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	Author	Schwiede, M.; Duijnisveld, W.H.M.; Böttcher, J.
	Title	Investigation of processes leading to nitrate enrichment in soils in the Kalahari Region, Botswana			Type	Journal Article
	Year	2005	Publication	Physics and Chemistry of the Earth, Parts A/B/C	Abbreviated Journal
	Volume	30	Issue	11	Pages	712-716
	Keywords	Nitrate, Arenosol soils, Semi-arid, Kalahari, Cattle, Chloride, Travel time
	Abstract	In Southern Africa elevated nitrate concentrations are observed in mostly uninhabited semi-arid areas. In the Kalahari of Botswana groundwater locally exhibits concentrations up to 600mg/l. It is assumed, that nitrate found in the groundwater originates mainly from nitrogen input and transformations in the soils. Our investigations in the Kalahari between Serowe and Orapa show that cattle raising is an important source for enhanced nitrate concentrations in the soils (Arenosols). But also in termite mounds very high nitrate stocks were found, and under natural vegetation (acacia trees and shrubs) nitrate concentrations were mostly unexpectedly high. This nitrate enrichment in the soils poses a serious threat to the groundwater quality. However, calculated soil water age distributions in the unsaturated zone clearly show that today’s nitrate pollution of the groundwater below the investigation area could originate from natural sources, but cannot be caused by the current land use for cattle raising.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1474-7065	ISBN		Medium
	Area		Expedition		Conference
	Notes	Integrated Water Resources Management (IWRM) and the Millennium Development Goals: Managing Water for Peace and Prosperity			Approved	no
	Call Number	THL @ christoph.kuells @ Schwiede2005712			Serial	276
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	Author	Vushe, A.; Amutenya, M.
	Title	Investigating nitrate retention capacity, elementary and mineral composition of Kalahari sandy soils at Mashare farm in Namibia, Okavango river basin			Type	Journal Article
	Year	2019	Publication	Scientific African	Abbreviated Journal
	Volume	6	Issue		Pages	00193
	Keywords	Irrigated field, Cultivated Kalahari sandy soil, Leaching, Nitrate retention capacity, Quartz mineral, Water saturated
	Abstract	Kalahari sands which cover a large part of Southern Africa and extend into Central Africa are infertile and marginal soils for intensive agriculture. Therefore, high nitrogen fertilisation rates may degrade ecosystems of rivers with catchments covered by the Kalahari sands. A study on Mashare Farm located in the Okavango River basin showed that irrigated Kalahari sandy soils had a nitrate retention capacity, which enabled the soil to resist nitrate leaching in water saturated conditions. The irrigated soils were modified by agricultural activities; hence this study investigated if uncultivated and cultivated Kalahari sand soils had similar nitrate retention properties. The elementary composition of the soils was investigated for obtaining an insight into chemical properties that may be causing the nitrate retention capacity. A permeameter was used to leach out nitrates from irrigated and uncultivated soil samples, and nitrate concentrations were measured on the leaching effluent from the permeameter. Elemental analysis was done on the cultivated and the uncultivated soil samples using a Scanning Electron Microscope, a portable X-Ray Fluorescence analyzer, and an X-Ray Diffraction machine, and the later was also used for crystalline structure analyses. Sieve analyses confirmed that the Mashare’s cultivated and uncultivated topsoils were similar, and both were similar to Botswana Kalahari topsoil. The irrigated and cultivated subsoil had a higher average nitrate retention capacity of 76% compared to 73% for the uncultivated subsoil. Both samples had the same elements, although the proportions were different. Both soil samples were dominated by a quartz mineral, but the field soil had traces of palygorskite. The presence of aluminum and transition metals outside the minerals structure, but as coatings on the quartz sand grains enhanced nitrate retention capacity properties of the Kalahari sand soils.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	2468-2276	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	no
	Call Number	THL @ christoph.kuells @ VUSHE2019e00193			Serial	277
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	Author	Heaton, T.H.E.
	Title	Sources of the nitrate in phreatic groundwater in the western Kalahari			Type	Journal Article
	Year	1984	Publication	Journal of Hydrology	Abbreviated Journal
	Volume	67	Issue	1	Pages	249-259
	Keywords
	Abstract	Elevated levels of nitrate occur in phreatic groundwater in the western Kalahari, Namibia. Nitrate in water containing 0.4–3.1 meq NO−3l−1, of widespread occurrence, has δ15N values in the range +4.9 to +8.0‰, suggesting natural derivation from the soil. The sporadic occurrence of very high levels of nitrate (> 4 meq NO−3l−1), which has δ15N between +9.3 to +18.7‰, reflects pollution derived from animal waste. The importance of considering the possible isotopic effects of denitrification, and the significance of leaching in the nitrogen budget of the Kalahari soil, are also discussed.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0022-1694	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	no
	Call Number	THL @ christoph.kuells @ Heaton1984249			Serial	278
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	Author	Stone, A.E.C.; Edmunds, W.M.
