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 and Zhang 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 (25-50), 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, Figure 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 (field corroboration showed that the main invasive exotic species wereSpartium 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 116580.76 hectares, of which 6428.41 hectares are affected by this mining activity (5.22%).
Table 2 and Figure 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 Figure 4. Table 2 also shows that in 2022 the number of active quarries is 71, corresponding to 44.93% of the total.
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 reflected 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 6142.66 hectares, 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; 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; Xu et al., 2022). Woody invasive species colonize 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 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 insignificant.
The Impact index that categorized the landscape impact as Severe could significantly affect the following environmental parameters: air quality, noise and vibrations, soil quality, groundwater quality water resource depletion, diversity and abundance of fauna and flora, 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 significant (Duinker & Greig, 2007).
Given that mining activity in the Tandilia System follows the global trend of increasing surface area and poses a significant threat to the native ecosystems on which it is developed (Akanwa et 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. 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 confirmed 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 decision-makers to integrate these findings 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 official 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 confirm the threat posed to the Pampean grassland by this extractive activity and is the first 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.
ACKNOWLEDGEMENTS
The authors are grateful for funding from the Universidad Nacional del Centro de la Provincia de Buenos Aires (03-PIO-65H). We would like to thank Felisa for their commentaries and support. I. Carabia-Sanz was supported by fellowships from the Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CICPBA). A. Cortelezzi, M.V. Simoy and I Berkunsky are Research Fellows of Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina CONICET.
CONFLICT OF INTERESTS
The authors have no conflict of interest to declare.
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