Ecological effects of impoundments in the Buffalo River, Eastern Cape, with particular reference to the distribution of blackflies (Diptera : simuliidae)
- Authors: Palmer, Robert William
- Date: 1992
- Subjects: Stream ecology -- South Africa -- Buffalo River (Eastern Cape) Dipter -- South Africa -- Buffalo River (Eastern Cape)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6028 , http://hdl.handle.net/10962/d1006157
- Description: This thesis examines the extent and intensity of the effects of impoundments on selected physical, chemical and biotic conditions in an impounded southern African river. Life-history characteristics and environmental requirements which determine the success of impoundment-outlet blackflies in southern Africa were studied. Difficulties with the identification of immature blackflies led to a search for additional diagnostic characters, the description of larvae of seven species previously unknown, and the development of new keys to the species of Simulium (larvae and pupae) in southern Africa. Distribution records for each species are presented, and their ecology is summarised. Three pairs of closely related species, which were formerly indistinguishable, can now be recognised by differences between the structure of their cephalic fan microtrichia. Monthly physical, chemical and invertebrate samples at 16 sites upstream and downstream of four impoundments in the Buffalo River, eastern Cape, were taken over a period of two years. The downstream effects of impoundments on these parameters depended on the variable examined, the position of the impoundment along the river profile, the depth from which water was released, and the quality of the inflowing water. Impoundments in the Buffalo River caused an upstream shift of the thermal and suspended organic conditions, and the distribution of blackfly species. Surface-release impoundments in the clean, upper-reaches of the river caused increases in water temperature (by as much as 8ºC) and chlorophyll a (by as much as 600%). Recovery to riverine conditions was within 2.6 to 18.4 km, depending on flow. A polluted, surface-release impoundment in the middle-reaches of the river had a slight dampening effect on river temperatures, converted the particle size spectrum of the river from small (<80 μm) to large (250-1000 μm), and improved the water quality of the downstream reaches (with the exception of nitrate concentrations, which were higher in the tailwaters compared to inflowing water). An impoundment in the lower reaches caused reductions in maximum temperature of up to 6ºC when releasing water from the surface, and up to 16ºC when releasing water from the bottom. Bottom-released water carried high concentrations (36 to 190 g m³) of small (<5 μm) and largely inorganic (86 to 93%) material.Twenty species of blackflies were found in the Buffalo River, of which 18 were distinguishable as larvae. They were divided into those which were widespread (5 taxa), those restricted to waterfalls and mountain torrents (2 taxa), those found in the foothill stony run zone (6 taxa), and rare taxa (5 taxa). Impoundments in the Buffalo River did not alter population densities of blackfly larvae, but did alter blackfly species composition, favouring five species commonly found in mid-order streams in southern Africa (s. meduseaforme, S. hargreavesi, S. nigritarse, S. adersi and s. damnosum s.l.) at the expense of upper-reach species (s. rutherfoordi, S. letabum and s. impukane). These five species are regarded as typical of impoundment-outlets, and were small, multivoltine flies whose larvae shared a generalised cephalic fan microtrichial structure, consisting of a single row of moderately differentiated microtrichia. A strong relation was found between cephalic fan microtrichial structure and larval habitats: Taxa found in fast-flowing, clear water had a more complex fan structure compared to those found in slow-flowing, turbid water. It is concluded that impoundment-induced changes to hydrodynamics and transported material (food) are important factors which have changed the distribution of blackflies in southern Africa in recent times. These changes are more severe downstream of upper-reach impoundments than middle or lower-reach impoundments.
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- Date Issued: 1992
Bioenergetics of Simuliidae (Diptera) larvae in the Buffalo River (Eastern Cape Province)
- Authors: Scott, Penelope Jane
- Date: 1991
- Subjects: Simuliidae -- South Africa Diptera - -South Africa Bioenergetics , Simuliidae -- South Africa , Diptera -- South Africa , Bioenergetics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5591 , http://hdl.handle.net/10962/d1002041
- Description: Ingestion, assimilation and egestion rates of different sized filter-feeding blackfly larvae Simulium medusaeforme/hargreavesi (Diptera: Simuliidae) were determined. The effects of food type, food concentration and larval size on ingestion rates were tested. These bioenergetic parameters were used to obtain an indication of the importance of blackfly larvae in processing of particulate organic matter in the Buffalo River. Mean ingestion rates for S. medusaeforme/hargreavesi larvae feeding in the field ranged from 900 - 1600 μg/mg/h compared with those for larvae feeding in the laboratory on the same food type (260 - 680 μg/mg/h) and on algae, Chlorella sp. (590 - 1110 μg/mg/h) and Selenastrum sp. (340 - 1140 μg/mg/h). Ingestion rates obtained in this study were much higher than those reported by previous workers. These high ingestion rates are thought to be related to the low organic fraction of the suspended solids in transport in the Buffalo River. Larger larvae were found to ingest between three and six times as much food as smaller larvae. Ingestion rates were affected by the presence of nematodes and by imminent pupation. Assimilation rates on algae ranged from 2.3 - 49.0 μg/mg/h and were comparable with results of previous workers. The low assimilation efficiencies obtained for larvae feeding on algae (0.4 - 15.1 %) are due to the high ingestion rates. From a survey of the Buffalo River larvae were found to ingest between 0.00011 - 0.15 % of the suspended solids per metre of stream bed, about 1 - 7 times more than what has been reported by other workers. In the upper reaches of the Buffalo River larvae were potentially able to ingest all the suspended solids in the size class 0 - 250μ.m within a distance of 3.2km. Blackfly larvae play an important qualitative role in the functioning of a river system as they remove seston from transport and facilitate the action of gut microflora. Blackfly larvae in association with micro-organisms and other invertebrates are responsible for the majority of the retention and mineralisation of organic matter in the river
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- Date Issued: 1991