OALib Journal期刊

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匹配條件: “H.H du Preez” ,找到相關結果約160157條。
Lethal copper concentration levels for Clarias gariepinus (Burchell, 1822) @ a preliminary study
Marinda Van der Merwe,J.H.J. van Vuren,H.H. du Preez
Koedoe : African Protected Area Conservation and Science , 1993, DOI: 10.4102/koedoe.v36i2.376
Abstract: Lethal copper concentrations were determined for both adult and juvenile Clarias gariepinus at representative mean summer and winter temperatures. Fish were exposed to copper for 96 hours in an experimental system and mortalities monitored. Toxicity curves of percentage mortality versus actual copper concentration were drawn, and the LC50 calculated for winter and summer temperatures. The lethal copper concentrations, expressed as LC50, found in laboratory exposures, ranged for adults from 1,29 mg/1 during summer to 1,38 mg/1 in winter. These values are considerably higher than the levels of copper in the water of the Olifants River in the Kruger National Park during summer (0,055 @ 0,016 mg/1) and winter (0,085 @ 0,032 mg/1). The derived LC50 values predict the level of copper which should be prevented at all cost. The fish in the Olifants River are already exposed to sublethal concentrations (40 of LC50) of copper. The results can be used as an indication of what the safe concentrations of copper should be.
The development of an aquatic toxicity index as a tool in the operational management of water quality in the Olifants River (Knsger National Park)
V. Wepener,N. Euler,J.H.J. van Vuren,H.H. du Preez
Koedoe : African Protected Area Conservation and Science , 1992, DOI: 10.4102/koedoe.v35i2.400
Abstract: The development of an aquatic toxicity index and its application is described. In this index the protection of aquatic life is always referred to in terms of toxic effects of different water quality variables to fish, as health indicators of the aquatic ecosystem. The final index score is produced by means of standard additive techniques as well as by using the water quality variable giving the lowest index score (minimum operator). The minimum operator is employed in order not to conceal important water quality information. The aquatic toxicity index development has been linked to toxicological data, international water quality standards and South African guidelines. The index provides valuable information concerning toxic effects of a specific variable on fish should the threshold level for normal maintanence of aquatic life be exceeded. This index is intended as an aid in the interpretation of water quality information in order to facilitate management decisions.
The implementation of an aquatic toxicity index as a water quality monitoring tool in the Olifants River (Kruger National Park)
V. Wepener,J.H.J. van Vuren,H.H. du Preez
Koedoe : African Protected Area Conservation and Science , 1999, DOI: 10.4102/koedoe.v42i1.225
Abstract: Large sets of water quality data can leave water quality managers and decision-makers totally overwhelmed. In order to convey the interpretation of the data in a simplified and understandable manner, the water quality results from bi-monthly surveys undertaken at seven different sampling sites in the Letaba, Olifants, and Selati rivers over a two year period (February 1990 to April 1992) were reduced to index values, using a water quality index. The water quality index (Aquatic Toxicity Index or ATI) revealed spatial and temporal trends. The higher index values, recorded for the sampling sites towards the eastern part of the Kruger National Park (KNP), revealed that the water quality was better than the quality measured in the Olifants River on the western bound-ary. The lowest index values were calculated for the Selati River, with index values consistently below 50. Index values indicate that the water quality in the Selati River was unsuitable for supporting normal physiological processes in fish. The water quality of the Selati River had an immediate impact on the water quality of the Olifants River directly below the confluence. Lower index values recorded at sites further downstream was also attributed to the influence of the Selati River since there are no known point sources of contaminants within the boundaries of the KNP. The index scores also elucidated temporal trends with lower scores evident during winter months. This was due to reduced flow in the Olifants River and a greater contribution of contaminated water from the Selati River. Index values increased following the first seasonal rains due to a dilution effect. Very low index values were recorded at certain sites during flood periods due to increased turbidity, reduced oxygen, and increased metal concentrations.
