[en] Abstract
Study region: Groundwater in the southern part of the Saloum Basin in Senegal.
Study focus: The Saloum estuary is a hypersaline and ‘inverse’ estuary where the salinity of river water increases in the upstream direction. This region is problematic in that due to the underlain superficial Continental Terminal aquifer bordered by the hypersaline estuary constitutes the unique fresh groundwater reservoir for water supply for its estimated 466,000 residents living in 18 rural districts (belonging to the regions of Fatick, Kaolack and Kaffrine). This is of high value given that the deep Maastrichtian aquifer (200-300m depth) is saline. This study aims to describe and understand temporal changes in the chemical and isotopic compositions of groundwater, the geochemical processes and especially the groundwater salinization.
New hydrological insights for the region: The analytical data were discriminated into 3 groups on the basis of the water types. Na-Cl, Ca-Cl and Ca-SO4 rich waters derived from saline water intrusion at the vicinity of the Saloum River accompanied by ion exchange reactions and pollution dominate the first group. The second group located mainly in the centre and eastern parts of the region is featured fresh groundwater of Ca-HCO3 derived from calcite dissolution reactions. The third group of Na-HCO3 type and less mineralized indicates freshening processes by recently infiltrating rainwaters. Slight seasonal chemical variations are observed due to new infiltrating water reaching the water table.
High variation in rainfall between the 2 reference years (2003 and 2012) also changes chemical patterns in the groundwater. Chemical evolution of the groundwater is geographically observed and is due to a combination of dilution by recharge, anthropic contamination and seawater intrusion. The results of environmental isotopes (δ18O, δ2H) compared with the local meteoric line indicate that the groundwater has been affected by evaporation processes before and during infiltration. The results also clearly indicate mixing with saltwater and an evolution towards relative freshening between 2003 and 2012 in some wells near the Saloum River.
Abid, K., Zouari, K., Dulinski, M., Chkir, N., Abidi, B., Hydrologic and geologic factors controlling groundwater geochemistry in the Turonian aquifer (Southern Tunisia). Hydrogeol. J. 19:2 (2011), 415–427, 10.1007/s10040-010-0668-z.
Allen, R., Pereira, L., Raes, D., Crop Evapotranspiration – Guidelines for Computing Crop Water Requirements – FAO Irrigation and Drainage Paper 56. 1998, Food and Agriculture Organization of the United Nations (FAO).
Appelo, C.A.J., Postma, D., Geochemistry, Groundwater and Pollution. second ed., 2005, Balkema Rotterdam (656p).
Aranyossy, J.F., Guere, A., Sidoro, M., Étude par les isotopes de l'environnement des dépressions piézométriques; premières données sur des exemples au Mali. Hydrogéologie 3 (1989), 151–158.
Barusseau, J.P., Diop, E.H.S., Saos, J.L., Evidence of dynamics reversal in tropical estuaries, geomorphological and sedimentological consequences (Saloum and casamance rivers, Senegal). Sedimentology 32:4 (1985), 543–552.
Belkhiri, L., Mouni, L., Boudoukha, A., Geochemical evolution of groundwater in an alluvial aquifer: case of El Eulma aquifer, East Algeria. J. Afr. Earth. Sci. 66–67 (2012), 46–55, 10.1016/j.jafrearsci.2012.03.001.
Bellion, Y.J.C., Histoire géodynamique Post-paléozoïque De l'Afrique De l'Ouest d'après l'étude De Quelques Bassins sédimentaires (Sénégal, Taoudéni, Iullemmeden, Tchad). Thèse Sciences. 1987, Univ. Avignon. 296p.
Conrad, G., Lappartient, J.R., The Continental terminal; its position within the Cenozoic geodynamic evolution of the Senegalo-mauritanian basin. J. Afr. Earth Sci. 6:1 (1987), 45–60.
Coplen, T.B., Normalization of oxygen and hydrogen isotope data. Chem. Geol. 72 (1988), 293–297.
