*Email: nfrankli@mail.usyd.edu.au

This ongoing study aims to add to our understanding of environmental change and European environmental impact by investigating the Holocene sedimentary record preserved in Redhead Lagoon, located at Dudley, in coastal, east-central NSW. The lake is a small, closed drainage basin. It has therefore acted as an efficient sediment trap preserving a near-continuous depositional record of past environmental conditions.

The catchmnent was originally used as a camping ground for the Awabakal Aborigines (Dyall 1972). Permanent European settlement began in the mid 19^th Century, when the early settlers cleared the land for small-scale agricultural activities, such as citrus orchards. In the 1890s, however, Dudley was transformed into a coal mining community and land use in the lake catchment was modified dramatically (Tonks 1987). Mining continued until 1940 and in the 1950s the surface infrastructure was removed and the mine waste dumps transformed into playing fields. Large-scale urbanisation began in 1964, with the largest subdivision taking place in 1968. Two sediment trap dams were installed in the mid 1980s to prevent sediment run off from the landfill.

Caesium-137 and AMS Radiocarbon techniques were used to date the upper and lower parts of the sedimentary sequence respectively. A tentative chronology for the middle part of the sequence has been constructed from the evidence of sediment geochemistry. The simultaneous rises in heavy metal concentrations at a depth of 0.44 m, for example, are interpreted as resulting from the opening of the nearby lead-zinc smelter at Cockle Creek in 1897. The first divergence up-core in the behaviour of Phosphorus and the alkali and alkaline earth elements (Mg, Na, K, Ca) at 0.76 m, is likely to represent initial European contact at ~1860. The Caesium-137 analysis has provided a chronology to ~1955 at a depth of 0.20 m. Two basal dates have been provided by AMS analysis, indicating that the sequence extends back to mid Holocene times.

The most significant and damaging impacts of European settlement occurred during the initial post-contact period as a result of activities such as deforestation and clearance of the land for settlement and orchards, and the early establishment of Dudley Colliery. Site-specific sedimentation rates increased massively during this period to 0.815 kg m^-2 a^-1, more than a 60-fold increase from pre-European rates of ~ 0.0132 kg m^-2 a^-1. The results indicate that even though the initial impacts of European settlers on the catchment surface were of low intensity, they had an enormous effect on what is likely to have been a sensitive natural system. This may have depleted the available sediment stores, with the result that subsequent, much larger impacts were left with less material to erode because new regolith was unable to reform in the interim.

Sedimentation rates have been steadily declining since 1897. However, there was a brief increase in rates between 1968 and 1976, the 'peak construction' phase of urbanisation in the catchment. A sharp decline in deposition rates during the most recent period, the 'final urban' phase (1976 to 1996) probably reflects the success of recent soil conservation measures (sediment trap dams) and the increased area of impervious urban surfaces.