Hydrology, sediment transport dynamics and geomorphology of a variable flow river: The Mfolozi River, South Africa

The co-efficient of variation for inter-annual streamflow of the Mfolozi River is extremely high at 79%. An analysis of flow frequency indicated that streamflow is skewed towards low-flow values, with a number of extremely large flood events occurring as outliers on the histogram. Streamflow variability in the Mfolozi River may be linked to multiple factors including a large catchment size, a seasonal climate of a dry winter and wet summer, evergreen vegetation in the catchment, variable precipitation and the occurrence of regionally pervasive climatic oscillations. This research aimed to address how streamflow variability impacted upon sediment transport and thus, geomorphology. It was found that sediment transport variability occurred at the intra- and inter-annual scale. Analysis of mean monthly sediment concentration and discharge showed a hysteresis effect, such that sediment concentration peaked prior to discharge in the early wet season. During the late wet season, peak discharges often had unexpectedly low sediment concentrations. Furthermore, data suggested the existence of long-term hysteresis that may be related to decadal-scale climatic oscillations that alter sediment availability and stream capacity, resulting in discharge peaking in 2000 and sediment concentration in 2005. However, more data are required to confirm this relationship. Variability in streamflow appears to share a causal relationship with sediment transport variability, as both are linked to variation in precipitation and the resultant impacts on vegetation growth and evapotranspiration rates. The variability of streamflow and sediment transport has implications for stream and floodplain geomorphology, and the hydrology of variable rivers should be considered when interpreting their geomorphology

A synthesis of past, current and future research for protection and management of papyrus (Cyperus papyrus L.) wetlands in Africa

Papyrus wetlands (dominated by the giant sedge Cyperus papyrus L.) occur throughout eastern, central and southern Africa and are important for biodiversity, for water quality and quantity regulation and for the livelihoods of millions of people. To draw attention to the importance of papyrus wetlands, a special session entitled ‘‘The ecology of livelihoods in papyrus wetlands’’ was organized at the 9th INTECOL Wetlands Conference in Orlando, Florida in June 2012. Papers from the session, combined with additional contributions, were collected in a special issue of Wetlands Ecology and Management. The current paper reviews ecological and hydrological characteristics of papyrus wetlands, summarizes their ecosystem services and sustainable use, provides an overview of papyrus research to date, and looks at policy development for papyrus wetlands. Based on this review, the paper provides a synthesis of research and policy priorities for papyrus wetlands and introduces the contributions in the special issue. Main conclusions are that (1) there is a need for better estimates of the area covered by papyrus wetlands. Limited evidence suggests that the loss of papyrus wetlands is rapid in some areas; (2) there is a need for a better understanding and modelling of the regulating services of papyrus wetlands to support trade-off analysis and improve economic valuation; (3) research on papyrus wetlands should include assessment of all ecosystem services (provisioning, regulating, habitat, cultural) so that trade-offs can be determined as the basis for sustainable management strategies (‘wise use’); (4) more research on the governance, institutional and socio-economic aspects of papyrus wetlands is needed to assist African governments in dealing with the challenges of conserving wetlands in the face of growing food security needs and climate change. The papers in the special issue address a number of these issues

Applications of multi-walled carbon nanotube in electronic packaging

Thermal management of integrated circuit chip is an increasing important challenge faced today. Heat dissipation of the chip is generally achieved through the die attach material and solders. With the temperature gradients in these materials, high thermo-mechanical stress will be developed in them, and thus they must also be mechanically strong so as to provide a good mechanical support to the chip. The use of multi-walled carbon nanotube to enhance the thermal conductivity, and the mechanical strength of die attach epoxy and Pb-free solder is demonstrated in this work

Cryptic speciation and chromosomal repatterning in the South African climbing mice Dendromus (Rodentia, Nesomyidae)

