Lake Burragorang Research Articles

Energy dispersive spectroscopy of granular concretions in the mantle of the freshwater mussel Hyridella depressa from Lake Burragorang as a technique to monitor metals in aquatic systems

Concerns for river health and water quality have led to aquatic organisms being used as bioindicators of these resources. X-Ray microanalysis with Energy Dispersive Spectroscopy was utilised to analyse the metal-ion content of granular concretions in the mantle of the Australian freshwater mussel Hyridella depressa from an uncontaminated water storage, Lake Burragorang. This study established a baseline level of potential contaminants for future work using mussels as bioindicators of metal pollution. Eleven elements were analysed: Cu, Zn, Pb, Al, Mg, P, Ca, Mn, S, Ba and Fe. Analysis of data from five sites in the lake determined that Lake Burragorang could be used as a baseline reference site which would allow replication.

Reproduction of river and lake populations of Hyridella depressa (Unionacea: Hyriidae) in New South Wales: implications for their conservation

The freshwater mussel Hyridella depressa is an important component of the macrobiota of freshwater systems of south-eastern Australia. This species has declined in river habitats but is abundant in impounded water storages. Reproduction of river and lake populations of H. depressa was investigated to document details of their gametogenic cycle and to determine when the females incubate embryos in their gill marsupia. Four populations in Lake Burragorang and two populations in the Hawkesbury-Nepean River were studied over two breeding seasons. Reproduction was documented by anatomical and histological examination of the gonads. The study sites differed in anthropogenic influence and trophic status and the influence of these factors on reproduction in H. depressa was assessed. A skewed sex ratio in favour of females was common in the populations and histology revealed that some of these females were microhermaphrodites. It appears that sexuality in H. depressa is labile with the potential for self-fertilisation by individuals that largely function as females. H. depressa is a long-term brooder with progeny present in the marsupia for up to eight months of the year from mid-winter to late summer. Across all sites brooding started in July or August and finished in January or February of the following year. In parallel with the prolonged spawning pattern, gametogenesis in H. depressa was continuous. At the eutrophic sites the gonads contained advanced gametes throughout the year. H. depressa at these sites had a high annual reproductive output with the females producing several clutches each year. In contrast, gametogenesis in mussels at the oligotrophic sites was more seasonal. At one of the oligotrophic sites reproductive failure was common and in 1996 most females failed to brood a single clutch. Implications of this research for conservation of H. depressa are discussed.

Current and Historical Occurrence of Platypuses, Ornithorhynchus anatinus, around Sydney.

No formal survey of platypus (Ornithorhynchus anatinus) distribution around the greater Sydney area has previously been carried out. However, using 126 records of 0. anatinus from various sources (Pre-1900 (7), 1900-69 (43), 1970-89 (57), 1990-96 (19)), an assessment of the current and historical occurrence of the species in this area has been made. The species has been observed regularly since European settlement in the upper reaches of the Nepean River and its tributaries above the sites of the current Sydney water storages. Apparently once common in the Nepean River between the current water storages and the Warragamba River junction, the species is now seldom observed in this section of the river. It was previously more common in the lower reaches of the Nepean and upper Hawkesbury Rivers and platypuses are still occasionally recorded in this part of the river system. The species also still occurs upstream of the Lake Yarrunga storage in the Kangaroo River. It is currently found in streams of the Lake Illawarra catchment and the south coast, as far south as Berry, and in the Wollondilly and Coxs Rivers upstream of Lake Burragorang. Platypuses are no longer reported from the streams flowing through the Wollongong metropolitan area. Some recent records exist for the Sydney metropolitan area, but most are from national parks. The river systems around Sydney, Wollongong and their satellite settlements have been severely degraded by a range of human activities since early European settlement. At present it is not possible to attribute changes in 0. anatinus distribution to any single human activity over that period.

Chlorophyll-total phosphorus relationships in Lake Burragorang, New South Wales, and some other Southern Hemisphere lakes

Linear regression of chlorophyll concentration on total phosphorus concentration for phosphorus- limited Lake Burragorang, N.S.W., yields regression coefficients within the range reported for individual lakes in the Northern Hemisphere. Some variation in slope of published regressions is attributable to the choice of different regression subvariables (e.g. annual mean or annual maximum). The extent of this variation is quantified. Data from Lake Burragorang and other sites indicate that chlorophyll-phosphorus relationships in the Southern Hemisphere are concordant with those in the north if turbid waters are excluded from consideration. This is obviously significant in Australia, with so many turbid waters. The notion of 'growing season', as applied to Northern Hemisphere studies, is inappropriate for the warm temperate conditions of Lake Burragorang, and it was necessary instead to use the annual maximum chlorophyll concentration. Prediction of annual maximum chlorophyll concentration is of particular significance to water-quality management. Despite highly significant regressions, 95% confidence intervals and 95% prediction limits are wide, so that prediction of chlorophyll concentration from single values of total phosphorus, using double-In regressions, gives a wide arithmetic range. Use of annual mean total phosphorus concentration as the predictor variable limits the forecasting ability of the Lake Burragorang regressions but facilitates future coupling with a phosphorus loading model. This would assist in the assessment of projected management plans and the formulation of protective loading criteria.

Environmental Implications of Warragamba, a Dam for Water Supply of Sydney, New South Wales, Australia

Construction of the Warragamba Dam made a most important stream available for water supply to Sydney. Lake Burragorang created by the Dam necessitated extensive land acquisitions, caused loss of some agricultural area, a popular tourist resort and a unique Aboriginal relic. Tree removal required to maintain water quality is likely to have had some influence on the microclimate. The crest area around the Dam has been attractively landscaped. The catchment which includes significant forests has been divided to facilitate management. Cattle and sheep farming, some towns and coal mining contribute to pollution of the stream. Recreation is not permitted on the Lake and access is prohibited within 3 km of the waterʼs edge. Because of the method of operation of the Dam it has not significantly assisted in ameliorating flooding of the Hawkesbury River flood plains downstream of the Dam. Re-examination of the environmental implications of the structure from time to time is considered desirable.