{'fraction_non_alphanumeric': 0.02615212884707383, 'fraction_numerical': 0.01461755169297826, 'mean_word_length': 4.803207896360272, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Normalized Difference Vegetation Index Analysis of the first part impacted with the breaking of the Fundão Dam in Mariana-MG

This paper addresses the exploitation of mineral resources and suggests that an environmental management that meets a set of measures and mutual cooperation between public and private managers, civil society, and mining companies that exploit natural, renewable, and non-renewable resources is needed. Cooperation between managers and joint safety measures can prevent present and future accidents like the one that occurred in Mariana City in Minas Gerais State (MG). The questioning presented puts into discussion the disaster that occurred in Mariana City due to the rupture of the ore tailings dam (Fundão dam) in November 2015. With an estimated population of 60,000 inhabitants, Mariana City has a local economy directly linked to mining activities. Due to the impact caused by the rupture of the Fundão dam, both city and vegetation were destroyed, among other factors observed along the path followed by the tailings. However, what is discussed in this article with greater emphasis is the loss of vegetation in the watershed. The methodology compared the degree of vegetation coverage in the basin area through the analysis of the Normalized Difference Vegetation Index – NDVI for 2013, 2016, 2017, 2018, and 2019 in different months. Some images refer to August and other samples are from September, complementing the process through the use of Landsat 8 satellite images OLI sensor, acquired from the United States Geological Survey (USGS) repository. 299 points were distributed in the quadrant to perform the analyses (n = 299). The level of significance was set at 5% with a 95% confidence, to ascertain and verify whether the data distribution is in an acceptable condition (dense or semi-dense vegetation cover). Regarding vegetation analysis, the Kolmogorov-Smirnov and Shapiro-Wilk tests were used. Both tests indicated a non-normal distribution for the NDVI data set, which indicates the absence of a vegetation index that was covered by the tailings, resulting in an area with large spaces without the coverage previously registered in 2013. We conclude that the vegetation suffered a drastic alteration provoked by the rupture of the Fundão dam which also led to homeless residents, negative impacts on the livelihood of the small farmers and fishermen, silting up of rivers and streams, death of several animal and plant species, and also affected the ecosystem and the local and regional biodiversity. Edição Especial Submissão: 06/11/20 Aprovação: 06/11/20 Publicação: 04/12/20 Normalized Difference Vegetation Index Analysis of the first part impacted with the breaking of the Fundão Dam in Mariana-MG 2 REGET, Santa Maria, v. 24, Ed. Especial, e27 p. 1-21, 2020


