Spatial Distribution and Landscape Impact Analysis of Quarrying in the Highly Fragmented Ecosystem of Tandilia System (Province of Buenos Aires, Argentina)

Quarrying generates signi�cant changes in the grasslands, by reducing ecological functions, reducing connectivity, impairing biodiversity, and degrading soil. Unlike other forms of destruction such as agriculture or urbanization, mining is characterized by eliminating soil and exposing the bedrock, facilitating groundwater contamination processes. Quarrying in Pampean grassland has been expanding for a century and little is known about the extent and distribution of quarries over the native environment. In this work, we analyze the spatiotemporal variation of quarrying activity on the Highland grassland in the Tandilia mountains of Argentina. Based on Landsat 5, 7, and 8 satellite imagery, from 1996 to 2022, and using QGIS software, we identi�ed the location and extension of quarries, and we analyzed their change through time. Quarries covered 6428 ha, which was originally part of the Pampean grassland. The number of open quarries increased by 129%, from 69 in 1996 to 158 in 2022, and the area used for this activity increased by 172%, with a greater expansion being detected in the last ten years. At least 87 quarries were abandoned in 2022. Quarries are often abandoned without any kind of remediation, leading to further ecosystem deterioration. The current extension of quarrying activity (active and abandoned quarries) reduced the connectivity and a signi�cant area (5.2%) of the Highland grassland of the Tandilia Mountains. Grassland conservation planning should include quarrying as a signi�cant threat, and management actions must be considered to reduce its impact.


INTRODUCTION
Quarrying is an extractive activity that causes major environmental changes in grasslands (Lameed & Ayodele, 2010;Gbedzi et al., 2022).The environmental impacts of these changes range from preoperational mining activities (e.g., construction of access roads, conduits, and installation of drains and ditches) to the mining activity itself (e.g., creation of openings, perforation, blasting, machinery movements; Matías et al., 2007;Souza & Sánchez, 2018).Quarrying impacts result in severe modi cations of land cover at the local scale and affect the whole environment, including the lithosphere (rock excavation and geomorphic changes of the landscape), atmosphere (dust and air pollution), hydrosphere (changes in surface water), and biosphere (habitat destruction and biodiversity loss; Lameed & Ayodele, 2010; Bétard, 2013).The habitat destruction and fragmentation severely reduce the grassland's ability to provide ecosystem services with severe impacts on the native ora and fauna surrounding the quarries (Sala et al., 2010).For example, in areas affected, successional processes cannot proceed and are stuck at the early stages of colonization, mainly due to thin topsoil, without seed banks and rootstocks (Flavenot et al., 2015;Lamare & Singh, 2016).
The rapid population growth coupled with industrialization has increased tremendous pressure on natural resources resulting in the rapid exploitation of mineral resources worldwide (Bhatnagar et al., 2014).For example, in Lebanon, quarrying had an increase of 117% in 20 years (Darwish et al., 2011), while Bijolia (India) showed an increase of 3570% in land use from 1971 to 1992 (Sinha et al., 2000) and Odublasi quarry in Ghana 107,66% increase from 2007 to 2014 (Koranteng & Adu-Asare, 2018).Even when quarrying affects small areas at the regional scale (e.g.; less than 1% of French national territory; Bernaud & Le Bloch, 1998), this extractive activity still has important consequences on the local scale (Flavenot et al., 2014).There is a gap in scienti c knowledge about increased quarrying activity on Neotropical native grasslands (Le Stradic et al., 2014).Moreover, in the Neotropic, there are no guidelines that decision-makers can follow to reduce the negative effects of this activity and its abandonment by carrying out environmental impact studies or ecological restoration projects (Figueiredo et al., 2023).
In the Pampa ecoregion, one of the largest grassland regions of the world, the effect of quarries has been overlooked, and the evolution of this activity could be following the global trend.The quarrying activity in Pampa has more than a century of history, and the number of deposits and the number of grassland remnants affected by the activity increased in the last decade (Secretaría de Minería, 2020).
Considering the overall context, the general objective of this study is to accomplish a spatiotemporal analysis of habitat loss due to opencast mining activities in the Tandilia mountains, southern of the Pampean ecoregion.Our speci c objectives were: (1) to identify the locations where quarrying takes place, (2) to determine the area of active and inactive quarries, their expansion speed, and their evolution over the last 20 years, and (3) to assess the impact of the extractive activity on the landscape.These objectives are achieved by obtaining Landscape 5, 7, and 8 satellite images and processing them with Geographic Information Systems (QGIS 3.24.2).

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 (Fig. 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 1.231.400ha, 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 lls 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 intensi ed 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.

