Gilberto Aparecido Rodrigues
gilberto.rodrigues3@fatec.sp.gov.br
Taquaritinga School of Technology, Taquaritinga, São Paulo, Brazil
Maria Aparecida Bovério
Sertãozinho School of Technology, Sertãozinho, São Paulo, Brazil
Kátia Cristina Galatti
Faculdade de Tecnologia de Taquaritinga – Taquaritinga – São Paulo – Brasil.
Most vulnerability identified in a watershed is due to anthropogenic interference in rural and urban areas. Sensitivity and common sense in joint action by the different agents of society can minimize the negative impacts on a basin through planned action. This study aimed to determine the environmental vulnerabilities of the highest region of the Taquaritinga watershed, SP, Brazil. The study methodology was the observation of satellite images using the free Google Earth Pro software by photocomparison of images in a sample area of 3,581 ha, divided into four quadrants. The results showed that the positive points of the area are the presence of straw on the ground and contour lines as conservation measures. However, it deserves special attention from the authorities to dispose properly of solid urban waste and the development of projects to re-establish native flora associated with the construction of more containment basins along the access roads to rural producers, which could contribute, in the long term, to improving the flow of water resources in the basin.
Keywords: Watershed; Environmental impact; Environmental vulnerability
In any watershed, various positive or negative actions constantly occur, which can directly influence the impact degree to which the watershed is subject (Lanna, 2000; Almeida, 2010). A hydrographic basin is essentially characterized by a main watercourse fed by its tributaries, which, in the higher parts, is delimited by a watershed. Within this space, there are processes of runoff and sediment transportation (Sousa, Martins Filho, and Matias, 2012) that impact water quality and can lead to erosive processes, loss of agricultural productivity, reduction of permanent preservation areas, and silting of watercourses (Vischi Filho et al., 2016).
Each watershed can be subdivided into smaller watersheds, which means that a watershed is formed by a set of small watersheds (Rosa et al., 2004). A watershed is an area topographically defined by the drainage area of a river channel or by a system of connected river channels in a way that all the water draining into this space has a single direction of exit, information corroborated by geotechnologies (Pereira et al., 2017).
The vulnerabilities of a basin are generally the result of anthropogenic interference in rural and urban areas (Costa, 2018), and it is possible that such interference can be aggravated by the geomorphological conditions of a given region and intensified by the characteristics of the economic activities carried out by various segments of human activity, especially those that use natural resources (Candido et al., 2010).
Almeida (2010) broadens the concept of vulnerability by reporting an enormous coincidence between social vulnerability in urban environments and regions where the population is exposed to higher risks, factors linked to urban sprawl (Jatobá, 2011), and soil sealing. It also points out that the risk areas with the greatest potential for impact are those of permanent preservation (APP) in urban environments.
The environmental assessment of a region allows identification of its potential for use (or non-use) of occupation, vulnerabilities, dynamics, and complexity of the ecosystem, leading to actions that enable its preservation and conservation (Vischi Filho et al., 2016). Determining environmental vulnerability enables the assessment of the risk conditions of the area in question for geo-environmental processes such as erosion (Figure 6), soil contamination, water resources, and loss of agricultural use (Zonta, 2012; Vischi Filho et al., 2016). With proper planning, areas of environmental vulnerability in the watershed can be avoided by giving them uses compatible with their current state, in addition to carrying out studies to identify the factors that trigger this situation of environmental vulnerability and then seeking remediation alternatives (Cunha and Borba, 2014; Vischi Filho et al., 2016).
Geotechnologies have allowed studies to be performed on the environmental conditions of a river basin (Candido et al., 2010). In this respect, Candido et al. (2010) studied the vulnerabilities of the Uberaba river basin in Minas Gerais and found that more than half of the basin area had degrees of severity, ranging from "accentuated to severe." In the analysis of the vegetation in the studied basin, the presence of very sparse vegetation cover was evident, denoting one of the marked vulnerabilities in the study, which are closely associated with negative anthropogenic actions, the result of soil degradation processes, and data that agrees with Zonta (2012) and Vischi Filho et al. (2016).
