Groundwater discharges to aquatic ecosystems associated with the Table Mountain Group (TMG) aquifer: a conceptual model

This paper reports on a conceptual model that was developed to describe the different groundwater discharge ‘types’ from the Table Mountain Group (TMG) aquifer, that contributes to the different components of the flow regime in each of the recognised river reaches for streams and rivers associated with the TMG. This model integrates hydrogeological, ecological and geomorphological understandings into an ecohydrological perspective linking ground- and surface water systems. Through geospatial intersections of existing GIS layers a GIS model was also developed to highlight the quaternary catchments containing sensitive aquatic ecosystems that could be vulnerable to groundwater use from the TMG. The conceptual model demonstrates the intimate link between groundwater from the TMG aquifer and aquatic ecosystems in the mountain and foothill reaches of streams and rivers in the Cape Folded Mountains in particular. It also identifies two primary zones of interaction between groundwater and surface water in the TMG, namely, the ‘TMG aquifer daylight- domain’, located in the recharge zone, and the ‘TMG aquifer surface water interface-domain’, located at the discharge end of the aquifer. The conceptual model clearly indicates the difference between real groundwater, and perceived groundwater contributions to streamflow in the TMG. It is the lower flows of the flow regime that will be most vulnerable to groundwater use from the TMG aquifer in the ‘TMG aquifer daylight-domain’, which are unfortunately also the most important flows from an ecological perspective. However, any groundwater use from the TMG aquifer will also affect the discharge end of the aquifer, located far from the higher elevation recharge areas, or the point of groundwater abstraction, in lowland settings in the ‘TMG aquifer surface water interface-domain’. The GIS model integrated the conceptual understanding into a management tool by highlight all quaternary catchments associated with TMG containing sensitive aquatic ecosystems and gave the variable vulnerability for each.Web of Scienc

Will climate warming exceed lethal photosynthetic temperature thresholds of lichens in a southern African arid region?

Predicted elevated temperatures and a shift from a winter to summer rainfall pattern associated with global warming could result in the exposure of hydrated lichens during summer to more numerous temperature extremes that exceed their thermal thresholds. This hypothesis was tested by measuring lethal temperature thresholds under laboratory and natural conditions for four epilithic lichen species (Xanthoparmelia austro-africana, X. hyporhytida, Xanthoparmelia sp., Xanthomaculina hottentotta) occurring on quartz gravel substrates at a hot arid inland site two epigeous lichen species (Teloschistes capensis, Ramalina sp.) occurring on gypsum-rich topsoil at a warm humid coastal site. Extrapolated lethal temperatures for photosynthetic quantum yield under laboratory conditions were up to 4°C higher for lichens from a dry inland site than those from a humid coastal site. Lethal temperatures extrapolated for photosynthetic quantum yield at a saturating photosynthetic photon flux density of ≥11,000 µmol photons m-2s-1 under natural conditions were up to 6°C higher for lichens from the dry inland site than the more humid coastal site. It is concluded that only under atypical conditions of lichen exposure in a hydrated state to temperature extremes at high midday solar irradiances during summer could lethal photosynthetic thresholds in sensitive lichen species be potentially exceeded, but whether the increased frequency of such conditions with climate warming would lead to increased likelihood of lichen mortality is debatable.Web of Scienc

Salinity of irrigation water in the Philippi farming area of the Cape Flats, Cape Town, South Africa

This paper explores the nature, source and spatial variation of the salinity of water used for irrigation in a coastal urban farming area in Cape Town, South Africa, where water from the Cape Flats aquifer is drawn into storage ponds and used for crop irrigation. Water samples were collected in summer and winter from selected sites across the study area and were analysed for salinity as well as for concentrations of major and minor ions. Each site consists of one borehole and one pond. Isotope analysis was done for the summer samples so as to assess effects of evaporation on water quality and salinity. Descriptive statistics were used to compare the variation in range of concentration of specific ions with the recommended ranges set by the South African Department of Water Affairs and Forestry (DWAF) and the Food and Agriculture Organisation (FAO). Geographical information system (GIS) analysis was used to describe the spatial distribution of salinity across the study area, and hydro-geochemical analysis was used to assess the possibility of seawater intrusion into the aquifer system and to characterise groundwater in the study area. The results of the research showed that the concentrations of chloride, nitrate, potassium and sodium exceeded the target maximum limit according to DWAF and FAO guidelines. Groundwater and pond water were also observed to be brackish in most parts of the research area in terms of total dissolved salts content, and fresh water was only found in the middle section of the research area. It is concluded that the accumulation of salts in groundwater and soil in the study area is mainly due to the agricultural activities and partially due to the natural movement of water through the geological formation of the Cape Flats region. These findings permit the formulation of a conceptual model of the occurrence of the salinization process, which implies that the groundwater and pond water in the study area are generally suitable for irrigation purposes, but need to be used with caution as the vegetables grown are classified as sensitive and moderately sensitive to salt according to DWAF guidelines for irrigation water quality (1996). The research paves a way for possible quantitative simulation of salt mass balance in future.Web of Scienc

Morphological and physiological responses of Calobota sericea plants subjected to water limitation and subsequent rewatering