Currell, M.J., Cartwright, I., Bradley, D.C., Han, D., Recharge history and controls on groundwater quality in the Yuncheng Basin, North China. J. Hydrol. 385 (2010), 216–229, 10.1016/j.jhydrol.2010.02.022.
Dailey, D., Sauck, W., Sultan, M., Milewski, A., Ahmed, M., Laton, W.R., Elkadiri, R., Foster, J., Schmidt, C., Al Harbi, T., Geophysical, remote sensing, GIS, and isotopic applications for a better understanding of the structural controls on groundwater flow in the Mojave Desert, California. J. Hydrol.: Reg. Stud. 3 (2015), 211–232.
Degallier, R., Hydrogéologique du ferlo septentrional (Sénégal). Mémoire BRGM, 19, 1962 44 p.
Dieng, N.M., Faye, S., Dinis, J., Gonçalves, M., Caetano, M., Combined uses of supervised classification and Normalized Difference Vegetation Index techniques to monitor land degradation in the Saloum saline estuary system. Diop, S., et al. (eds.) The Land/Ocean Interactions in the Coastal Zone of Westand Central Africa, Estuaries of the World, 2014 10.1007/978-3-319-06388-1_2.
Diluca, C., Hydrogeology of the Continental Terminal Aquifer Between the Sine and the Gambia. Technical Report., 1976, BRGM Dakar 33p.
Diop, E.S., Tropical Holocene Estuaries. Comparative Study of the Physical Geography Features of the Rivers from the South of Saloum to the Mellcorée (Guinea Republic). (PhD. Thesis). 1986, Univ. Louis Pasteur, Strasbourg, France.
Edmunds, W.M., Gaye, C.B., Estimating the spatial variability of groundwater recharge in the Sahel using chloride. J. Hydrol. 156:1–4 (1994), 47–59, 10.1016/0022-1694(94)90070-1.
Favreau, G., Leduc, C., Marlin, C., Guéro, A., Une dépression piézométrique naturelle en hausse au Sahel (Sud-Ouest du Niger). C.R. Geosci. 334:6 (2002), 395–401, 10.1016/S1631-0713(02)01763-7.
Faye, S., Evans, D., Cissé Faye, S., Origin and distribution of saline groundwater in the Saloum (Senegal) coastal aquifer, proceed. Second International Conference on Saltwater Intrusion and Coastal Aquifers, Mérida, Yucatán, México, 2001.
Faye, S., Cissé Faye, S., Ndoye, S., Faye, A., Hydrogeochemistry of the Saloum (Senegal) superficial coastal aquifer. Environ. Geol. 44:2 (2003), 127–136, 10.1007/s00254-002-0749-y.
Faye, S., Maloszewski, P., Stichler, W., Trimborn, P., Cissé Faye, S., Gaye, C.B., Groundwater salinization in the Saloum (Senegal) delta aquifer: minor elements and isotopic indicators. J. Sci. Total. Environ., 2004, 17, 10.1016/j.scitotenv.2004.10.00.
Faye, S., Diaw, M., Ndoye, S., Malou, R., Faye, A., 2009. Impacts of climate change on groundwater recharge and salinization of groundwater resources in Senegal. In Proc. Groundwater and Climate in Africa, Kampala, IAHS Publ, 334: 163–173.
Faye, S., Ba, M.S., Diaw, M., Ndoye, S., The groundwater geochemistry of the Saloum delta aquifer: importance of silicate weathering, recharge and mixing processes. J. Afr. Environ. Sci. Tech. 4:12 (2010), 815–830, 10.5897/AJEST09.180.
Ford, M., Tellam, J.H., Hughes, M., Pollution-related acidification in the urban aquifer, Birmingham, UK. J. Hydrol. 140:1-4 (1992), 297–312, 10.1016/0022-1694(92)90245-Q.
Güler, C., Thyne, G.D., McCray, J.E., Turner, A.K., Evaluation of graphical and multivariate statistical methods for classification of water chemistry data. Hydrogeol. J. 10:4 (2002), 455–474, 10.1007/s10040-002-0196-6.
