Compositions and mobility of major, dD, d18O, trace, and REEs patterns in water sources at Benue River Basin-Cameroon: Implications for recharge mechanisms, geoenvironmental

Hydrogeochemical data are required for understanding of water quality, provenance and chemical composition for the 2117700 km2 Niger River Basin. This study presents hydrogeochemical analysis of the Benue River Basin, a major tributary of the Niger River. The distribution of, major ions, Si, δD and δ18O, Trace and Rare Earth Elements (TE and REEs, respectively) composition in 86 random water samples, revealed mixing of, groundwater with surface water to recharge shallow aquifers by July and September rains. Equilibration of groundwater with kaolinite, and montmorillonites by, incongruent dissolution imprints hydrochemical signatures that vary from Ca+Mg-NO3 in shallow wells to Na+K-HCO3 in boreholes and surface waters, with undesirable concentrations of fluoride identified as major source of fluorosis in the local population. Our results further indicate nonisochemical dissolution of local rocks by water, with springs, wells and borehole waters exhibiting surface watergaining, weakest water-rock interaction, and strongest water-rock interaction processes, respectively. Poorly mobile elements (Al, Th and Fe) are preferentially retained in the solid residue of incongruent dissolution, while alkalis, alkaline earth and oxo-anion-forming elements (U, Mo, Na, K, Rb, Ca, Li, Sr, Ba, Zn, Pb) are more mobile and enriched in the aqueous phase, whereas transition metals display an intermediate behaviour. Trace elements vary in the order of Ba > Sr > Zn > Li > V > Cu > Ni > Co > As > Cr > Sc > Ti > Be > Pb > Cd, with Potentially Harmful Elements such as Cd, As, and Pb mobilized in acidic media attaining near undesirable levels in populated localities. With the exception of Y, REEs distribution in groundwater in the order of Eu > Sm > Ce >Nd > La > Gd > Pr > Dy > Er > Yb > Ho > Tb > Tm, differ slightly with surface water composition. Post-Archean Average Australian Shale normalized REEs patterns ranging from 1.08-199, point to the dissolution of silicates as key sources of trace elements to groundwater, coupled to deposition by eolian dust