Introduction
This research was supported by available studies and bibliographic materials, such as academic articles, books, theses, and dissertations that served as a basis to carry out the study developed and presented in this article. The article proposes to evaluate the loss of vegetation using the Normalized Difference Vegetation Index (NDVI) through remote sensing. This technological procedure allows data to be collected from a specific place and region, that is, without direct contact with the location allowing for gathering of the information remotely.
The NDVI is an index that seeks to analyze the situation of the vegetation collected through remote sensing. With the application of the index, it is possible to observe the extent and proportion of the effects produced by the rupture of the Fundão dam. The event not only impacted the environment but also reached the political and administrative limits of the territories. This is the reason why it is essential to take measures to combat the disordered and exploratory use of natural resources, and at the same time, contribute to reduce the damage to the environment attributed to human mining activities Borges (2018).
This theme needs to be addressed in political, scientific, and social discourses, since the incident caused damage to a large area of the country due to the rupture of the dam.
Mining activities for exploration and removal of soil resources can cause incalculable damage to historical, social, economic, and cultural heritage. The heritage built over the years by the local population can be wiped out in a few seconds by the volume of tailings caused by the rupture of dams and devastate almost all of its memory, history, and the identity of this community as highlighted by Gonçalves. et al. (2015). So it is necessary to ask some questions to the managers such as: How to prevent? How to avoid accidents of this proportion? What measures should be taken to prevent accidents with dams?
The measures taken for prevention must be periodically approached by technical professionals, according to the types of risks and the possible potential damage close to urbanized places. This procedure aims to monitor problems or anomalies which may affect and damage the dam. Regions of broad biological importance are prone to serious environmental accidents and, therefore, it is necessary to avoid the lack of maintenance in the facilities and also make routine inspections to identify potential risks to determine preventive Rodrigues subdistrict 35 km from the city center of Mariana-MG on November 5, 2015. As a consequence due to the dam burst, there was a flood of mud and mining waste.
The robustness of the vegetation prior to the accident is no longer seen but rather a trail of destruction through which the mud passed modifying the entire local and regional landscape, which also suffered a change in the landscape. In fact, the path taken by the tailings has come a long way, invaded other states, and entered the ocean. The lack of plants observed on the maps is related to the areas impacted by the accident in Mariana City. The Vegetation Indices, in addition to the Normalized Difference Vegetation Index (NDVI), made it possible to show the behavior of the vegetation and the destruction left by the accident as shown by Zanzarini (2013) and Lourenço and Landim, (2004).
Thus, this study aims to analyze the spatiality of the incident so that the methodology that was applied, linked to other analysis materials, can assist in the delimitation procedure of the impacted areas. When choosing the method to be adopted, it is necessary to be clear As the accident proportions were of a large scale, these methods were not applied to the study. Therefore, the remote sensing and the application of the NDVI index were chosen to develop this paper. In fact, this study was carried out using images from the Landsat 8 satellite -OLI sensor and the images were acquired in the United States Geological Survey (USGS) repository. Ortiz and Freitas (2005) used remote sensing and geoprocessing to spatialize and quantify the changes produced by man in nature using (GIS). In this way, the authors observed, through the methodology applied, damage to the environment and vegetation around the city of Rio Claro in São Paulo State. There are so many other methods, but as previously mentioned by authors such as Freitas and Magalhães (2012), Ortiz and Freitas (2007) and Lourenço and Landim, (2004), it is necessary to choose the method that best fits the interests Normalized Difference Vegetation Index Analysis of the first part impacted with the breaking of the Fundão Dam in Mariana-MG 6 of the research and the location chosen to carry out the study, that is, in the field trip (on site) or in an office.
Martim and Santos (2013 p. 3250) point out that the "methodological lines for assessing environmental impacts are structured mechanisms for comparing, organizing, and analyzing information about these impacts arising from any activity, including the means of written and visual presentation of this information". The authors evaluated the environmental impacts in a copper mining company using the interaction network method to assess environmental impacts in a mining company and identified the activities that generate the greatest number of environmental impacts in the extraction of ore. The analysis using the method and methodology applied in the study, according to the authors, can be used as a diagnostic tool to adopt measures for the prevention or correction of negative impacts on the environment promoting sustainability.
Thus, this study is related to the impacts caused by the rupture of the Fundão dam in  Regarding hypsometry, the city presented a minimum of 421 m to the east and southeast.
The highest altimetric levels were determined from north to south at the west end; the maximum value found was 2,068 m. The amplitude was 1,641 m. In the highlighted area, the amplitude is lower and more homogeneous in relation to the whole with a sharp decline from northwest to southeast ( Figure 01). In order to understand the displacement of the tailings, it is crucial to visualize the elevation dimensions of the area. Regarding the declivity of Mariana-MG, a variation of 0-15.32% was found at percentages greater than 56%. However, the slope classes are distributed practically homogeneously throughout the city. In the study area, the slope tends to increase from west to east ( Figure 02). Nevertheless, with the rupture of the Fundão dam, the tailings went from west to east. This fact occurred due to physiographic conditions as can be seen in figure 03.
The vegetation in the impacted area corresponds to the Atlantic Forest Ferreira;Scotti, 2015). Where: Lλ is the monochromatic spectral radiance W m -2 sr -1 μm -1 ; ML is the multiplicative factor of each band; is the addition coefficient found in the metadata file; are the digital numbers (DN) corresponding to each band in the image.
The monochromatic reflectance was calculated with the OLI sensor bands, converted to planetary reflectance using the reflectance rescheduling coefficient informed in the image metadata file (MTL file) through Equation 2.
However, it is necessary to correct the reflectance according to the zenith angle. In order to do so, Equation 3 was used.
= 1 + ( ) + ( ) (Eq.3) Where: is the planetary reflectance, with correction of the zenith angle; 0 is the solar elevation angle present in the MTL file; Normalized Difference Vegetation Index Analysis of the first part impacted with the breaking of the Fundão Dam in Mariana-MG 10 0 is the solar zenith angle which is calculated according to the MDU.

NDVI INDEX
The enhancement of vegetation by NDVI takes into account the relationships between the reflectance of the soil and the vegetation. In fact, the vegetation has a high reflectance in the near infrared region, whereas the soil has a high reflectance in the red region. Thus, the higher the densities of the vegetation cover, the lower the reflectance in the visible regionred. However, the reflectance in the near infrared region will be higher. For the calculation of NDVI, Equation 4 was used:
The values obtained in NDVI varied between +1 to -1, in which, the closer to -1, the lower the density of the vegetation cover, and the closer to +1, the greater the density.

Statistical analysis
The IBM SPSS 22® software was used for the statistical analysis. 299 points were distributed in the quadrant under study to promote the analyses (n = 299). To reach n (sample), equation 5 was used based on the number of pixels (N). It should be noted that the equation uses the standardized normal distribution table. The significance level of 5% and 95% confidence were adopted.

NDVI= (ρNIR-ρRED) /(ρNIR+ρRED) (Eq.4)
Where: NDVI is the Normalized Difference Vegetation Index; pNIR is the reflectance in the near infrared band; pRED is the reflectance in the red band. The values obtained in NDVI varied between +1 to -1, in which, the closer to -1, the lower the density of the vegetation cover, and the closer to +1, the greater the density.

Statistical analysis
The IBM SPSS 22® software was used for the statistical analysis. 299 points were distributed in the quadrant under study to promote the analyses (n = 299). To reach n (sample), equation 5 was used based on the number of pixels (N). It should be noted that the equation uses the standardized normal distribution table. The significance level of 5% and 95% confidence were adopted.

