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Hydrochemical and isotopic characteristics of groundwater in the Ndop plain,northwest Cameroon: resilience to seasonal climatic changes |
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| Authors: | Mengnjo Jude Wirmvem Takeshi Ohba Justice Yuven Suila Wilson Yetoh Fantong Nchemty Oscar Bate Seigo Ooki Engome Regina Wotany Asobo Nkengmatia Elvis Asaah Samuel Ndonwi Ayonghe Gregory Tanyileke Joseph Victor Hell |
| Institution: | 1. Department of Chemistry, School of Science, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, 259-1211, Japan 2. G.B.H.S. Atiela, Nkwen, P.O. Box 5147, Bamenda, Cameroon 3. Institute of Geological and Mining Research, P.O. Box 4110, Yaoundé, Cameroon 4. Cameroon College of Arts and Science Kumba, P.O. Box 10, Kumba, Cameroon 5. Department of Environmental Science, University of Buea, P.O. Box 63, Buea, Cameroon 6. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, 152-8551, Japan |
| Abstract: | Shallow groundwater (>30 mbgl) is an essential source of drinking water to rural communities in the Ndop plain, northwest Cameroon. As a contribution to water management, the effect of seasonal variation on the groundwater chemistry, hydrochemical controls, drinking quality and recharge were investigated during the peaks of the dry (January) and rainy (September) seasons. Field measurements of physical parameters were preceded by sampling 58 groundwater samples during both seasons for major ions and stable isotope analyses. The groundwater, which was barely acidic (mean pH of 6) and less mineralised (TDS < 272 mg/l), showed no significant seasonal variation in temperature, pH and TDS during the two seasons. The order of cation abundance (meq/l) was Na+ > Ca2+ > Mg2+ > K+ and Na+ > Mg2+ > Ca2+ > K+ in the dry and rainy seasons, respectively, but that of anions ( \( {\text{HCO}}_{3}^{ - } \) > \( {\text{NO}}_{3}^{ - } \) > Cl? > \( {\text{SO}}_{4}^{2 - } \) > F?) was similar in both seasons. This suggests a negligible effect of seasonal variations on groundwater chemistry. The groundwater, which was CaMgHCO3 and NaHCO3, is chemically evolved rainfall (CaMgSO4Cl) in the area. Silicate mineral dissolution and cation-exchange were the main controls on groundwater chemistry while there was little anthropogenic influence. The major ions and TDS concentrations classified the water as suitable for human consumption as per WHO guidelines. The narrow cluster of δ18O and δD of same groundwater from both seasons between the δ18O and δD values of May–June precipitation along the Ndop Meteoric Water Line indicates meteoric origin, rapid recharge (after precipitation) and timing of recharge between May and June rainfall. Diffuse groundwater recharge mainly occurs at low altitudes (<1,400 m asl) within the plain. Besides major ions and TDS, the similar δ18O and δD of groundwater from both seasons indicate a consistent groundwater recharge and flow pattern throughout the year and resilience to present day short-term seasonal climatic variations. However, controlled groundwater abstraction is recommended given the increasing demand. |
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