| 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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no |
| Call Number |
THL @ christoph.kuells @ VUSHE2019e00193 |
Serial |
277 |
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| Author |
Joseph, J.; Külls, C.; Arend, M.; Schaub, M.; Hagedorn, F.; Gessler, A.; Weiler, M. |
| Title |
Application of a laser-based spectrometer for continuous in situ measurements of stable isotopes of soil CO2 in calcareous and acidic soils |
Type |
Journal Article |
| Year |
2019 |
Publication |
Soil |
Abbreviated Journal |
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| Volume |
5 |
Issue |
1 |
Pages |
49-62 |
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Copernicus |
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THL @ christoph.kuells @ Joseph2019application |
Serial |
15 |
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| Author |
Zhang, Y.; Liu, X.; Yuan, S.; Song, J.; Chen, W.; Dias, D. |
| Title |
A two-dimensional experimental study of active progressive failure of deeply buried Qanat tunnels in sandy ground |
Type |
Journal Article |
| Year |
2023 |
Publication |
Soils and Foundations |
Abbreviated Journal |
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| Volume |
63 |
Issue |
3 |
Pages |
101323 |
| Keywords |
Qanat tunnel, Sand, Failure effect, Soil arching, Model test |
| Abstract |
As an ancient underground hydraulic engineering facility, the Qanat system has been used to draw groundwater from arid regions. A qanat is a horizontal tunnel with a slight incline that draws groundwater from a higher location and delivers it to lower agricultural land. During long-term water delivery, the qanat tunnel has experienced different degrees of aging and collapse, which may result in the significant ground settlement and even disasters. This paper developed a two-dimensional laboratory system to investigate the influence of progressive failure on the stability of deeply buried qanat tunnels. The developed system is fully instrumented with a particle image velocimetry (PIV) system and earth pressure and displacement monitoring. A special cylindrical membrane tube is designed and connected to an advanced pressure–volume controller to simulate the step-wise failure process of the tunnel. Three model tests were conducted on a dry sand considering the buried qanat tunnels at three different depths. Experimental results clearly show the progressive evolution of soil arching effect in the dry sand associated with the progressive failure of the tunnels. The failure of the Qanat ground starts from the vault and develops upwards, which is closely related to the evolution of stress contour at three consecutive stages. Ground surface settlement and volume loss corresponding to three burial depths were compared. A deeply buried qanat tunnel has a small effect on surface settlement. Earth pressure evolution on the 2D plane shows the load redistribution when the qanat collapses. The maximum arch and the initial point of the limit state correspond to a volume loss of 12.5 % and 50 %, respectively. For the collapse of the deep buried qanat tunnel, ground earth pressure evolution can be divided into a stress-increasing region, stress-decreasing region, and no redistribution region. Furthermore, a multi trap-door model considering soil expansion is proposed to describe the progressive failure behavior and its effects. |
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0038-0806 |
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no |
| Call Number |
THL @ christoph.kuells @ Zhang2023101323 |
Serial |
274 |
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| Author |
Li, X.; Shen, K.; Li, Q.; Deng, Y.; Zhu, P.; Wang, D. |
| Title |
Roll-over behavior in current-voltage curve introduced by an energy barrier at the front contact in thin film CdTe solar cell |
Type |
Journal Article |
| Year |
2018 |
Publication |
Solar Energy |
Abbreviated Journal |
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| Volume |
165 |
Issue |
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Pages |
27-34 |
| Keywords |
AlO HRT layer, Band alignment, CdTe solar cell, Roll-over behavior |
| Abstract |
Roll-over phenomenon in the current–voltage (J–V) curve is often observed in a CdTe thin film solar cell. The roll-over phenomenon, which is occurred near the open-circuit voltage in a light J–V curve, is due to Schottky energy barrier formed at the CdTe/metal interface in a CdTe solar cell back contact. In this study we report a J–V roll-over phenomenon which is induced by an energy barrier at the front contact of a CdTe solar cell. Two kinds of oxides, namely, Al2O3 and SnO2, were deposited as high-resistance transparent (HRT) layer between the window layer CdS and the fluorine doped tin oxide (FTO) front electrode in CdTe solar cells. These two oxides present much different electronic band alignment with FTO and CdS. SnO2 formed almost no energy barrier with CdS, this allowed smooth transport for photo-generated electrons from CdTe to CdS and FTO. However, Al2O3 formed a high energy barrier with CdS. The rather high energy barrier with a value of 3.43 eV at the CdS/Al2O3 interface induced a J–V roll-over phenomenon in a CdTe thin film solar cell, which dramatically led to a quick decrease for the cell device efficiency. The electron transport at the FTO/Al2O3/CdS interface is governed by tunneling effect. The results presented in this study demonstrate that the band structure at the front electrode plays an important role for the performance of a CdTe thin film solar cell. |
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0038-092x |
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no |
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THL @ christoph.kuells @ li_roll-over_2018 |
Serial |
187 |
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| Author |
Holmes, M.; Campbell, E.E.; Wit, M. de; Taylor, J.C. |
| Title |
Can diatoms be used as a biomonitoring tool for surface and groundwater?: Towards a baseline for Karoo water |
Type |
Journal Article |
| Year |
2023 |
Publication |
South African Journal of Botany |
Abbreviated Journal |
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| Volume |
161 |
Issue |
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Pages |
211-221 |
| Keywords |
Bioindicator, Diatom, Hydraulic fracturing, Karoo, Water quality |
| Abstract |
The environmental risks from shale gas extraction through the unconventional method of ‘fracking’ are considerable and impact on water supplies below and above ground. Since 2010 the recovery of natural shale gas through fracking has been proposed in parts of the fragile semi-arid ecosystems that make up the Karoo biome in South Africa. These unique ecosystems are heavily reliant on underground water, intermittent and ephemeral springs, which are at great risk of contamination by fracking processes. Diatoms are present in all water bodies and reflect aspects of the environment in which they are located. As the possibility of fracking has not been removed, the aim of the project was to determine if diatoms could be used for rapid biomonitoring of underground and surface waters in the Karoo. Over a period of 24 months, water samples and diatom species were collected simultaneously from 65 sites. A total of 388 diatom taxa were identified from 290 samples with seasonal and substrate variation affecting species composition but not the environmental information. Species diversity information, on the other hand, often varied significantly between substrates within a single sample. Analysis using CCA established that the diatom composition was affected by lithium, oxidized nitrogen, electrical conductivity, and sulphate levels in the sampled water. We conclude that changes in diatom community composition in the Karoo do reflect the water chemistry and could be useful as bioindicators. |
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0254-6299 |
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no |
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THL @ christoph.kuells @ holmes_can_2023 |
Serial |
163 |
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