AN ASSESSMENT OF THE POTENTIAL IMPACT OF ALIEN INVASIVE VEGETATION ON THE GEOMORPHOLOGY OF RIVER CHANNELS IN SOUTH AFRICA

Summary

Invasion of the riparian zone by alien vegetation is recognised as a serious problem in many areas of South Africa. Vegetation is a dynamic component of river channels. It is an important control variable affecting channel form whereas the flow and sediment regime influences vegetation growth. Wherever alien vegetation invades the riparian zone it can be expected that there will be some impact on the physical structure of the riparian habitat. This paper reviews the effect of riparian vegetation on channel processes and channel form and discusses the implications of the invasion of riparian zones by alien vegetation. Woody species in particular are seen as having a significant potential for inducing channel modification, whilst their removal could lead to significant channel instability and mobilisation of sediment. The need for further research into the impact of alien vegetation on the geomorphology of South African river channels is stressed.     

A simulation of the process of sedimentation of suspended solids in the Yoshii River estuary

A vertical plane 2D model has been applied to the Yoshii River estuary, Japan, as a means of simulating the process of sedimentation. The current velocity and isohaline distributions were well reproduced in the estuary and the model simulated the concentration distribution of suspended solids for 8 particle size classes by using a transport equation based only on physical processes. The changes of the particle size distribution in surface water were well reproduced by the model. The vertical velocity component plays an important role in the behaviour of suspended solids.     

Characteristics of settling matter and its role in nutrient cycles in a deep oligotrophic lake

The settling flux of seston (dry weight, DW), chlorophyll a (Chl a), particulate organic carbon (POC), particulate organic nitrogen (PON), and particulate phosphorus (PP) was measured monthly in 1981–1983 at 10 different depths in Lake Chuzenji, Japan; an oligotrophic lake with a maximum depth of 163 m. The Ti concentration in entrapped matter was used to separate the sedimentation flux into allochthonous and autochthonous components. Inflow loads of dissolved nutrients (DN: 4.5, DP: 0.48 g m^-2a^-1) were almost sufficient to supply the autochthonous fluxes at 30 m (PON: 2.9, PP: 0.51 g m^-2a^-1 ), and this flux of POC (26.6 g m^-2a ^-1) was about one-third of primary production (84 g C M^-2a^-1). Sedimentation of particulate matter was the main path of losing nutrients from lake water, explaining more than 80% removal of inflow loads (TN, TP). Decomposition rates during sedimentation which were calculated from the vertical difference in the autochthonous flux agreed very closely with the results obtained by laboratory experiments of a 100-day incubation (content ratios from field observations were: POC 0.67, PON 0.65, PP 0.85; and from laboratory experiments they were: POC 0.68, PON 0.70, PP 0.94). These decomposition rates and those near the sediment interface were used to explain dissolved oxygen depletion and nitrate increase in the hypolimnion during stratification. The average sinking velocities were 1.82m d^-1 for seston and 1.16 m d^-1 for Chl a at 30m, they were influenced by Chl a content of seston.     

A new non-equilibrium enzyme linked immunosorbent assay for a glycogen-derived urinary tetrasaccharide

The tetrasaccharide, Glc1-6Glc1-4Glc1-4Glc, denoted (Glc)₄, is a limit dextrin formed by amylolytic degradation of glycogen. In order to evaluate the possible clinical importance of (Glc)₄ excretion as an indicator of certain physiological and pathological conditions, we have developed a new rapid and inexpensive immunoassay using a monoclonal antibody raised against (Glc)₄ glycosidically-linked to a carrier protein. As the antibody is highly specific, it can be used to measure native (Glc)₄ directly, without the chemical reduction step required in previous methods. A new type of non-equilibrium ELISA inhibition test was developed based on the capacity of free (Glc)₄ to decrease initial rates of antibody binding to (Glc)₄-coated microtiter wells. The method is highly reproducible and is as sensitive and accurate as the gas chromatography method or radioimmunoassay used previously.Abbreviations (Glc)₄ Glc1-6Glc1-4Glc1-4Glc - KLH keyhole limpet hemacyanin - BSA bovine serum albumin - PEG polyethylene glycol     