Gamble, A., Babbar-Sebens, M., On the use of multivariate statistical methods for combining in-stream monitoring data and spatial analysis to characterize water quality conditions in the White River Basin, Indiana. USA. Environ. Monit. Assess. 184:2 (2012), 845–875, 10.1007/s10661-011-2005-y.
Garcia, L.A., Shigidi, A., Using neural networks for parameter estimation in groundwater. J. Hydrol. 318:1–4 (2006), 215–231, 10.1016/j.jhydrol.2005.05.028.
Garcia, M.G., Hidalgo, M., Blessa, M.A., Geochemistry of groundwater in the alluvial plain of Tucuman province. Argentina Hydrogeol. J. 9:6 (2001), 597–610, 10.1007/s10040-001-0166-4.
Ghesquière, O., Walter, J., Chesnaux, R., Rouleau, A., Scenarios of groundwater chemical evolution in a region of the Canadian Shield based on multivariate statistical analysis. J. Hydrol.: Reg. Stud. 4(B (2015), 246–266.
Gning, A.A., Etude Et Modélisation Hydrogéologique Des Interactions Eaux De Surface-Eaux Souterraines Dans Un Contexte d'agriculture Irriguée. (Ph.D Thesis). 2015, Univ. Liege 285p.
Hidalgo, M.C., Cruz-Sanjulián, J., Sanroma, A., Geochemical Evolution of underground waters in a sedimentary river basin (water-bearing of Baza-Caniles, Granada, Spain). Tierra y Technol. 20 (1995), 39–48.
Hong, Y.S., Rosen, M.R., Intelligent characterization and diagnosis of the effect of storm water infiltration on ground water quality in a fractured rock aquifer using artificial neural network. Urban Water 3 (2001), 193–204, 10.1016/S1462-0758(01)00045-0.
Hong, S., Kim, H., Kumar, N., Kim, J., Park, N., Experimental investigations on groundwater flow in coastal aquifers. Groundwater and Saline Intrusion, 2004, 15 21p.
Ibrahima, M., Moctar, D., Maguette, D.N., Diakher, M.H., Malick, N.P., Serigne, F., Evaluation of water resources quality in sabodala gold mining region and its surrounding area (Senegal). J. Water Res. Protect. 7:3 (2015), 247–6363, 10.4236/jwarp.2015.73020.
Jankowski, J., Acworth, R.I., Impact of debris-flow deposits on hydrogeochemical processes and the development of dry land salinity in the Yass River Catchment, New South Wales. Aust. Hydrogeol. J. 5:4 (1997), 71–88, 10.1007/s100400050119.
Jones, B.F., Vengosh, A., Rosenthal, E., Yechieli, Y., 1999. Geochemical investigations. In: Seawater Intrusion in Coastal Aquifers-Concepts, Methods and Practices. Springer Netherlands. 14, 51–71. 10.1007/978-94-017-2969-7_3.
Kim, Y., Lee, K.S., Koh, D.C., Lee, D.H., Lee, S.G., Park, W.B., Koh, G.W., Woo, N.C., Hydrogeochemical and isotopic evidence of groundwater salinization in coastal aquifer: a case study in Jeju volcanic island. J. Hydrol. 270:3 (2003), 282–294, 10.1016/S0022-1694(02)00307-4.
Kohonen, T., 2001. An Overview of SOM Literature. In Self-Organizing Maps Springer Berlin Heidelberg. 30, 347–371. 10.1007/978-3-642-56927-2_10.
Koussoube, Y., 2010. Hydrogéologie des séries sédimentaires de la dépression piézométrique du Gondo (bassin du Sourou) – Burkina Faso/Mali. (Ph.D thesis). Paris VI − Pierre et Marie Curie Univ. 285p.
Kristensen, E., Holmer, M., Bussarawit, N., Benthic metabolism and sulfate reduction in a South-East Asian mangrove swamp. Mar. Ecol. Prog. Ser. 73 (1991), 93–103.
Lappartient, J.R., The Continental Terminal and the Early Pleistocene of the Senegalo-mauritanian Basin. Stratigraphy, Sedimentology, Diagenesis, Alterations, Paleoshore Reconstitutions from the Ferralitic Formations, (PhD Thesis). 1985, Univ. Marseille, France 294p.
