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Influência da seca severa em indicadores de águas superficiais
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Abstract(s)
RESUMO: Durante a seca que afetou Portugal no ano hidrológico de 2021/2022, foram realizadas cinco campanhas de monitorização das águas superficiais na bacia hidrográfica do Rio Mondego. A amostragem ocorreu de março a novembro de 2022 e os indicadores de qualidade da água medidos foram comparados com um fundo geoquímico criado a partir de dados abertos. Durante o período de seca, as águas superficiais parecem tendencialmente mais alcalinas potencialmente devido à menor diluição ou a uma influência bicarbonatada proveniente de águas subterrâneas. No mesmo período as concentrações de NO2 tenderam a aumentar, quase sempre acima de teores normais. No início do ano hidrológico seguinte, com eventos de chuva intensa, e um aumento do escoamento, erosão e transporte de partículas do solo, notou-se um aumento da turbidez, com valores acima do normal, associado a concentrações excessivas de Al, Fe e Mn, enquanto se verificou o regresso aos valores normais de pH e NO2.
ABSTRACT: During the drought that affected Portugal in the hydrological year 2021/2022, five monitoring campaigns of surface waters were conducted in the Mondego River basin. These monitoring campaigns took place from March to November 2022 and involved measurements of electric conductivity, pH, and turbidity. Additionally, samples were collected for the chemical analysis of major and minor ions, as well as metals and metalloids. The results from these campaigns were then compared with a geochemical background created from open data for nearby quality stations. The reduced water availability, and consequently, the dilution capacity, coupled with an increased influence of groundwater on surface water, appears to have led to shifts towards more alkaline waters and an increase in NO2 concentrations. Reduced precipitation also restricts the mobilization of soil elements into water bodies, resulting in lower concentrations of certain metals (Al, As, Fe, and Mn) in surface water. In the post-drought period, at the beginning of the rainy season, increased runoff, erosion, and sediment transport seem to have caused an increase in surface water turbidity and concentrations of Al, Fe, and Mn above normal levels. However, during this same period, as water availability increases and the course’s dilution capacity improves, water flow enhances surface water aeration, and NO2 concentrations return to normal levels.
ABSTRACT: During the drought that affected Portugal in the hydrological year 2021/2022, five monitoring campaigns of surface waters were conducted in the Mondego River basin. These monitoring campaigns took place from March to November 2022 and involved measurements of electric conductivity, pH, and turbidity. Additionally, samples were collected for the chemical analysis of major and minor ions, as well as metals and metalloids. The results from these campaigns were then compared with a geochemical background created from open data for nearby quality stations. The reduced water availability, and consequently, the dilution capacity, coupled with an increased influence of groundwater on surface water, appears to have led to shifts towards more alkaline waters and an increase in NO2 concentrations. Reduced precipitation also restricts the mobilization of soil elements into water bodies, resulting in lower concentrations of certain metals (Al, As, Fe, and Mn) in surface water. In the post-drought period, at the beginning of the rainy season, increased runoff, erosion, and sediment transport seem to have caused an increase in surface water turbidity and concentrations of Al, Fe, and Mn above normal levels. However, during this same period, as water availability increases and the course’s dilution capacity improves, water flow enhances surface water aeration, and NO2 concentrations return to normal levels.
Description
Keywords
Seca Água superficial Qualidade Parâmetros físico-químicos Fundo geoquímico Drought Surface water Quality Physical chemical parameters Geochemical background
Citation
Sequeira, M.D., Tavares, A.O., Castilho, A. & Dinis, P.A. (2025). Influência da seca severa em indicadores de águas superficiais. In: Comunicações Geológicas, 2025, vol. 112, Fascículo Especial I, pp. 225-228. https://doi.org/10.34637/ba3s-sv17
Publisher
LNEG - Laboratório Nacional de Energia e Geologia