Indicator microbes correlate with pathogenic bacteria, yeasts and helminthes in sand at a subtropical recreational beach site

Aims: Research into the relationship between pathogens, faecal indicator microbes and environmental factors in beach sand has been limited, yet vital to the understanding of the microbial relationship between sand and the water column and to the improvement of criteria for better human health protection at beaches. The objectives of this study were to evaluate the presence and distribution of pathogens in various zones of beach sand (subtidal, intertidal and supratidal) and to assess their relationship with environmental parameters and indicator microbes at a non‐point source subtropical marine beach. Methods and Results: In this exploratory study in subtropical Miami (Florida, USA), beach sand samples were collected and analysed over the course of 6 days for several pathogens, microbial source tracking markers and indicator microbes. An inverse correlation between moisture content and most indicator microbes was found. Significant associations were identified between some indicator microbes and pathogens (such as nematode larvae and yeasts in the genus Candida), which are from classes of microbes that are rarely evaluated in the context of recreational beach use. Conclusions: Results indicate that indicator microbes may predict the presence of some of the pathogens, in particular helminthes, yeasts and the bacterial pathogen Staphylococcus aureus including methicillin‐resistant forms. Indicator microbes may thus be useful for monitoring beach sand and water quality at non‐point source beaches. Significance and Impact of the Study: The presence of both indicator microbes and pathogens in beach sand provides one possible explanation for human health effects reported at non‐point sources beaches.     

Pollen as a chronometer and sediment tracer,Burrinjuck Reservoir,Australia

Pollen analysis is widely used to reconstruct vegetation and land use histories, but can also provide sedimentological information. At Burrinjuck Reservoir, in south-eastern Australia, annual grass pollen peaks are used to distinguish each year's sediment, even when there are no visible laminations. In conjunction with other dating methods, this allows the determination of year by year influxes of all sediment components. Pollen grains in the Burrinjuck sediments are shown to be predominantly waterborne so that they can be used to trace sediment to its source in particular vegetation stands. Pollen concentration and the proportion of damaged pollen might also distinguish sediment eroded from topsoils and that from subsoils. Pollen analysis can thus be used to locate specific erosion events in both time and space.     

Three manganese oxide-rich marine sediments harbor similar communities of acetate-oxidizing manganese-reducing bacteria

Dissimilatory manganese reduction dominates anaerobic carbon oxidation in marine sediments with high manganese oxide concentrations, but the microorganisms responsible for this process are largely unknown. In this study, the acetate-utilizing manganese-reducing microbiota in geographically well-separated, manganese oxide-rich sediments from Gullmar Fjord (Sweden), Skagerrak (Norway) and Ulleung Basin (Korea) were analyzed by 16S rRNA-stable isotope probing (SIP). Manganese reduction was the prevailing terminal electron-accepting process in anoxic incubations of surface sediments, and even the addition of acetate stimulated neither iron nor sulfate reduction. The three geographically distinct sediments harbored surprisingly similar communities of acetate-utilizing manganese-reducing bacteria: 16S rRNA of members of the genera Colwellia and Arcobacter and of novel genera within the Oceanospirillaceae and Alteromonadales were detected in heavy RNA-SIP fractions from these three sediments. Most probable number (MPN) analysis yielded up to 10⁶ acetate-utilizing manganese-reducing cells cm⁻³ in Gullmar Fjord sediment. A 16S rRNA gene clone library that was established from the highest MPN dilutions was dominated by sequences of Colwellia and Arcobacter species and members of the Oceanospirillaceae, supporting the obtained RNA-SIP results. In conclusion, these findings strongly suggest that (i) acetate-dependent manganese reduction in manganese oxide-rich sediments is catalyzed by members of taxa (Arcobacter, Colwellia and Oceanospirillaceae) previously not known to possess this physiological function, (ii) similar acetate-utilizing manganese reducers thrive in geographically distinct regions and (iii) the identified manganese reducers differ greatly from the extensively explored iron reducers in marine sediments.     

