Identificação de áreas prioritárias para recuperação em uma bacia hidrográfica intermunicipal no oeste maranhense
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Data
2022-07-15
Autores
Rizzo, Felipe Alexandre
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Universidade Estadual Paulista (Unesp)
Resumo
Diante da necessidade de conhecer a qualidade ambiental da Bacia Hidrográfica do Córrego Pequiá, no oeste maranhense, inserida nos municípios de Açailândia, São Francisco do Brejão e João Lisboa foi proposto este estudo objetivando a elaboração de uma ferramenta de gestão que permita identificar áreas degradadas necessárias à recuperação. A ocupação irregular do solo, evidenciou a alteração da paisagem na bacia, que encontra-se inserida no bioma Amazônico com algumas áreas transicionais do Cerrado, onde se destaca a presença de grandes fazendas, distrito industrial e áreas urbanas, alterando consequentemente a qualidade da água. Para a execução deste estudo foram utilizados os softwares ArcGIS 10.6, QGIS 2.18 e Trackmaker para o cálculo e análise de índices morfométricos das sub-bacias hidrográficas presentes na área de estudo, das variáveis da Equação Universal de Perdas de Solo, da espacialização dos Índices de Qualidade da Água (IQA) e Índice de Estado Trófico (IET) nos exutórios das sub-bacias hidrográficas, da relação espacial da temperatura da superfície terrestre (TST) com o índice de vegetação por diferença normalizada (NDVI) em dois períodos distintos 1984 e 2020 e, por fim, a determinação de áreas prioritárias à recuperação (APR). Os resultados permitiram identificar uma tendência a não circularidade para todas as sub-bacias hidrográficas e o maior gradiente do canal principal observado foi de 38,70 m/km na sub-bacia do Mosquito. Os índices de sinuosidade foram classificados como reto para as sub-bacias do baixo Pequiá e Mosquito, ficando as demais como muito sinuoso com maior tendência de aporte de sedimentos. Para os resultados dos índices de rugosidade mostram terreno suavemente ondulado para as sub-bacias do Mosquito e alto Pequiá com valores 165,92 e 187,88 e a perda média anual de solo foi estimada em 17.180,07 t/ha/ano que variou entre 12,65 e 34.349,4 t/ha/ano. Para o IQA alguns parâmetros divergiram do que preconiza a Resolução CONAMA 357/05, para Classe 2, sendo observado IQA ruim para dois exutórios localizados no baixo Pequiá e Brejão e um IET classificado como supereutrófico para os exutórios Mosquito e alto Pequiá, indicando um possível quadro de eutrofização do rio. Na análise das imagens ocorreu diferença de vegetação existente em 36 anos de atividades antrópicas que alterou a dinâmica da floresta em diversos pontos da bacia, ocasionando um aumento médio de temperatura de 4ºC, evidenciando-se a necessidade da recomposição florestal. Na bacia 1,73 % das áreas possuem risco alto de diminuição da capacidade de recuperação, uma vez que o desenvolvimento bacteriano e de microorganismos poderá se tornar menor a cada ano, por consequência do aumento da temperatura do solo. Concluiu-se que existe a necessidade de gestão compartilhada entre os municípios onde está inserida a Bacia Hidrográfica do Pequiá para a manutenção da dinâmica hidrológica da região. A perda de solo nos pontos mais críticos da bacia se deve ao tipo de solo, elevada declividade e falta de práticas conservacionistas. O IQA e IET trazem informações relevantes das alterações geradas pelas ações antrópicas nas águas superficiais. Portanto, essa proposta possibilita a tomada de decisão em áreas estritamente prioritárias, dependendo de menores investimentos por se tratar áreas pontuais na Bacia do Córrego Pequiá.
