Hydrogeology and hydrogeochemistry of an alkaline volcanic area: the NE Mt. Meru slope (East African Rift – Northern Tanzania)

Abstract

Abstract. The objective of this study is to analyze the geochemical conditions associated with the presence of fluoride (F − ) in the groundwater of an area of Northern Tanzania. The studied aquifers are composed of volcanic rocks such as phonolitic and nephelinitic lavas, basalts, lahars of various ages and mantling ash. Sedimentary rocks consisting of fine-grained alluvial and lacustrine deposits occur as well. Samples collected from springs, borehole and surface water, during two monitoring surveys, were analyzed for the various physico-chemical and isotopic parameters. The geochemical composition of water is typically sodium bicarbonate. High values of F − (up to 68 mg l −1 ) were recorded. The highest values of fluoride agreed with the highest values of pH, sodium and bicarbonate. Dissolution of major ions, exchange processes and precipitation of Ca 2+ from supersaturated solutions joined with the local permeability and hydraulic gradients, control the fluoride mobilization and the contamination of the area.

Hydrogeochemical characteristics and spatial distribution of groundwater quality in Arusha well fields, Northern Tanzania

“…Sodium ion was generally dominant in all samples with Magnesium being the least cation in the study area (Na + > Ca 2+ > K + > Mg 2+ ). Such chemical behavior in groundwater is explained by cations exchange reactions between Na + and Ca 2+ which occur as a result of Green color indicates negative correlation (r < − 0.5) and pink color, positive correlation (r > 0.5) water-rock interaction as water moves through different mineralogical composition (Cerling et al 1989;Ghiglieri et al 2012;Utom et al 2013). The ions distribution ( Fig.…”

“…Mount Meru region is dominated by volcanic and sedimentary hydrogeologic formations with various mineralogy compositions. These include fluorapatite, natrite, halite, sylvite, aphthitalite, calcite, goethite, phillipsite, chabazite, augite, sanidine, analcime, leucite, nepheline, anorthoclase, biotite, cancrinite, riebeckite, albite and illite (Ghiglieri et al 2012).…”

“…This necessitates the need of undertaking hydrogeochemical investigations to determine the quality of water intended for public supplies by ensuring compliance with local and international standards. Ghiglieri et al (2012) conducted hydrogeological and hydrochemistry study on the northeastern part of Mt. Meru in Arusha Tanzania where fluoride levels of up to 68 mg/l was observed in alkaline volcanic zones.…”

Groundwater flow processes and mixing in active volcanic systems: the case of Guadalajara (Mexico)

“…The combination of different environmental tracer techniques helps elucidate the groundwater's origin, recharge, flow velocity and direction, residence or travel times, connections between aquifers, and surface and groundwater interrelations (Edmunds and Smedley, 2000;De Vries and Simmers, 2002;Appelo and Postma, 2005;Ako et al, 2013;Stumpp et al, 2014). These techniques have been applied in large semiarid to arid rift systems (Bretzler et al, 2011;Furi et al, 2011;Ghiglieri et al, 2012;Siebert et al, 2012;Panno et al, 2013;Forrest et al, 2013;Williams et al, 2013). Stable isotopes ( 2 H, 18 O) provide information regarding origins, recharge processes, flow paths and residence times, especially in fractured rock aquifers.…”

“…6b). On the other hand, it is possible that only a displacement of δ 18 O is occurring, which could correspond to a geothermal effect and mixing with meteoric waters(Giggenbach and Lyon, 1977;Herrera and Custodio, 2003). The increased Cl concentrations compared to other groups evidences mixture with hy-www.hydrol-earth-syst-sci.net/19/3937/2015/ Hydrol.…”