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Déterminants spatio-temporels de la qualité des cours d’eau dans un contexte de déprise et de changement des activités : rôle possible des facteurs du passé

Abstract : Human activities have been continuously affecting natural ecosystems functioning during the Holocene and it actually have an impact at a global scale. There is particular concern over the integrity of freshwater ecosystems, however local past activities can also still impact these ecosystems and are rarely considered for the management of streams. The headwater streams especially, whose functioning is based on terrestrial organic matter inputs, are sensitive to human uses of neighboring lands, and so may be actually affected by stresses of historical origin. It seems pertinent to identify such effects of past activities on freshwater ecosystems and to understand the mechanisms involved in these processes. During this thesis project we conducted a prospective in situ study, to determine the influence of the legacy of potential historical activities on the current ecological quality of headwater catchment streams. We combined an approach of historical ecology of landscapes (anthracology, study of old maps, …) with a study of biotic and abiotic parameters of streams. The first approach aimed to study the woodland composition of last centuries and to georeference old human uses (deforested areas, charcoal production sites, homes, ponds, …). The second aimed to determine the integrity of stream by multiparametric analyses. The results of this study, realized on forested catchments of northern Vosges mountains, revealed that the streams which are situated in a low-impacted landscape, globally have a good ecological quality. Some ponds with different ages have an impact on the composition of aquatic macroinvertebrates communities and deviation to good ecological state, maybe due to urban pollutions or acidic rainfalls. Nevertheless the exploitation of forest for the production of wood charcoal until the beginning of XXth century lead to the creation of thousands of charcoal production sites (CPS) that affect the availability of phosphorus both in environment. Moreover, woodland dynamic seems to have been conditioned by the sylviculture, leading to a higher proportion of coniferous species today than in the past (before the beginning of charcoal production). These aspects lead us to believe that human activities have been influencing organic matter inputs into streams. We can conclude that the historical building of ponds and the charcoal production in these woodlands have an influence on actual characteristics of streams, in parallel to modern stresses. Thus, this project open strong lines of research about the nutrients fluxes in aquatic and terrestrial ecosystems under the influence of charcoal production sites. This could help us to better understand the impact of this activity across history.
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Submitted on : Saturday, October 17, 2020 - 11:48:05 AM
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David Gocel-Chalte. Déterminants spatio-temporels de la qualité des cours d’eau dans un contexte de déprise et de changement des activités : rôle possible des facteurs du passé. Sciences de l'environnement. Université de Lorraine, 2020. Français. ⟨NNT : 2020LORR0094⟩. ⟨tel-02970022⟩

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