This study aimed at comparing toxic element (Hg, Cd) bioaccumulation in relation to age for bottlenose (Tursiops truncatus) and striped dolphins (Stenella coeruleoalba) from Mediterranean and Atlantic waters. Metal concentrations were also measured in selected prey to infer metal exposure through the diet. As expected, Mediterranean prey exhibited the highest Hg levels, probably as a consequence of the Hg enrichment of the Mediterranean Sea. Comparing the predators from each area and taking age into account, Mediterranean bottlenose dolphins displayed higher Hg levels than Atlantic dolphins (p = 0.032), whereas Mediterranean striped dolphins did not (p = 0.691). The consumption of Myctophid fish, which showed the highest Hg levels (105 +/- 80 ng g(-1) w.wt.) among Atlantic prey, may explain the high Hg levels in the liver of the Atlantic striped dolphins and suggested a preferential offshore feeding behaviour in this area. Concerning Cd, no clear differences were found between geographical areas. (c) 2006 Elsevier Ltd. All rights reserved.

[Departement_IRSTEA]MA [TR1_IRSTEA]TED / EPURE | The constraints on sanitation in Mayotte, a small French island with a tropical climate in the straight of Mozambique are strong: The interior landscape is rugged with seep slopes, a dense and very rapidly increasing population lives mostly along the coastline, where space for human activity becomes scarce. Yet, the generalization of access to tap water on a household or community level immediately created a need for sanitation programs. Because of the size of the plots and the nature of the subsoil however, onsite sanitation is often impossible and centralized sewerage systems not affordable in the near future. The most appropriate solutions seem to be decentralized low maintenance treatment systems of a capacity of a few hundred person-equivalent, which can be build using mostly local resources, do not require high technical expertise and have low running costs. In order to meet these challenges, SIEAM, the local syndicate which will operate all sewage treatment equipment on the island, asked for expert back-up from Cemagref and asked SINT to design two pilot plants using constructed wetlands. The first constructed wetland plant consists of an Imhoff tank followed by a sub-surface horizontal flow filter with local filter material; divided in three compartments, each planted with different local plants. The second plant is a local adaptation of the type of vertical flow systems working with raw sewage, like the one SINT designs and constructs in Europe. Because sand for a second stage vertical filter is not found on the island, a design with a single stage filter with recirculation was chosen. Both pilot plants are working very well, but in order to optimize dimensioning and to reduce the required surface area, they will have to be tested under higher loadings. | Les contraintes de l'assainissement à Mayotte, une petite île dont le climat est tropical dans le canal du Mozambique, sont fortes: la topographie est très pentue, une population dense et croissant rapidement vit le long de la côte où les espaces pour les activités humaines sont réduits.

To improve total nitrogen removal, a full-scale experimental study was conducted on a hybrid constructed wetlands plant designed for 100 p.e.. The plant composed of a 1st stage of vertical filters (fed with raw wastewater) followed by a 2nd stage of horizontal filters was monitored over one year measuring hydraulic conditions, physico-chemical conditions, gas emission, oxygen of the gas phase and regular treatment performances by 24 h composite samples. Different vertical filter configurations (media depth, intermediate and passive aeration system) were tested as well as two horizontal filter designs. The N removal is discussed on efficiency of each stage in relation to the season and the load applied. This study leads to draw the limit of the plant configuration and gives some design avenues of hybrid systems to reach high and regular level of nitrogen removal with acceptable surface area per person.

Within the scope of studying the hydraulic behaviour of vertical-flow wetland in order to model these systems, differential pressure transducers were used on experimental vertical sand columns to understand the effects of a batch feed on the gaseous and hydraulic phases. Three transducers were set up at three different depths in the column. The system operates in a batch mode. Two types of flow regime were tested. The first one consists of one batch of 10 litres every 8 hours. In this regime, the transducer signal shows four consecutive phases: the influence of the water head on the top of the filter and the infiltration of the batch inside the filter that both increase the pressure, the drainage of the pores that decrease the pressure to a depression and finally the aeration of the pores that restore the pressure to atmospheric pressure. For the second flow regime (a batch of 4 litres every 3 hours) the same consecutive steps are present except the infiltration of the batch. In addition, the drainage and the aeration of the pores are simultaneous over the entire depth of the column and are incidental to the end of the surface dewatering. This is not the case for the first regime where occurrence of those steps depends on the depth. In addition to the understanding of the different steps occurring when a batch volume percolates, those measurements provide useful information on the saturation of the media, the rate of drainage and aeration of the pore, the gas flow, the infiltration rate.

[Departement_IRSTEA]MA [TR1_IRSTEA]TED / EPURE | To improve total nitrogen removal, a full-scale experimental study was conducted on a hybrid constructed wetlands plant designed for 100 p.e.. The plant composed of a 1st stage of vertical filters (fed with raw wastewater) followed by a 2nd stage of horizontal filters was monitored over one year measuring hydraulic conditions, physico-chemical conditions, gas emission, oxygen of the gas phase and regular treatment performances by 24 h composite samples. Different vertical filter configurations (media depth, intermediate and passive aeration system) were tested as well as two horizontal filter designs. The N removal is discussed on efficiency of each stage in relation to the season and the load applied. This study leads to draw the limit of the plant configuration and gives some design avenues of hybrid systems to reach high and regular level of nitrogen removal with acceptable surface area per person.

