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In estuarine water, the knowledge of the resources bioavailability is indispensable for understanding phytoplankton dynamics. For assessing nitrogen and phosphorus bioavailability, algal bioassays are the most indicated. Nutrient limitations of an alga exhibit a threshold rather than an additive or a multiplicative response (ELRIFI et al., 1985). In contrast, numerous nutrient limitations are described for an algal population (TILMAN,1982).Samples are taken monthly at 1 meter's depth from two French river estuaries, Noyalo River and Vannes River, in the Morbihan Gulf from April to July. Main physico-chemical measures (temperature, salinity, nitrate, nitrite, ammonia, total nitrogen, reactive phosphorus and total phosphorus) were taken. Total soluble nitrogen and total soluble phosphorus concentrations were determined after filtration en 0,2 µm, for comparison with bioassays. In addition two kinds of batch bioassays with 250 ml erlenmeyers into controlled environment (17 °C and 180~200 µEinstein), were employed :- Estuarine waters filtered on 200 µm, to remove most of the zooplankton, were enriched with sodium nitrate and/or dipotassium hydrogen phosphate. Algal Growth response, was recorded by fluorescence « in vivo », against a blank.- With the total growth on sterilely filtered (0,2 µm) estuarine waters of two test algae, starved simultaneously in phosphorus and nitrogen in artificial sea water, it was possible to determine the bioavailability of these two elements in the soluble traction. The cellular density of the two test algae : Fragilaria elliptica Schumann and Phaeodactylum tricornutum Bohlin, was related to optical density measures at 750 nm. Nitrogen and phosphorus intracellular concentrations, in the whole culture at the end of the growth, gave their bio-availability for the test algae provided. Nitrogen and phosphorus cell quotas, intracellular concentration per cell, were then compared with their higher and lower cell quotas. Higher and lower cell quotas were measured at the end of the test algae growth in an artificial medium without phosphorus or nitrogen resources. They were similar to those described by DAUTA (1982).In 1989, an exceptional drought reduced the river flow. Consequently, nutrient flux decreased and phytoplankton density, mainly diatoms, was reduced to between 100 and 800 cells/ml. Sea water dominated in the Morbihan Gulf with salinities higher Chan 30 %o.First, waters filtered on 200 µm and added to which was nitrate and/or phosphate revealed a nitrogen limitation of natural phytoplankton.Secondly, phosphorus limitation were found in bioassays on sterilely filtered waters, in all the test algae starved for phosphorus and nitrogen. At the end of the growth in bioassays, phosphorus cell quotas of the test algae were generaly similar to the lower ones. The growth of the tests algae was limited by that resource.These contrary results are related to the intracellular storage by the natural phytoplankton and/or the major role of particulate fractions in phosphorus bioavailability.Phosphorus and nitrogen concentrations assimilated by the test alga : Fragilaria elliptica, were inversely related. From May to July 1989 the results showed a simple linear relation between soluble nitrogen source (filtered on 0.2 µm) which was bioavailable for the test alga and natural phytoplankton density (R2 = 0.98). The two measurements of April did not agree with the latter relation, rather because of environmental factors such as temperature (11 °C against 20~21 °C for the next ones), than because of the resources. Moreover, the station B in July exhibited a natural phytoplankton density significantly lower than the station A and independent of the nitrogen bioavailability for the two test algae. The bioavailable phosphorus for Phaeodactylum tricornutum, was also significantly lower at station B. That resource can explain the difference in density monitored in July.The total soluble nitrogen source, inorganic and organic, and just a fraction of the total soluble phosphorus source, were assimilated. The soluble phosphorus assimilated by test algae, after sterile filtration, is not the total bioavailable phosphorus in the water of the Morbihan Gulf and seems to be inversely related to the natural phytoplancton density. A part from mineral phosphorus adsorbed on suspended matter is also bioavailable (BERLAND et al., 1973). However, for the phosphorus resource, bioassays have to be performed on particulate fractions.
Keywords: Phytoplancton, estuaire, bioessais, azote, phosphore, biodisponibilité, Phytoplankton, estuary, bioassays, nitrogen, phosphorus, bioavailabitity
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First climate change effects, especially in the coastal zone, stress the adoption of a long term strategy at all decision levels. Even if disruptions are unavoidable, there are still doubts concerning their extent and local effects. They will partly depend on our reaction capacities, especially concerning the mitigation of greenhouse gas emissions. Even quite recently perceived as distant and hypothetical, gradually the phenomenon is beginning to take shape.The increasing concern of local collectivities is stressed by its context: international (United Nations Framework Convention on Climate Change and Kyoto Protocol), european (climate energy package) and national (Grenelle de l'environnement). In France, their willingness of action can become concrete through a specific tool, the territorial climate plan. But, the cross-cutting feature of the subject overflows this framework. The Bretagne region strongly integrate climatic concern especially in the Morbihan gulf regional natural parc project and in its energy plan. Strategies developed in those texts are elaborated following the building of climate stakes at local level. Dispositions adopted at local level aim essentially to mitigate greenhouse gaz emissions but adaptation measures begin to appear. Those strategies are the result of a cautiousness approach which optimize chances of success in front of a new stake with a lot of uncertainties.
