Highveld Region Of South Africa Research Articles

Phosphorus supplementation to natural pasture grazing for beef cows in the Western Highveld region of South Africa

Simmentaler cows grazing Cymbopogon-Themeda veld in the western Highveld region of South Africa (1985/86-1989/90) received three levels of phosphorus (P) supplementation. Dicalcium phosphate content of the supplement was manipulated to give intakes of 8 (CS), 4 (HS) or 0 (ZS) g P/cow/day during summer. All cows received supplemental P (10 g/cow/day) during winter (1986-1989). In 1990, supplemental P (10 (CW), 5 (HW) or 0 (ZW) g P/cow/day) was given in a winter maintenance supplement (protein, energy and minerals). Rainfall was above average during the trial period. Reproductive performance was not influenced by P supplementation. Mean livemass of the CS group was greatest (p < 0.01), and that of HS was greater (p < 0.01) than ZS at the end of summer. Both CS and HS had better (p < 0.01) condition scores than ZS. Bone P content was lowest and indicative of deficiency (p < 0.01) in ZS cows (112.6 vs 141.9 and 130.8 mg P/cm 3 bone for CS and HS respectively). Calf performance was not affected (p > 0.05) by P supplementation. Cow mass was ffected by winter P supplementation (p < 0.05). Both CW and HW displayed improved (p < 0.01) condition scores and higher (p < 0.01) bone P content than ZW. Fatalities (4) occurred in ZW due to P deficiency (74.5 mg P/cm 3 bone), and deficiency symptoms were manifested in the entire group. Both summer and winter veld is deficient in P, which makes continuous supplementation a recommended practice in this area. (South African Journal of Animal Science, 2000, 30(1): 43-52)

Modelled transport and deposition of sulphur over Southern Africa

Ambient SO 2 concentrations and atmospheric deposition of sulphur resulting from emissions on the industrialised highveld region of South Africa are estimated using the multi-scale atmospheric transport and chemistry (MATCH) modelling system, developed at the Swedish Meteorological and Hydrological Institute (SMHI), and compared with an inferential model driven by measured input quantities. Modelled SO 2 concentrations on the central highveld mostly range between 10 and 50 ppb, exceeding 50 ppb in source areas. Dry deposition rates for sulphur exhibit a similar spatial pattern to the ambient SO 2 concentrations and both are consistent with synoptic-scale transport patterns. Maximum dry deposition rates for sulphur of more than 10 kg S ha −1 a −1 occur over the central highveld with a well-defined gradient decreasing away from the source region. Despite the significant differences in modelling approaches, the estimates of dry deposition provided by MATCH are in reasonable agreement with those of the inferential model. The maximum modelled wet deposition rates occur over the South African highveld and its periphery and range between 1 and 5 kg S ha −1 a −1 and compare favourably with measurements from an acid rain network. Wet deposition generally exceed dry deposition on the highveld and the adjacent areas except in the central highveld source region. Over the drier western half of South Africa MATCH-modelled dry and wet deposition rates are again similar and are less that 1 kg S ha −1 a −1. Wet deposition exceeds dry in the higher rainfall regions along the south and east coasts of South Africa.

Industrial aerosol characterisation at a remote site in South Africa

South Africa is the most industrialised country in southern Africa with approximately 1.1 Tg of sulphur emitted from anthropogenic activities per annum. Complex circulation patterns and highly stable vertical atmospheric conditions promote the accumulation of pollutants below 700 hPa or 3000 m asl. A remote site in the Eastern Cape of South Africa, Ben Macdhui (30.5°S 27.9°E, 3001m) was selected for testing the hypothesis that industrial emissions, specifically sulphate, are transported over thousands of kilometres in anticyclonic type patterns of flow and exported from the subcontinent towards the Indian Ocean at about 30°S. Time resolved particulate sampling (streaker) was conducted between June 1995 and January 1997. To characterise the industrial aerosol signal, two intensive sampling campaigns (summer and winter) were undertaken in 1996. Aerosol samples were collected by a streaker sampler and an open-faced stacked filter unit (SFU). Samples were PIXE analysed to obtain elemental concentrations. The industrial signature detected at Ben Macdhui was characterised by elevated concentration of sulphur and iron in the fine fraction and fine sulphur detected in the coarse mode. Other sources identified from the elemental data were soil (Al, Si, Ca, Mg, K, S, Mn), biomass burning (fine K) and marine (Cl, Ca, Mg, S and coarse K). These four sources accounted for approximately 70% of the total detected elemental mass. Major individual contributions came from the crustal (53%) and industrial components (21%). Air parcel trajectory analyses confirmed that peak episodes of enhanced aerosol sulphur were related to transport from the industrial Highveld region of South Africa and conversely that clean air masses originated over the southern oceans.

