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Submerged aquatic weeds may colonize freshwater shallow lakes by forming dense mats: when this occurs, their invasion interferes with human activities and generates several impacts on aquatic processes. In this paper, we present the preliminary results of an investigation concerning the dissolved gas and nutrient dynamics within a bed of Egeria densa Planch. in a bay of Lacanau Lake (southwestern France). Two 24-h cycles were carried out during summer and autumn 2013, for the measurement of dissolved oxygen (O2), carbon dioxide (CO2), methane (CH4) and dissolved inorganic nitrogen (DIN). Our results show that Egeria densa seasonal dynamics might strongly influence the colonized area: during summer, steady levels of O2 (O2 > 0.15 mm) were coupled to the macrophyte photosynthetic activity, while during autumn respiration processes were mostly pronounced (0.02 mm < O2 < 0.25 mm). High concentrations of CH4 (0.6–53.9 μm) and CO2 (0.03–0.83 mm) were measured within the bed during both sampling campaign...

Resume Les communautes de macrophytes des lacs medocains (lac de Carcans-Hourtin et lac de Lacanau) ont fait l’objet en 2011 d’observations et de prelevements sur la totalite de la peripherie des rives, ainsi que sur des profils perpendiculaires vers le large de ces plans d’eau. Les communautes vegetales aquatiques comportent diverses especes communes aux milieux lacustres, ainsi que des especes patrimoniales, telles que les especes des pelouses a littorelles, mais egalement des especes exotiques a caractere envahissant. Les Characees sont bien representees sur les lacs medocains. Chara fragifera colonise les deux tiers du lineaire des rives sur les deux lacs, jusqu’a une profondeur de 4,5 m sur le lac de Carcans-Hourtin. Nitella confervacea est moins abondante et moins frequente, elle semble cependant coloniser les secteurs plus profonds des lacs. La repartition de ces deux especes sur les rives des lacs est relativement homogene, les especes n’ont pas ete observees dans les secteurs d’anses protegees de...