The Etosha National Park (ENP) is a large protected area in northern Namibia. While the ENP has received a lot of research attention in terms of terrestrial ecosystem process understanding in recent decades, aquatic and hydrological research has to date been limited to a descriptive form. This study provides a baseline hydrological data set of the spatial representation of O- and H-isotope ratios in the groundwater at a park scale, with a focus on three water point types utilised by game, namely natural artesian and contact springs as well as artificial boreholes. The data are used to infer broad-scale hydrological process from groundwater recharge mechanisms dominated by direct rainfall recharge in the west of the ENP to evaporative controls on surface water recharge pathways in the east of the ENP close to Fishers Pan. The findings are used to recommend further targeted research and monitoring to aid management of water resources in the ENP.
The requisite holistic understanding of natural and social environments within and around protected areas includes determining the complexities and challenges of managing water in their terrestrial environment (González
The hydrochemical sampling of the water points in ENP was conducted between 05 and 11 May 2013 and took the form of both a west-east and a south-north transect ( Groundwater borehole: By collection from borehole taps (ensuring that the pump was running continuously to the water trough in order that an unevaporated sample was collected from the aquifer). Artesian springs: A sink-bottle sampler (500 mL plastic drinks bottle with weight tied to the bottle opening and three pin holes introduced at the base, so that bottle sinks into the water column) tied to a rope and thrown as close to the artesian spring eye as possible. Contact spring: Free flowing water in the contact spring.
Location of groundwater sampling points following an approximate west-east (Dolomietpunt to Kameldoring) and south-north (Eindpal to Mbari) transect in the Etosha National Park, May 2013.
Field samples were stored in a cooler bag and then stored in a fridge before transport to the laboratory.
A second sample was taken in the field to determine temperature (°C) ± 0.5 °C, electrical conductivity (mS/cm) ± 1% full scale and pH ± 0.01 pH using a calibrated EUTECH Instruments PCSTestr 35 pocket tester. Samples were then sent to the University of KwaZulu-Natal to measure the stable isotope compositions of oxygen-18 (O18) and deuterium (H2) using a Los Gatos Research (LGR) DT-100 Liquid Water Isotope Laser Analyser and analysed six times to provide a high-value precision using in-house standards of Indian Ocean Water (δ2H 4.75‰ ± 0.41‰; δ18O 0.06‰ ± 0.30‰) and Spring Water (Avian Bottled Water δ2H -61.43‰ ± 0.56‰; δ18O -4.05‰ ± 0.29‰) and a 50:50 mixture of these. The standards were prepared against International Atomic Energy Agency (IAEA) standards LGR2, VSMOW2 and IA-RO53 during which standard deviations of δ2H were less than 2‰ and δ18O less than 0.3‰. At each point, a differential GPS reading was also taken with Trimble GeoExplorer 3® to determine accurate elevations above the mean sea level (± 10 cm).
Field data may be found in
Water hydrochemical parameters recorded in the Etosha National Park during May 2013.
