The role of organisms in hyporheic processes : gaps in current knowledge, needs for future research and applications

Fifty years after the hyporheic zone was first defined (Orghidan, 1959), there are still gaps in the knowledge regarding the role of biodiversity in hyporheic processes. First, some methodological questions remained unanswered regarding the interactions between biodiversity and physical processes, both for the study of habitat characteristics and interactions at different scales. Furthermore, many questions remain to be addressed to help inform our understanding of invertebrate community dynamics, especially regarding the trophic niches of organisms, the functional groups present within sediment, and their temporal changes. Understanding microbial community dynamics would require investigations about their relationship with the physical characteristics of the sediment, their diversity, their relationship with metabolic pathways, their inter- actions with invertebrates, and their response to environmental stress. Another fundamental research question is that of the importance of the hyporheic zone in the global metabolism of the river, which must be explored in relation to organic matter recycling, the effects of disturbances, and the degradation of contaminants. Finally, the application of this knowledge requires the development of methods for the estimation of hydro- logical exchanges, especially for the management of sediment clogging, the optimization of self-purification, and the integration of climate change in environmental policies. The development of descriptors of hyporheic zone health and of new metrology is also crucial to include specific targets in water policies for the long-term management of the system and a clear evaluation of restoration strategies

ESTIMKART: plate-forme de modèles sur SIG pour la gestion écologique des débits à large échelle. Simulations et interprétation des premiers résultats sur le bassin Rhône-Méditerranée. Cemagref- Agence de l'eau RM&C

[Departement_IRSTEA]MA [TR1_IRSTEA]QSA / HYDRECOLe projet prospectif Estimkart a été réalisé dans le cadre de l'accord cadre entre l'agence de l'eau RM&C et le Cemagref (2005-2008). Il a permis le développement d'une plate-forme de modèles pour la gestion des débits à large échelle. L'outil est actuellement opérationnel, documenté (Lamouroux et al. 2008), installé chez les partenaires scientifiques du projet et à l'agence de l'eau RM&C. Une suite nationale est engagée, coordonnée par l'Onema. L'outil Estimkart est décrit par ailleurs (Lamouroux et al. 2008). En résumé, il s’agit d’une plate-forme de données et de modèles cartographiés d'aide à la décision pour la gestion du réseau hydrographique à l'échelle nationale, implantée sous forme d'outil ArcGis. Les données et modèles intégrés dans Estimkart permettent de naviguer sur le réseau hydrographique pour visualiser un certain nombre de grandeurs hydrauliques et écologiques ainsi que leurs incertitudes. La version actuelle couple quatre types de modèles (modèles hydrologiques, modèles hydrauliques, modèles d'habitat physique pour les poissons, modèles de peuplements de poissons en place théoriques). Les modèles sont appliqués sur chaque arc du réseau de bassin afin de répondre à divers objectifs de gestion des débits

Le bacterioplancton Campagne 1986

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Le bacterioplancton du Leman - Campagne 1988

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Contribution of mathematical modeling to lake ecosystem understanding: Lake Bourget (Savoy, France)

This paper demonstrates how mathematical modeling can contribute to improve understanding of lake behavior. Since the 60's Lake Bourget, one of the largest in France, had been suffering from eutrophication which was checked in 1980 by the diversion of the main sewers entering the lake. A research program was implemented between 1987 and 1990, including an on-site sampling campaign conducted concurrently with thermal and biogeochemical modeling of lake behavior. The model helped provide a better understanding of the ecosystem, displaying some processes hitherto misunderstood: (1) Winter overturn does not reach the bottom of the water column when the weather is mild. This leads to a incomplete reoxygenation of the hypolimnion and to redox conditions inducing the release of orthophosphate from the sediment, (2) Grazing by herbivorous zooplankton is getting more important in the control of spring algal growth as eutrophication of the lake regresses, (3) Settling of particulate phosphorus seems a complex and very important process in Lake Bourget, showing high sedimentation rates for particulate mineral phosphorus