In view of the need to know the environmental quality of the Pequiá Stream Watershed, in the west of Maranhão, inserted in the municipalities of Açailândia, São Francisco do Brejão and João Lisboa, this study was proposed aiming at the elaboration of a management tool that allows the identification of degraded areas necessary for recovery. The irregular occupation of the soil has shown the alteration of the landscape in the basin, which is inserted in the Amazon biome with some transitional areas of the Cerrado, where the presence of large farms, industrial districts and urban areas stands out, consequently altering the quality of the water. For the execution of this study, the ArcGIS 10.6, QGIS 2. 18 and Trackmaker to calculate and analyze the morphometric indexes of the sub-watersheds present in the study area, the variables of the Universal Soil Loss Equation, the spatialization of the Water Quality Index (WQI) and the Trophic State Index (STI) in the outlets of the sub-watersheds, of the spatial relationship of land surface temperature (LST) with the normalized difference vegetation index (NDVI) in two distinct periods 1984 and 2020 and, finally, the determination of priority areas for recovery (PAR). The results allowed identifying a tendency to non-circularity for all sub-basins and the highest gradient of the main channel observed was 38.70 m/km in the Mosquito sub-basin. The sinuosity indices were classified as straight for the sub-basins of the lower Pequiá and Mosquito, while the others were classified as very sinuous with a greater tendency of sediment contribution. The results of the roughness indices show a gently undulating terrain for the subbasins of Mosquito and upper Pequiá with values of 165.92 and 187.88. The average annual soil loss was estimated at 17,180.07 t/ha/year, which varied between 12.65 and 34,349.4 t/ha/year. For the WQI some parameters diverged from what is recommended by the CONAMA Resolution 357/05, for Class 2, being observed a bad WQI for two outlets located in the lower Pequiá and Brejão and an STI classified as supereutrophic for the outlets Mosquito and upper Pequiá, indicating a possible picture of eutrophication of the river. In the analysis of the images there was a difference in the vegetation existing in 36 years of anthropic activities that altered the dynamics of the forest in several points of the basin, causing an average temperature increase of 4ºC, evidencing the need for forest recomposition. In the basin, 1.73% of the areas have a high risk of reducing their capacity to recover, since the bacterial and microorganism development may become less each year, as a result of the increase in soil temperature. It was concluded that there is a need for shared management between the municipalities where the Pequiá watershed is located in order to maintain the hydrological dynamics of the region. The loss of soil in the most critical points of the basin is due to the type of soil, high slope and lack of conservationist practices. The WQI and STI provide relevant information about the changes generated by anthropic actions in surface waters. Therefore, this proposal enables decision making in strictly priority areas, depending on smaller investments because they are punctual areas in the Pequiá Stream Watershed.
In view of the need to know the environmental quality of the Pequiá Stream Watershed, in the west of Maranhão, inserted in the municipalities of Açailândia, São Francisco do Brejão and João Lisboa, this study was proposed aiming at the elaboration of a management tool that allows the identification of degraded areas necessary for recovery. The irregular occupation of the soil has shown the alteration of the landscape in the basin, which is inserted in the Amazon biome with some transitional areas of the Cerrado, where the presence of large farms, industrial districts and urban areas stands out, consequently altering the quality of the water. For the execution of this study, the ArcGIS 10.6, QGIS 2. 18 and Trackmaker to calculate and analyze the morphometric indexes of the sub-watersheds present in the study area, the variables of the Universal Soil Loss Equation, the spatialization of the Water Quality Index (WQI) and the Trophic State Index (STI) in the outlets of the sub-watersheds, of the spatial relationship of land surface temperature (LST) with the normalized difference vegetation index (NDVI) in two distinct periods 1984 and 2020 and, finally, the determination of priority areas for recovery (PAR). The results allowed identifying a tendency to non-circularity for all sub-basins and the highest gradient of the main channel observed was 38.70 m/km in the Mosquito sub-basin. The sinuosity indices were classified as straight for the sub-basins of the lower Pequiá and Mosquito, while the others were classified as very sinuous with a greater tendency of sediment contribution. The results of the roughness indices show a gently undulating terrain for the subbasins of Mosquito and upper Pequiá with values of 165.92 and 187.88. The average annual soil loss was estimated at 17,180.07 t/ha/year, which varied between 12.65 and 34,349.4 t/ha/year. For the WQI some parameters diverged from what is recommended by the CONAMA Resolution 357/05, for Class 2, being observed a bad WQI for two outlets located in the lower Pequiá and Brejão and an STI classified as supereutrophic for the outlets Mosquito and upper Pequiá, indicating a possible picture of eutrophication of the river. In the analysis of the images there was a difference in the vegetation existing in 36 years of anthropic activities that altered the dynamics of the forest in several points of the basin, causing an average temperature increase of 4ºC, evidencing the need for forest recomposition. In the basin, 1.73% of the areas have a high risk of reducing their capacity to recover, since the bacterial and microorganism development may become less each year, as a result of the increase in soil temperature. It was concluded that there is a need for shared management between the municipalities where the Pequiá watershed is located in order to maintain the hydrological dynamics of the region. The loss of soil in the most critical points of the basin is due to the type of soil, high slope and lack of conservationist practices. The WQI and STI provide relevant information about the changes generated by anthropic actions in surface waters. Therefore, this proposal enables decision making in strictly priority areas, depending on smaller investments because they are punctual areas in the Pequiá Stream Watershed.
Descrição
Palavras-chave
Córrego Pequiá, Áreas Degradadas, Análise Espacial, Uso do Solo, Água