Assessing the effectiveness of terrestrial protected areas towards riverine ecosystems

Protected areas are one of the main tools for biological conservation worldwide. They have been designed largely focused on terrestrial and marine habitats and species, despite the worldwide deterioration of freshwater ecosystems. Yet, the effectiveness of terrestrial protected areas towards the protection freshwater ecosystems located within their borders is still poorly known and the few studies on the subject have yielded mixed results. Historical records on benthic diatom communities and environmental data, gathered in 174 Portuguese streams (128 inside terrestrial protected areas and 91 without any kind of statutory protection), were used to explore trends in biological quality and biodiversity in response to the existence of a protection status (spatial comparisons) and of different protection categories. Temporal comparisons were also made, when data was available. The biological quality was assessed using the Indice de Polluosensibilité Spécifique (IPS) and data on diatom traits such as life-forms, ecological guilds, or cell size. The results suggest that although terrestrial protected areas don't have the conservation of freshwater ecosystems as a priority, they can contribute nonetheless to their preservation, since both the biological quality and the average abundance of threatened species were significantly higher inside terrestrial protected areas. Yet, the diversity of diatom communities wasn't significantly different when comparing protected and unprotected sites. The existence of several cumulative protection categories towards que quality of freshwater ecosystems didn't always prove beneficial. In particular RAMSAR sites didn't provide additional protection when compared to other protection categories. Our results reinforce the need to designate dedicated freshwater protected areas as an effective way to preserve these ecosystems in all their components. © 2024 The Authors