Etosha National Park sites | Date | Water point type | Water level (m) | pH | EC (mS/cm) | Temp °C | Salinity (ppt) | TDS (ppt) | d2H (permil) | d18O (permil) | Altitude (m a.s.l.) | Latitude | Longitude |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
- | - | - | - | - | - | - | - | - | - | - | - | - | |
Nabrownii | 06/05/2013 | BH | - | 7.1 | 6.2 | 26.0 | 2.7 | 4.3 | −35.68 | −4.21 | 1120.5 | −19.16174 | 15.99463 |
Gemsbokvlakte | 06/05/2013 | BH | - | 7.2 | 4.8 | 26.9 | 2.1 | 3.4 | −42.06 | −5.26 | 1134.2 | −19.21406 | 16.05917 |
Olifantsbad | 06/05/2013 | BH | 6.32 | 7.2 | 1.4 | 26.4 | 0.6 | 1.0 | −39.38 | −5.51 | 1117.0 | −19.23725 | 16.12846 |
Dolomitepunt | 07/05/2013 | BH | 8.71 | 7.5 | 2.2 | 25.9 | 1.5 | 0.9 | −42.54 | −5.21 | 1275.6 | −19.00285 | 14.47264 |
Duineveld | 07/05/2013 | BH | - | 7.8 | 1.8 | 25.8 | 0.7 | 126.0 | −41.82 | −5.55 | 1227.7 | −18.95098 | 14.60858 |
Nomab | 07/05/2013 | BH | 4.17 | 7.9 | 2.7 | 26.1 | 1.1 | 1.9 | −38.39 | −4.99 | 1197.1 | −18.96113 | 14.76448 |
Olifantsrus | 07/05/2013 | BH | 11.35 | 8.1 | 2.1 | 26.6 | 0.9 | 1.5 | −44.97 | −5.42 | 1188.4 | −18.96552 | 14.86024 |
Teobron | 07/05/2013 | BH | - | 8.1 | 2.2 | 27.0 | 0.9 | 1.6 | −45.40 | −5.72 | 1177.3 | −18.97164 | 14.95716 |
Toespad | 07/05/2013 | BH | 26.25 | - | - | - | - | - | - | - | 1171.6 | −18.98002 | 15.06087 |
Duiwelsvuur | 07/05/2013 | BH | - | 8.1 | 3.3 | 27.8 | 1.4 | 2.3 | −47.69 | −5.97 | 1140.0 | −18.98666 | 15.25956 |
Sonderkop | 07/05/2013 | BH | 24.12 | 7.7 | 4.5 | 27.1 | 1.9 | 3.2 | −46.00 | −5.59 | 1154.8 | −18.96876 | 15.32755 |
Arendsnes | - | - | - | - | - | - | - | - | - | - | 1151.6 | −18.97806 | 15.40952 |
Halali seepage | 09/05/2013 | C | - | 8.4 | 10.6 | 19.4 | 4.8 | 7.5 | −44.88 | −5.89 | 1103.7 | −18.97565 | 16.43903 |
Halali Turnoff | 09/05/2013 | A | - | 8.6 | 4.0 | 25.2 | 1.7 | 2.8 | −49.38 | −6.41 | 1117.0 | −18.99623 | 16.40326 |
Rietfontein | 09/05/2013 | A | - | 8.4 | 4.7 | 24.2 | 2.0 | 3.3 | −45.24 | −5.88 | 1119.1 | −19.03658 | 16.34177 |
Salvadora | 09/05/2013 | C | - | 7.8 | 5.3 | 24.8 | 2.3 | 3.7 | −49.03 | −6.22 | 1108.3 | −19.03452 | 16.26956 |
Cheridsaub | 09/05/2013 | C | - | 8.1 | 6.9 | 26.3 | 3.0 | 4.8 | −47.82 | −5.80 | 1112.7 | −19.04295 | 16.26497 |
Sueda | 09/05/2013 | C | - | 8.4 | 9.7 | 20.3 | 4.3 | 6.8 | −46.00 | −6.21 | 1108.2 | −19.04280 | 16.25219 |
Homob | 09/05/2013 | A | - | 8.5 | 4.4 | 24.0 | 1.8 | 3.0 | −23.74 | −1.21 | 1109.7 | −19.05257 | 16.19316 |
Ondogab | 09/05/2013 | C - dry | - | - | - | - | - | - | - | - | - | - | - |
Quarry Artesian borehole | 09/05/2013 | A | 7.9 | 3.2 | 27.0 | 1.4 | 2.3 | −46.88 | −6.29 | 1113.1 | −19.10725 | 16.12656 | |
Kapupuheri | 09/05/2013 | C - dry | - | - | - | - | - | - | - | - | 1100.5 | −19.12305 | 16.07018 |