Competitive Displacement of Busseola fusca (Lepidoptera: Noctuidae) by Chilo partellus (Lepidoptera: Pyralidae)

Since the appearance of the stem borer Chilo partellus (Swinhoe) on the African continent in 1932, it has continuously expanded its distribution in the warm, low-altitude regions of eastern and southern Africa. The current study revealed that C. partellus is expanding its distribution into the high elevations of the eastern Highveld region of South Africa. The only stem borer already found there (elevation 1,600 m) is Busseola fusca (Fuller). After C. partellus invaded the region, it rapidly increased its share of the total borer population every year. On maize, it reached 32% of the total borer population within 6 yr and on grain sorghum 59% within 7 yr. The most rapid population increase by C. partellus occurred on the ratoon grain sorghum crop. Within 2 yr it became the predominant borer, constituting ≈90% of the total stem borer population. C. partellus has proven to be an efficient colonizer, and it seems to be displacing the indigenous B. fusca. C. partellus survives the dry winters (at subzero temperatures) of the Highveld region in South Africa by diapausing low in the dry stalks, often beneath the soil. Hibernating larval populations of C. partellus terminate diapause and emerge as moths ≈1 mo earlier than B. fusca . This enables C. partellus to infest the grain sorghum ratoon crop before B. fusca , thus becoming the predominant borer in this niche. The life cycle of C. partellus is 3 wk shorter than that of B. fusca , which gives it a further competitive advantage because of its higher potential rate of increase.

Susceptibility of dogs to West Nile virus: A survey and pathogenicity trial

A serological survey of dogs from the highveld region of South Africa showed that 37 per cent (138 of 377) had neutralizing antibodies to West Nile (WN) virus and only 2·7 per cent (10 of 377) had antibodies to Sindbis virus. WN virus was isolated from one of the WN-antibody negative sera. Because these results suggested that dogs may play an important part in the epidemiology of WN virus, a pathogenicity trial was carried out. Two of three dogs infected with WN virus had a mild recurrent myopathy, but no other abnormalities were detected in the biochemical or haematological tests performed on any of the dogs. All three dogs developed antibodies but a low titre-viraemia was detected in only one dog. It was concluded that dogs do not play an important part in the epidemiology of WN virus but they may play a small part in the maintenance of the virus.

An Examination of Double-Plate Ice Crystals and the Initiation of Precipitation in Continental Cumulus Clouds

Abstract Measurements within continental convective clouds in the Highveld region of South Africa indicate that the first appreciable nucleation of ice occurs between the −9° to −12°C levels as the cloud top rises through these levels. Moreover, these crystals usually take the form of double plates. Frozen drop centers were observed in 30% of the double crystals, with the diameter of the frozen drop between 10 and 20 μm. The growth of these ice crystals is investigated using ice crystal measurements collected in situ as well as a modeling study. New information regarding axial dimensions, bulk densities, and riming characteristics of double-plate crystals is presented. Numerical simulations were performed to compare the growth characteristics of ice crystals nucleated at different temperature levels between −6° and −16°C in updrafts of 1 and 3 m s−1. Crystals nucleated at temperatures ≥−12°C are shown to start riming at smaller sizes than previously thought and these crystals are potentially important as ...

Quantitative experiments on the vector capability of Culex (Culex) theileri Theobald with West Nile and Sindbis viruses.

Mosquitoes from a laboratory colony of Culex theileri originating from material collected at Lake Chrissie in the Eastern Transvaal, South Africa, were given infective blood-meals consisting of four l0-fold graded doses of either West Nile or Sindbis viruses. Transmission of virus by individual mosquitoes to individual chicks was attempted from 14 to 20 days after the infective feed. Soon after attempted transmission mosquitoes were tested individually for virus. For West Nile virus it was found that 1.5 logs of virus were necessary to infect 10% of the mosquitoes and 8 out of 50 infected mosquitoes transmitted the virus. For Sindbis virus the value determined for the 10% infection threshold was 2.0 logs while 2 out of 23 infected mosquitoes transmitted the virus. These results indicate that C. theileri is a potential vector of limited efficiencybut it is suggested that this species is probably responsible for some of the human infection by each virus which occurs in the highveld region of South Africa.

Quantitative experiments on the vector capability of Culex (Culex) pipiens fatigans Wiedemann with West Nile and Sindbis viruses.

Mosquitoes from 2 laboratory colonies of Culex pipiens fatigans originating from material collected in Johannesburg, South Africa, were given infective blood meals consisting of four 10-fold graded doses of either West Nile or Sindbis viruses. Transmission of virus by individual mosquitoes to individual chicks was attempted on the 19th or 20th day after the infective feed. Soon after attempted transmission, mosquitoes were tested individually for virus. For West Nile virus it was found that 3.9 4.7 logs of virus were necessary to infect 10% of mosquitoes and 3 of 19 infected mosquitoes transmitted the virus. For Sindbis virus the 10% infectivity threshold varied from 4.8–5.2 logs while 2 out of 6 infected mosquitoes transmitted the virus. It was concluded that C. pipiens faligans was unlikely to act as an important vector of either virus in the transfer of virus from birds to man or between human beings in the highveld region of South Africa.