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Background to this study
Aquatic ecosystem degradation at Loskop Dam
The Olifants River is widely regarded as one of South Africa’s most threatened river ecosystems (Ashton, 2010; Ashton & Dabrowski, 2011). The river flows in a northeasterly direction from its source on the Highveld region down the escarpment, through the Kruger National Park (KNP), and into the Massingir Dam in Mozambique, after which it flows into the Indian Ocean. Loskop Dam is an impoundment in the upper catchment of the Olifants River, which is the main inflow to the dam. Dominant land uses that impact water quality in this catchment include coal mining, power generation, industry, agriculture and effluent from wastewater treatment works (WWTWs). There is extensive evidence of the negative impact that acid mine drainage (AMD) from working and abandoned coal mines, and nutrientrich effluent discharged from WWTWs, in particular, are having on water quality in the upper catchment (Ashton & Dabrowski, 2011; Dabrowski & De Klerk, 2013).
Loskop Dam acts as a sink for these pollutants. Coal mining related impacts include increasing sulphate concentrations which have risen seven-fold since the 1970’s (De Villiers & Mkwelo, 2009). Periods of low pH (< 6) have been reported at the inflow to Loskop Dam, along with concentrations of aluminium (Al), iron (Fe), manganese (Mn) and copper (Cu) that exceeded water quality guidelines for ecosystem health (Oberholster et al., 2010). High inputs of phosphorous originating from WWTWs have led to increased eutrophication, and the dam has been variously classified as hyper-eutrophic (Oberholster et al., 2010) and meso- to eutrophic (Oberholster et al., 2013). The combination of these impacts, along with an extended drought period, culminated in serious environmental problems at several trophic levels during the mid-2000s at Loskop Dam.
Between the years 2002 and 2005, water levels in the dam failed to reach full supply level (FSL), with the lowest dam level of 26% recorded in early 2004. In 2007 the cyanobacterium Microcystis aeruginosa and the dinoflagellate Ceratium hirundinella started forming seasonal blooms, which were ongoing during this study. At least four large scale fish kills involving several species occurred between 2006 and 2007, and were attributed to AMD in combination with other environmental factors (Dabrowski, 2012). While investigating fish kills, veterinary pathologists from the Faculty of Veterinary Science at the University of Pretoria also observed a pattern of spring dieoffs of predominantly large (> 30 cm) male Oreochromis mossambicus (Mozambique tilapia) in the transitional zone of the dam. This area is a mixing zone characterised by reducing flows as water enters the lacustrine environment from the river. Algal blooms are most concentrated in this area. A diagnosis of pansteatitis (yellow fat disease) was made based on autopsies and histological examination of tissues.
These revealed that O. mossambicus were extremely fat, with extensive inflammation, and hardening of the fat caused by ceroid pigment associated with lipid peroxidation. Other fish species appeared to be unaffected by the disease. In 2005 the first Nile crocodile (Crocodylus niloticus) was diagnosed with pansteatitis.
Mortalities have been ongoing, and the most recent estimate of the crocodile population was around 6 individuals (Botha et al., 2011). Prior to this, estimates of the crocodile population ranged from 20 to 80 individuals (Jacobsen, 1984; Driescher, 2008).
An overview of pansteatitis in the Olifants River catchment
The events at Loskop Dam did not occur in isolation. During 2008 and 2009, downstream from Loskop Dam, at least 180 crocodiles were found dead at the Olifants River gorge in the KNP. After performing autopsies, veterinarians from the KNP determined that pansteatitis was the cause of death. Crocodile carcasses were extremely fat with extensive inflammation and hardening of the fat. Subsequent studies have also reported pansteatitis in Clarias gariepinus (sharptooth catfish), but no other fish species, from the same location (Huchzermeyer et al., 2011). Just prior to the crocodile deaths, the level of the Massingir Dam was raised in 2007. After this event, characteristics of the river in the gorge changed from a riverine to more lacustrine environment, and reduced flow resulted in increased deposition of clayrich sediments.
The distance along the Olifants River between Loskop Dam and the gorge is ca. 520 km, and no reports of pansteatitis in aquatic animals have been made between these two locations. Flag Boshielo Dam is located ca. 90 km downstream of Loskop Dam, and has the Olifants and Elands rivers as the main inflows. This reservoir has the largest population of crocodiles on the Olifants River outside of the KNP. To date, pansteatitis has not been reported in fish or crocodiles from this location, and fish kills are not frequently reported. Its location downstream of Loskop Dam means the potential exists for a similar range of pollutants to affect water quality. However, the combination of conditions that cause pansteatitis are not present at Flag Boshielo Dam, making it a suitable reference site for studies of the disease aetiology.
CHAPTER 1: INTRODUCTION.
1.1 Background to this study
1.1.1 Aquatic ecosystem degradation at Loskop Dam .
1.1.2 An overview of pansteatitis in the Olifants River catchment
1.2 Research foundatio
1.3 Study justification .
CHAPTER 2: LITERATURE REVIEW
2.1 Pansteatitis: Established pathology and aetiology
2.2 Aetiology in free-ranging animals
2.2.1 Fish kills and piscivor
2.2.2 Algal blooms, metal bioaccumulation, and interaction effects
2.2.3 Xenobiotics
2.2.4 Altered food webs
2.3 Local environmental drivers
2.4 Study aims
CHAPTER 3: CHEMICAL CHARACTERISTICS AND LIMNOLOGY OF
LOSKOP DAM ON THE OLIFANTS RIVER (SOUTH AFRICA), IN LIGHT OF
RECENT FISH AND CROCODILE MORTALITIE
3.1 INTRODUCTION
3.2 METHODS
3.2.1 Study site
3.2.2 Reservoir physiography
3.2.3 Surface water chemistry .
3.2.4 Near-bottom water chemistry and reservoir profiles
3.2.5 Statistical analyses
3.2.6 Trophic indicators
3.2.7 Trend analysis
3.3 RESULTS
3.4 DISCUSSION .
CHAPTER 4: WATER QUALITY OF FLAG BOSHIELO DAM, OLIFANTS RIVER,
SOUTH AFRICA: HISTORICAL TRENDS AND THE IMPACT OF DROUGHT
4.1 INTRODUCTION
4.2 METHODS
4.2.1 Study Site
4.2.2 Reservoir Physiography
4.2.3 Physico-chemical characteristics
4.2.4 Drought Characterisation .
4.2.5 Department of Water Affairs Monitoring Data
4.3 RESULTS
4.3.1 Reservoir physiography
4.3.2 Physico-chemical characteristics
4.3.3 Drought Characterisation .
4.3.4 Department of Water Affairs Monitoring Data
4.4 DISCUSSION
CHAPTER 5: PISCIVORY DOES NOT CAUSE PANSTEATITIS (YELLOW FAT
DISEASE) IN OREOCHROMIS MOSSAMBICUS FROM AN AFRICAN SUBTROPICAL
RESERVOIR*
CHAPTER 6: THYROID AND NUTRITIONAL STATUS OF OREOCHROMIS MOSSAMBICUS FROM TWO SUB-TROPICAL AFRICAN RESERVOIRS
CHAPTER 7: GENERAL DISCUSSION AND CONCLUSIONS
CHAPTER 8: REFERENCES .
APPENDIX: RESEARCH PUBLICATIONS RELATED TO THIS STUDY