We evaluate the intra- and interspecific diversity in the four South African rodent species of the genus Dendromus. The molecular phylogenetic analysis on twenty-three individuals have been conducted on a combined dataset of nuclear and mitochondrial markers. Moreover, the extent and processes underlying chromosomal variation, have been investigated on three species by mean of G-, C-bands, NORs and Zoo-FISH analysis. The molecular analysis shows the presence of six monophyletic lineages corresponding to D. mesomelas, D. mystacalis and four lineages within D. cfr. melanotis with high divergence values (ranges: 10.6% – 18.3%) that raises the question of the possible presence of cryptic species. The first description of the karyotype for D. mesomelas and D. mystacalis and C- and G- banding for one lineage of D. cfr. melanotis are reported highlighting an extended karyotype reorganization in the genus. Furthermore, the G-banding and Zoo-FISH evidenced an autosome-sex chromosome translocation characterizing all the species and our timing estimates this mutation date back 7.4 mya (Late Miocene). Finally, the molecular clock suggests that cladogenesis took place since the end of Miocene to Plio-Pleistocene, probably due to ecological factors, isolation in refugia followed by differential adaptation to the mesic or dry habitat

Female chacma baboons form strong, equitable, and enduring social bonds

Analyses of the pattern of associations, social interactions, coalitions, and aggression among chacma baboons (Papio hamadryas ursinus) in the Okavango Delta of Botswana over a 16-year period indicate that adult females form close, equitable, supportive, and enduring social relationships. They show strong and stable preferences for close kin, particularly their own mothers and daughters. Females also form strong attachments to unrelated females who are close to their own age and who are likely to be paternal half-sisters. Although absolute rates of aggression among kin are as high as rates of aggression among nonkin, females are more tolerant of close relatives than they are of others with whom they have comparable amounts of contact. These findings complement previous work which indicates that the strength of social bonds enhances the fitness of females in this population and support findings about the structure and function of social bonds in other primate groups

An analysis of plant species distributions on the floodplain of the Okavango River, Namibia, with respect to impacts of possible water ion

The proposed ion of water from the Okavango River in Namibia could potentially result in significant changes in the vegetation of floodplains downstream of the ion point. Direct gradient analysis was used to determine the distribution of the most common floodplain plant species in relation to elevation above the water surface and distance from the channel, and therefore to the depth and duration of flooding. Species could be ranked and scored according to their distribution in relation to both elevation and distance from the channel, reflecting a gradient from species intolerant of flooding to those that withstand prolonged flooding. In general, as distance from the channel increased, the elevation at which each of the species occurred decreased, but there was a great deal of variation in the range of elevations over which each species occurred, primarily as a consequence of the irregular topography of these floodplains. Furthermore, several ruderal species were restricted to elevated sites in close proximity to the channel, occurring on recently formed point bars which are the product of fluvial processes. Disturbance in the form of sediment deposition on point bars is thus an important determinant of species distribution on floodplains of the Okavango River. Given these patterns of species distributions it is difficult to predict with accuracy the effect of ion on vegetation distribution. A preliminary analysis of possible changes in the hydrological regime after ion has also been attempted as part of this study. This was achieved by comparing mean stage heights before and after ion assuming a constant rate of ion of 3 cumecs, and based on historical daily records from Rundu and Mukwe. Uniform ion would have a greater impact at low flows than at medium and high flows. Should ion proceed, it would therefore be more appropriate to remove water during periods of high discharge. However, since the Okavango River in Namibia recharges local and possibly regional groundwater, its discharge declines downstream. Rates of water loss from the river thus need to be determined prior to any decision being made about whether or not ion should take place, or where to locate the point of ion. Keywords: Okavango River; floodplain wetlands; water ion; fluvial disturbance (Afr J Aqua Sci: 2001 26(2): 121-129

The distribution of sweetveld and sourveld in South Africa's grassland biome in relation to environmental factors

The distribution of sweet- and sourveld in relation to climate, parent material and soil nutrients hs been examined in South Africa's grassland biome. Sourveld occurs in areas with high water supply and where parent material gives rise to soils with a high base status. Sweetveld occurs in areas with low water supplyand where parent material gives rise to soils with a high base status. The distribution of sweet- and sourveld does not seem to determined by base status itself, but by the concentration of phosphorous and the size of the eady mineralizable nitrogen pool in the soil. The difference between the temperatures in the growth (wet) and no-growth (dry) seasons also appears important, but the relation is not clear. We propose that aspects of the environment which promote carbon assimilation (water supply and temperature) in relation to nutrient supply, and sweetveld where nutrient supply is high relative to carbon assimilation. Mixed veld is intermediate between these two.Keywords: botany; carbon assimilation; distribution; environmental factors; forage quality; grassland; Grassland Biome; nutrient assimilation; sourveld; South Africa; sweetveldAfrican Journal of Range and Forage Science 1995, 12(1): 38–4