Alterations and changes that affect the conservation of the biodiversity of Estanho de Vilac (Aran Valley)

E. Carrillo, J. Ninot, T. Buchaca and M. Ventura. Blanes, LIFE+ LIMNOPIRINEUS Technical OfficeEstanho de Vilac is located in a small endorheic basin in the Aran Valley (Catalonia) at an altitude of 1640 m. Originally, it was a small pond of fluctuating level, but due to livestock interests it was recreated with an external water supply. In recent years, with the modification of the bed and the continuous increase in the volume of water accumulated, it has also been used for trout fishing. As a result of these modifications, there has been a notable alteration of the system jeopardising the conservation of various amphibian species, especially Alytes obstetricans and Rana temporaria, as well as Luronium natans, an aquatic plant that throughout the Pyrenees can only be found in this lake. All three are species protected at European level by the Habitats Directive. The aim of this work is to improve the conservation status of these species and the ecosystem as a whole. For this, a study of the water cycle has been conducted, calculating the water balance of the basin and the changes in level caused by altering the inlet of artificial water have been monitored; the variability of the nutrient cycle and of the aquatic biodiversity and especially of the indicator organisms has been studied. The results show that Estanho is a temporary pond that could remain dry for some time during the summer, but that a water supply that exceeds the natural loss values can continuously increase the volume of water that it would have without external alterations. It is also noted that the presence of trout has significantly altered the diversity of fauna in the body of water and this also affects amphibian populations. In addition, the presence of a large number of equine cattle causes eutrophication of the water, as well as the disturbance of the population of Luronium natans and the integrity of the substrate where it grows. This population is also affected by the entry of Potamogeton berchtoldii, a water-based macrophyte common to alpine lakes. The actions carried out to reverse the ecosystem towards a more natural state, include the extraction of all trout and the installation of a new watering hole with regulated water inlet. The elimination of trout has led to a rapid recovery of littoral macroinvertebrates and amphibians. Meanwhile, the decrease in the water level, caused by the decrease in the flow of the external contribution, has modified the extension of the Luronium natans population. This has been monitored in the two areas it occupies: in the area where the plant grows rooted to the floor, submerged with leaves floating on the surface of the water, and in the marginal area of the lake where the plant grows with amphibious forms that are exposed to the air. The decrease in water level has caused an increase in the density of the amphibious subpopulation, but in turn has been altered by the presence of livestock that deteriorates the edges of the lake. The aquatic subpopulation has been maintained, although it has low vitality. Plants have always been observed in a vegetative state and simultaneous flowering of multiple individuals was only seen in 2019. Based on these results, we propose that the existence of Habitats of Community Interest (HCI) 3150 and 3130 related to the water body and the two subpopulations of Luronium natans be recognized in the Estanho.Peer reviewe