International audience | Les changements de productivité des forêts ont été étudiés intensément à partir des années 1990, à la suite des événements relatifs au dépérissement des forêts européennes. Dans cette contribution, on analyse les problèmes méthodologiques soulevés par ce type d'étude, les sources de données disponibles pour l'analyse, et les éléments de diagnostic acquis sur plusieurs espèces forestières du territoire français. Les implications pour le cadre théorique qui prévalait dans les années 1980 concernant la productivité des peuplements forestiers sont enfin discutées. problèmes méthodologiques, sources de données, cadre théorique, éléments du diagnostic

[Departement_IRSTEA]MA [TR1_IRSTEA]TED / EPURE | Within the scope of studying the hydraulic behaviour of vertical-flow wetland in order to model these systems, differential pressure transducers were used on experimental vertical sand columns to understand the effects of a batch feed on the gaseous and hydraulic phases. Three transducers were set up at three different depths in the column. The system operates in a batch mode. Two types of flow regime were tested. The first one consists of one batch of 10 litres every 8 hours. In this regime, the transducer signal shows four consecutive phases: the influence of the water head on the top of the filter and the infiltration of the batch inside the filter that both increase the pressure, the drainage of the pores that decrease the pressure to a depression and finally the aeration of the pores that restore the pressure to atmospheric pressure. For the second flow regime (a batch of 4 litres every 3 hours) the same consecutive steps are present except the infiltration of the batch. In addition, the drainage and the aeration of the pores are simultaneous over the entire depth of the column and are incidental to the end of the surface dewatering. This is not the case for the first regime where occurrence of those steps depends on the depth. In addition to the understanding of the different steps occurring when a batch volume percolates, those measurements provide useful information on the saturation of the media, the rate of drainage and aeration of the pore, the gas flow, the infiltration rate.

An efficient way for assessing the nutrient status of an ecosystem is the establishment of nutrient input-output mass balance budgets at the catchment scale. For example, outputs (i.e. losses in streamwater, through havesting etc.) greater than inputs (i.e. weathering, dry and wet deposition, fertiliser) indicate that a depletion of the given element is taking place. In forest ecosystems, element input via throughfall is an important pathway in nutrient cycling. Precipitation interacts with the stand canopy, resulting in increased/decreased solute inputs to the forest floor. For example, acid deposition (H, N) may be substantially increased through the filtering action of the tree canopy. Indeed, canopy throughfall chemical composition includes wet deposition (rainfall), dry deposition intercepted by the canopy and elements leached from the foliar tissue (canopy leaching). Moreover, interactions between canopy and atmosphere or precipitation depend on several factors such as: season, tree species and physiology, stand structure and health. However, canopy leaching results from an internal nutrient cycling process. Ignoring this component in throughfall measurements thus leads to an overestimation of the inputs to the ecosystem. In this paper, main results of studies performed in the Belgian Ardennes at the watershed (80 ha) and plot scale are summarised. The aim of this research was to quantify long-term nutrient budgets in a forested watershed, within a context of sustainable management. In this area, soils are naturally acidic and poor in magnesium, so that forest dieback symptoms reported from 1983 onwards were related to increased pollution exacerbating magnesium deficiency. There is concern that acid (S and N) deposition, together with sylvicultural management (harvesting, spruce monocultures etc.) could deplete the available cation pool and that soils would not be able to support intensive sylviculture on the long term. We measured concentrations and fluxes of major ions in bulk deposition, throughfall and stream water over 13 years. Throughfall deposition under coniferous (Picea abies (L.) Karst.) and several deciduous tree species was also compared. A canopy budget method was used for distinguishing between external (dry deposition) and internal (canopy leaching) sources of ions in the throughfall flux. The contribution of canopy leaching in throughfall measurements and consequences for mass balance calculations will be discussed. Furthermore, nutrient fluxes through the ecosystem will be examined with regard to the long term nutrient status of the system.

[Departement_IRSTEA]MA [TR1_IRSTEA]TED / EPURE | With the aim of improving the WSP effluent quality, different types of Vertical Flow Constructed Wetlands and Intermittent Sand Filters were tested in a pilot plant in Aurignac (France). The effectiveness of each design for upgrading the effluent from the pond was studied over a period of two years. Physicochemical parameters were monitored by taking composite samples over 24 hours and weekly punctual samples. The hydraulic behaviour of the filters was studied by tracing methods (using NaCl) and monitoring the infiltration rate. This paper describes the influence of: (a) the characteristics of the medium (presence of Phragmites, depth, type of sand), (b) feeding modes and (c) the presence of an algae clogging layer on the performance of the beds. Overall, both Vertical Flow Constructed Wetlands and Intermittent Sand Filters are appropriate systems for retaining algae, completing organic matter degradation and nitrifying the WSP influent. The design and operation bases, the hydraulic behavior and the advantages and disadvantages (in terms of efficiency and maintenance) of the different configurations were determined.