Keywords: changements climatiques, gouvernance, collectivités locales, environnement, incertitude, droit, climate change, governance, local authorities, environment, uncertainty, law
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In response to the increasing demand from the food industry for fresh produce, many farms located in the administrative county of Morbihan (Brittany, France) have intensified their vegetable crop production (e.g. peas, beans, spinach) due to their high value. To obtain the best yields and to respect contracts signed with industrial partners, irrigation has been widely used by the farming community to support this production. Since 1989, 500 to 600 ha/year of irrigated farmland have been developed with financial support from state, regional and county agencies. The official purpose of this financing program is to irrigate 50% of the fields cultivated for vegetable crops. Water use for irrigation was estimated to be 6 million m3 in 1999. The demand for irrigation coincides with the period of low water levels in the stream. Thus, there is strong competition with drinking water demands and ecological flow requirements. Moreover, the potential use of groundwater to fulfill these demands is not possible. One of the solutions is to build small headwater dams to store winter flows and use this resource during the growing season. In order to help local public authorities assess their strategy, we need to develop a robust quantification method to study the impact of this development.The 302 km2 Yvel watershed is the site of a highly developed region of small headwater dams because the geological substratum is composed mainly of schist with low groundwater reserves, precipitation is less than the regional average, and the industrial demand for vegetable crops is high. For all these reasons, this watershed is particularly vulnerable. Moreover, from a regional policy point of view, the downstream part of the watershed is located within the Morbihan county whereas the upstream part is located within the Côtes d'Armor and Ille et Vilaine counties, which do not provide any financial support for irrigation development. The current concentration of headwater irrigation dams reflects these regional development incentives as dams are mostly built in the downstream part of the watershed.To study the impact of small headwater dams on watershed hydrology, we propose a conceptual tool built around a geomorphological instantaneous unit hydrograph (GIUH) modelling approach. The GIUH structure, which is based on the effective watershed normalized area function and an estimated mean flow velocity, allows for the explicit accounting of dams and, and thus, can be used for a priori assessment studies. It can also be used in a semi-distributed perspective, where spatial discretization is determined from rainfall variabilities instead of gauging station constraints. These two points allowed us to study three regional irrigation development scenarios: construction of 100, 200 and 300 future headwater irrigation dams. Using two observed rainfall events, we showed that the simulated hydrograph shape at the watershed outlet can be significantly modified. In conclusion, in situ observations and simulation results suggest that : (1) headwater dams do not have any impact when reservoirs are full - lamination is locally observed and thus, does not have any impact on the watershed hydrograph; (2) a spatially homogeneous implementation of headwater dams modifies the watershed hydrograph according to a contributing watershed area ratio; similar behaviour is observed for low water level periods; and (3) localized implementation can be studied through modelling with enough precision to give relevant information to decision makers.
Keywords: Retenues collinaires, scénario prospectif, hydrogramme unitaire géomorphologique, modèle pluie-débit semi-distribué, Headwater dams, prospective scenario, geomorphological unit hydrograph, semi-distributed rainfall runoff model
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In Morbihan, a department in the French region of Brittany, there are many “self” discovery practices involving the local megaliths. The schemes offered by these practices are thought to allow the practitioner to develop new relationships between the “self and self” and the “self and the other” by using their body and senses as factors essential to a personal transformation. At the heart of these practices, participants are invited to engage in a sensorial learning journey and cultivate their bodily attention by concentrating on their body and their sensations when they approach the megaliths and touch them. In this article, I analyze the somatic learning and personal transformation processes at the heart of these practices. More precisely, I focus on the three elements that account for the effectiveness of the practices and build the experience of the participants: the progressive learning of a sensorial language, the interpretation of somatic imagery, and the execution of bodily techniques. My theoretical reflections on these elements highlight the mechanisms that make these practices a continuum where “spiritual” experiences manifest as somatic experiences.
Keywords: expérience somatique, technique corporelle, spiritualité, transformation identitaire, Morbihan, Somatic experience, bodily technique, spirituality, identity transformation, Morbihan
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Keywords: oeuvre robotiques