Shallow groundwater recharge mechanism and apparent age in the Ndop plain, northwest Cameroon

Abstract

Knowledge of groundwater recharge and apparent age constitutes a valuable tool for its sustainable management. Accordingly, shallow groundwater (n = 72) in the Ndop plain has been investigated using the stable isotopes of oxygen ( 18 O) and hydrogen ( 2 H or D) and tritium ( 3 H) to determine the recharge process, timing and rate of recharge, and residence time. The shallow groundwater showed low variability in d18 O values (-2.7 to -4.1 %) and 3 H content (2.4-3.1 TU). The low variability suggests a similar origin, homogenous aquifer, good water mixing and storage capacity of the groundwater reservoir. Like surface water, a cluster of groundwater along the Ndop Meteoric Water Line (NMWL) and Global Meteoric Water Line indicates meteoric origin/recharge. The rainfall recharge occurs under low relative humidity conditions and negligible evaporation effect. About 80 % of the recharge is from direct heterogeneous/diffuse local precipitation at low altitude (\1,260 m) within the Ndop plain. Approximately 20 % is from high altitude precipitation (localised recharge) or is recharged by the numerous inflowing streams and rivers from high elevations. A homogenous cluster of d-values in groundwater (and surface water) between May and June monsoon rains on the NMWL suggests dominant recharge during these months. The recharge represents at least 16 % ([251 mm) of the annual rainfall (1,540 mm) indicating high annual recharge; high enough for development of the groundwater resource for agriculture. The 3 H content ([2.4 TU) in groundwater indicates post-1952 recharged water with an estimated residence time \30 years, suggesting short subsurface circulation, and subsequently a renewable aquifer.

Strategies trees use to overcome seasonal water limitation in an agroforestry system in semiarid West Africa

“…By knowing where and how much water trees use within the soil profile, we are able to better predict how changes in tree cover may influence groundwater recharge. This is especially relevant in this area, where it has been shown that shallow groundwater is periodically recharged by rainfall (Huneau et al, , Lutz, Thomas, & Panorska, , Wirmvem et al, ). The variation in the isotopic signature of shallow groundwater between the dry and wet season observed at our study site probably reflects this recharge process.…”

Global Isotope Hydrogeology―Review

“…For example, among all tropical International Atomic Energy Agency stations (i.e., within 25° of equator) reporting more than 50 monthly precipitation isotope measurements, the great majority (>95% of stations) record inverse correlations between precipitation rate and δ 18 O. Because tropical precipitation often correlates inversely with rainfall δ 18 O (Figure ), comparing precipitation and groundwater isotope compositions can help test the hypothesis that tropical groundwater recharge ratios are higher when rainfall rates are higher (Adanu, ; Alsaaran, ; Gill, ; Harrington et al, ; Jasechko & Taylor, ; Jones et al, ; Jones & Banner, , ; Kambuku et al, ; L. Li, et al, ; Meredith et al, ; Négrel & Petelet‐Giraud, ; Oiro et al, ; Sánchez‐Murillo & Birkel, ; Vogel et al, ; Vogel & Van Urk, ; Wirmvem, Mimba, et al, ; Yeh et al, , ).…”

Spatial Variability and Contamination Levels of Fresh Water Resources by Saline Intrusion in the Coastal Low Lying Areas of the Douala Metropolis-Cameroon

“…EC, imply that sodium in the irrigation water may replace calcium and magnesium ions in the soil, potentially causing damage to the soil structure as in [39]. Such studies have been carried out elsewhere with promising implications for policy measures as in [55] [56] [57] [58] [59]. The analytical data for ground water chemistry that was plotted on the US salinity diagram (Figure 7) illustrates that 8 samples, representing 42%, are found in the low salinity and low alkalinity (C1S1) area and is good for irrigation purposes.…”