Ombika | 09/05/2013 | A | - | 7.2 | 1.5 | 29.1 | 0.6 | 1.1 | −46.50 | −6.21 | 1143.8 | −19.31617 | 15.94117 |
Halali 1 | 08/05/2013 | A | - | 7.6 | 3.7 | 28.5 | 1.6 | 2.6 | −48.40 | −6.12 | 1061.7 | −18.95604 | 16.50579 |
Agab Turnoff | 08/05/2013 | C | - | 9.0 | oor | oor | oor | - | −34.00 | −3.65 | 1103.2 | −18.95270 | 16.62231 |
Agab | 08/05/2013 | A | - | 8.6 | 3.1 | 25.1 | 1.3 | 2.2 | −49.05 | −6.20 | 1129.3 | −18.97503 | 16.65568 |
Springbok Fontein | 08/05/2013 | C | - | 8.9 | 4.4 | 26.2 | 1.9 | 3.1 | −45.67 | −5.62 | 1105.5 | −18.93895 | 16.69600 |
Ngobib | 08/05/2013 | A | - | 8.2 | 3.1 | 25.6 | 1.9 | 4.3 | −33.20 | −3.18 | 1128.6 | −18.89722 | 16.76986 |
Kalkheuwel | 08/05/2013 | A | - | 7.4 | 3.1 | 28.1 | 1.3 | 2.2 | −50.52 | −6.72 | 1117.9 | −18.89741 | 16.82648 |
Chudop | 08/05/2013 | A | - | 8.7 | 4.4 | 23.0 | 1.9 | 3.1 | −22.47 | −1.51 | 1117.8 | −18.85855 | 16.92502 |
Koinahas | 08/05/2013 | A | - | 9.0 | 6.0 | 24.4 | 2.6 | 4.3 | −23.87 | −1.34 | 1113.1 | −18.81918 | 16.92883 |
Klein Namutoni | 08/05/2013 | A | - | 9.0 | 4.5 | 24.8 | 2.1 | 3.4 | −16.93 | −0.81 | 1115.0 | −18.82686 | 16.95048 |
Groot Okevi | 08/05/2013 | A | - | 8.8 | 4.7 | 25.7 | 2.0 | 3.3 | −36.26 | −3.47 | 1097.8 | −18.78025 | 16.89852 |
Mushara | 08/05/2013 | A | - | 7.7 | 5.0 | 29.2 | 2.2 | 3.5 | −49.64 | −6.74 | 1099.0 | −18.58763 | 16.88717 |
Kameldoring | 08/05/2013 | A | - | 7.9 | 3.8 | 26.9 | 1.6 | 2.7 | −50.55 | −6.66 | 1107.1 | −18.61819 | 16.98820 |
- | - | - | - | - | - | - | - | - | - | - | - | - | |
Mbari | 10/05/2013 | BH | - | 9.44 |
1.34 |
- | - | 0.66 |
−45.78 | −6.05 | 1146.9 | −18.97636 | 15.50411 |
Okahakana | 10/05/2013 | BH | - | - | - | - | - | - | - | - | 1128.8 | −18.88073 | 15.58623 |
Pan Point | 10/05/2013 | BH | - | 9.37 |
1.1 |
- | - | 0.55 |
−47.22 | −6.28 | 1129.7 | −18.78652 | 15.61755 |
Narawandu | 10/05/2013 | BH | - | 9.73 |
5.15 |
- | - | 2.56 |
−45.41 | −5.89 | 1127.6 | −18.73846 | 15.50196 |
Gruneveld | 10/05/2013 | BH | 15.88 | 9.2 |
1.04 |
- | - | 0.57 |
−48.90 | −6.74 | 1113.1 | −19.12602 | 15.63597 |
Okondeka | 10/05/2013 | C | - | 10.96 |
0.52 |
- | - | 0.25 |
−32.50 | −3.12 | 1107.6 | −18.99344 | 15.86985 |
Eindpaal | 10/05/2013 | BH | - | 9.62 |
6.94 |
- | - | 3.47 |
−47.83 | −6.09 | 1172.9 | −19.21308 | 15.52981 |
A, Artesian Spring; C, Contact Spring; BH, Borehole.
†, Meter not working, had to use spare not calibrated.
As seen in
Stable isotope results (δ18O/δ2H) for samples of different water point types in the Etosha National Park, May 2013 (Windhoek Meteorological Water Line developed from International Atomic Energy Agency Global Network of Isotopes in Precipitation database 1961–2001).
