Desvendando a movimentação da água em área de recarga do Sistema Aquífero Guarani (SAG), utilizando análise hidrológica e traçadores isotópicos
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Data
2019-08-27
Autores
Batista, Ludmila Vianna [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A necessidade do estudo os diferentes processos do ciclo hidrológico de forma integrada tem se tornado cada vez mais urgente, uma vez que o uso do termo “crise hídrica” se torna cada vez mais frequente. Nesse sentido, a determinação de taxas de recarga e quantificação dos fluxos subterrâneos, aliados ao uso de isótopos estáveis (2H e 18O), que são excelentes traçadores da movimentação da água no ciclo hidrológico, impulsionaram esse estudo, buscando gerar informações científicas fundamentais para uma melhor gestão dos recursos hídricos. Situada numa porção de afloramento do Sistema Aquífero Guarani (SAG), a área de estudo está inserida em uma pequena bacia hidrográfica na porção oeste do estado de São Paulo, onde as águas subterrâneas e superficiais são responsáveis pelo abastecimento de inúmeras cidades da região. O estudo teve como principal objetivo compreender a dinâmica entre os diversos compartimentos do ciclo hidrológico, buscando mudanças nos padrões de precipitação e de recarga subterrânea, por métodos de fácil aplicação, como balanço hídrico e flutuações dos níveis d’água (WTF), bem como a aplicação de traçadores isotópicos (δ2H e δ18O) em diferentes sazonalidades. Ao considerar a sazonalidade dos dados isotópicos na chuva, águas superficiais e subterrâneas, pode-se observar que os valores de δ18O são mais empobrecidos durante a estação chuvosa e mais enriquecidos durante a estação seca. A diferença entre os sinais isotópicos permitiu compreender a movimentação da água dentro do ciclo hidrológico, indicativo que as águas do SAG são responsáveis pela recarga dos rios, sobretudo quando comparado os valores de d-excess durante a estação seca (10,19 e 12,10‰ V-SMOW para as águas superficiais e subterrâneas, respectivamente). A estimativa de recarga foi mais sensível frente as mudanças nos padrões da chuva e variou de 25,5 a 34,6% pelo método WTF e de 28 a 37% pelo método de separação do escoamento. Os valores encontrados para a separação do fluxo de base (BFImáx = 0,65, 0,80 e 0,90, para os filtros de Eckhardt, Inverso e Q90/Q50, respectivamente) se mostraram primordiais para manutenção das águas superficiais ao longo de todo o ano.
The need to study the different processes of the hydrological cycle in an integrated way has become increasingly urgent since the use of the term "water crisis" becomes more and more frequent. In this sense, the determination of rates of recharge and quantification of the underground flows, together with the use of stable isotopes (2H and 18O), which are excellent tracers of water movement in the hydrological cycle, stimulated this study, seeking to generate scientific information fundamental to better management of water resources. Located in a portion of the outcrop of the Guarani Aquifer System (SAG), the study area is in a small hydrographic basin in the western portion of the state of São Paulo, where groundwater and surface waters are responsible for the supply of numerous cities located there. The main objective of this study is to understand the dynamics between the various compartments of the hydrological cycle, searching for changes in precipitation and underground recharge patterns, using easy-to-apply methods such as water balance and water level fluctuations (WTF), as well as the application of isotopic tracers (δ2H and δ18O) in different seasonal conditions. When considering the seasonality of the isotopic data in rainfall, surface water, and groundwater, it can be observed that δ18O values are more depleted during the rainy season and more enriched during the dry season. The difference between the isotopic signals allowed to understand the movement of the water within the hydrological cycle, indicating that the waters of the SAG are responsible for the recharge of the rivers, especially when compared the dexcess values during the dry season (10.19 and 12.10 ‰ V-SMOW for surface and groundwater, respectively). The recharge estimate ranged from 25.5 to 34.6% by the WTF method and from 28 to 37% by the runoff separation method and was more sensitive to changes in rainfall patterns, while the values found for (BFImáx = 0.65, 0.80 and 0.90 for the Eckhardt, Inverse and Q90/Q50 filters, respectively) were essential for the maintenance of surface water throughout the year.
The need to study the different processes of the hydrological cycle in an integrated way has become increasingly urgent since the use of the term "water crisis" becomes more and more frequent. In this sense, the determination of rates of recharge and quantification of the underground flows, together with the use of stable isotopes (2H and 18O), which are excellent tracers of water movement in the hydrological cycle, stimulated this study, seeking to generate scientific information fundamental to better management of water resources. Located in a portion of the outcrop of the Guarani Aquifer System (SAG), the study area is in a small hydrographic basin in the western portion of the state of São Paulo, where groundwater and surface waters are responsible for the supply of numerous cities located there. The main objective of this study is to understand the dynamics between the various compartments of the hydrological cycle, searching for changes in precipitation and underground recharge patterns, using easy-to-apply methods such as water balance and water level fluctuations (WTF), as well as the application of isotopic tracers (δ2H and δ18O) in different seasonal conditions. When considering the seasonality of the isotopic data in rainfall, surface water, and groundwater, it can be observed that δ18O values are more depleted during the rainy season and more enriched during the dry season. The difference between the isotopic signals allowed to understand the movement of the water within the hydrological cycle, indicating that the waters of the SAG are responsible for the recharge of the rivers, especially when compared the dexcess values during the dry season (10.19 and 12.10 ‰ V-SMOW for surface and groundwater, respectively). The recharge estimate ranged from 25.5 to 34.6% by the WTF method and from 28 to 37% by the runoff separation method and was more sensitive to changes in rainfall patterns, while the values found for (BFImáx = 0.65, 0.80 and 0.90 for the Eckhardt, Inverse and Q90/Q50 filters, respectively) were essential for the maintenance of surface water throughout the year.
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Palavras-chave
Hidrologia, Isótopos estáveis, Separação escoamento, Sistema Aquífero Guarani (SAG), Hidrology, Stable isotopes, Hydrograph separation, Guarani Aquifer System (SAG)