Bio-accumulation of selected metals in African sharptooth catfish Clarias gariepinus from the lower Olifants River, Mpumalanga, South Africa
H.H Du Preez,M van der Merwe,J.H.J van Vuren
Koedoe : African Protected Area Conservation and Science , 1997, DOI: 10.4102/koedoe.v40i1.265
Abstract: The level of metal (Cr, Cu, Mn, Ni, Pb and Zn) bio- accumulation in tissues (muscle, gill, kidney, liver and gonads) and bile of the African catfish Clarias gariepinus, from the lower Olifants River was investigated. These metals were detected in all the tissues as well as in the bile, with the highest concentration found in either the gills, liver or gonadal tissue. The lowest concentration was usually detected in the muscle tissue. Although statistic comparisons revealed no significant differences between the localities, fish from the Selati River (Locality 1) generally had higher metal levels than fish from the localities along the Olifants River inside the Kruger National Park. The higher levels in the fish from the Selati River may be attributed to anthropogenic activities resulting in point and/or diffuse sources of metal pollution. These sources should be identified and reduced.
Variations in selected water quality variables and metal concentrations in the sediment of the lower Olifants and Selati rivers, South Africa
T. Seymore,H.H. du Preez,J.H.J. van Vuren,A. Deacon
Koedoe : African Protected Area Conservation and Science , 1994, DOI: 10.4102/koedoe.v37i2.334
Abstract: A survey of the water and sediment quality of the lower Olifants River and lower Selati River was carried out. Metal concentrations (Cr, Cu, Fe, Mn, Ni, Pb, Sr and Zn) in the water and sediment, as well as the physical and chemical characteristics of the water were determined over a two-year period (April 1990 - February 1992). The water quality of the lower Selati River, which flows through the Phalaborwa area, was found to be influenced by the mining and industrial activities in the area. It was also the case with the lower Olifants River after the Selati-Olifants confluence, although the concentrations of most variables did decrease from the western side of the Kruger National Park to the eastern side due to dilution of the water by tributaries of the Olifants River. Variables of special concern were sodium, fluoride. chloride, sulphate, potassium, the total dissolved salts and the metal concentrations (except strontium). The water quality of the Selati River in the study area is a great cause of concern and a further degradation thereof cannot be afforded.
Bioaccumulation of copper in the tissues of Potamonautes warreni (Calman) (Crustacea, Decapoda, Branchiura), from industrial, mine and sewage-polluted freshwater ecosystems
V.E. Steenkamp,H.H du Preez,H.J. Schoonbee
African Zoology , 2012,
Abstract: ENGLISH ABSTRACT: The copper concentration detected in the water and sediments of the Natalspruit River, Bronkhorstspruit River and Nooitgedacht Dam exceeded certain stated limits for the protection of aquatic life. Despite considerable individual variation, the general ranking of copper concentrations in the various tissues was carapace < muscle < gonads < midgut gland < gills. Seasonal variation was detected in the bioaccumulation of copper in crabs sampled from the Natalspruit River. However, this phenomenon did not occur in crabs from the other two water bodies. A significant increase in copper concentrations was detected with a decrease insize, indicating that the size of the crabs is an important influencing factor in the bioaccumulation of copper. It was also found that more copper accumulated in the ovary than in the testis per unit weight. The bioaccumulation factors (BF) calculated for the different tissues with respect to the water were highest in the gills and midgut gland (785,00 - 1257,50 and 432,00 - 1340,00, respectively). The BF with respect to the copper concentration in the sediments was comparatively low for all the tissues (<0,1O- 2,74). lt appears that P.warreni is able to regulate the copper concentrations in its various tissues and is therefore not a suitable indicator of the presence of copper in the aquatic environment. ********* AFRIKAANSE OPSOMMING: Die koperkonsentrasies wat gevind is in die water en sedimente van die Natalspruitrivier, Bronkhorstspruitrivier en Nooitgedacht Dam het sekere neergelegde riglyne vir die beskerming van akwatiese lewe oorskry. Ten spyte van ho individuele variasies, was die algemene verhouding in die koperkonsentrasies tussen die verskillende weefsels, karapaks < spier < gonades < spysverteringsklier
Bioaccumulation of chromium and nickel in the tissues of Barbus marequensis A. Smith, 1841 from the Lower Olifants River, Mpumalanga
Tharina Seymore,H.H. Du Preez,J.H.J. Van Vuren
African Zoology , 2011,
Abstract: Bioaccumulatlon of chromium and nickel in selected tissues and organs of the freshwater fish Barbus marequensis was investigated. According to the monthly data, the blood accumulated the highest amount of chromium, followed by the bile and vertebrae, while the skin accumulated the lowest amount. Nickel mainly accumulated in the blood, followed by the vertebrae and gills, while the lowest nickel concentrations occurred in the fat tissue. Although significant differences (p <= 0,05) between localities were detected, no definite trend as to where the highest bioaccumulation had occurred could be established. The levels in the tissues and organs of B. marequensis suggested no serious chromium or nickel pollution in the study area.