Z_ (∝ 2) is the value calculated based on the Z test;
is the probability of the value found is not true.
When the population size (N) is finite, that is, less than 10,000, the correction factor must be used (Equation 6). Where: is the sample size with correction factor; N is the statistical universe; is the sample size without the correction factor.
To determine whether the data distribution is normal, the Kolmogorov-Smirnov and Shapiro-Wilk tests were used. Both tests showed non-normal distribution for the NDVI data set. Thus, the hypothesis H1 of the test was accepted. This fact is also confirmed by the random points around the line in figure 04. Libardi et al. (1996) recommend promoting exploratory data analysis with the purpose of confirming normality tests and understanding the data distribution.
Normalized Difference Vegetation Index Analysis of the first part impacted with the breaking of the Fundão Dam in Mariana-MG 12 Figure 4 shows that the data set is not normal. Accordingly, figure 05 also shows the non-normality of the data, highlighting a high number of outliers and extreme values.
In order to verify if there are differences between the NDVI for each year worked in this study, the Friedman test -non-parametric test was used.
The test statistic (called 2 ) is given by Equation 7: Where: N is the number of lines; K is the number of columns; Rj the sum of the orders in the column.
This variable follows a Chi-Square distribution with k-1 degrees of freedom.
If the probability obtained by this method does not exceed α, H0 is rejected.  (Table 01) Iron ore tailings are extremely harmful to soil and vegetation (Ribeiro Filho et al., 1999). Foesch (2017) also identified an abnormality in the spectral behavior of water in river beds in Mariana-MG, determining the impact by sediments rich in heavy metals through physical-chemical analyzes.  The increase in the orange class -in the comparison of the years 2013 and 2019 -plus the spatial analysis, indicate a possible difficulty in regenerating tree vegetation, especially on the banks of the Gualaxo do Norte River (Figure 07). It can also be seen in the image that the least affected area is located in the central-north region, which consists predominantly of tree vegetation at altitudes higher than the impacted area, thus containing the highest NDVI values ( Figure 07).  The 2013 spatial analysis served as a basis to understand the distribution of NDVI values before the dam was built, in which the presence of a clear body of water with a low amount of sediments was detected east of the Gualaxo do Norte River in the floodplain by the spectral response. This river before the dam burst was impacted with mercury and arsenic in the sediments, in addition to mining structures installed and in operation to extract gold (Rodrigues et al., 2007;Rholes, 2010). In line with the statements of this study, Vieira (2019) showed that the regeneration of vegetation is occurring naturally, with the following families most present in the environment: Fabaceae, Euphorbiaceae, Asteraceae, and Malvaceae. In a pollen analysis carried out by the author, the herbaceous and shrub families were predominant in the trees, since they take longer time for regeneration and development.

Final Considerations
The environmental disaster that occurred in Mariana City reveals one of the current problems in the face of the environmental crisis that has arisen and witnessed in the country.
Therefore, all the economic return that the mining company Samarco grants to Minas Gerais State, Mariana City and its population, tends to be meaningless in the face of the disaster caused by the exploitation of minerals and socio-environmental damage. Not to mention the lives that they lost due to the event that occurred with the rupture of the dam, leaving a trail of destruction through the path covered by the mud of the tailings.
The constancy of the anthropization processes of nature are one of the contradictions of modernity, as they conceive the impasse of solving the difficulty found in environmental preservation and the sustainable use of natural resources. For the extraction of ore, mainly iron, the largest fluid constituent on the planet uses water on a large scale. Moreover, mining activity puts water resources at risk, among other essential elements for life on Earth. For this reason, the importance of the participation of society and public and private managers in the construction of a policy that reduces environmental risks is currently emphasized.
Through the study of the relief, it was possible to generate significant cartographic information for the analysis of the influence of the altimetric distribution in the entire extension of the tragedy. They were observed in the images after the rupture of the Fundão dam in the northwest portion between 2013 and 2016, which continues to reach tailings at the bed of the Gualaxo do Norte River. In this way, with the application of the vegetation index (NDVI), it is possible to observe the impacted area after the tragedy.
Thematic maps generated with the use of GIS are tools for analyzing future studies and provide information to managers for the creation of actions in order to mitigate situations such as what happened in Mariana City. The results obtained in this study carried out in an office show the dimension of the tragedy in the city, even though it is necessary to study in locu. Furthermore, the results achieved are shown to be positive to analyze the referred accident through satellite images and the vegetation index (NDVI) in order to identify areas with loss of vegetation and transport of tailings that head towards the Gualaxo do Norte River.
REGET, Santa Maria, v. 24, Ed. Especial, e27, p. 1-21, 2020 The impacted area was presented visually through maps that are cartographic products generated to clearly present the impacted areas to public and private managers and society in general. Through the Geographic Information System (GIS), information regarding the change in the landscape and the destruction of the Bento Rodrigues District caused by the mud spill can be verified and visualized on the maps after the rupture of the Fundão dam which belongs to the Samarco Company located in Mariana City.
Therefore, it is necessary that other similar studies can contribute with results and suggestions that allow dialogue about the problems presented in this study.