation des apports azotés au milieu naturel, et a ainsi provoqué une augmentation des concentrations en nitrate dans les eaux de surface. Bien souvent au-delà les normes sanitaires, cette augmentation entraîne des surcoûts (assainissement, respect des directives européennes, coût environnemental). Les recherches menées au sein de l`équipe TERREAU (Cemagref Rennes), notamment dans le cadre de 2 thèses, ont pour but de mieux comprendre les mécanismes de transformation de l`azote lors de son transfert de la parcelle agricole à l`exutoire du bassin versant. Ces travaux sont nécessaires à la mise en oeuvre et l`amélioration des modèles agro-hydrologiques spatialisés à l`échelle du bassin versant, qui sont les outils les plus élaborés d`aide à l`aménagement et à la reconquête de la qualité de l`eau.Un des axes de recherche est la mesure spatialisée, dans un bassin versant agricole, de la dénitrification hétérotrophe. En effet, en Bretagne, on constate une déconnexion entre les pratiques agricoles et les flux d`azote. Quelle que soit la méthode de calcul, il y a en général une différence entre le solde du bilan de l `azote et le flux annuel mesuré dans l `eau à l`exutoire (abattement). Une partie de cet abattement est attribuable à la dénitrification hétérotrophe dans les zones humides, mais de fortes incertitudes existent encore sur sa quantification à l`échelle du paysage. Grâce à un suivi exhaustif des pratiques agricoles et des flux d`azote du bassin versant de la Fontaine du Theil, complété par des mesures in-situ régulières et réparties dans tout le bassin de la dénitrification, un modèle agro-hydrologique spatialisé permettra une estimation mieux contrainte et plus fiable de la dénitrification et des autres termes du bilan azoté. Cette étude est réalisée en lien avec de nombreux programmes de recherche portés par le CAREN auquel l`unité GERE est associée.L`autre axe de recherche se focalise sur les transferts et transformations de l`azote au sein du système zone riparienne / cours d`eau / sédiments. En effet, il existe des relations importantes mais non quantifiées des évolutions. L`un des objectifs de cette seconde thèse est la quantification fine des interactions entre les petits cours d`eau et leurs sédiment à travers des bilans de matière (flux d`azote et carbone) entrée-sortie sur des tronçons de réseau hydrographique. Ces études des flux portent sur différents types de substrats sédimentaires et différentes concentrations en nitrates dans la colonne d`eau. Une relation simple est recherchée entre la rétention d`azote, la concentration en nitrate et la typologie des sédiments, afin de permettre une intégration dans les modèles. Ces deux axes de recherche, de part leur complémentarité spatiale, permettront à terme de modéliser plus finement les processus d` auto-épuration et de rétention de l`azote à l`échelle du bassin-versant.Nous présenterons les méthodes employées pour l`évaluation des flux, c`est à dire les techniques de traçage et les techniques d`évaluation des émissions gazeuses utilisées (traçage au brome et blocage à l`acétylène), et les premiers résultats obtenus.

[Departement_IRSTEA]MA [TR1_IRSTEA]RURAMEN / AMANDE | Dans le cadre de l`opération Ferti-Mieux « le Don, l`eau, la vie », les équipes de la Chambre d`agriculture de Loire Atlantique et du Cemagref se sont associées depuis 1997 pour quantifier le risque de pollution des eaux superficielles par l`azote et les produits phytosanitaires issus de l`activité agricole, et amorcer la proposition de solutions correctives sur ce bassin versant. Pour cela, nous travaillons sur trois bassins emboîtés, le Don (650 km2), le Cétrais (35 km2), et le micro-bassin du Coisbrac (0,5 km2). Pour appuyer les propositions de solutions correctives, nous avons choisi de montrer leurs effets sur les sols et l`eau, en nous appuyant sur le micro bassin de démonstration du Coisbrac. Sur ce micro-bassin, les agriculteurs ont accepté de modifier leurs pratiques. Nous constatons, dès la première année, que la mise en place d`outils d`aide à la fertilisation raisonnée se traduit par une diminution nette des apports d`engrais azotés aux cultures sur le micro-bassin du Coisbrac. Cette année a de plus vu des rendements exceptionnels sur céréales. Ces deux facteurs se sont conjugués pour diminuer les quantités d`azote potentiellement transférables vers les eaux. Cette diminution est cependant tempérée par la minéralisation de l`azote organique du sol et les arrière-effets des pratiques des années antérieures, qui sont dorénavant prépondérants dans les quantités d`azote minéral du sol.

