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 two...
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| Published in: | Proceedings of the International Association of Hydrological Sciences Vol. 378; pp. 93 - 98 |
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| Main Authors: | , , , , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Copernicus Publications
01-01-2018
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| Online Access: | Get full text |
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| Summary: | 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 (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. |
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| ISSN: | 2199-899X 2199-8981 2199-899X |
| DOI: | 10.5194/piahs-378-93-2018 |