Des applications informatiques pour faciliter l'acquisition des données Macrophytes dans les réseaux de surveillance des masses d'eau continentales

International audienceLes macrophytes ont été reconnus élément de qualité biologique mais, pour exploiter au mieux les informations qu'ils fournissent, il convient de mettre en place des outils performants. Quels choix techniques ont été retenus pour rendre ces données les plus pertinentes possibles

Effects of macrophytes on potential nitrification and denitrification in oligotrophic lake sediments

Macrophytes may either stimulate or depress nitrogen-related microbial processes via radial oxygen loss (ROL), production of exudates or uptake of inorganic N. ROL can favor aerobic processes as nitrification, exudates may stimulate denitrification, whereas N assimilation and competition with microbes may depress both processes. We measured rates of potential nitrification (PN) and denitrification (PD) in oligotrophic lacustrine sediments colonized by submersed and emergent macrophytes. Potential rates were also analyzed in adjacent control sediments devoid of vegetation. Aim of the work was to verify if the presence of macrophytes alters the potential activity of nitrifying or denitrifying bacteria. Vertical profiles (0−10 cm depth) of PN and PD rates were measured via oxic (nitrification) and anoxic (denitrification) slurries, where we measured the accumulation of NOx− from added NH4+ and the production of 30N2 from added 15NO3−, respectively. Results suggest that under oligotrophic settings macrophytes produced small effects on potential nitrification and denitrification activities. Despite elevated oxygen release demonstrated for most of the tested macrophytes, nitrification was likely constrained by significant plant-bacteria competition. Potential denitrification was comparatively more stimulated by macrophytes, but we address this result to a general increase of heterotrophic microbial activity in organic-richer vegetated sediments, due to dead root biomass or exudates. The highest PN and PD rates were measured in sediments colonized by Littorella uniflora, likely due to its large underground biomass (root:shoot ratio ∼3.5), root porosity and oxygen leakage

Impact des rejets de l'établissement Manufacture Landaise de Produits Chimiques (MLPC) sur le Luzou

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCACe document fait suite à l'expression des besoins de connaissance de la part de l'Agence de l'Eau Adour-Garonne, concernant l'impact des rejets de la Manufacture Landaise de Produits Chimiques (MLPC) sur le Luzou. Afin de caractériser cet impact, il est prévu d'étudier 4 stations (amont lointain de l'usine, amont proche, aval direct du rejet et aval lointain) du point de vue de leurs caractéristiques physicochimiques, ainsi que du point de vue des communautés de diatomées, macrophytes et macro-invertébrés qu'elles abritent. Les résultats issus des 4 maillons biologiques convergent vers une conclusion unique : l'impact des rejets du complexe MLPC sur le Luzou est très net, et se confirme sur les 4 campagnes