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Links between stream reach hydromorphology and land cover on different spatial scales in the Adour-Garonne Basin (SW France) Relations entre l’hydromorphologie de section de cours d’eau et l’occupation du sol à différentes échelles spatiales dans le bassin Adour-Garonne (S-O France)

DOI: 10.1051/kmae/2011031

Keywords: hydromorphology , land cover , spatial scale , Random Forests , stream , échelle spatiale , hydromorphologie , occupation du sol , Random Forests , rivière

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Abstract:

We report an investigation aimed at improving the understanding of the relationships between hydromorphology and land cover, and in particular aimed at identifying the spatial scale on which land cover patterns best account for the hydromorphology at a stream reach. This investigation was carried out in the Adour-Garonne basin. Several key findings emerged from the use of a new modeling procedure called “Random Forests”. Firstly, we established a typology of sites showing an upstream/downstream gradient structured by geographical descriptors and catchment hydromorphological features. Secondly, we found that the relationships between hydromorphology and the different spatial scales of land cover responded to a longitudinal gradient. Upstream, no noticeable difference was observed whatever the land cover pattern considered, whereas downstream, larger scales were strongly related to the hydromorphology. Thirdly, a specific land cover effect on each hydromorphological type was seen. Along the gradient, the contribution of the land cover variables structuring the hydromorphological types decreased and become homogeneous. Fourthly, stronger correlations were established with individual hydromorphological variables using the larger scales of land cover. This paper contributes to a better understanding of landscape ecology and fits well with the European Water Framework Directive that requires long-term sustainable management. In the context of natural conditions, we advise that the catchment scale should be given high priority when connected with land cover/uses; local and riparian environments being more valuable and complementary in the case of impacted sites. Nous présentons les résultats d’une étude destinée à accro tre la compréhension des relations entre l’hydromorphologie d’une portion de cours d’eau et l’occupation du sol, et particulièrement à identifier l’échelle spatiale pour laquelle l’emprise de l’occupation du sol est la plus déterminante. Cette étude a été conduite dans le bassin Adour-Garonne. Plusieurs résultats majeurs ont émergé suite à l’utilisation d’une technique récente de modélisation appelée Ramdom Forests . Premièrement, nous avons mis en évidence une typologie des sites d’étude, montrant un gradient amont/aval, structurée à la fois par les descripteurs géographiques et les caractéristiques hydromorphologiques des bassins. Deuxièmement, nous avons trouvés que les relations entre l’hydromorphologie et les différentes échelles spatiales répondaient également à un gradient longitudinal. Dans les zones amont, aucune différence notables n’

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