Browsing by Author "Xu, Y"

Now showing 1 - 4 of 4
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    Assessing the adverse effects of a mixture of AMD and sewage effluent on a sub-tropical dam situated in a nature conservation area using a modified pollution index
    (Springer Nature, 2021) Oberholster, P.F; Goldin, J; Xu, Y
    Currently water resources in nature conservation areas are under severe pressure due to external drivers of anthropogenic pollution. There is a lack of monitoring tools to determine water quality status of dams situated in nature reserves receiving a mixture of pollutants over space and time. The present study was conducted over a 12-month period with the aim of applying a modified pollution index (PILD) to determine the water quality and phytoplankton status of the Loskop Dam situated in the Loskop nature reserve, South Africa. From the data generated in the current study, it was evident that the PILD effectively determined nutrient enrichment and heavy metal pollution in the dam. Furthermore, the study showed that the most pollution tolerant phytoplankton species was the diatom Melosira varians followed by the dinoflagellate Ceratuim hirundinella and the cyanobacteria Microcystis aeruginosa. Chemical variables during the sampling period that exceeded the limits of the South African, Canadian, Australia and New Zealand guideline levels were Zn, TP, Cl, Fe, Mn and NH4. The occurrence of concentrations of Cl above the target water quality range for aquatic ecosystems (5 µgl−1) over the entire sampling period, may have been related to point source sewage pollution in the upper catchment. The PILD showed poor water quality conditions during the months of September and October during the dam’s destratification (lake overturn).
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    Fracture development and fractal characteristics of overburden rock under repeated mining
    (Spinger, 2021) Zhang, Z; Zhang, Y; Xu, Y
    The purpose of this paper is to provide scientific basis for the stability evaluation of overburden rock of repeated mining goaf under the expressway. The objectives of the present study are to reveal the development of overburden rock fractures under repeated mining and to identify the fractal characteristics of the overburden rock fractures. The results show that (1) the separation fracture and vertical fracture fissure are developed in the overburden rock under repeated mining; (2) after the mining of the lower coal seam, the fractures developed in the overburden rock of the goaf are obviously retained in general. The number of fractures on both sides of the goaf is relatively large, while in the central part, it is relatively small and the fractures in most areas are basically closed; (3) under the same advancing length of working face in the lower coal seam, the fractal dimension in the caving zone is larger than that of the fractured zone; (4) with the increase of the advancing length of working face in the lower coal seam, the variation trend of the fractal dimension appears from small to large and then to small and stable; (5) when the repeated mining is over and the overburden rock movement is basically stable, the ratio of the fractal dimension in the caving zone and the fractured zone is 1.067:1. The results have an important reference value for ensuring the safety of the expressways above the repeated mining goaf in Shanxi region and similar areas.
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    Hydro geochemical characteristics of the basement aquifers in namaqualand
    (University of the Western Cape, 2003) Titus, R.A; Xu, Y
    At the onset of this research programme it became apparent that there is a dearth of research studies focusing on the groundwater resources of the region. As a result, a conceptual representation of the hydrogeological system (i.e. specific aquifer systems, groundwater flow regime, etc.) for the perceived problematic aquifer systems in the Namaqualand region did not exist. The research project contributes significantly to conceptual representation of the aquifer system, in particular a quantitative understanding of the regions' groundwater resources in terms of its hydrochemical development and the construction of a groundwater flow model at regional scale as well as at a local scale. The groundwater resources for the Namaqualand region are developed predominantly in the basement rocks. The infiltration and flow of water is controlled by the prevailing complex fracture network and can vary in space and time. Such observations relate to structurally controlled flow systems and varying water chemistry amongst closely spaced fracture systems.
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    Implementation of groundwater protection measures, particularly resource directed measures in South Africa: a review paper
    (Water Policy, 2021) Pienaar, H; Xu, Y; Braune, E
    This review paper on groundwater protection measures in South Africa focuses on the actual implementation of groundwater protection measures, in particular, the resource-directed measures (RDM) as described in Chapter 3 of the National Water Act (NWA). Significant catchment-wide implementation of RDM has taken place in a phased manner throughout various catchments since 2012. By 2015, approximately R380 million had been expended on the catchment-wide implementation of the water resource protection measures over a period of 15 years. Considerable effort went into refining the RDM methodology, taking into account the groundwater component of the overall resource. In this paper, we contend that RDM, in its present form, will not make a significant contribution to groundwater resource protection and security in the country. This is a major concern because the Groundwater Strategy of the Department of Human Settlements, Water and Sanitation (DHSWS) had declared the protection of groundwater as a national priority. This paper also examines institutional and governance arrangements (or lack thereof) as well as providing recommendations to support the effective implementation of groundwater protection provisions as prescribed by South Africa’s water legislation.