Geotechnology tools can be used to identify and map the geo-environmental characteristics and natural and environmental vulnerabilities of a given river basin and, through consistent public policies and orderly river basin management involving the various players in society, the ongoing process of vulnerability can be mitigated (Costa, 2018). In this study, Costa (2018) found that areas previously considered preserved have been making way for the growth of annual or perennial crops and short-cycle crops. These anthropogenic actions have significantly changed the local landscape due to inappropriate land use and conservation, easily observable from satellite images, even in areas close to urban centers, motivated by disordered urban sprawl. This study aimed to identify the environmental vulnerabilities of the highest region of the watershed in Taquaritinga, SP, Brazil, using the free Google Earth Pro software.
MATERIAL AND METHODS
The study was carried out in the region of Latitude 21° 22′ 12.94″S and Longitude 48° 26′ 29.97″O of the highest region of the Taquaritinga hydrographic basin, which belongs to the Tietê-Batalha Hydrographic Basin Council (CBH-TB) (Figure 1). A sampling area of approximately 3581ha was designated for the study (Figures 2 and 3) using the "line" tool in the "circle" tab of the free Google Earth Pro software (2021). The sample area of 3581ha was divided into four quadrants using the Google Earth Pro tools, according to the findings of Rodrigues, Bovério, and Ferrarezi (2020). Figures 2 and 3 show the main study area highlighted in color and the elements of Quadrant 1.
The elements of the rural landscape to be identified in the four quadrants consisted of the quantification of sugar cane haulers (CA), impermeable area (AI), represented by the asphalt network, permanent preservation area (APP), construction areas (AC), woody crop areas (CL), and water sheet areas (LD). The "polygon" tool was used to obtain information on the perimeter and area of each element in each quadrant. Semi-perennial crops (CSP), represented by sugar cane, were measured by subtracting the total area of each quadrant from the landscape elements present in the respective quadrant. The "path" tool was used specifically to measure the lengths of the path elements and the impermeable area, corresponding to the area covered by the asphalt road in the four quadrants (Figure 4). To calculate the area of paths (bare soil), the various types of paths in the quadrant were considered, varying in width. For this, ten widths of the tracks in each quadrant were sampled (at random) to obtain their average width, and the use of the total length of the tracks multiplied by their average width allowed us to estimate the probable area devoid of soil. The asphalting areas followed the same logic. Once the lengths of all the asphalted areas in the quadrant had been determined, the area resulted from multiplying the length by the width of the asphalt paving.
The Permanent Preservation Areas (PPA), Construction Areas (CA), Woody Crop Areas (CL), and Water Sheet Areas (WLA) had their perimeter and area directly determined using the “polygon” tool. Semi-perennial crops (CSP), represented by sugar cane, were determined by subtracting the total quadrant area and all the elements of the rural landscape. The construction areas were considered the clear images of houses or masonry sheds and part of a contour, sometimes made up of pastures, sometimes composed of various fruit trees or native species, and finally, degraded areas.
Excel software was used to organize the data in the case of data measured in hectares when corresponding to the area and to calculate the percentages of each landscape element compared to the total quadrant area. For the data's statistical analysis, the quadrants were considered repetitions, and the treatments were only those with repetitions greater than or equal to four evaluations in each quadrant. In this case, only APP areas, paths, and sugarcane crop areas (plots) could be statistically analyzed. The other elements could only be ascertained. A completely randomized design (CRD) with four replications was used for the analysis of variance using the Fisher-Snedecor F test, and for the test of means, the Scott Knott test was used. Both tests were performed at 11% probability using the free software Sisvar, version 5.6, by Ferreira (2008).
The results of the analysis of variance of the landscape elements that stood out most in the visualizations during the study showed that there was no significant effect of the size of the sugarcane fields (CSP), the length of the sugarcane tracks, or the permanent preservation areas (APP) at the 11% probability level (Table 1). The test of means showed a significant difference (P < 0.11) only in the size of the sugar cane plots. The results of the quantification of the elements of the rural landscape that can be quantified or visually identified are shown in Graph 1. The four most significant elements in the landscape are sugar cane crops (75%), followed by permanent preservation areas (APP = 15.1%), woody crops (3.1%), paths (CA = 3.96%), construction areas (AC = 1.12%), paved (impermeable) areas (AP = 0.76%), institutional areas (AI = 0.42%), and water slides (0.06%), totaling 3581ha. Since the total area of this study corresponds to 3581ha, according to the new forestry code, the areas set aside for legal reserves (RL) should correspond to almost 20% of the quadrant's area, i.e., 716.2ha.
