Testing an integrated river-ocean mathematical tool for linking marine eutrophication to land use: The <i>Phaeocystis</i>-dominated Belgian coastal zone (Southern North Sea) over the past 50 years

The RIVERSTRAHLER model, an idealized biogeochemical model of the river system has been coupled to MIRO, a complex biogeochemical model describing diatom and Phaeocystis blooms in the marine domain, to investigate the link between changing human activities over the past 50 years and coastal eutrophication in the eastern Channel and Southern Bight of the North Sea with a focus on the Belgian coastal zone (BCZ). The whole area, submitted to the influence of two main rivers (Seine and Scheldt) is invaded each spring by massive blooms of Phaeocystis colonies which impact on the structure and functioning of the coastal ecosystem. For the present application MIRO is implemented in a simplified multi-box description of the coastal zone and is run over the last 50 years using average 1989–1999 meteorological conditions (global solar radiance and temperature) and RIVERSTRAHLER simulations of Seine and Scheldt nutrient loads as forcing conditions. Model validation is obtained by visual and statistical comparison of nutrients, Chl a, diatom and Phaeocystis simulations with data collected in the central BCZ (51°26.05 N; 02°48.50 E) over the 1992–1998 period.The simulated Phaeocystis and diatom trends (yearly average and maxima reached) in BCZ, over the past 50 years are discussed with respect to changing nutrient loads, especially NO3 and PO4. Historical reconstruction back to the fifties suggests that Phaeocystis colonies were already blooming in BCZ in the early 1950's and were sharing almost equally with diatoms, the bulk of annual primary production. Over the 1960–1992 period, the increased loads of both N and P were beneficial to both Phaeocystis colonies and summer diatoms with however a little advantage to the latter. Since 1989, the decrease in P loads subsequent to the removal of PO4 in washing powders and the maintenance of elevated NO3 loads had a positive feedback to both diatoms and Phaeocytis production with however a significantly larger impact on diatoms than on Phaeocytis. This is due to the fact that Phaeocystis has strong affinity for low PO4. Consequently Phaeocystis development is mainly controlled by NO3 loads. We conclude that future management of nutrient emission reduction aiming at decreasing Phaeocystis blooms in BCZ without impacting on diatoms would target decrease of NO3 loads by both the rivers Seine and Scheldt

Effects of water soaking and/or sodium polystyrene sulfonate addition on potassium content of foods

In this study, we determined, by atomic absorption spectrophotometry, the potassium amount leached by soaking or boiling foods identified by children suffering from chronic renal failure as "pleasure food' and that they cannot eat because of their low-potassium diet, and evaluated whether addition of sodium polystyrene sulfonate resin (i.e. Kayexalate (R)) during soaking or boiling modulated potassium loss. A significant amount of potassium content was removed by soaking (16% for chocolate and potato, 26% for apple, 37% for tomato and 41% for banana) or boiling in a large amount of water (73% for potato). Although Kayexalate (R) efficiently dose-dependently removed potassium from drinks (by 48% to 73%), resin addition during soaking or boiling did not eliminate more potassium from solid foods. Our results therefore provide useful information for dietitians who elaborate menus for people on potassium-restricted diets and would give an interesting alternative to the systematic elimination of all potassium-rich foods from their diet

Intraparenchymal injection of bone marrow mesenchymal stem cells reduces kidney fibrosis after ischemia-reperfusion in cyclosporine-immunosuppressed rats.