Image analysis
The satellite imagery used in this study was of Landsat 5, Landsat 7, and Landsat 8 satellites (30x30 resolution) obtained from the Google Earth Engine (GEE) website.Different satellites were necessary to obtain images from different years, so Landsat 5 was used for 1996, 1999, and 2002 maps, Landsat 7 for 2005, 2008, and 2011 maps, and Landsat 8 for 2013, 2016, 2019, and 2022 maps (Chandler et al., 2009).In recent times Google Earth Engine has become an important database of earth observation data and land cover classi cation in many mining-related studies and other applications such as vegetation mapping and monitoring, agricultural application, disaster management, and earth science (Gbedzi et al., 2022).In addition to these satellite images, information obtained from the remnants of Pampean grassland identi ed and delineated with Google Earth Imagery was added.
To analyze the different land uses, images from 27 October to 27 May in each year of study were used.This date was chosen due the spring/summer season is when the vegetation associated with the quarry is in bloom.NDVI index (Normalized Difference Vegetation Index) in GEE was applied, paying special attention to the threat posed by quarries in the Tandilia Mountains.The application of the NDVI index has been used to monitor characteristics of vegetation cover and health status but also for the detection of changes in an ecosystem over time (Paruelo, 2008;Tong et al., 2016).Calculation of NDVI for a given pixel always results in a number that ranges from minus one (-1) to plus one (+ 1): bare soils (quarries in that case), giving a value close to zero, and very dense green vegetation have values close to + 1 (Musa & Jiya, 2011).In general, land covers are often mixtures of several types, so even ne-resolution remote sensing data do not measure pure spectra, but instead mixed re ectance of vegetation and nonvegetation, rendering it di cult to clearly identify exposed bedrock (Yue et al., 2012).For this reason, the satellite images were then processed with QGIS software.
The image was processed using QGIS 3.24.2, a Geographic Information Systems (GIS) software.QGIS allows the input, manipulation, analysis, and presentation of data and information related to a place on the earth's surface and therefore works with geo-referenced points (Ershad, 2020).With this tool was possible to locate and characterize quarries (dimensions and associated threats).To do this a visual interpretation of land use was made: quarries with a lot of vegetation or water are considered inactive, and quarries with bare soil are active.The resulting maps show the evolution of the quarries during the years of the study.Some characteristics of the quarries, such as the state of their activity, only were reliable in the current year (2022).The state of quarrying activity was con rmed from the information obtained in the Mining Cadastre of the province of Buenos Aires (https://www.gba.gob.ar/produccion/areas_de_trabajo/mineria).Moreover, the area of each remnant and the total amount of Pampean grassland were calculated using the QGIS software.

Quarrying impact
The quarrying environmental impact focused on the impact on vegetation cover and the loss of Pampean grasslands (Darwish et al., 2011), was evaluated using QGIS software and information obtained from the Direction of Mining Cadastre of the province of Buenos Aires (https://www.gba.gob.ar/produccion/areas_de_trabajo/mineria).This government agency records the materials extracted from each quarry.This information added to the degree of permeability of the rocks of the Tandilia Mountains in each quarry site, was used to associate the type of the extraction to the impact level.A higher level of permeability increases the vulnerability of groundwater due to the increased passage of water contaminated with heavy metals, other minerals, and toxic waste (Darwish et al. 2011 andZhang 2013).
The area of Pampean grassland affected by mining activity in each county was estimated and it was possible to obtain a quotient indicating the loss of native habitat due to extractive activity and its percentage.
Finally, to measure the impact of all quarries in the landscape Tandilia Mountains, an Impact index which includes a set of qualitative variables, was used (Soriano et al. 2015).These variables are the extent of the impact, the periodicity, the intensity, the reversibility of the impact, and the recoverability of the environment.Each variable has a value according to the degree of impact on the landscape.The sum of these values will give a level of importance to the impact, which allows us to characterize it.There are four categories of the levels of impact: Irrelevant (0-25), Moderate , Several (50-75) and Critical (75-100).

