Introduction
Habitat loss and fragmentation, over-exploitation of natural resources,
climate change, and introduction of invasive species are listed among
the main causes of the current environmental crisis, characterized by an
impressive extinction rate (Dirzo, Ceballos, & Ehrlich, 2022). Among
the various strategies implemented to contrast this negative trend, the
increase and extension of protected areas are considered one of the most
useful and immediate (Lovejoy, 2006; Acreman, Hughes, Arthington,
Tickner, & Dueñas, 2020). Unfortunately, however, while the creation of
natural parks can be effective in protecting and conserving terrestrial
ecosystems and species, the difficulties are often much greater
regarding lotic environments and organisms living within them. In fact,
because of their longitudinal and dendritic shape, streams are subject
to stressors that affect their structure and functioning over large
spatial scales. Usually, protected areas cover only a part of the
catchment through which a river flows, so the pressures exerted in the
downstream and especially in the upstream section can have dramatic
repercussions on the integrity of the protected area. For these reasons,
despite being among the most threatened environments (Harrison et al.,
2018), stream ecosystems paradoxically are among the most difficult to
protect, unless the protected area is located at the head of the
drainage area.
Alpine and mountain low-order lotic systems are incomparable hotspots of
biodiversity, rich in highly sensitive and stenothermic taxa strongly
adapted to harsh conditions such as low temperatures, seasonal high
flows, and physical instability of channels (Petts, Gurnell, & Milner,
2000; Smith, Hannah, Gurnell, & Petts, 2001). Unfortunately, these
environments are increasingly threatened by factors acting on a global
scale, such as temperature growth, changes in precipitation amounts,
patterns, and seasonality, and at a local scale, in particular human
derived alterations of the hydro-morphological characteristics (Piano et
al., 2020; Doretto et al., 2021). Even in relatively pristine areas, the
hydro-morphology of Alpine rivers is often altered by human
interventions such as bank reinforcement, water abstractions, presence
of dams and weirs. These interventions are becoming more and more
frequent in recent decades due to the growing need for water and
modification in the natural hydrological cycle induced by climate
change, representing a major threat to Alpine lotic ecosystems and
related aquatic communities.
About 90% of all alpine water courses are used and capitalized on for
producing electricity through hydropower (CIPRA, 2014), also in
protected areas. Regardless of the plant size and typology, water
storage and abstraction imply morphological alterations of river bottoms
and banks which can threaten aquatic biodiversity. In recent years, the
estimation of local and species contributions to ß-diversity is
receiving increasing scientific interest (Vilmi, Karjalainen, & Heino,
2017; Bo, Doretto, Levrino, & Fenoglio, 2020). Indeed, ß-diversity
plays a key role in conservation and bioassessment viewpoints because it
allows the identification of spatial trends and sites that most
contribute to regional diversity and may address specific restoration
programs. This can be achieved by considering species and local
contribution to ß-diversity in addition to more traditional metrics
widely used in environmental bioassessment, such as biotic or diversity
indices.
In 2005 we carried out a study that was the first evaluation of
high-altitude river morphological alterations in an Alpine protected
area, the Gran Paradiso National Park, the oldest National Park in
Italy, and their effect on the benthic (macroinvertebrates and diatoms)
communities included in the EU Water Directive Framework 2000/60 (Bona,
Falasco, Fenoglio, Iorio, & Badino, 2008, in this journal).
In this study, we sought to assess if the presence of the protected area
prevented significant local alteration of the stream habitat and if the
aquatic biodiversity and ecological quality of the sampled stretches
were comparable after 15 years or underwent significant changes,
measured as biotic indices and ß-diversity-related metrics. With this
aim, we repeated the same samplings, on the same sites and with the same
team and methods.