International audienceIschemia-reperfusion and immunosuppressive therapy are a major cause of progressive renal failure after kidney transplantation. Recent studies have shown that administration of bone marrow mesenchymal stem cells (MSCs) improves kidney functional recovery in the acute phase of post ischemia-reperfusion injury. In the present study, we used an original model of renal ischemia-reperfusion in immunosuppressed rats (NIRC) to investigate the effects of bone marrow MSCs on progression of chronic renal failure and the mechanisms potentially involved. Left renal ischemia-reperfusion (IR) was induced in unilateral nephrectomized Lewis rats. After IR, rats were treated daily with cyclosporine (10 mg/kg SC) for 28 days. MSCs were injected into the kidney at day 7 after IR. At day 28 after IR, kidneys were removed for histomorphological, biochemical, and gene expression analysis. The effect of conditioned media from MSCs on epithelial-mesenchymal transition was studied in vitro on HK2 cells. Our results show that, as compared to untreated NIRC rats, rats treated by intrarenal injection of MSCs 7 days after IR displayed improvement in renal function, reduction of interstitial fibrosis, and decrease in chronic tubule injury. These effects were associated with a decrease in interstitial α-SMA accumulation and MMP2 activity, markers of fibroblast/fibroblast-like cell activation, and renal remodeling, respectively. Finally, experiments in vitro showed that MSC-conditioned medium prevented epithelial-mesenchymal transition induced by TGF-β in HK2 cells. In conclusion, our results show that, in immunosuppressed animals, a single intrarenal administration of MSCs reduced renal fibrosis and promoted the recovery of renal function

Seuils physico-chimiques dans la distribution des espèces de poissons dans les plans d'eau français

International audienceThe management of lakes requires the definition of physico-chemical thresholds to be used for ecosystem preservation or restoration. According to the European Water Framework Directive, the limits between physico-chemical quality classes must be set consistently with biological quality elements. One wayto dothis consists in analyzing the response of aquatic communitiesto environmental gradients across monitoring sites and in identifying ecological community thresholds, i.e. zones in the gradients where the species turnover is the highest. In this study, fish data from 196 lakes in France were considered to derive ecological thresholds using the multivariate method of gradient forest. The analysis was performed on 25 species and 36 environmental parameters. The results revealed the highest importance of maximal water temperature in the distribution offish species. Otherimportant parametersincluded geographical factors, dissolved organic carbon concentration and watertransparency, while nutrients appearedto havelowinfluence. In spite ofthe diversity of species responses to the gradients, community thresholds were detected in the gradients of the most important physico-chemical parameters and of total phosphorus and nitrate concentrations as well. The thresholds identifiedin such macroecological studymay highlight new patterns of species natural distribution andimprove niche characterization. Moreover, when factors that may be influenced by human activities are involved, the thresholds could be used to set environmental standards for lake preservation.La gestion des plans d'eau nécessite la définition de seuils physico-chimiques pour la préservation ou la restauration des écosystèmes. Selon la Directive Cadre européenne sur l'Eau, les limites de classes de qualité physico-chimiques doivent être fixées en cohérence avec les éléments de qualité biologique.Une façon de faire consiste à analyser les réponses des communautés aquatiques aux gradients environnementaux formés par les sites de monitoring et d'identifier des seuils écologiques de communautés, c'est-à-dire des zones dans les gradients où le turnover des espèces est le plus important. Dans cette étude, les données de pêches provenant de 196 plans d'eau ont été considérées pour rechercher des seuils écologiques avec la méthode de gradient forest. L'analyse a porté sur 25 espèces avec 36 paramètres environnementaux. Les résultats ont révélé que la température maximale était le facteur le plus important dans la distribution des espèces de poissons. Les autres paramètres importants étaient les facteurs géographiques, la concentration en carbone organique dissous et la transparence de l'eau alors que les nutriments semblaient avoir peu d'influence. Malgré la diversité de réponses des espèces aux gradients, des seuils de communautés ont été détectés dans les gradients des paramètres physico-chimiques les plus importants ainsi que dans ceux des concentrations en phosphore total et en nitrates. Les seuils identifiés dans une telle étude macroécologique peuvent faire apparaître de nouveaux patrons de distribution naturelle des poissons et améliorer la caractérisation des niches spécifiques. De plus, quand des facteurs influencés par les activités humaines sont impliqués, ces seuils pourraient être utilisés pour fixer des limites pour la protection des plans d'eau

Utilisation du biofilm comme indicateur fonctionnel pour la caractérisation et la surveillance des cours d'eau : développement et validation de dispositifs de détection et de mesure de la croissance de biofilms in situ (capteurs biofilms)