[Departement_IRSTEA]RE [TR1_IRSTEA]RIE / PHYLEAU | Passive capillary samplers, which sample water from the vadose zone via a hanging water column in a fiberglass wick, have shown potential to provide better estimates of actual soil percolation fluxes than alternative field methods. Unsaturated and saturated flows (water and solutes) are extracted continuously and without external vacuum generator from a nondisturbed soil volume, through a significant area (typically 600cm2). In order to achieve a minimal disturbance of the native flow regime, the wick type (hydraulic conductivity and section), length and number and the contact area have to be dimensioned to match as close as possible the expected soil pressure/flow conditions. First, the Hydrus 2D code (Simunek et al., 1999) solving the Richards equation for simulating two dimensional unsaturated flow was used to evaluate the uncertainties in flux estimation by such passive capillary samplers. Two sources of uncertainties were examined. Those associated with the theoretical assumptions of the dimensioning of the wick and those associated to experimental uncertainties. A numerical experimentation was conducted on two reference soils submitted to a 11 days actual hyetograph. Results showed that an analytical dimensioning method proposed in the literature is relevant. But significant errors on the observed fluxes occur when the soil and wick properties do not exactly match, which is the common case since the range of available characteristics of fiberglass wicks is limited. Also, uncertainties in the hydraulic conductivity properties of the soil, in wick length appear to have an important influence on the representativity of the wick fluxes against the actual soil drainage fluxes. Elsewhere, eight such samplers have been installed for an in situ long term experimentation ,initiated this year in the Ardière Watershed (France). The objective is to measure water and pesticides percolation fluxes, at a 50cm depth under a grassed strip receiving contaminated runoff. Flow rate and pesticide concentration in surface runoff water are also measured so as to determine the soil boundary condition above each sampler. Soil water content and soil matric potential are measured at three different depth very close to each instrumented profile in order to explain the volumes extracted by each sampler. We present here the experimental methodology and first results obtained with simulated runoff events.

Passive capillary samplers, which sample water from the vadose zone via a hanging water column in a fiberglass wick, have shown potential to provide better estimates of actual soil percolation fluxes than alternative field methods. Unsaturated and saturated flows (water and solutes) are extracted continuously and without external vacuum generator from a nondisturbed soil volume, through a significant area (typically 600cm2). In order to achieve a minimal disturbance of the native flow regime, the wick type (hydraulic conductivity and section), length and number and the contact area have to be dimensioned to match as close as possible the expected soil pressure/flow conditions. First, the Hydrus 2D code (Simunek et al., 1999) solving the Richards equation for simulating two dimensional unsaturated flow was used to evaluate the uncertainties in flux estimation by such passive capillary samplers. Two sources of uncertainties were examined. Those associated with the theoretical assumptions of the dimensioning of the wick and those associated to experimental uncertainties. A numerical experimentation was conducted on two reference soils submitted to a 11 days actual hyetograph. Results showed that an analytical dimensioning method proposed in the literature is relevant. But significant errors on the observed fluxes occur when the soil and wick properties do not exactly match, which is the common case since the range of available characteristics of fiberglass wicks is limited. Also, uncertainties in the hydraulic conductivity properties of the soil, in wick length appear to have an important influence on the representativity of the wick fluxes against the actual soil drainage fluxes. Elsewhere, eight such samplers have been installed for an in situ long term experimentation ,initiated this year in the Ardière Watershed (France). The objective is to measure water and pesticides percolation fluxes, at a 50cm depth under a grassed strip receiving contaminated runoff. Flow rate and pesticide concentration in surface runoff water are also measured so as to determine the soil boundary condition above each sampler. Soil water content and soil matric potential are measured at three different depth very close to each instrumented profile in order to explain the volumes extracted by each sampler. We present here the experimental methodology and first results obtained with simulated runoff events.