Variation of altitude, δ2H and δ18O (above) and δ2H excess (below) along an approximate east-west transect for different water point types in the Etosha National Park, May 2013, with altitude reference.
Variation of altitude, δ2H and δ18O (above) and δ2H excess (below), along an approximate north-south transect for different water point types in the Etosha National Park, May 2013, with altitude reference.
The boreholes in the west of ENP all show relatively low delta values compared with the entire range of samples. It was noted by Department of Water Affairs and Forestry (
In general, the EC readings (
Spatial distribution of EC (mS/cm) for different water point types in the Etosha National Park, May 2013. (Possible instrument error as uncalibrated spare multi-parameter meter had to be used for all the south-north transect points, 10 May 2013.)
The spatial distribution of temperature (°C) in ENP is shown in
Spatial distribution of temperature for different water point types in the Etosha National Park, May 2013.
The distinction in water point types that arises from the temperature data is reaffirmed in
Ternary plot with normalised data (percentiles) for EC (mS/cm), temperature (°C), and δ2H excess for different water point types in the Etosha National Park, May 2013, inclusive of
Class | δ2H excess | EC (mS/cm) | Temp °C | |
---|---|---|---|---|
1 | 1.08 | 3.61 | 26.6 | 22 |
2 | −10.71 | 4.52 | 24.6 | 6 |
3 | 2.99 | 10.15 | 19.9 | 2 |
Based on this snapshot analysis of groundwater in the ENP, a preliminary picture is inferred from the data to broadly distinguish two hydrogeological areas: the west of the ENP is likely to have groundwater that is recharged relatively directly from incoming rainfall through the sandy substrate in that landscape and from the dolomite ridge that runs along the south-western boundary of the park; meanwhile, the east is much more complex, as revealed by the
There are a number of questions and recommendations raised by this limited study that could be used to inform future water availability and management strategies in the ENP. First and more locally would be to determine the hydrological processes maintaining the Okondeka freshwater spring, which makes it geographically distinct from other springs in the region, because it is the only active contact spring on the western shores of the Etosha Pan. The possibility that the dune fields to the west supply local recent event rainfall freshwater could be explored, as this would warrant that spring system a unique ecosystem type within the ENP. The second broader, pertinent issue is to develop a groundwater hydrodynamic and hydrochemical monitoring programme for the ENP and its groundwater catchments. The purpose of this will be to further characterise the hydrogeological processes in different water regions of the park, for example, western region and eastern region. For instance, feedback from managers in the ENP suggests that there has been a steady desiccation of the springs along the south-west of the pan. It will need to be determined whether this is as a result of inter-glacial climate cycling or something more serious, such as groundwater over-abstraction elsewhere in the catchment and/or enhanced precipitation interception and transpiration from bush thickening in the karst aquifer of the region (e.g. Namibia Agriculture Union
The results of this snapshot hydrochemical and stable isotope characterisation of groundwater in the ENP have revealed a close clustering of borehole water properties towards the west of the park and the d-excess values there suggest direct recharge by rainfall through the Kalahari sands. The west of the park clearly has a more complicated groundwater flow pathway and the variable hydrochemistry reported here for artesian and contacts springs along the southern shore of the Etosha Pan support the conceptualised flow paths of other studies. The results of this baseline study could be used in future long-term hydrological change monitoring of the Etosha ecosystem, especially with respect to understanding the causes for apparent desiccation of contact springs along the southern shores of the pan.
Dr Jaco Nel of Groundwater Consulting Services is acknowledged for his advice in preparation for the field study and lending of some field equipment. Mr Cobus Pretorius is acknowledged for analysing the water samples for stable isotopes at Soil & Water Laboratory of the Centre for Water Resources Research at the University of KwaZulu-Natal.
The authors declare that they have no financial or personal relationships which may have inappropriately influenced them in writing this article.
E.S.R. led the research design and was responsible for data analysis and compiling the manuscript. W.K., W.V. and M.K. assisted with field data collection and site interpretation.