Largier, J.L., Smith, S.V., Hollibaugh, J.T., Seasonally hypersaline estuaries in Mediterranean-climateregions. Est. Coast. Shelf Sci. 45:6 (1997), 789–797, 10.1006/ecss.1997.0279.
Le Priol J., Dieng B., 1985. Synthèse hydrogéologique du Sénégal (1984–1985). Etude géologique structurale par photo-interprétation. Géométrie et limites des aquifères souterrains. Rap. Min. Hydraul. 0l/85fMHIDEH.
Lebel, T., Ali, A., Recent trends in the Central and Western Sahel rainfall regime (1990–2007). J. Hydrol. 375:1–2 (2009), 52–64, 10.1016/j.jhydrol.2008.11.030.
Lebigre, J.M., Marius, C., Etude d'une séquence mangrove-tanne en milieu équatorial, baie de la Mondah (Gabon). Photo Ann. Trav. Doc. Géogr. Trop. CGET, 1984, 131–145.
Ly, A., Aglanda, R., Le bassin sénégalo-mauritanien dans l'évolution des marges périatlantique au Tertiaire. Cah. Micropaléontol., 6(2), 1991, 47p.
Magaritz, M., Nadler, A., Koyumdjiski, H., Dan, J., The use of Na/Cl ratios to trace solute sources in a semiarid zone. Water Resour. Res. 17:3 (1981), 602–608.
Mercado, A., The use of hydrogeochemical patterns in carbonate sand and sandstone aquifers to identify intrusion and flushing of saline water. Ground Water 23 (1985), 635–645, 10.1111/j.1745-6584.1985.tb01512.x.
Mikhailov, V.N., Isupova, M.V., Hypersalinization of river estuaries in West Africa. Water Resour. 35:4 (2008), 367–385, 10.1134/S0097807808040015.
Montcoudiol, N., Molson, J., Lemieux, J.M., Groundwater geochemistry of the Outaouais Region (Québec, canada): a regional-scale study. Hydrogeol. J. 23:2 (2015), 337–396.
Mudry, J., Discriminant analysis an efficient means for the validation geohydrological hypothesis. Rev. Sci. Eau. 4:1 (1991), 19–37, 10.7202/705088ar.
Ndiaye B., Aranyossy J.F., Faye A., 1993. Le rôle de l'évaporation dans la formation des dépressions piézométriques en Afrique Sahélienne; hypothèses et modélisation. In: Les ressources en eau au Sahel. Etudes hydrogéologiques et hydrologiques en Afrique de l'Ouest par les techniques isotopiques, IAEA-TECDOC-721:53-63.
Ngom, F.D., Caractérisation Des Transferts Hydriques Dans Le Bassin De La Nema Au Sine Saloum. These 3eme Cycle. 2000, Univ. Dakar 130p.
Ngounou Ngatcha, B., Mudry, J., Aranyossy, J.F., Naah, E., Reynault, S.J., Apport de la géologie, de l'hydrogéologie et des isotopes de l'environnement à la connaissance des nappes en creux̋ du Grand Yaéré (Nord Caméroun). Rev. Sci. Eau. 20:1 (2007), 29–43.
Nicolini, E., Rogers, K., Rakowski, D., Baseline geochemical characterisation of a vulnerable tropical karstic aquifer; Lifou, New Caledonia. J. Hydrol.: Reg. Stud. 5 (2016), 114–130.
Noël, Y., Etude Hydrogéologique Du Continental Terminal De Sine Gambie Première Phase Et Rapport De Synthèse. 1975, BRGM Dakar 30p.
Page, J., Citeau, J., Rainfall and salinity of a Sahelian estuary between 1927 and 1987. J. Hydrol. 113:1–4 (1990), 325–341, 10.1016/0022-1694(90)90182-w.
