1. Die invloed van papierpulpmeule-aktiwiteite op die visgemeenskapstruktuur van die Elandsrivier, Mpumalanga.
- Author
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FERREIRA, M., WEPENER, V., and VAN VUREN, J. H. J.
- Subjects
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EFFECT of human beings on fishes , *PAPER mills , *FISH communities , *WATER pollution , *RIVERS - Abstract
River systems on a global level are heavily degraded by various human activities and impacts. The Elands River in Mpumalanga is just one of these river systems that is under constant threat. The Elands River, a major tributary of the Crocodile River, rises in a gently sloping highveld zone near the town of Machadodorp. There are various anthropogenic activities in the area, including the Sappi Ngodwana Mill, situated near the confluence of the Elaads and the Ngodwana Rivers. An effluent spill in 1989 caused major fish mortalities and changed invertebrate assemblages. Other anthropogenic activities include nutrient loading (due to the inadequate treatment of the sewage), various agricultural activities and the presence of exotic fish that has either been released into the river or entering the river from the dam that has been constructed on the Ngodwana River. The aim of the study was to determine whether the fish communities of the Elands and the Crocodile Rivers are affected due to unthropogenic activities. In general, fish communities and individuals have various qualities that make them useful in biological monitoring. Fish in general have a long lifespan and would thus be able to reflect changes in the integrity of the system over long periods of time. Two sampling surveys, representing high and low-flow periods, were undertaken in March and June 2005 respectively. The habitats sampled (when present) include shallow and deep section of the river in fast and slow flowing water. Sampling techniques include the use of seine nets, gill nets and electroshocking. A medium size seine net was hauled through the pooled areas and gill nets were placed in some of these pools. The technique most commonly applied in the study was electroshocking as it proved to be the most effective. This technique was applied at all the sites in the study. Linking community structure and environmental variables are possible when enough data is available. For this particular study, enough site specific data was available to make such an assessment. Results indicate that the fish communities of the Elands and Crocodile Rivers appear to be in a largely natural state. A change in community characteristics may have taken place at some sites downstream of the Ngodwana mill, but species richness and presence of sensitive species indicate little modification. This change was brought about largely by changes in water quantity and not water quality. During both flow regimes, Barbus argenteus dominated the community structure at some sites downstream of the Mill. The fact that this species of fish is sensitive to water quality changes (based on its perceived tolerance to water quality changes) is a good indication that this species of fish does not dominate the community structure due to pollution. This further supports the assumption that changes to flow at some site may be driving the community structure. This change in flow was brought about by the increase in water quantity from springs situated near the Mill and this increase can be linked to the activities of the Mill. One of the biggest concerns regarding the fish communities sampled during the study was the low numbers of Chiloglanis bifurcus recorded in the community. This critically endangered species occurs in the Elands River and has a high preference for clean, fast-flowing water through all its life stages. [ABSTRACT FROM AUTHOR]
- Published
- 2008