Navegando por Assunto "Recharge"

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Texto publicado em jornal
A hydrogeological conceptual model for the groundwater dynamics in the ferricretes of Capão Xavier, Iron Quadrangle, Southeastern Brazil
(2021-12) Dias, Jordania Cristina dos Santos; Bacellar, Luis de Almeida Prado
In the Iron Quadrangle (IQ), southeastern Brazil, ferricretes usually overlie the banded iron formations (BIFs) of the Cauê Formation, rocks that not only host the most important iron ore deposits of this region but are also its major groundwater source. Little is known about the water dynamics in ferricretes and therefore how they influence the recharge of the subjacent aquifer (Cauê aquifer). The objective of this research was to identify ferricrete typologies and investigate their water dynamics in the Capão Xavier region, northwest of IQ. Field work consisted of macroscopic description of ferricretes, infiltration tests and multitemporal electrical resistivity surveys. Two ferricrete typologies were distinguished: structured ferricretes, which are older and occur on top of plateaus, and detrital ferricretes of colluvial-alluvial origin, which were deposited downslope and in topographic lows. The structured ferricretes preserve the medium- to high-angle foliation inherited from the underlying BIFs, whereas the detrital ferricretes constitute thick packs subparallel to the topographic surface and are intercalated with argillaceous layers in areas of karstic depressions. The structured ferricretes are more porous (20.8% to 24.4%) than the detrital ferricretes (14.4% to 17.6%), hence they have higher mean basic infiltration rates (8.3x10-6 m/s) than detrital ferricretes (2.8x10-6 m/s). Despite these low mean basic infiltration rates, infiltration advances thanks to the karstic-fissural porosity (fractures and joints widened by karstification), and superficial cavities that are connected to caves in the interface between the ferricrete and the subjacent, less resistant, transition horizon. Karstification is controlled by the subvertical foliation in the structured ferricretes and subparallel layering in the detrital ferricretes. Some factors that favor infiltration and deep percolation of water are superficial rugosity in structured ferricretes, and karstic depressions in both typologies. The recharge of the Cauê aquifer is diachronic, firstly taking place via the karstic-fissural system and later via the ferricrete matrix.
Texto publicado em jornal
Origin of spring waters employing a multiparametric approach with special focus on stable isotopes 2H and 18O in the Lagoa Santa Karst region, Southern Brazil*
(2020-01-19) Ribeiro, Carolina; Velásquez, Leila; Fleming, Peter
Karst environments have an inherent complexity that interferes with their hydrogeology comprehension. Hence, isotope hydrology can be a valuable tool to assess trajectory of subsurface flows in an unexplored setting. The study area is located in the Lagoa Santa Karst, an environmental protection area of great economic, cultural and ecological importance, where Neoproterozoic metalimestones accommodate karst-fractured aquifers, characterized by complex water dynamics, essential vulnerability and high productivity. The purpose of this study was to investigate groundwater flow origins of springs using principally environmental stable isotopes 2H and 18O. Rainwater and spring water were sampled and analysed. The LMWL presents angular and linear coefficients strongly similar to those of the GMWL. Spring isotopic signatures, which represent the base flow and present wide-ranging of 2H and 18O, were separated into two groups. The first group can be associated with recent rainwater major contributions, while the second group shows significant evaporated water contributions, largely represented by resurgences. Tritium concentration and physico-chemical parameter data supported this interpretation, pointing that waters of the second group remained more time on the surface and subsurface. Therefore, using isotope tracers to evaluate upper groundwater zone in this tropical karst system is a powerful instrument for water resources management.