Isotopic composition and elemental concentrations in groundwater in the Kuiseb Basin and the Cuvelai-Etosha Basin, Namibia

Proceedings of the International Association of Hydrological Sciences

Knoeller, Kay^3¹  Motsei, Lebogang^4²  Ithindi, Johanna^1³  Kgabi, Nnenesi A.^1⁴  Atekwana, Eliot^2⁵  Uugwanga, Martha^1⁶ 

[1]Centre for Applied Radiation Science and Technology, North-West University, Mafikeng, South Africa^5

[2]Department of Agriculture & Natural Resources Sciences, Namibia University of Science and Technology, Windhoek, Namibia^6

[3]Department of Catchment Hydrology, Helmholtz Centre for Environmental Research, Leipzig, Germany^3

[4]Department of Civil and Environmental Engineering, Namibia University of Science and Technology, Windhoek, Namibia^1

[5]Department of Geological Sciences, University of Delaware, Newark, Delaware, USA^2

[6]School of Agriculture, North-West University, Mafikeng, South Africa^4

DOI  :  10.5194/piahs-378-93-2018

学科分类：地球科学(综合)

来源: Copernicus Publications

【 摘 要 】

We assessed environmental tracers in groundwater in two contrasting basins in Namibia; the Kuiseb Basin, which is a predominantly dry area and the Cuvelai-Etosha Basin, which is prone to alternating floods and droughts. We aimed to determine why the quality of groundwater was different in these two basins which occur in an arid environment. We analysed groundwater and surface water for the stable isotope ratios of hydrogen (δ²H) and oxygen (δ¹⁸O) by cavity ring-down spectroscopy and metals by inductively coupled plasma mass spectrometry. The δ²H and δ¹⁸O of surface water in the Cuvelai-Etosha Basin plot on an evaporation trend below the global meteoric water line (GMWL) and the local meteoric water line (LMWL). The δ²H and δ¹⁸O of some groundwater samples in the Cuvelai-Etosha Basin also plot on the evaporation trend, indicating recharge by evaporated rain or evaporated surface water. In contrast, the δ²H and δ¹⁸O of groundwater samples in the Kuiseb Basin plot mostly along the GMWL and the LMWL, indicating direct recharge from unevaporated rain or unevaporated surface water. Fifty percent of groundwater samples in the Cuvelai-Etosha Basin was potable (salinityK > Ca > Mg vs. Na > Mg > Ca > K for the Cuvelai-Etosha Basin. For metals in the Kuiseb Basin the order of abundance is Fe > Al > V > As > Zn vs. Al > Fe > V> As > Zn for the Cuvelai-Etosha Basin. The relative abundance of cations and metals are attributed to the differences in geology of the basins and the extent of water-rock interaction. Our results show that the quality of groundwater in Cuvelai-Etosha Basin and Kuiseb Basin which vary in the extent of aridity, is controlled by the extent of water-rock interaction at the surface and in the groundwater aquifer.

【 授权许可】

CC BY