	Title	Naturally-high nitrate in unsaturated zone sand dunes above the Stampriet Basin, Namibia			Type	Journal Article
	Year	2014	Publication	Journal of Arid Environments	Abbreviated Journal
	Volume	105	Issue		Pages	41-51
	Keywords	Kalahari, Namibia, Nitrate in the unsaturated zone, Stampriet Basin, Transboundary basin, Unsaturated zone recharge
	Abstract	Elevated groundwater nitrate levels are common in drylands, often in excess of WHO guidelines, with concern for human and animal health. In light of recent attempts to identify nitrate sources in the Kalahari this paper presents the first unsaturated zone (USZ) nitrate profiles and recharge rate estimates for the important transboundary Stampriet Basin, alongside the first rainfall chemistry records. Elevated subsurface nitrate reaches 100–250 and 250–525 mg/L NO3–N, with NO3–N/Cl of 4–12, indicating input above evapotranspiration. Chloride mass balance recharge rates range from 4 to 27 mm/y, indicating a vertical movement of these nitrate pulses toward the water table over multi-decadal timescales. These profiles are sampled from dune crests, away from high concentrations of animals and without termite mounds. Given low-density animal grazing is unlikely to contribute consistent spot-scale nitrate over decades, these profiles give an initial estimate of naturally-produced concentrations. This insight is important for the management of the Stampriet Basin and wider Kalahari groundwater. This study expands our knowledge about elevated nitrate in dryland USZs, demonstrating that it can occur as pulses, probably in response to transient vegetation cover and that it is not limited to long-residence time USZs with very limited downward moisture flux (recharge).
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0140-1963	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	no
	Call Number	THL @ christoph.kuells @ Stone201441			Serial	279
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	Author	Vogel, J.C.; Talma, A.S.; Heaton, T.H.E.
	Title	Gaseous nitrogen as evidence for denitrification in groundwater			Type	Journal Article
	Year	1981	Publication	Journal of Hydrology	Abbreviated Journal
	Volume	50	Issue		Pages	191-200
	Keywords
	Abstract	By investigating the nitrate, oxygen, nitrogen and argon concentrations and 15N14N ratios in artesian groundwater with radiocarbon ages ranging up to 27,000 yr. a process of very slow denitrification in a confined aquifer is demonstrated. The calculated nitrogenisotope fractionation factor associated with this reaction is comparable to that reported for bacterial cultures in vitro and in vivo.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0022-1694	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	no
	Call Number	THL @ christoph.kuells @ Vogel1981191			Serial	280
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	Author	Wilson, G.B.; McNeill, G.W.
	Title	Noble gas recharge temperatures and the excess air component			Type	Journal Article
	Year	1997	Publication	Applied Geochemistry	Abbreviated Journal
	Volume	12	Issue	6	Pages	747-762
	Keywords
	Abstract	The calculation of a groundwater recharge temperature based on the dissolved concentrations of Ne, Ar, Kr and Xe requires a correction for noble gas supersaturation due to excess air entrainment. This entrainment is commonly attributed to the recharge process or to air contamination at the wellhead during sample collection. With the exception of some local studies, most work has concentrated on interpretation of the recharge temperature or quantification of the radiogenic content for palaeoclimatic and dating purposes. The magnitude and source of the excess air is not directly relevant to these studies and so is often ignored. In this work, excess air Ne and other data have been calculated from new and published noble gas data sets for several groundwater systems. For younger groundwaters which have been recharged under one broad climatic regime, the amount of air entrainment increases according to lithology in the order granites, sandstones and limestones respectively. A negative correlation between precipitation and excess air entrainment is identified in at least one aquifer, and some of the mechanisms which may influence the entrainment process are discussed.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0883-2927	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	no
	Call Number	THL @ christoph.kuells @ Wilson1997747			Serial	281
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	Author	Heaton, T.H.E.; Talma, A.S.; Vogel, J.C.
	Title	Origin and history of nitrate in confined groundwater in the western Kalahari			Type	Journal Article
	Year	1983	Publication	Journal of Hydrology	Abbreviated Journal
	Volume	62	Issue	1	Pages	243-262
	Keywords
	Abstract	Data are presented for nitrate, dinitrogen and argon concentrations and 15N14N ratios in groundwater, with radiocarbon ages up to 40,000 yr. for three confined sandstone aquifers in the western Kalahari of South West Africa/Namibia. The nitrate is probably generated within the soil of the recharge areas, and its production rate during the period 3000-40,000 B.P. has remained between 0.5 and 1.6 meq NO−3l−1 of recharge water, with ° 15N between + 4 and + 8‰. Variations in the amount of nitrate and of “excess air” in groundwater recharge are found, and can only reflect changes in the environmental conditions during recharge. They must therefore be caused by the climatic changes that have taken place during the past 25,000 yr.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0022-1694	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	no
	Call Number	THL @ christoph.kuells @ Heaton1983243			Serial	282
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	Author	Doulgeris, C.; Tziritis, E.; Pisinaras, V.; Panagopoulos, A.; Külls, C.
	Title	Prediction of seawater intrusion to coastal aquifers based on non-dimensional diagrams			Type	Conference Article
	Year	2020	Publication	EGU Geophysical Abstracts	Abbreviated Journal
	Volume		Issue		Pages	4073
	Keywords
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN		ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	no
	Call Number	THL @ christoph.kuells @ Doulgeris2020prediction			Serial	41
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	Author	Leibundgut, C.; Maloszewski, P.; Külls, C.
	Title	Tracers in Hydrology			Type	Book Whole
	Year	2009	Publication		Abbreviated Journal
	Volume		Issue	1. Ed.	Pages
	Keywords
	Abstract
	Address
	Corporate Author				Thesis
	Publisher	John Wiley & Sons, Ltd	Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN		ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	no
	Call Number	THL @ christoph.kuells @ Leibundgut2009tracers			Serial	37
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	Author	Külls, C.
	Title	Groundwater of the North-Western Kalahari, Namibia: estimation of recharge and quantification of the flow system			Type	Book Whole
	Year	2001	Publication	Hydrogeologie und Umwelt	Abbreviated Journal
	Volume		Issue		Pages
	Keywords
	Abstract
	Address
	Corporate Author				Thesis	Doctoral thesis
	Publisher	Hydrogeologie und Umwelt	Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN		ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	no
	Call Number	THL @ christoph.kuells @ Kuells2003groundwater			Serial	38
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