Study area
The Tandilia Mountains extend along a 350 km long diagonal in the
Province of Buenos Aires (Argentina), covering the districts of Azul,
Balcarce, Benito Juárez, General Pueyrredón, Lobería, Necochea,
Olavarría and Tandil (figure 1). The maximum width is in its central
part and reaches an extension of 63 km, and the maximum height is 525 m
(Cerro la Juanita, Benito Juárez district). The whole region occupies an
area of approximately 1.231.400 ha, including scattered hills separated
by valleys and plains (Herrera et al., 2019). The agricultural
expansion, and other anthropogenic activities (such as mining), added to
the lack of natural protected areas (Nanni et al., 2020), produced
changes in grassland species richness, composition, and abundance, and
the increase of exotic species (Filloy & Bellocq, 2007). Of a total of
505 plant species that have been found in the Pampean hills, 139 are
exotic (27%) (Sánchez & Núñez, 2004; D’Alfonso et al., 2014). Despite
the great impact, the Tandilia Mountains continue to be considered one
of the last refuges of Pampean grassland and one of the most biodiverse
sites in the Province of Buenos Aires (Chebez, 2005; Pedrana et al.,
2008).
In the Tandilia Mountains, is typical granite and limestone opencast
mining, where topsoil is removed to expose the rock to be extracted
(Cingolani, 2011). Opencast mining usually requires the removal of large
quantities of soil and rock and involves the use of machinery and
explosives, which has a negative impact on the landscape, air, and water
quality (Iwanoff, 1998). The rainwater fills these opencast mine pits
dissolving the minerals such as calcium and magnesium, which percolate
downwards through fractures and joints. This increases groundwater
pollution by increasing the calcium and magnesium, along with their
carbonates, sulfates, and chlorides affecting its hardness (Milgrom,
2008; Bhatnagar et al., 2014). All these described impacts are
intensified when the lack of control by governmental authorities results
in abandoned pits without mitigation actions (Marchevsky et al., 2017;
Zhang et al., 2018). The latter is the case of many abandoned quarries
along the Tandilia mountains.
Due to the fragmentation of this habitat, the Pampas grassland has been
relegated to remnants of different sizes, mainly on hills where the
presence of rock and shallow soils make it impossible to use plows to
cultivate annual crops (Herrera & Laterra, 2007). However, other
activities such as quarrying and forestry remain as important threats.