Estuarine acidification, caused by disturbance of acid sulfate soils (ASS), is a recurrent problem in eastern Australia. Affected waters are characterised by low pH and elevated concentrations of metals, principally aluminium and iron. The effects of acid and elevated metal concentrations associated with ASS, on adult Sydney rock oysters, have not been previously investigated. This study tested links between ASS-affected drainage, subsequent estuarine acidification and Sydney rock oyster production problems on the Hastings and Manning Rivers, mid north coast New South Wales. The primary objective of this thesis was to establish if estuarine acidification causes mortality and slow growth in individual Sydney rock oysters by exposing oysters to low pH, iron and aluminium using field and laboratory experiments. Water quality data showed that estuarine acidification was spatially extensive in the Hastings and Manning Rivers following heavy rainfall and was due to mineral acids originating from drained or excavated ASS. Estuarine acidification regularly affected areas used for Sydney rock oyster production following heavy rainfall. Field experiments showed that Sydney rock oyster mortality rates were significantly higher at sites exposed to ASS-affected waters compared to locations that were isolated from ASS-affected waters. Oyster mortality increased with the time of exposure and smaller oysters (mean weight = 5 g) experienced significantly higher mortality relative to larger oysters (mean weight = 29 g). This was caused by acid-induced shell degradation resulting in perforation of the smaller oysters??? under-developed shells. Additionally, Sydney rock oyster growth rates were dramatically reduced at sites exposed to ASS-affected waters and the overall mean condition index of oysters at ASS-affected field sites was significantly lower than the overall mean condition index of oysters at non-impacted sites. Findings from laboratory experiments showed that ASS-affected water alters oyster valve movements and significantly reduces oyster feeding rates at pH 5.5. Acidic treatments (pH 5.1) containing 7.64 mg L-1 of aluminium or ASS-affected water caused changes in the mantle and gill soft tissues following short-term exposure. Degenerative effects described in oysters in this study were also due to iron contained in ASS-affected waters. Iron precipitates accumulated on the shell, gills and mantle and were observed in the stomach, intestine, digestive tubules and rectum. This study concluded that Sydney rock oysters are unable to tolerate acidic conditions caused by ASS outflows and cannot be viably cultivated in acid-prone areas of the estuary.

Estuarine acidification, caused by disturbance of acid sulfate soils (ASS), is a recurrent problem in eastern Australia. Affected waters are characterised by low pH and elevated concentrations of metals, principally aluminium and iron. The effects of acid and elevated metal concentrations associated with ASS, on adult Sydney rock oysters, have not been previously investigated. This study tested links between ASS-affected drainage, subsequent estuarine acidification and Sydney rock oyster production problems on the Hastings and Manning Rivers, mid north coast New South Wales. The primary objective of this thesis was to establish if estuarine acidification causes mortality and slow growth in individual Sydney rock oysters by exposing oysters to low pH, iron and aluminium using field and laboratory experiments. Water quality data showed that estuarine acidification was spatially extensive in the Hastings and Manning Rivers following heavy rainfall and was due to mineral acids originating from drained or excavated ASS. Estuarine acidification regularly affected areas used for Sydney rock oyster production following heavy rainfall. Field experiments showed that Sydney rock oyster mortality rates were significantly higher at sites exposed to ASS-affected waters compared to locations that were isolated from ASS-affected waters. Oyster mortality increased with the time of exposure and smaller oysters (mean weight = 5 g) experienced significantly higher mortality relative to larger oysters (mean weight = 29 g). This was caused by acid-induced shell degradation resulting in perforation of the smaller oysters??? under-developed shells. Additionally, Sydney rock oyster growth rates were dramatically reduced at sites exposed to ASS-affected waters and the overall mean condition index of oysters at ASS-affected field sites was significantly lower than the overall mean condition index of oysters at non-impacted sites. Findings from laboratory experiments showed that ASS-affected water alters oyster valve movements and significantly reduces oyster feeding rates at pH 5.5. Acidic treatments (pH 5.1) containing 7.64 mg L-1 of aluminium or ASS-affected water caused changes in the mantle and gill soft tissues following short-term exposure. Degenerative effects described in oysters in this study were also due to iron contained in ASS-affected waters. Iron precipitates accumulated on the shell, gills and mantle and were observed in the stomach, intestine, digestive tubules and rectum. This study concluded that Sydney rock oysters are unable to tolerate acidic conditions caused by ASS outflows and cannot be viably cultivated in acid-prone areas of the estuary.

Human activities such as urbanisation, sewage treatment, industrialisation and agriculture represent major human interference in water resources. The water resources are affected both quantitatively as well as qualitatively by these activities. The impact of human interference in the Mukuvisi River catchment hydrology was studied by determining the concentration values of eight selected physico - chemical and biological parameters. These are pH, temperature, total nitrates, total phosphates, Dissolved Oxygen, Biological Oxygen Demand, lead, copper and Total Faecal Coliform Count. Seven sites were sampled along the river, from up the river in Mukuvisi woodlands up to the point where the river discharges into Lake Chivero. Analysis of the results obtained was undertaken using SPSS (paired sample T test) and descriptive graphs were drawn using Microsoft Excel 2010. Nitrates, phosphates, copper, lead and Total Faecal Coliform Counts were found to be higher than the Zimbabwe National Water Authority (ZINWA) maximum and World Health Organisation, 2011 (WHO) permissible standards from site 3 to site 7. Site 6 recorded the highest concentrations of all the measured parameters, except for pH and Dissolved Oxygen. Mean DO and BOD concentrations were 2.53 mg/l and 40 mg/l respectively at site 6. Mean total nitrates were 17.5 mg/l at site 6 above the ZINWA and WHO threshold of 10 mg/l. Site 6 also recorded a mean total phosphate of 5.9 mg/l which was above the ZINWA and WHO threshold of 0.5 mg/l. Mean TFCC was 992.6 mpn100ml-1 higher than the threshold of nil according to ZINWA and WHO threshold. Site 3 recorded the mean DO and TFCC of 2.4 mg/l and 2.80 mpn100ml-1 respectively. Site 2 had the lowest mean TFCC concentrations of 2.80 mpn100ml-1, which did not differ significantly from the WHO and ZINWA threshold of nil at p<0.05. The quality of water in the river varied from site to site in direct relation to the intensity and type of human activities along the river course. Levels of all the water quality indicators increased after discharge from the Firle sewage treatment plant at site 6 with the exception of temperature and pH. Sewage effluents, agricultural runoff and industrial effluents were found to be responsible for the high nutrient levels and high metal concentrations in the river which in turn reduced DO levels and increased BOD / College of Agriculture and Environmental Sciences / M. Sc. (Environmental Science)