Resumen:
This work studied the ecological integrity of river ecosystems inside the Ordesa-Viñamala Biosphere Reserve in the central Spanish Pyrenees. Despite its protected status, the reserve endures a considerable number of human stresses, thus the aim was to evaluate the conservation status of the two river basins inside the protected area: The Gállego River Basin, inside the transition zone of the protected area and which allows a wide range of human activities; and the Ara River Basin, inside the buffer zone where only sound ecological practices are authorised. The environmental status of river ecosystems was analysed by studying fish and macroinvertebrate communities, hydrochemical and habitat characteristics and by calculating environmental quality indices. From August to September 2011, a total of 14 sites were sampled. Fish sampling was conducted using electrofishing gear, and macroinvertebrate were sampled by applying the IBMWP and IASPT procedures. Results showed that, while the Ara River Basin maintains a solid ecological integrity, the Gállego River Basin endures important habitat alteration. Trout, the dominant and exclusive species in the Ara River, were absent and replaced by translocated native cyprinids in the Gállego River Basin. This colonisation was explained by the alteration of the stream ecosystems and their homogenisation. The study of macroinvertebrate communities and the diagnosis obtained with the environmental quality indices also enhanced the deficient ecological integrity of some sites in the Gállego River. The results suggest that the Biosphere Reserve is not providing adequate protection to streams inside its boundaries, leading to major degradation of their biological integrity.