Background, Aims and Scope: Current dredged material disposal alternatives have several limitations. Options for dealing with dredged materials include leaving them alone, capping them with clean sediments, placing them in confined facilities, disposing of them at upland sites, treating them chemically, or using them for wetlands creation or other beneficial uses. The ability to reuse lake-dredge materials (LDM) for agricultural purposes is important because it reduces the need for offshore disposal and provides an alternative to disposal of the materials in landfills. Often these materials can be obtained at little or no cost to the farmers or landowners. Thus, forage production offers an alternative to waste management since nutrients in the LDM are recycled into crops that are not directly consumed by humans. The objective of this study (Part 2) were to: (1) assess dredge materials from Lake Panasoffkee, Florida as a soil amendment to establish bahiagrass (BG) in a subtropical beef cattle pasture in Sumter County, Florida; and (2) determine the effect of LDM application on the crude protein (CP) and nutrient uptake of BG. This series of two papers aims at providing assessment of the efficacy of lake-dredged materials especially its implication to environment (soil quality, Part 1) and agriculture (forage quality and pasture establishment. Part 2). Methods: The experimental treatments that were evaluated consisted of different ratios of natural soil (NS) to LDM: LDMO (100% NS:0% LDM); LDM25 (75% NS:25% LDM); LDM50 (50% NS:50% LDM); LDM75 (25% NS:75% LDM); and LDM100 (0% NS:100% LDM). Bahiagrass plots at its early establishment were cut to a 5-cm stubble height on Julian days 112 and harvested to the same stubble height on Julian days 238 and on Julian days 546 following the double-ring method. Field layout was based on the principle of a completely randomized block design with four replications. Plant samples harvested at 546 Julian days were ground to pass through a 1-mm mesh screen in a Wiley mill. Ground forage was analyzed for crude protein. Ground forage samples were also analyzed for tissue P, K, Ca, Mg, Mn, Cu, Fe, Al, and Mo concentrations using an ICP spectroscopy. The effects of dredged materials addition on forage yield and on crude protein and nutrient uptake that were taken at 546 Julian days were analyzed statistically following the PROC ANOVA procedures. Results and Discussion: Part 1 of this study demonstrated that the heavy and trace metal contents of LDM were below the probable effect levels and threshold effect levels. As such, the agricultural or livestock industry could utilize these LDM to produce forages. Results showed consistently and significantly (p < or = 0.001) higher BG biomass production and CP from plots amended with LDM than those of BG planted on plots with 0% LDM. Forage yield of BG during its establishment increased linearly (Forage Yield = 1724.3 + 25.64*LDM; R2 = 0.83; p < or = 0.0001) with increasing rates of LDM application. The CP of BG also varied significantly with varying levels of LDM applications. The tissues of BG with 100% LDM had the greatest CP content while the lowest CP content was from the control plots (LDMO). The CP of BG increased linearly with increasing rates of LDM application. The crude protein response to BG application can be described by a linear equation: Crude Protein = 10.38 + 0.052*LDM; R2 = 0.85 p < or = 0.0001. Addition of LDM had increased the levels of Ca by about 1811 % when compared with the level of soil Ca among plots with no LDM application. Liming the field could have some direct and indirect effects on the chemical status of the soils. The physiological functions performed by Ca in plants are not clearly defined, but it has been suggested that Ca favors the formation of and increases the protein content of mitochondria. Conclusions: Beneficial uses of dredged materials from LP, Florida are both economical and environmental. Often these materials can be obtained at little or no cost to the farmers or landowners. Results showed that dredged materials can be used as soil amendments (lime and fertilizer) for early establishment of BG in beef cattle pastures. Environmentally, dredging of sediments that are rich in CaCO3 should restore the 19.4-sq km LP by removing natural sediments from the lake bottom to improve the fishery, water quality, and navigation of the lake. The nutritional uptake of BG grown in unfertile sandy soils of Sumter County was enhanced significantly (p < or = 0.001) by LDM addition. Uptake of TKN, TP, K, Ca, and Mg were remarkably increased as a result of LDM. Recommendation and Outlook: Land application of LDM from LP may not only provide substantial benefits that will enhance the environment, community, and society in south Florida, but also in other parts of the world especially those areas with forage-based beef cattle pastures and similar climatic conditions. The heavy and trace metal contents of these materials were below the PEL and TEL (see Part 1). As such, the agricultural or livestock industry could utilize these LDM to produce forages. LDM should be regarded as a beneficial resource, as a part of the ecological system. Although our results have demonstrated the favorable and beneficial effects of added LDM on the early establishment of BG in pasture fields., further studies are still needed not only in pastures of south Florida, but also in other areas with subtropical or tropical climatic conditions to determine whether the environmental and ecological implications of LDM application are satisfied over the longer term.

