Modifications d'une zone alluviale suite à l'endiguement : approche méthodologique/Evolution of an alluvial flood plain after embanking: a methodological approach

Abstract We compare two methodological approaches with the aim to understand the effects of embankments on soil and vegetation spatial distribution along an alpine river. Modifications will be explained by comparing present conditions (soil, vegetation, geomorphological position) with different situations in the past. Two complementary approaches are being used : first, traditional photo-interpretation allow us to describe variations along the alluvial plain. Second, a GIS enables us to make maps showing the changes in the land use (qualitatively and quantitatively) in time. These maps are useful to identify the current typical situations and to explain the present spatial distribution of soil and vegetation.Résumé Les modifications d'une zone alluviale alpine suite à l'endiguement ont été étudiées en comparant la situation actuelle (sol, végétation et position géomorphologique) avec différentes situations dans le passé. Pour cette reconstitution historique, deux approches complémentaires ont été employées : la première, traditionnelle, basée sur la photo-interprétation, a permis de décrire l'état du site à différentes dates; la seconde, s'appuie sur un SIG et a permis d'établir des cartes montrant les changements (qualitatifs et quantitatifs) du mode d'occupation du sol au cours du temps. Ces cartes sont utiles pour identifier les situations-types actuelles et expliquer la distribution spatiale actuelle du sol et de la végétation.Mendonça Santos Maria de Lourdes, Guenat Claire, Thevoz Corinne, Bureau Fabrice. Modifications d'une zone alluviale suite à l'endiguement : approche méthodologique/Evolution of an alluvial flood plain after embanking: a methodological approach. In: Géomorphologie : relief, processus, environnement, Décembre 1997, vol. 3, n°4. pp. 365-374

The role of vegetation and litter in the nitrogen dynamics of riparian buffer zones in Europe

International audiencePlant uptake and denitrification are considered to be the most important processes responsible for N retention and mitigation in riparian buffers. In many riparian buffers, however, nutrients taken up by plants remain in the system only temporarily and may be gradually released by mineralization later. Still, plants increase the residence time of nutrients considerably by reducing their mobility. We investigated the importance of plant N uptake and N immobilization in litter for N retention in riparian buffers. Nitrogen uptake in vegetation and N dynamics in litter were measured over a two-year period in a range of forested and herbaceous riparian buffers along a climatic gradient in Europe, receiving different loadings of N-enriched groundwater. Plant production, nitrogen uptake, and N retention were significantly higher in the forested buffer sites compared to the herbaceous buffer sites. However, in herbaceous buffers, periodic harvesting of herbaceous biomass contributed considerably to the N retention. No relationship between lateral N loading and plant productivity or N uptake was observed; this indicated that plant growth was not N-limited. In the winter period, decaying leaf litter had a small but significant role in N retention in a majority of the riparian ecosystems studied. Moreover, no responses to the climatic gradient were found. Generally, we can state that annual N retention in the vegetation and litter compartment is substantial, making up 13–99% of the total N mitigation