Study area and data collection
The study was conducted in the Gran Paradiso National Park (hereinafter
GPNP). This park is the oldest protected area in Italy, born in 1856 as
a royal hunting reserve for Alpine Ibex and then established as Natural
Park in 1922. GPNP is located in North-Western Italy, in the Graian Alps
region between Piemonte and Aosta Valley, encompassing 703
km2 and ranging from 800 to 4061 m a.s.l. The land use
is typically alpine, with a small portion (approximately 16%) used for
agriculture and pasture and the rest occupied by alpine prairies, woods,
rocks, and glaciers.
Fifteen years after the sampling campaign of 2005, we sampled the same
12 (Figure 1): the two sampling campaigns are faultlessly comparable
because we sampled the same stream reaches, in the same month (July),
with the same sampling team and by applying the same methods.
FIG1
In the present paper, we describe methods in brief, while more detailed
information is reported in Bona et al. (2008). All sampled stretches are
characterized by a prevailing siliceous substrate, altitude ranging from
1200 and 1900 m a.s.l., and similar human activities nearby (hiking,
summer tourism, pasture) but different levels of morphological
alterations. To quantify them, we applied the South European River
Habitat Survey (hereafter RHS) and related indices (Raven, Holmes,
Dawson, & Everard, 1998; Buffagni & Kemp, 2002; Buffagni, 2004):
Habitat Quality Assessment (HQA), Habitat Modification Score (HMS) and
Lentic-Lotic River Descriptor (LRD). We examined also the available
climatic data in correspondence with the two sampling years (data
available for the meteorological station inside the GPNP, located in
Ceresole and available from
1999; www.arpa.piemonte.it). We considered data
from 1999 to 2005 (before the summer 2005 sampling campaign) and those
from 2014 to 2020 (before the summer 2020 sampling campaign), focusing
on temperature (average, minimum, and maximum monthly values) and
precipitation (monthly averages of precipitation and the number of rainy
days).
All the aquatic samples were taken in spot-check 2 of the RHS procedure.
Water physical and chemical parameters were measured following the same
methods as in Bona et al. (2008). Benthic diatoms were collected by
scraping five cobbles for each sampling station and analyzed following
the same procedure as Bona et al. (2008). Concerning diatoms, we
computed the following indices: IPS (Coste, 1982), TI (Rott et al.,
1999), and ICM (Mancini & Sollazzo, 2009), which replaced the EPI_D in
the Italian application of the Water Framework Directive. In addition,
we also compared the two years in terms of richness (number of species)
and diversity (Shannon Index and Evenness). Furthermore, we analyzed
diatom communities in terms of ecological preferences (Carayon,
Tison-Rosebery, & Delmas, 2019), guilds (Passy, 2007; Rimet & Bouchez,
2012) and by classifying each taxon according to the most recent diatom
Red List (Hofmann, Lange-Bertalot, Werum, & Klee, 2018). Benthic
macroinvertebrates were sampled using a 250 μm mesh kick net on diverse
habitats and substrate grain size and typology within each sampling
station. The taxonomy level went from species to family (for some
Trichoptera, Coleoptera, and Diptera). The following indices were
calculated: BMWP, ASPT, IBE, N families, N taxa, N EPT families, and %
stenoecious taxa (see Bona et al., 2008, for more details).
For both communities, we also calculated the local and the species
contribution to ß-diversity, as explained in the following section.