Influence of an ecosystem engineer,the emergent macrophyte Sparganium erectum,on seed trapping in lowland rivers and consequences for landform colonisation

1. Plant physical ecosystem engineers can influence vegetation population and community dynamics by modifying, maintaining or creating habitats. They may also have the potential to act upon biotic processes, such as seed dispersal. 2. Examples exist of reduction in seed dispersal distances in vegetated compared to unvegetated terrestrial environments, and concentration of seed deposits associated with plant patches. Such effects in aquatic environments have been little studied, but the engineering effect of plant patches on patterns of flow velocity and sediment deposition in streams suggests that they may play a similar role. 3. In this study, we assess the potential of an emergent aquatic species, Sparganium erectum, to play a role in physically modifying river habitats and trapping seeds by examining patterns of seed deposition and substrate type in 47 river reaches across England and southern Scotland, U.K. 4. Areas of the river channel within or adjacent to S. erectum patches harboured more plant seeds and more species than unvegetated areas and had finer, sandier substrates with higher organic matter, total nitrogen and total phosphorus content. Most seed species were competitive, indicating that they were well suited to colonise the competitive environment of an S. erectum patch, and could potentially further stabilise accumulated sediments and contribute to landform development. 5. We demonstrate that S. erectum patches influence both the physical environment and the retention of seeds, in consistent patterns across the channel bed, for a range of lowland rivers that vary in stream power and geology and which can be expected to vary in levels of supply of fine sediment and seeds. 6. Our findings support the hypothesis that the fundamental influence of a riverine ecosystem‐engineering species on slowing fluid flow links the habitat creation process of sediment sorting and retention to seed trapping. We suggest the process is applicable to a wide range of aquatic and riparian vegetation. We also suggest that the mono‐specific and competitive growth, which is typical of these engineering species, will strongly influence the recruitment of trapped seeds.     

A ‘minimum stress inflexion’ in relation to environmental and biotic influences on the dynamics of subtidal encrusting communities?

The sedentary fauna of sublittoral boulders was studied at five sites with very different environmental conditions within Lough Hyne Marine Nature Reserve (51° 30 N, 9° 18 W). The degree of competition was assessed through the construction of competitive hierarchies built up from the results of nearly 3000 interactions between organisms. Communities at all sites were predominantly hierarchically organised with few stand-offs recorded. Density of interactions was correlated with total space occupation. Flow speed at all sites was logged over 24 h and this factor also correlated with space occupation. Degree of disturbance was assessed through the use of marked boulders at each site. Species diversity peaked where all factors were moderate and was lowest at extreme sites. The effects of these environmental variables and biotic factors in determining community composition are discussed, and a working model detailing a Minimum Stress Inflexion is described. This represents an extension of the intermediate disturbance hypothesis in that it is proposed that disturbance in this system may serve to reduce sediment load as opposed to preventing space monopolisation in the classical model.     

Tenascin-C and carcinoma cell invasion in oral and urinary bladder cancer

Carcinoma invasion is a complex process regulated by genetic and epigenetic factors as well. A relevant supportive condition for cancer cell migration is the reorganization of the extracellular matrix (ECM), which is realized in an orchestrated multicellular manner including carcinoma cells and stromal fibroblasts. An important key player in the process of ECM reorganization is Tenascin-C (Tn-C). The molecule occurs as different isoforms generated by alternative splicing and de novo glycosylation. Large variants of Tn-C are abundantly re-expressed in the invasive front of many carcinoma types. A special role for initiating migration and accompanied epithelial to mesenchymal transition has been suggested. Here, we review the current knowledge concerning the tumor biological importance of Tn-C, the synthesis and alternative splicing during the invasive process in general, and give an overview on the impact of Tn-C in urothelial carcinoma of the urinary bladder (UBC) and oral squamous cell carcinoma (OSCC).