RESULTS
The mining activity has increased over the years in the Tandilia Mountains.Based on the satellite imagery, the increase is both in the amount of area occupied by the quarries and in the amount of quarries (Table 1, Fig. 2).Some of these quarries are active, and others have been abandoned without carrying out a mitigation plan.By visual interpretation of satellite images, it was possible to detect that 100% of inactive quarries are invaded and surrounded by exotic vegetation ( eld corroboration showed that the main invasive exotic species were Spartium junceum, Pinus radiata, Laurus nobilis, Acacia melanoxylon).In the satellite imagery of 1996, 69 quarries were observed and for 2022 the increase was more than double: 159 quarries.The total area of native Pampean grassland is fragmented in 1971 remnants and they cover a surface of 116580.76hectares, of which 6428.41 hectares are affected by this mining activity (5.22%).
Table 2 and Fig. 3 show the area affected by mining activity and the current area of Pampean grassland in each county that comprises the Tandilia Mountains.Olavarría and Benito Juárez are the most affected counties: they have lost 35.41% and 12.37%, respectively, of Pampean grassland because of the extractive activity.Balcarce and Lobería are the counties with less percentage of habitat lost by quarrying activity (0.35% and 0.78% respectively).Also Olavarría, is the county with the largest number of quarries (63) followed by Tandil (31) (see Table 1).In Olavarría most of the quarries are clay (19) and granite (18) and in Tandil there are 9 granite quarries and one clay quarry; for the other quarries from Tandil, there is no information on the materials they exploit.The percentage of the area used to extract the different types of materials in the Tandilia Mountains is shown in Fig. 4.More than 80% of the area occupied for this extractive activity is associated with the extraction of clays, granite, and limestone.Those are the materials with the highest permeability.Table 3 shows the value of different variables considered to estimate the Impact index.The result of this index was 69, which categorizes as Severe the landscape impact of quarries.The variables Intensity of the impact, effect, periodicity, and the moment were the top contributors to the index.

DISCUSSION
In the last 28 years, the number of quarries in the Tandilia Mountains doubled.Likewise, the area occupied by quarries also increased, being three times larger than in 1996.This trend towards an increase in this extractive activity is also re ected in the mining cadastre of the Province of Buenos Aires which shows quarries already exploited and quarries that are being explored to start extraction works.In this cadastre, it can be seen that the projected area to be exploited in the future in the Tandilia mountains is 6142.66hectares, which represents an increase of the affected area of 95.56%.
This increase in the area and number of quarries in the Pampean grassland indicates that quarrying activity is indeed a threat to the conservation of the native ecosystem of the Tandilia Mountains.Moreover, many of them are abandoned and the environmental problem related to landscape destruction, and loss of native vegetation remains unsolved (Chase et al., 1999;Akanwa et al., 2017).As seen in satellite imagery from 1996 to 2022 the degradation commences through the destruction of the natural habitat itself, followed by the sheet erosion of the delicate soil layer resulting from the breakdown of exposed solid rocks, and concludes with changes to biodiversity and the alteration of the natural recolonization process: the colonization by woody invasive species (Khater et al., 2003 erosion, resulting in a greater loss of substrates that enable growth.This reduces the ability of the surrounding area to support plant life and makes it impossible for native species to colonize the area, leading to their displacement or disappearance (Akanwa et al., 2017;Said et al., 2016).In addition to this, there are a large number of exploration points that, although not selected for material extraction, still have an impact on the ecosystem.
The results show that Olavarría and Benito Juárez are the counties the most affected, with one-third and one-sixth (respectively) of their native habitat lost.Mainly Olavarría is an area with a strong mining culture.This extractive activity gained strength in the 1850s when new techniques were introduced which were the basis for the take-off of the large-scale capitalist mode of production, forming the original capital of numerous productive enterprises.An understanding of the different processes that determined regional growth makes it possible to explain the way in which the Human Society-Nature mediation took place in the region, and clearly shows an environmental rationality based on the idea of progress and increased productivity (Paz, 2000).This anthropic activity, closely linked to the culture of the region, has been maintained and increased over time, as can be seen in the amount of area affected.
On the contrary, Lobería and Balcarce are the counties with the least habitat loss due to extractive activity, with a tiny percentage that could indicate that they are exemplary conservation sites for the Pampean grassland of the Tandilia Mountains.Finally, Tandil County is another example of an attempt to conserve its native ecosystem, with only 0.93% of habitat lost to mining activity.Due to different social protests since 2010, there has been an environmental protection law (Law 14.126) aiming to conserve and preserve the integrity of the geographical, geomorphological, touristic, and urban landscape (Grosman & Kristensen, 2012).
Inconsistency can be seen between the governmental information and the results obtained from analyzing the materials extracted from the quarries.These discrepancies may be due to the lack of control over the quarry activity in Argentina, as well as a delay in the timing of information on these activities or in the updating of government databases.On the one hand, 52 of the quarries found by visual interpretation are not registered in the mining cadastre of the Province of Buenos Aires.On the other hand, according to the bibliography, the most extracted material from quarries in the province is limestone rock, whereas the cadastre shows that only four quarries in the entire Tandilia Mountains extract it (3.8%).The limestone rock is used for construction in the entire province, so urbanization and population growth demand a hike in the extraction (Bhatnagar et al., 2014).Although there is a low percentage of quarries dedicated to extracting limestone rock, their exploited area is high.The same happens with iron oxide, its extraction in the whole Tandilia Mountains is 0.9%, while the surface area taken up by its extraction is ten times bigger.This means that these two mining exploitations, particularly, have a considerable impact on the Tandilia Mountains: they require a lot of surface area, and the amount of extraction is insigni cant.
The Impact index that categorized the landscape impact as Severe could signi cantly affect the following environmental parameters: air quality, noise and vibrations, soil quality, groundwater quality water resource depletion, diversity and abundance of fauna and ora, and habitat alteration (Soriano et al., 2015).Moreover, the most extracted materials are the most permeable.That means that those allow access to water possibly contaminated with heavy metals and other chemicals in the groundwater and lead to a larger ecosystem-wide problem and human consumption of water (Darwish et al., 2011;Milgrom, 2008).This qualitative impact assessment is another way of showing that the threat to the native ecosystem and the environment is signi cant (Duinker & Greig, 2007).
Given that mining activity in the Tandilia System follows the global trend of increasing surface area and poses a signi cant threat to the native ecosystems on which it is developed (Akanwa et  Establishing semi-natural grasslands by using seeds from wild harvesting is an effective method to restore vegetation with high natural value, such as Eryngium regnellii which is a key species in a possible ecological restoration because of its great diversity of pollinating visitors (Herrera, 2019;Scotton, 2018).This could be the beginning of the restoration process of the area altered by the mining activity, started by quarry companies, always advised or accompanied by biologists specialized in ecological restoration and environmental impact assessment.
This work has con rmed the usefulness of these tools by detecting by visual interpretation the quarries themselves and their state of activity and studying their evolution over time by measuring geometric parameters.However, the lack of studies on the environmental impacts of mining and remote sensing in the Tandilia Mountains indicates the under-utilization of those tools in this sector.Hence, the conclusions drawn from this study will provide enhanced resources for governments, and decisionmakers to integrate these ndings into restoring initiatives.This will, in turn, manifest the research into tangible actions on the ground.

