カメルーン地質鉱山研究所水文学研究センターにおける水文学研究の紹介

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1. Introduction The Institute of Geological and Mining Research (IRGM) was. created by decree No79/495 of 4th December 1979 organizing the General Delegation of Scientific and Technical Research (GDSTR), which after many changes, has today become the Ministry of Scientific Research and Innovation (MINRESI). The institute with head office in Yaounde (Fig. 1) under the auspices of MINRESI is a specialized institute that implements Government policy on scientific and technical research. Specifically, and according to article 21 of the above decree, the mission of IRGM is to elaborate and carry out research projects to generate and manage information in geology, hydrology, energy and mining in Cameroon (https://www.irgm- cameroon.org). IRGM has various research centers including the Hydrological Research Center (CRH).. Figure 1. Head Office of the Institute of Geological and Mining. Research, Cameroon.. The objectives of CRH include the creation of knowledge on surface and underground water resources in relation with the physical milieu and climatic regimes of Cameroon; develop and apply cutting-edge research techniques in hydrology and hydrogeology particularly in the collection, analysis and interpretation of data; and carry out water quality control studies and create a related database (https://www.irgm-cameroon. org). The CRH is equipped with a hydrogeochemical laboratory (LAGE) with several analytical equipments including AAS, PICARRO, IC and 13C/12C CO2 Isotope Analyzer.. Our research team under CRH has been conducting research on groundwater, surface water quality and recharge for the past. years in collaboration with several Japanese Researchers and Institutions (Ako et al., 2013a, b; Mengnjo et al., 2017, 2020). Since 2012, besides groundwater studies, we installed several rain sampling stations in 16 localities across Cameroon to sample rainwater for chemical and stable isotope analysis (Figs. 2 and 3).. Figure 2. Rain sampling 16 stations installed across Cameroon as. functions of (a) elevation and (b) climate and vegetation.. Elevation map in (a) is modified after Sodalmelik (2007). and the map in (b) is after GLC2000 ; http://bioval.jrc.. ec.europa.eu/).. Research Introduction. Introduction of Hydrological Research at the Hydrological Research Centre of the Institute of Geological and Mining Research, Cameroon. Mengnjo Jude WIRMVEM 1） and Ako Andrew AKO 2）. 1） Institute of Geological and Mining Research, P.O Box 4110, Yaoundé, Cameroon. E-mail: [email protected] 2） Institute of Geological and Mining Research, P.O Box 4110, Yaoundé, Cameroon. E-mail: [email protected]. 15. Figure 3 . Rain water sampling station and groundwater sampling. for chemical and stable isotope analyses.. The key objectives are to evaluate the suitability of the rainwater for drinking, produce local/regional and the Cameroon meteoric water lines, and assess the spatial and temporal variation inδ18O & δD and their relationship to regional precipitation cycle. Multiple geoscientific data such as geological, tectonic, topographical and land use/cover information are integrated into our research works using GIS and remote sensing techniques.. 