Vol.:(0123456789) 1 3 Sustainable Water Resources Management (2020) 6:2 https://doi.org/10.1007/s40899-020-00357-z ORIGINAL ARTICLE Multi‑tracer (δ 18 O, δD, 3 H, CFCs and SF 6 ) investigation of groundwater recharge and apparent age at the Bamenda Highlands along the Cameroon volcanic line Mengnjo Jude Wirmvem 1  · Brice Tchakam Kamtchueng 1  · Engome Regina Wotany 2  · Mumbfu Ernestine Mimba 1  · Wilson Yetoh Fantong 1  · Ako Andrew Ako 1  · Takeshi Ohba 3 Received: 14 May 2019 / Accepted: 11 January 2020 © Springer Nature Switzerland AG 2020 Abstract The Bamenda Highlands contains numerous dilute and soda springs of unknown hydrological provenance. These dilute springs are a vital source of drinking water to the inhabitants. As a contribution to water management, this study investigated the spring water recharge, residence time and sub-surface circulation using δ 18 O, δD, 3 H, CFCs, SF 6 and TDS. A plot of both water types along the local meteoric water line indicated the meteoric origin and rapid recharge following precipitation. Dilute springs with a δ 18 O altitude efect of 0.27/100 m suggested recharge at diferent elevations. The CFC-12, CFC-11 and CFC-113 dating (complemented by 3 H) showed reasonable young apparent ages of dilute springs ranging from 21 to > 52 (mean/median of 25) years and old soda springs (> 52 years). SF 6 concentrations in dilute springs revealed exceptionally young ages relative to CFCs modelled ages suggesting a terrigenous enrichment of the former. Thus, groundwater dating with SF 6 is unreliable in the area. Besides the old apparent ages of soda springs, their highly depleted δ 18 O and high TDS (mean of 1396 mg/l) indicated palaeo-recharge and high water–rock interaction, respectively. In contrast, the low TDS of dilute springs (< 140 mg/l) indicated low-water interaction. Most dilute springs showed exponential mixing models indicat- ing heterogeneous recharge under unconfned aquifer conditions. Conversely, the old soda springs displayed piston fow and binary mixing models. The meteoric recharge and similar residence time of the shallow dilute springs suggested natural resilience to short-term changes in climatic conditions. Thus, low shallow groundwater abstraction is sustainable at the Bamenda Highlands. Keywords Groundwater recharge · Groundwater age · Cfcs dating · Terrigenic SF 6  · Tritium · Cameroon volcanic line Introduction In Sub-Saharan Africa, increasing population, economic development and poverty reduction drive the develop- ment of groundwater to provide water for human livelihood (Adelana and MacDonald 2008; Lapworth et al. 2013). Over 500 million Africans depend on water sources, especially groundwater found close to their communities for drinking and other domestic uses (Bonsor et al. 2011). The water is mainly accessed through hand-dug wells (> 50-m deep) in low-lying terrains and springs in volcanic settings (Adelana and MacDonald 2008; Bonsor et al. 2011). Although Cam- eroon is endowed with abundant water resources (Katte et al. 2003; Molua and Lambi 2006) including groundwater, a hydrological assessment of these resources has not been sys- tematically carried out in most regions (Katte et al. 2003). The Bamenda Highlands in North-West Cameroon, which constitutes part of the main volcanic watershed in the coun- try (the Cameroon volcanic line, so-called CVL), is one of the most populated regions with over 2 million inhabitants. The continuous increase in population has resulted in high water demand, depletion in quantity and deterioration in the quality of water. The situation is being compounded by the changing climate and land use (Molua and Lambi 2006). * Mengnjo Jude Wirmvem judevom@yahoo.co.uk 1 Institute of Geological and Mining Research, P.O. Box 4110, Yaounde, Cameroon 2 Department of Geology, University of Buea, Box 63, Buea, Cameroon 3 Department of Chemistry, School of Science, Tokai University, Hiratsuka 259-1211, Japan