Suspended silt concentrations in the lower Olifants River (Mpumalanga) and the impact of silt releases from the Phalaborwa Barrage on water quality and fish survival
Y. Buermann,H.H. Du Preez,G.J. Steyn,J.T. Harmse
Koedoe : African Protected Area Conservation and Science , 1995, DOI: 10.4102/koedoe.v38i2.312
Abstract: Silt loads in the Olifants and Sabie river systems inside the Kruger National Park, were monitored by collecting water samples every consecutive week for a period of 20 months. The variation in silt concentration, changes in selected physico-chemical water quality variables and fish mortalities during flushing (i.e. release of silt, by sluicing) of the Phalaborwa Barrage, were also monitored. The Olifants River inside the Kruger National Park carried high silt loads in summer; in the dry season the suspensoid load was greatly reduced. A similar pattern was observed in the Sabie River, but the silt loads were generally lower. It was apparent that silt loads released from the Phalaborwa Barrage led to large variations in the natural silt loads of the Olifants River. These increased amounts of silt (25 000 mg/1 to >70 000 mg/1) caused drastic reductions in the dissolved oxygen concentration of the water, ranging from >6 mg/1 to 0 mg/1. Depending on the severity and duration of the flushing, fish succumb to such silt loads. These findings, as well as published information, indicate that the management strategy of flushing to improve storage capacity is ecological unacceptable. It is therefore suggested that the use of the Phalaborwa Barrage as a future reservoir should be critically re-evaluated.
Influence of natural silt on the survival of Oreochromis mossambicus yolk sac larvae
L. Smit,H.H. Du Preez,G.J. Steyn
Koedoe : African Protected Area Conservation and Science , 1998, DOI: 10.4102/koedoe.v41i1.246
Abstract: This study investigates the tolerance of Oreochromis mossambicus yolk sac larvae to natural silt from the Phalaborwa Barrage. Larvae survived silt concentrations lower than 13.2 g silt/I, but were highly active, indicating sublethal stress effects. When silt concentrations exceeded 29 g silt/I, stress reactions such as floating at the surface, gulping air, reduced fin and opercular movements and partial and complete loss of equilibrium were observed. Fish that succumbed exhibited darker pigmentation, and silt and mucus covered bodies. LC,() values were derived as 53.4 g silt/I, 31.7 g silt/I and 19.1 g silt/I for 1 hour, 24 hour and 48 hour exposure periods, respectively. Since these concentrations are much lower than the silt released from the Phalaborwa Barrage during flushing, it can be concluded that the release of high silt concentrations can severely impact the larval fish populations in the Olifants River below the Barrage.
Tooth replacement of tigerfish Hydrocynus vittatus from the Kruger National Park
C.L. Gagiano,G.J. Steyn,H.H. du Preez
Koedoe : African Protected Area Conservation and Science , 1996, DOI: 10.4102/koedoe.v39i1.288
Abstract: Evidence of tooth replacement was observed in 14 tigerfish which had been caught during the period 1991 - 1993 in the Olifants and Letaba rivers in the Kruger National Park. Replacement of teeth is a quick process (3-5 days) and first replacement of adult coni- cal dentition takes place at six to seven months post hatch, at a body length of 100 mm (FL). Swollen gums are evident prior to tooth replacement and newly erupted teeth are loosely embedded in the gums. Tooth replacement occurs in both the upper and lower jaws simultaneously. It was observed in the laboratory that the feeding behaviour was affected when adult conical dentition was replaced in @ 287 mm (FL) specimens.

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