CONCLUSION
After this analysis, it can be concluded that mining activity in the Tandilia Mountains is a major threat to the area, which has increased in recent decades, and that the tendency (as at the global level) will continue to increase.This threat involves the fragmentation and loss of the Pampean grassland with the consequent loss of biodiversity and the invasion of exotic plants capable of colonizing areas altered by human activity.In addition to this, quarries produce a landscape impact that cannot be ignored.This threat is aggravated by the lack of control by governmental agencies, whose o cial data related to the number of quarries does not coincide with the results obtained in this study.Furthermore, despite the existence of a law that obliges the remediation of natural areas affected by mining activity, there is no control to ensure that this process of ecological restoration is carried out.Quarrying operations without environmental control could affect the very existence of ecosystems and the hydro-geological conditions of the area to a greater extent.Therefore, extractive management plans must be developed based on the capacity of ecosystems that support life.Our work responds to a need to con rm the threat posed to the Pampean grassland by this extractive activity and is the rst approach to this problem in the region.The intention is to continue analyzing the degradation gradient associated with the quarrying activity in the Pampean grassland remnants and the surrounding areas.This analysis has also shown that using remotely sensed images provides data and allows the temporal evolution of different land uses to be known, thus enabling better management of human activities in natural systems.This is why the visualization of remotely sensed data and its processing into maps with software such as QGIS are used as good analytical tools to understand the impairment of nature by human activities and to be able to determine the magnitude or degree of the threat.Analysis of vegetation and detection of changes in vegetation patterns are keys to natural resource assessment and monitoring.Thus it comes as no surprise that the detection and quantitative evaluation of green vegetation is one of the most important applications of remote sensing for environmental management and decision-making.These same tools could be used by enforcement agencies to monitor threats impacting the native ecosystem to be protected.

Figure
Figure 4

Table 1
Amount of detected quarries by year and county in Tandilia Mountains, southern Argentinean Pampa.

Table 2
Table 2 also shows that in 2022 the number of active quarries is 71, corresponding to 44.93% of the total.Impact of mining activity on the Tandilia Mountains during 2022, separated by county.

Table 3
Landscape impact values of the qualitative variables to categorize the landscape impact of all Tandilia Mountains quarries, southern Argentinean Pampa.
(Pitz et al., 2019;D'Alfonso et al., 2014 )onize relatively rapidly and hamper the establishment of native vegetation with high conservation value, so the abundance and richness of those native species have decreased(Pitz et al., 2019;D'Alfonso et al., 2014 ).Moreover, less vegetation exposes the soil to ; Darwish et al., 2011).So the ecosystem changes induced by the mining activity itself are multiplied by the risk of further ecosystem deterioration in and around abandoned sites (Darwish et al., 2011; Lake & Leishman, 2004; al., 2017; Howarth & Farber, 2002; Jiya & Musa, 2012; Darwish et al., 2010; Chitade & Katyar, 2000), we propose that ecological restoration should be included in the extractive activity budget.This should consist, at least, of a smoothing of the slopes with the substrate removed by the works carried out and a spreading of native seeds of the Pampa grassland on it.