Les biofilms de rivière constituent un modèle de biofilms original intégrant une forte composante de microorganismes photosynthétiques. Comme d'autres, ce modèle a permis d'explorer les propriétés des biofilms (dynamique de colonisation, relation avec l'hydrodynamique) et doit continuer à alimenter les recherches actuelles sur les biofilms et les organismes qui les composent (électro-activité, ). Leur étude peut s'enrichir des techniques développées pour d'autres biofilms (capteurs, mesure d'épaisseur) comme nous l'avons constaté dans le cadre de ce projet. Pour plusieurs raisons, ces biofilms peuvent représenter des outils d'évaluation de la qualité de la rivière et d'aide à la décision en matière de gestion. Par exemple, au cours de leur développement, à l'interface entre l'eau et le lit de la rivière, ces biofilms intègrent des flux d'eau et d'éléments dissous importants. Dans le cas de contaminants toxiques organosolubles, leur accumulation peut notamment se produire dans la matrice d'exopolymères extracellulaires. Les microorganismes du biofilm sont alors localement exposés à des concentrations plus fortes en toxiques. La mise en oeuvre de descripteurs, comme la présence d'individus déformés par l'action tératogène du toxique, permet une détection précoce de la présence de toxiques dans un système aquatique. Au niveau des populations, les espèces de diatomées, organismes constitutifs du biofilm à un endroit donné reflètent la qualité du milieu. Des indices (IPS, DAIPo,) basés sur la composition de l'assemblage de diatomées permettent d'évaluer cette qualité de façon relativement représentative d'un cours d'eau à l'autre. A l'échelle du biofilm enfin, les flux d'éléments dissous, nutritifs ou contaminants, ont un impact sur la vitesse de colonisation du support. La mesure de cette vitesse d'accrétion peut donc constituer un indicateur de la qualité du milieu signalant certaines atteintes au milieu comme l'eutrophisation ou une contamination. Ceci justifie la recherche de moyens de détection automatisés du développement de ces biofilms qui sont à la fois témoins et acteurs du fonctionnement de la rivière, afin de progresser vers l'acquisition d'un outil de surveillance de l'état de santé des rivières

Modelling phytoplankton succession and nutrient transfer along the Scheldt estuary (Belgium, The Netherlands)

The freshwater (RIVE) and the marine (MIRO) biogeochemical models were coupled to a 1D hydro-sedimentary model to describe contemporary phytoplankton succession and nutrient transfers in the macrotidal Scheldt estuary (BE/NL) affected by anthropogenic nutrient loads. The 1D-RIVE-MIRO model simulations are performed between Ghent and Vlissingen and the longitudinal estuarine profiles are validated by visual and statistical comparison with physico-chemical and phytoplankton observations available for the year 2006. Results show the occurrence of two distinct spatial phytoplankton blooms in the upper and lower estuary, suggesting that neither the freshwater nor the marine phytoplankton gets over the maximum turbidity zone (MTZ) at the saline transition. Sensitivity tests performed to understand how changing conditions (salinity, turbidity and nutrients) along the estuary are controlling this bimodal spatial phytoplankton distribution identify salinity and light availability as the key drivers while the grazing pressure and nutrient limitation play a negligible role. Additional tests with varying salinity-resistant (euryhaline) species in the freshwater assemblage conclude that the presence (or absence) of euryhalines determines the magnitude and the spreading of freshwater and marine phytoplankton blooms in the estuary. Annual nutrient budgets estimated from 1D-RIVE-MIRO simulations show that biological activities have a negligible impact on nutrient export but modify the speciation of nutrients exported to the coastal zone towards inorganic forms, thus directly available to phytoplankton. The implementation of nutrient reduction options (upgrading of waste water treatment plants, conversion to organic farming) on the Scheldt watershed influences the whole estuary and affects both the magnitude and the speciation of nutrients exported to the coastal zone with expected impact on coastal phytoplankton dynamic. © 2012 Elsevier B.V.SCOPUS: ar.jinfo:eu-repo/semantics/publishe