2. Preliminary findings Rain water in most of the sampling stations were acidic, going. from 4.92 (in Ndawara) to 6.41 (in Dang). The dominant ions in both rural and urban sites were Ca2+, K+ and NO3－ except for Nsimi, where HCO3- was the most representative anion. A significant contribution of Ca2+ was observed in all sites; mainly due to incorporation of soil dust in precipitation. The K+ and NO3－ contributions to ionic load of rainwater in rural sites are a reflection of the dominant agricultural activities across Cameroon. High Ca2+, Mg2+, SO42－ and K+ to Na+ enrichment ratios relative to seawater ratios indicated the significant terrigenous influence on water chemistry, mainly from the Sahara dusts. Based on seasonality, the highest concentrations of major ions and trace metals in both rural and urban areas were observed during the pre-monsoon season. This could be attributed to build up of concentrations of species due to lack of wet removal of species and the dispersion effect of the Harmattan winds. About 62.5% of the samples (in Bamenda, Kumbo, Ndop Ndawara and Dang) were Ca2+－Mg2+－Cl－－SO42－ water type. Based on TDS, major ion and trace metal contents, the rainwater is considered suitable for human consumption; hence, rainwater harvesting is recommended as an alternative source of drinking water across Cameroon.. Preliminary results of stable isotopes in rainwater show a wide variation in δ18O & δD (Fig. 4), suggesting varied controls on precipitation. The slope of the Cameroon meteoric line (CMWL) is similar to that of the Global meteoric line (GMWL) of Craig (1961).. Figure 4. P re l iminary resu l t s o f s tab le i so topes showing the. Cameroon meteoric line (CMWL) with a similar slope to. the Global meteoric water line (GMWL).. 3. Future research As a result of limited data on stable isotopes, major ions. and trace elements rainwater, surface water and groundwater in Cameroon that is highly dependent upon for drinking water, domestic use and agriculture, our team hope to carry more detailed studies in across various regions in Cameroon for a rich database. Studies on the bottled waters sold across Cameroon and the entire Central African region are envisaged.. Geoinformatics tools such as GIS and remote sensing techniques are very useful in the spatio-temporal analysis of hydrological, hydrogeological and hydrochemical data.. References Ako, A. A., Gloria, E. E., Shimada, J., Koike, K., Hosono, T.. Ichiyanagi, K., Akoachere, A. R., Beatrice, K. T., George, E. N., and Ntankouo, N. R. (2013a) Nitrate contamination of groundwater in two areas of the Cameroon Volcanic Line (Banana Plain and Mount Cameroon area). Applied Water Sciences, vol. 4, no 2, pp. 99-113.. https://doi.org/10.1007/s13201-013-0134-x Ako, A. A., Shimada, J., Hosono, T., Kagabu, M., Akoachere,. A. R., George, E. N., Aka,T. F., Masahiko, O., Gloria, E. E., Beatrice, K. T., and Oumar, F. M. (2013b) Flow dynamics and age of groundwater within a humid equatorial active volcano (Mt. Cameroon) deduced by∂D,∂18O, 3H and chlorofluorocarbaons (CFCs). Journal of Hydrology, vol. 502, pp. 156-176. https://doi.org/10.1016/j.jhydrol.2013.08.032. Craig, H. (1961) Isotopic variations in meteoric waters. Science,. δD= 8.08δ18O + 14.20 R² = 0.97. δD = 8δ18O + 10. ‐130. ‐100. ‐70. ‐40. ‐10. 20. 50. ‐18 ‐8 2. δD (‰. ) δ18O (‰). Cameroon rain (n=302) Hail fall rain Hail fall associated rain CMWL GMWL. 16. vol. 133, pp. 1702-1703. https://doi.org/10.1126/science.133.3465.1702 Mengnjo, J. W., Brice, T. K., Engome, R. W., Mumbfu, E. M.,. Wilson, Y. F., Ako, A. A., and Ohba, T. (2020) Multi-tracer (δ18O,δD, 3H, CFCs and SF6) investigation of groundwater recharge and apparent age at the Bamenda Highlands along the Cameroon Volcanic Line. Sustainable Water Resources Management, vol. 6, no. 2, pp. 1-16.. https://doi.org/10.1007/s40899-020-00357-z. Mengnjo, J. W., Ohba, T., Linus, A. N., Brice, T. K., Wiylahnyuy, E. K., Mumbfu, E. M., Tasin, G. B., Muga; Y., Gloria, E. T., Wilson, Y. F., and Ako, A. A. (2017) Effect of diffuse recharge and wastewater on groundwater contamination in Douala, Cameroon. Environmental Earth Sciences, vol. 76, pp. 1-23. https://doi.org/10.1007/s12665-017-6692-8. Sodalmelik (2007) Topographic map of Cameroon, created with GMT from public domain GLOBE data.. http://commons.wikimedia.org/wiki/File:Cameroon_ Topography.png. 17