Isotopic composition and elemental concentrations in groundwater in the Kuiseb Basin and the Cuvelai-Etosha Basin, Namibia
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...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2018-05-01
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| Series: | Proceedings of the International Association of Hydrological Sciences |
| Online Access: | https://www.proc-iahs.net/378/93/2018/piahs-378-93-2018.pdf |
| _version_ | 1818777290748723200 |
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| author | N. A. Kgabi E. Atekwana J. Ithindi M. Uugwanga K. Knoeller L. Motsei M. Mathuthu G. Kalumbu H. R. Amwele R. Uusizi |
| author_facet | N. A. Kgabi E. Atekwana J. Ithindi M. Uugwanga K. Knoeller L. Motsei M. Mathuthu G. Kalumbu H. R. Amwele R. Uusizi |
| author_sort | N. A. Kgabi |
| collection | DOAJ |
| description | 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 (<i>δ</i><sup>2</sup>H) and oxygen (<i>δ</i><sup>18</sup>O) by cavity
ring-down spectroscopy and metals by inductively coupled plasma mass
spectrometry. The <i>δ</i><sup>2</sup>H and <i>δ</i><sup>18</sup>O 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
<i>δ</i><sup>2</sup>H and <i>δ</i><sup>18</sup>O 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 <i>δ</i><sup>2</sup>H and <i>δ</i><sup>18</sup>O 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 (salinity
< 1 ppt) compared to 79 % in the Kuiseb Basin. The high salinity
in the groundwater of the Cuvelai-Etosha Basin does not appear to be caused
by evaporation of water (evapo-concentration) on surface prior to
groundwater recharge, but rather by the weathering of the Kalahari
sediments. The low salinity in the Kuiseb Basin derives from rapid recharge
of groundwater by unevaporated rain and limited weathering of the
crystalline rocks. The order of abundance of cations in the Kuiseb Basin is
Na > K > 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. |
| first_indexed | 2024-12-18T11:26:29Z |
| format | Article |
| id | doaj.art-84ee90744f034edca07b384bac24b8b3 |
| institution | Directory Open Access Journal |
| issn | 2199-8981 2199-899X |
| language | English |
| last_indexed | 2024-12-18T11:26:29Z |
| publishDate | 2018-05-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Proceedings of the International Association of Hydrological Sciences |
| spelling | doaj.art-84ee90744f034edca07b384bac24b8b32022-12-21T21:09:41ZengCopernicus PublicationsProceedings of the International Association of Hydrological Sciences2199-89812199-899X2018-05-01378939810.5194/piahs-378-93-2018Isotopic composition and elemental concentrations in groundwater in the Kuiseb Basin and the Cuvelai-Etosha Basin, NamibiaN. A. Kgabi0E. Atekwana1J. Ithindi2M. Uugwanga3K. Knoeller4L. Motsei5M. Mathuthu6G. Kalumbu7H. R. Amwele8R. Uusizi9Department of Civil and Environmental Engineering, Namibia University of Science and Technology, Windhoek, NamibiaDepartment of Geological Sciences, University of Delaware, Newark, Delaware, USADepartment of Civil and Environmental Engineering, Namibia University of Science and Technology, Windhoek, NamibiaDepartment of Civil and Environmental Engineering, Namibia University of Science and Technology, Windhoek, NamibiaDepartment of Catchment Hydrology, Helmholtz Centre for Environmental Research, Leipzig, GermanySchool of Agriculture, North-West University, Mafikeng, South AfricaCentre for Applied Radiation Science and Technology, North-West University, Mafikeng, South AfricaDepartment of Civil and Environmental Engineering, Namibia University of Science and Technology, Windhoek, NamibiaDepartment of Agriculture & Natural Resources Sciences, Namibia University of Science and Technology, Windhoek, NamibiaDepartment of Civil and Environmental Engineering, Namibia University of Science and Technology, Windhoek, NamibiaWe 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 (<i>δ</i><sup>2</sup>H) and oxygen (<i>δ</i><sup>18</sup>O) by cavity ring-down spectroscopy and metals by inductively coupled plasma mass spectrometry. The <i>δ</i><sup>2</sup>H and <i>δ</i><sup>18</sup>O 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 <i>δ</i><sup>2</sup>H and <i>δ</i><sup>18</sup>O 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 <i>δ</i><sup>2</sup>H and <i>δ</i><sup>18</sup>O 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 (salinity < 1 ppt) compared to 79 % in the Kuiseb Basin. The high salinity in the groundwater of the Cuvelai-Etosha Basin does not appear to be caused by evaporation of water (evapo-concentration) on surface prior to groundwater recharge, but rather by the weathering of the Kalahari sediments. The low salinity in the Kuiseb Basin derives from rapid recharge of groundwater by unevaporated rain and limited weathering of the crystalline rocks. The order of abundance of cations in the Kuiseb Basin is Na > K > 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.https://www.proc-iahs.net/378/93/2018/piahs-378-93-2018.pdf |
| spellingShingle | N. A. Kgabi E. Atekwana J. Ithindi M. Uugwanga K. Knoeller L. Motsei M. Mathuthu G. Kalumbu H. R. Amwele R. Uusizi 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 |
| title | Isotopic composition and elemental concentrations in groundwater in the Kuiseb Basin and the Cuvelai-Etosha Basin, Namibia |
| title_full | Isotopic composition and elemental concentrations in groundwater in the Kuiseb Basin and the Cuvelai-Etosha Basin, Namibia |
| title_fullStr | Isotopic composition and elemental concentrations in groundwater in the Kuiseb Basin and the Cuvelai-Etosha Basin, Namibia |
| title_full_unstemmed | Isotopic composition and elemental concentrations in groundwater in the Kuiseb Basin and the Cuvelai-Etosha Basin, Namibia |
| title_short | Isotopic composition and elemental concentrations in groundwater in the Kuiseb Basin and the Cuvelai-Etosha Basin, Namibia |
| title_sort | isotopic composition and elemental concentrations in groundwater in the kuiseb basin and the cuvelai etosha basin namibia |
| url | https://www.proc-iahs.net/378/93/2018/piahs-378-93-2018.pdf |
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