Palaeolimnology as a management tool for Australian aquatic ecosystems

Many aquatic and terrestrial ecosystems in Australia have been extensively modified and in some cases degraded beyond rehabilitation since European settlement began over 200 years ago. Land and water management practices, including the introduction of exotic species, in combination with Australia's variable rainfall and river flows, have led to many of the environmental problems faced by the country today, particularly the deteriorating water quality in many coastal and inland waters. With continued population growth and an increasing demand for resources, significant pressure is being placed on Australia's aquatic and terrestrial ecosystems. This Thesis applies a palaeolimnological approach in two contrasting Australian aquatic environments, each with different problems and human impact histories. The sites were chosen to reflect two different key environmental issues currently facing Australia and to demonstrate the wide range of aquatic environments to which palaeolimnological techniques can be applied. The first site was Lake King, southeast mainland Australia. Lake King is one of a series of lakes that form the Gippsland Lakes, the largest estuarine system in Australia. The Gippsland Lakes have high conservation value, but human activities since European settlement began in the 1840s, in particular the construction of a permanent entrance connecting the lakes to the sea in 1889, have led to a series of environmental issues primarily resulting in declining water quality and nuisance algal blooms. Improving the water quality of the Gippsland Lakes is currently a focus of management efforts, but little is known about the pre-permanent entrance state of Lake King, which makes identifying baselines and targets difficult. Consequently, a palaeolimnological approach to determine the pre-permanent entrance status of Lake King has a valuable contribution to make to future management. The second site was Emerald Lake, sub-Antarctic Macquarie Island. Macquarie Island has experienced extensive feral animal impacts since humans arrived in 1810. In particular, widespread destruction of vegetation and landslides have occurred. A rabbit and rodent eradication programme is currently being planned, but little is known about the environment of Macquarie Island prior to 1810. Successful restoration and rehabilitation of Macquarie Island requires an understanding of pre-impact conditions and the role of natural climate variability and the implications of future climate change in order to assess the response of the island once the feral animals have been removed. Consequently, a palaeolimnological approach provides an opportunity to determine the pre-impact conditions and past natural climate variability. The specific Aims of this Thesis are to: (i) Use a palaeolimnological approach to assess human impacts and ecological changes that occurred since European settlement in southeast Australian estuaries and to determine reference conditions for developing management strategies; (ii) Use a palaeolimnological approach to assess recent environmental changes on World Heritage listed sub-Antarctic Macquarie Island in terms of human occupation, the introduction of feral animals and climate variability and the implications of these changes for future management strategies. The overall objective of this Thesis is to demonstrate the value of palaeolimnology, using diatom transfer functions, in identifying the impacts and consequences of human activities and in developing future management strategies.