On s'interroge sur la qualité physico-chimique et biologique de l'eau des rivières en étudiant les zones actives, les flux et biodisponibilité du phosphore (région du lac Léman), les zones actives et production de matières en suspension (Basse-Normandie) et les zones tampons et teneurs en nitrate dans les cours d'eau (Basse-Normandie). | Wonders about the physicochemical and biological quality of the water of the rivers by studying the active zones, flows and biodisponibility of phosphorus (area of the lake Léman), the active zones and production of suspended matter (Low-Normandy) and the buffer zones and nitrate contents in the rivers (Low-Normandy).

On étudie le phénomène de la diminution de la population des salmonidés, dû à la modification de la gestion de l'espace agricole et l'intensification des pratiques culturales, associées à des conditions climatiques et pédologiques particulières.

BACKGROUND, AIM AND SCOPE:Problems of long-term existence of the environmental contaminant 2,4,6-trinitrotoluene (TNT) and necessities for the use of trees ('dendroremediation') in sustainable phytoremediation strategies for TNT are described in the first part of this paper. Aims of the second part are estimation of [14C]-TNT uptake, localisation of TNT-derived radioactivity in mature tree tissues, and the determination of the degree of TNT-degradation during dendroremediation processes. METHODS:Four-year-old trees of hybrid willow (Salix spec., clone EW-20) and of Norway spruce (Picea abies) were cultivated in sand or ammunition plant soil (AP-soil) in wick supplied growth vessels. Trees were exposed to a single pulse application with water solved [U-14C]-TNT reaching a calculated initial concentration of 5.2 mg TNT per kg dry soil. Two months after application overall radioactivity and extractability of 14C were determined in sand/soil, roots, stem-wood, stem-bark, branches, leaves, needles, and Picea May sprouts. Root extracts were analysed by radio TLC. RESULTS:60 days after [14C]-TNT application, recovered 14C is accumulated in roots (70% for sand variants, 34% for AP-soil variant). 15-28% of 14C remained in sand and 61% in AP-soil. 3.3 to 14.4% of 14C were located in aboveground tree portions. Above-ground distribution of 14C differed considerably between the angiosperm Salix and the gymnosperm Picea. In Salix, nearly half of above-ground-14C was detected in bark-free wood, whereas in Picea older needles contained most of the above-ground-14C (54-69%). TNT was readily transformed in tree tissue. Approximately 80% of 14C was non-extractably bound in roots, stems, wood, and leaves or needles. Only quantitatively less important stem-bark of Salix and Picea and May shoots of Picea showed higher extraction yields (up to 56%). DISCUSSION:Pulse application of [14C]-TNT provided evidence for the first time that after TNT-exposure, in tree root extracts, no TNT and none of the known metabolites, mono-amino-dinitrotoluenes (ADNT), diaminonitrotoluenes (DANT), trinitrobenzene (TNB) and no dinitrotoluenes (DNTs) were present. Extractable portions of 14C were small and contained at least three unknown metabolites (or groups) for Salix. In Picea, four extractable metabolites (or groups) were detected, where only one metabolite (or group) seemed to be identical for Salix and Picea. All unknown extractables were of a very polar nature. CONCLUSIONS:Results of complete TNT-transformation in trees explain some of our previous findings with 'cold analytics', where no TNT and no ADNT-metabolites could be found in tissues of TNT-exposed Salix and Populus clones. It is concluded that 'cold' tissue analysis of tree organs is not suited for quantitative success control of phytoremediation in situ. RECOMMENDATIONS AND OUTLOOK:Both short rotation Salicaceae trees and conifer forests possess a dendroremediation potential for TNT polluted soils. The degradation capacity and the large biomass of adult forest trees with their woody compartments of roots and stems may be utilized for detoxification of soil xenobiotics.