Are protected areas effective in preserving Alpine stream morphology and biodiversity? A field study in the oldest Italian National Park

Global changes and local pressures related to the exploitation of water resources are significantly reducing streams' biodiversity and threatening their ecological balance. This trend concerns both the lowland rivers flowing in densely populated areas and the mountain headwaters, where the effects of global change are dramatically evident and often accompanied by alterations in river hydro-morphology. From mountains to lowlands, regulation and morphological alterations such as bank reinforcement, water abstractions, dams, and weirs are among the most significant threats for river ecosystems. Protected areas and especially large national parks constitute an effective strategy to face the loss of biodiversity, but little is known about their effectiveness regarding lotic environments. To examine the recent trend in aquatic communities in Alpine protected areas, we carried out biological sampling of benthic communities and hydro-morphological status assessment in 12 high-altitude streams within the oldest Italian National Park, that is, the Gran Paradiso National Park, located in the heart of the Western Alps, and we compared results with a previous survey performed in 2005, by keeping the same experimental design. Our results detected minimal changes in the hydro-morphology of the studied watercourses. Biomonitoring indices associated with benthic communities likewise did not provide evidence of significant differences. Conversely, diatom communities were more uniform in 2020 compared to 2005, and a slight species turnover occurred over the 15-year interval. Despite this, our findings underline the effectiveness of protected areas for the conservation of running water environments because they limit hydro-morphological alterations, thus increasing the resilience of aquatic communities to climate change.