Understanding the origin and fate of nitrate in groundwater of semi-arid environments

Though nitrate enrichment in groundwater is a worldwide phenomenon and mainly related to human impact, processes leading to nitrate enrichment in scarcely inhabited semi-arid regions are not yet well understood. In those regions, elevated nitrate concentrations put additional pressure on the scarce...

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Bibliographic Details
Published in:Journal of arid environments 2008-10, Vol.72 (10), p.1830-1842
Main Authors: Stadler, S., Osenbrück, K., Knöller, K., Suckow, A., Sültenfuß, J., Oster, H., Himmelsbach, T., Hötzl, H.
Format: Article
Language:English
Subjects:
Animal and plant ecology
Animal, plant and microbial ecology
biogeochemical cycles
Biological and medical sciences
eutrophication
Fundamental and applied biological sciences. Psychology
geochemistry
Groundwater
groundwater contamination
groundwater recharge
hydrogeology
hydrology
Isotopes
Kalahari
land use
Natural nitrate
nitrate nitrogen
nitrogen
public health
Recharge
Semi-arid
semiarid zones
soil transport processes
stable isotopes
Synecology
Terrestrial ecosystems
water quality
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Summary:Though nitrate enrichment in groundwater is a worldwide phenomenon and mainly related to human impact, processes leading to nitrate enrichment in scarcely inhabited semi-arid regions are not yet well understood. In those regions, elevated nitrate concentrations put additional pressure on the scarce water resources, as they pose a serious health risk. This study applies a multidisciplinary approach (hydrogeology, isotope hydrology, and geochemistry) to understand the origin and fate of nitrate in groundwater of the semi-arid Kalahari of Botswana. Our investigations suggest that nitrate in groundwater of the study area is of natural origin, leached from a pool in the unsaturated zone that was actively involved in the soil nitrogen cycle. The presence of active (minor) recharge was found, showing that nitrate may be transported into the groundwater under the present conditions. Yet, slow travel times of replenishing water and the low recharge amounts render the thick unsaturated zone into a long-term reservoir for nitrate. Being only little influenced by reactive processes, nitrate has a high persistency in the observed groundwater system. Concentration increases induced by the present land-use do not yet appear to affect the groundwater quality but may within decades.
ISSN:0140-1963
1095-922X
DOI:10.1016/j.jaridenv.2008.06.003