Records |
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 |
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Volume |
6 |
Issue |
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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. |
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2468-2276 |
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THL @ christoph.kuells @ VUSHE2019e00193 |
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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 |
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Volume |
67 |
Issue |
1 |
Pages |
249-259 |
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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. |
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0022-1694 |
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THL @ christoph.kuells @ Heaton1984249 |
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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 |
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Volume |
105 |
Issue |
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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). |
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0140-1963 |
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THL @ christoph.kuells @ Stone201441 |
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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 |
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Volume |
50 |
Issue |
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Pages |
191-200 |
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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. |
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0022-1694 |
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THL @ christoph.kuells @ Vogel1981191 |
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280 |
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Author |
Wilson, G.B.; McNeill, G.W. |
Title |
Noble gas recharge temperatures and the excess air component |
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Journal Article |
Year |
1997 |
Publication |
Applied Geochemistry |
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12 |
Issue |
6 |
Pages |
747-762 |
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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. |
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0883-2927 |
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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 |
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62 |
Issue |
1 |
Pages |
243-262 |
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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. |
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0022-1694 |
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THL @ christoph.kuells @ Heaton1983243 |
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282 |
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Author |
Rajfur, M.; Kłos, A.; Wacławek, M. |
Title |
Sorption properties of algae Spirogyra sp. and their use for determination of heavy metal ions concentrations in surface water |
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Journal Article |
Year |
2010 |
Publication |
Bioelectrochemistry |
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80 |
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1 |
Pages |
81-86 |
Keywords |
Biomonitoring, Heavy metal ions, Algae sp., Sorption kinetics, Langmuir isotherm |
Abstract |
Kinetics of heavy-metal ions sorption by alga Spirogyra sp. was evaluated experimentally in the laboratory, using both the static and the dynamic approach. The metal ions – Mn2+, Cu2+, Zn2+ and Cd2+ – were sorbed from aqueous solutions of their salts. The static experiments showed that the sorption equilibria were attained in 30min, with 90-95% of metal ions sorbed in first 10min of each process. The sorption equilibria were approximated with the Langmuir isotherm model. The algae sorbed each heavy metal ions proportionally to the amount of this metal ions in solution. The experiments confirmed that after 30min of exposition to contaminated water, the concentration of heavy metal ions in the algae, which initially contained small amounts of these metal ions, increased proportionally to the concentration of metal ions in solution. The presented results can be used for elaboration of a method for classification of surface waters that complies with the legal regulations. |
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1567-5394 |
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A Selection of Papers presented at the 4th International Workshop on Surface Modification for Chemical and Biochemical Sensing (SMCBS 2009) |
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THL @ christoph.kuells @ Rajfur201081 |
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283 |
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Konapala, G.; Mishra, A.K.; Wada, Y.; Mann, M.E. |
Title |
Climate change will affect global water availability through compounding changes in seasonal precipitation and evaporation |
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Journal Article |
Year |
2020 |
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Nature Communications |
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11 |
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1 |
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3044 |
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Both seasonal and annual mean precipitation and evaporation influence patterns of water availability impacting society and ecosystems. Existing global climate studies rarely consider such patterns from non-parametric statistical standpoint. Here, we employ a non-parametric analysis framework to analyze seasonal hydroclimatic regimes by classifying global land regions into nine regimes using late 20th century precipitation means and seasonality. These regimes are used to assess implications for water availability due to concomitant changes in mean and seasonal precipitation and evaporation changes using CMIP5 model future climate projections. Out of 9 regimes, 4 show increased precipitation variation, while 5 show decreased evaporation variation coupled with increasing mean precipitation and evaporation. Increases in projected seasonal precipitation variation in already highly variable precipitation regimes gives rise to a pattern of “seasonally variable regimes becoming more variable”. Regimes with low seasonality in precipitation, instead, experience increased wet season precipitation. |
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English |
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2041-1723 |
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THL @ christoph.kuells @ Konapala2020 |
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284 |
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Author |
United Nations |
Title |
Stampriet Transboundary Aquifer System Assessment: governance of Groundwater resources in Transboundary Aquifers (GGRETA), phase 1: technical report |
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Miscellaneous |
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1998 |
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Incl. bibl. |
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THL @ christoph.kuells @ |
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286 |
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Author |
Brutsaert, W. |
Title |
Global land surface evaporation trend during the past half century: Corroboration by Clausius-Clapeyron scaling |
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Journal Article |
Year |
2017 |
Publication |
Advances in Water Resources |
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106 |
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Pages |
3-5 |
Keywords |
Evaporation, Climate change, Evaporation trend |
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Analyses of satellite data mainly over the world’s ocean surfaces have shown that during 1986–2006 global average values of atmospheric water vapor, precipitation and evaporation have increased at a relative rate of 0.0013a−1; this is roughly in accordance with the Clausius-Clapeyron equation for the average temperature trend during this period, and amounts to 0.065K−1 at the average temperature of T=14∘C. Application of this concept over the world’s land surfaces yields an average global evaporation trend during the past half century of around 0.4 to 0.5 mma−2; this confirms the values obtained in previous studies with totally different methods. |
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0309-1708 |
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Tribute to Professor Garrison Sposito: An Exceptional Hydrologist and Geochemist |
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THL @ christoph.kuells @ Brutsaert20173 |
Serial |
287 |
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