Índices biológicos fluviales en espacios naturales protegidos: ¿son adecuadas las clases de calidad de uso general?

Abstract

The National Parks Master Plan specifies that the monitoring of ecological status must be carried out according to the parame-ters of the Water Framework Directive (WFD). However, mountain National Parks are characterized by small basins (< 10 km2) that are outside the scope of the WFD. The objective of this article is to assess whether the biotic indices usually used by the WFD are appropriate to assess the ecological status of small and generally well conserved basins in protected mountain areas. For this purpose, the results of the monitoring of ecological status of the main rivers in the Sierra de Guadarrama National Park are presented. The spatial and temporal variability of the biological indices (IBMWP, IASPT and EPT) in small basins (generally less than 10 km2) has been evaluated, based on data from 26 sampling stations over a period of 13 years. The main characteristics that determine the variability of the sampling stations have been established (PCA). Afterwards, the response of the biological indices with respect to the characteristics of the sub-basins and the intensity of the impacts was evaluated (RDA). The main results indicate that the biological indices are influenced by altitude, seasonality, the existence of lowland vegetation and livestock, in addition to other less relevant factors and impacts. In addition, altitude is a limiting factor for the diversity of fluvial macroinvertebrates at the most elevated stations. In this way, the biotic indices respond both to the characteristics of the subbasin and to the possible impacts present in them. Nevertheless, the boundaries between IBMWP quality classes established by legislation for the type of Mediterranean silica mountain rivers (R-T11) are not very sensitive with regard to relatively well conserved mountain areas, so more restrictive and better adapted thresholds are proposed in order to detect impacts in the river sub-basins of the Sierra de Guadarrama National Park.