Peeters, L., Baçao, F., Lobo, V., Dassargues, A., Exploratory data analysis and clustering of multivariate spatial hydrogeological data by means of GEO3DSOM, a variant of Kohonen's Self-Organizing Map. Hydrol. Earth Syst. Sci. 11:4 (2007), 1309–1321, 10.5194/hess-11-1309-2007.
Piper, A.M., A graphical procedure in the geochemical interpretation of water analyses. Trans. Am. Geophys. Union, 25(6), 1944, 10.1029/TR025i006p00914.
Pritchard, D.W., 1967. What is an Estuary: Physical Viewpoint. In Lauff, G.H. (Ed.) Estuaries. Am. Ass. Advanc. Sci Pub. 83, 3–5.
Ridd, P.V., Stieglitz, T., Dry season salinity changes in arid estuaries fringed by mangrovesandsaltflats. Estuar. Coast. Shelf. Sci. 54:6 (2002), 1039–1049, 10.1006/ecss.2001.0876.
Roger, J., Barusseau, J.P., Castaigne, P., Duvail, C., Noël, B.J., Nehlig, P., Serrano, O., Banton, O., Comte, J.C., Travi, Y., Sarr, R., Dabo, B., Diagne, E., Sagna, R., Programme d'Appui Au Secteur Minier Cartographie géologique Du Bassin sédimentaire. Projet 9 ACP SE 009. 2009.
Sarr, R., Etude biostratigraphique et paléoenvironnementale des séries d’âge Crétacé Terminal à Eocène moyen du Sénégal occidental. Systématique Et Migration Des Ostracodes. (Thèse d'Etat), 1995, Univ. C.A.D. Dakar 335p.
Savenije, H., Pagès, J., Hypersalinity: a dramatic change in the hydrology of Sahelian estuaries. J. Hydrol. 135 (1992), 157–174.
Shahul Hameed, A., Resmi, T.R., Suraj, S., Unnikrishnan Warrier, C., Sudheesh, M., Deshpande, R.D., Isotopic characterization and mass balance reveals groundwater recharge pattern in Chaliyar River basin, Kerala, India. J. Hydrol.: Reg. Stud. 4(A (2015), 48–58.
Smith, A.J., Turner, J.V., Density-dependent surface water-groundwater interaction and nutrient discharge in the Swan – Canning estuary. Hydrolog. Process. 15:13 (2001), 2595–2616, 10.1002/hyp.303.
Travi, Y., Gac, J.Y., Fontes, J.C., Fritz, B., Chemical and isotopic survey of rain waters in Senegal. Geodyn 2:1 (1987), 43–53.
Travi, Y., Hydrogéochimie Et Hydrogéologie Des Aquifères Fluorés Du Bassin Du Sénégal. Origine Et Conditions De Transport Du Fluor Dans Les Eaux Souterraines. Thesis Sci. 1988, Univ. Paris Sud (Orsay) 190p.
Vengosh, A., Spivack, A.J., Artzi, Y., Ayalon, A., Geochemical and boron, strontium, and oxygen isotopic constraints on the origin of the salinity in groundwater from the Mediterranean soast of Israel. Water Resour. Res. 3:6 (1999), 1877–1894, 10.1029/1999WR900024.
Vengosh, A., 2013. Salinization and Saline Environments. In: Sherwood Lollar, B. (Ed.), Environmental geochemistry, Treatise in Geochemistry. Second Ed. 11, 325–378. 10.1016/B978-0-08-095975-7. 00909-8. (Chapter 9 Salinization Treatise in Geochemistry).
WHO, Guidelines for Drinking-Water Quality. third ed. 1, 2008, Recommendations, World Health Organization (WHO), Geneva, Switzerland 515pp.
Werner A.D., Lockington D.A., 2004. Dynamic groundwater and salt transport near a tidal, partially penetrating estuary. In: Miller C.T., Pinder G.F. (Eds). Computational methods in water resources. 55 (2), 1535–1547. 10.1016/S0167-5648(04)80164-3.
Wolanski, E., An evaporation-driven salinity maximum zone in Australian tropical estuaries. Estuar. Coast. Mar. Sci. 22:4 (1986), 415–424, 10.1016/0272-7714(86)90065-X.