Calobota sericea is a native legume of South Africa, confined to the water-limited rangelands, and it has recently been prioritised for additional characterisation regarding its pasture potential. In this study, we examined the growth characteristics of C. sericea under glasshouse conditions where water limitation was implemented at different plant ages, and for different durations. Results indicate that preferential resource allocation to the roots, as well as reduced stomatal conductance and transpiration, were early responses to water limitation, irrespective of the age at which water limitation was imposed, or the duration of water limitation. Under water-limited conditions, increased production of protective pigments, such as carotenoids and anthocyanins, was also observed, which helped in recovery after rewatering. It was concluded that after rewatering, all negative impacts of water limitation on morphology and physiology of C. sericea plants were generally returned to well-watered levels. This suggests that C. sericea plants employ a wide range of phenotypic adjustments in response to water limitation, which makes the plants well adapted to areas with high rainfall variability

Review of phytoplankton dynamics in tropical African lakes

Article #64This paper provides a synthesis of current knowledge on phytoplankton production, seasonality, and stratification in tropical African lakes and considers the effects of nutrient enrichment and the potential impacts of climate warming on phytoplankton production and composition. Tropical African lakes are especially sensitive to climate warming as they experience wide fluctuations in the thermocline over a narrow range of high water temperatures. Recent climate warming has reduced phytoplankton biomass and production in the lakes. A decline in the production of palatable chlorophytes and an increase in cyanobacteria has led to reduced zooplankton production and a consequent decline in fish stocks, all of which can be associated with the elevated water temperatures. This indicates that even moderate climate warming may destabilise phytoplankton dynamics in tropical African lakes, thereby reducing water quality and food resources for planktivorous fish, with consequent negative impacts on human livelihoods

Conservation status of large branchiopods in the Western Cape, South Africa

Temporary wetlands are an ecologically and economically important habitat in South Africa. They harbor large branchiopods, known to be flagship species of nonpermanent aquatic habitats, and sensitive to land use changes. In this study we review the current status of large branchiopods in the Western Cape, a South African province subject to increasing agriculture and urbanization. We studied the species diversity and distribution of large branchiopods by sampling 58 temporary wetlands in an area covering about 30% of the Western Cape. Information obtained from field samples was supplemented by incubating resting egg banks from the sampled wetlands. Our data were compared with all known distribution records for large branchiopods in the target region. Based on this combined information, the International Union for the Conservation of Nature and Natural Resources (IUCN) Red List category was assessed for each species. Four of the eight large branchiopod species known to occur in the sampling area were collected. Of all wetlands sampled, 40% harbored large branchiopods. Most anostracan populations were small, and species co-occurred in only one wetland. From the entire Western Cape, 14 species have been recorded in the past. Two of these are already included in the IUCN Red List. Insufficient data are available to determine the IUCN Red Data Category of six other species. A large variation in the telsonic appendages of S. dendyi was found across the studied area. In view of possible ongoing speciation and subsequent radiation, individual populations need protection. Since little information is available, it is difficult to evaluate recent changes in the conservation status of large branchiopods. Their populations are currently very low and have probably diminished in the last few decades. More knowledge about the functioning of temporary systems is needed to manage these vulnerable habitats and conserve their threatened species.Web of Scienc

Aspects of the ecophysiology of Didelta L'Herit

Thesis (Ph.D.) -- University of Stellenbosch, 1988.Full text to be digitised and attached to bibliographic record

Sodium tolerance in Didelta l'herit

Thesis (M. Sc.) -- University of Stellenbosch, 1974.Full text to be digitised and attached to bibliographic record

A review of phytoplankton dynamics in tropical African lakes

This paper provides a synthesis of current knowledge on phytoplankton production, seasonality, and stratification in tropical African lakes and considers the effects of nutrient enrichment and the potential impacts of climate warming on phytoplankton production and composition. Tropical African lakes are especially sensitive to climate warming as they experience wide fluctuations in the thermocline over a narrow range of high water temperatures. Recent climate warming has reduced phytoplankton biomass and production in the lakes. A decline in the production of palatable chlorophytes and an increase in cyanobacteria has led to reduced zooplankton production and a consequent decline in fish stocks, all of which can be associated with the elevated water temperatures. This indicates that even moderate climate warming may destabilise phytoplankton dynamics in tropical African lakes, thereby reducing water quality and food resources for planktivorous fish, with consequent negative impacts on human livelihoods

Essential metal and metalloid elements in the Philippi Horticultural area, and their uptake into selected vegetable crops

This study evaluated Co, Cr, Mn, Ni, Se, Sn and V status in the soils of the PHA, as well as the vegetables produced on these soils. We also determined the agronomic sources of these elements to the soils in the PHA. Farmyard manures applied as fertilizer amendments to the soils in the PHA were found to be the major agronomic sources of the metal and metalloid elements. These elements were however, retained in significantly higher concentrations in the soils compared to the concentrations found in the edible portions of the vegetable crops collected. This, in turn, resulted in these vegetables being poor sources of several of the essential mineral nutrients. It is therefore suggested that: (1) a wider variety of crops are assessed for their mineral nutrient status, (2) to find ways to increase the availability of these mineral nutrients and (3), that the possibilities of micronutrient and trace element deficiencies be assessed in the communities surrounding the PHA