Compositions and mobility of major, δD, δ18O, trace, and REEs patterns in water sources at Benue River Basin-Cameroon: implications for recharge mechanisms, geo-environmental controls, and public health.

Hydro-geochemical data are required for understanding of water quality, provenance, and chemical composition for the 2,117,700 km2 Niger River Basin. This study presents hydro-geochemical 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 hydro-chemical 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 non-isochemical dissolution of local rocks by water, with springs, wells and borehole waters exhibiting surface water-gaining, 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 behavior. 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 differs slightly with surface water composition. Post-Archean Average Australian Shale-normalized REEs patterns ranging from 1.08 to 199 point to the dissolution of silicates as key sources of trace elements to groundwater, coupled to deposition by eolian dust.

Hydrogeochemistry and quality of surface water and groundwater in the vicinity of Lake Monoun, West Cameroon: approach from multivariate statistical analysis and stable isotopic characterization.

With the use of conventional hydrogeochemical techniques, multivariate statistical analysis, and stable isotope approaches, this paper investigates for the first time surface water and groundwater from the surrounding areas of Lake Monoun (LM), West Cameroon. The results reveal that waters are generally slightly acidic to neutral. The relative abundance of major dissolved species are Ca(2+) > Mg(2+) > Na(+) > K(+) for cations and HCO3 (-) â‰« NO3 (-) > Cl(-) > SO4 (2-) for anions. The main water type is Ca-Mg-HCO3. Observed salinity is related to water-rock interaction, ion exchange process, and anthropogenic activities. Nitrate and chloride have been identified as the most common pollutants. These pollutants are attributed to the chlorination of wells and leaching from pit latrines and refuse dumps. The stable isotopic compositions in the investigated water sources suggest evidence of evaporation before recharge. Four major groups of waters were identified by salinity and NO3 concentrations using the Q-mode hierarchical cluster analysis (HCA). Consistent with the isotopic results, group 1 represents fresh unpolluted water occurring near the recharge zone in the general flow regime; groups 2 and 3 are mixed water whose composition is controlled by both weathering of rock-forming minerals and anthropogenic activities; group 4 represents water under high vulnerability of anthropogenic pollution. Moreover, the isotopic results and the HCA showed that the CO2-rich bottom water of LM belongs to an isolated hydrological system within the Foumbot plain. Except for some springs, groundwater water in the area is inappropriate for drinking and domestic purposes but good to excellent for irrigation.