Avaliação da vulnerabilidade e riscos de contaminação em aquíferos cársticos no Cerrado

Abstract

Karst environments are characterized by areas of intense rock dissolution, which allows for the creation of various typical features such as sinkholes, resurgences, caves, and others. In Brazil, studies have been strengthening since the 1990s, resulting in scientific production that gradually expands into new areas and deepens knowledge of already studied regions. The identification and analysis of the distribution of these features are of great importance for the assessment of aquifer vulnerability. This study aims to identify, characterize, and zone the vulnerability and risk of groundwater contamination of the Bambuí karst aquifer in its western part. In this sense, the specific objectives are to present the state of the art of speleological studies in Brazil, identify karst features through available databases and the semi-automatic method of sinkhole identification, zone the intrinsic vulnerability to contamination of karst aquifers, and identify areas with the highest risk of groundwater contamination. Various methods were used to achieve the proposed objectives, ranging from a bibliographic survey in specific databases to the processing of satellite images and unmanned aerial vehicles. For sinkhole identification, the methodology presented in Carvalho Júnior et al. (2014) was used, and for vulnerability calculation, the EPIK method (Doerfliger et al., 1999) and COP method (Vías et al., 2002) were employed. The risk was calculated based on the methodology present in COST Action 620 (Zwahlen, 2004). The main results found that karst studies in Brazil are concentrated in the areas of Geology and Zoology, primarily produced in the Southeast region. The caves are predominantly located in the Southeast region of the Cerrado Biome, in the Neoproterozoic Cratons, mainly over the Bambuí Group. Regarding the semi-automatic method, 777 depressed features were identified, concentrated in the Paraopeba subgroup in the Lagoa do Jacaré Formation. Based on the sinkholes analyzed in high-resolution images, it was possible to calculate soil loss for the analyzed features, ranging from 663.47 to 4,241.68 tons. In the study of the Terra Ronca region, the analysis unit with the highest vulnerability was PETeR, with 9.9% of the area classified between high and very high vulnerability. In the comparison between methods, both identified high vulnerability areas within PETeR, with the EPIK method pointing to a larger extent of high vulnerability area due to not considering non-karst terrains in the area. In the analysis of vulnerability and risk of contamination for the western region of Bambuí, five vulnerability classes (Very High, High, Moderate, Low, and Very Low) were identified for both methods. The most vulnerable classes are over the Bambuí carbonate rocks, specifically on karst features (caves and sinkholes). The greatest risks are associated with activities such as mining, intensive agriculture, and the presence of Small Hydroelectric Plants (PCHs). It is noteworthy that conservation units proved to be territorial units that contribute to this conservation, as they help protect critical areas and mitigate the impacts of potentially contaminating activities. It is concluded that due to the natural fragility of the Bambuí karst aquifer, the zoning of natural vulnerability and contamination risk has proven to be an effective tool in the protection and conservation of karst aquifers, providing important support for the sustainable management of these groundwater resources