Interaction between surface waters and the Quaternary shallow alluvial aquifer of Lake Maga downstream: influence of ponds, streams, irrigation canals, and geological features (Far North, Cameroon)
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Abstract
The valorization of Lake Maga for agricultural purposes has not only contributed to the socio-economic development of the study area, but has also modified the surface water (SW) and groundwater (GW) flow regimes. Understanding the interaction between the SW and the shallow Quaternary aquifer, under land use change and soil structure modification, is still a challenge, especially in the semi-arid area. In this study, GW level, hydrogeochemical characterization, and geological features are used to understand, locally, the influence of Lake Maga, its associated hydraulic components, and the other SW bodies on the GW behaviour. GW levels were measured in 51 wells in December 2012 and monitored in February 2013, and in 15 wells (beyond the 51) in June 2017 and December 2018. Physicochemical parameters of SWs and GWs were measured in the field, and 15 water samples were collected for major ion characterization. The GW levels were close (mean value ≈5 m) to the land surface, with zero to very low (< 1 m) water level fluctuations near SW bodies. The GW levels (< 2 m) are influenced more by their proximity to irrigation canals, ponds, and streams than Lake Maga (mean ≈3.5 m). The analysis of electrical conductivity (EC) values and GW levels showed that the weakly mineralized (< 200 µS.cm−1) GW were associated with the shallower GW table level. The moderate GW mineralization (200 < EC < 700 µS.cm−1) were more influenced by the geological texture of the shallow aquifer. The analysis of the geological characteristics of the sub-shallow aquifer structure in the locality of Pouss is mainly sandy, while in the localities of Maga and Guirvidig, clay, clayey-sand and sandy-clay materials dominate. There are no trends in GW chemical evolution from Lake Maga waters towards the shallow groundwater table (SGWT). The mixing-ratios values showed that the SW contributed for more than 65% (mean) to the sub-shallow aquifer in the study area, and the highest SWs (80%) contribution occurred in the locality of Pouss, close to Lake Maga, pond, Logone River, irrigation canal, and seasonal stream, associated with the shallowest GW levels (< 1.5 m). The proximity to SW bodies and the texture of the fluvio-lacustrine deposit of the shallow aquifer strongly influenced GW table levels and their hydrogeochemical characteristics. This work could be a prerequisite to understand how the physicochemical and chemical properties of GW in the shallow aquifer evolve and respond under the influence of SW bodies.
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Geosciences Journal opens a new era for the publication of geoscientific research articles in English, covering geology, geophysics, geochemistry, paleontology, structural geology, mineralogy, petrology, stratigraphy, sedimentology, environmental geology, economic geology, petroleum geology, hydrogeology, remote sensing and planetary geology.
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