The existence of significant areas of legal reserve (LR) in the four quadrants was not clearly identified, occurring in part in the southern region of quadrants 3 and 4 due to the layout, the sampling area inserting part of the hillside area of the Serra de Jaboticabal. Observing the study area, it can be seen that the areas of sufficient environmental fragility correspond to the areas surrounding the controlled landfill in Quadrant 3 (Figure 5), which has significant potential for contaminating the water table (Gouveia and Prado, 2010; Giacomazzo and Almeida, 2020) in the short term and the Bauru aquifer in the longer term, due to leachate percolation.
It can also be seen that the waterproofing area is present in all four quadrants, represented by the asphalt of two highways, one linking Taquaritinga to Jaboticabal, SP, and the other linking Taquaritinga to Monte Alto, SP. The road edges linking Taquaritinga to Jaboticabal are formed by dual carriageways with properly maintained embankments and internal rainwater drainage channels between the two carriageways. In addition, it is easy to see the construction of rainwater containment basins (Figure 5) on the side of one of the lanes, which is a positive measure for conserving water resources. The study area is still well endowed with contour lines (Figure 5) and the presence of straw on the ground due to the mechanized harvesting of sugar cane, especially in Quadrants 3 and 4, which is a highly recommended practice that can mitigate any degree of erodibility of a given region or even prevent erosion by rain, which can place the watershed in a degree of environmental fragility (Santiago et al., 2019). Figure 6 shows an area in an advanced process of erodibility, showing the greater environmental frangibility of quadrant 4. In this study, the presence of straw shown by the satellite images can be inferred as a very positive aspect for mitigating possible losses of soil and organic matter, contributing to the sustainability of the agricultural production system (Sousa, Martins Filho, and Matias, 2012).
Artificial and natural water depths are rare in the APP areas of the study area. These elements of the landscape have the natural function of conserving the ecosystem as they enrich the habitat, which can be better exploited by wild animals for watering; however, their banks and interiors are contaminated by grasses. In addition, it is perfectly observable that there are native plants, but they are very sparse, denoting a source of food and shelter for wild animals in precarious conditions. These vulnerabilities agree with the vulnerabilities of a watershed reported by Candido et al. (2010) in the region of Uberaba, MG, and in the studies by Almeida (2010).
It is possible that the factors triggering environmental vulnerability in the studied basin could be reversed in the medium and long term by seeking alternative remedies (Cunha, Ritter, and Borba, 2014). According to Costa (2018), consistent public policies and the orderly management of river basins can mitigate the ongoing process of vulnerability as long as they involve various agents (Castro, 2012), including rural producers, public extension agents or not, the river basin committee, the municipal government, and the sugar-alcohol sector operating in the river basin. Therefore, it is essential to adopt geotechnologies to respond faster and with greater quality to the growing and diverse demands of public policies (Guia et al., 2016).
Soil and water conservation management practices (containment basins, contour lines, and straw on the ground), cited by Tucci (2005), if implemented in a given basin, allow positive changes to the landscape and positively influence agricultural yields. Satellite images can prove different changes to the landscape through photocomparison, a feasible methodology for monitoring, and even agri-environmental rehabilitation for managing micro-watersheds (Vichi Filho et al., 2016).
The main vulnerabilities detected in the region under study concern the environmental protection areas, the legal reserve proportional to the studied area, which is probably out of step with the legislation. The permanent preservation areas are contaminated with various forage grasses, there are few native woody plants, and surface watercourses are not apparent. The area under study also presents risks of contamination of the water table and the Bauru aquifer due to the presence of a controlled landfill. The overgrowth of sugarcane areas, divided by tracks, results in a considerable area of bare soil. The positive points of the area in question are the presence of straw on the ground, contour lines, and containment basins; however, they are few in number as conservation measures, but the area under study indicates that attention should be paid to developing projects to re-establish native plants associated with the construction of more containment basins, which could contribute in the long term to improving the flow of the basin's water resources.
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Received: December 13, 2022
Approved: August 2, 2023
DOI: 10.20985/1980-5160.2023.v18n2.1845
How to cite: Rodrigues, G.A., Bovério, M.A., Galatti, K.C. (2023). Environmental conditions of the elements of a rural landscape in the highest region of the Taquaritinga watershed, SP, Brazil. Revista S&G 18, 2. https://revistasg.emnuvens.com.br/sg/article/view/1845