Research School of Earth Sciences
Microbialtes of Hamelin Pool and Lake Clifton, Western Australia
Robert Burne1, Murray Batchelor2,
B, Gumpei Izuno3 and Linda Moore4
1 Research School of Earth Sciences, Australian National University,
Canberra, ACT 0200, Australia
The Hamelin Pool stromatolites show great morphological variation and extend from the high intertidal zone to subtidal depths of about 2 metres. Analysis of variation in stromatolite height shows that the tallest structures occur in the shallow subtidal zone, and that stromatolite relief decreases toward both the upper intertidal zone and toward the deeper subtidal limit of occurrence. Stromatolites at similar depths all have similar relief. The shape of the stromatolites also varies consistently depending on the position relative to present sea-level. Flat forms dominate the high intertidal zone, cauliflower-shaped stromatolites are found in the lower intertidal zone, columnar-shapes dominate in shallow subtidal environments and the deepest examples are all small domes. Several authors have related variation in stromatolite shape to the occurrence of different types of microbial communities at different elevations. Burne (1991-1992) suggested that stromatolite growth was initiated in subtidal environments, and the present distribution is the result of falling sea levels and modification by intertidal microbial communities.
We have now (a) precisely surveyed the distribution of stromatolites in Hamelin Pool, and (b) modelled stromatolite growth variation by stipulating depth limits for stromatolite growth; suggested stromatolite growth rates; likely rate and direction of sea-level change; and period of time of that conditions for stromatolite growth have existed. We conclude that the morphological variation of stromatolites in Hamelin Pool can be accounted for by a model in which principal growth occurs only between mean low sea level and a depth of 2 metres, growth rate is 5 mm/decade, conditions suitable for stromatolite growth commenced 1,500 years ago, and relative sea level has fallen by 2 metres in the past 4000 years.
In 2007 research on Lake Clifton, a RAMSAR wetland south of Perth was resumed. Despite the recognised significance and importance of Lake Clifton and its protection as part of a National Park (Burne and Moore 1987, Moore and Burne 1994), there has been very serious environmental degradation over the past 15 years. There appear to have been three major causes of environmental degradation - Nutrient levels in the Lake - The naturally low nutrient levels of Lake Clifton were essential for the health of the thrombolite-based ecosystem. Despite the importance of monitoring of nutrient levels and limiting nutrient input to the Lake being emphasised by the Scientific Advisors in the Management Plan for the Lake, no monitoring appears to have been undertaken and nutrient levels appear to have risen considerably, possibly as a consequence of sub-division of the Lake's eastern border.
Introduction of Black Bream into Lake Clifton - The introduction of Black Bream into Lake Clifton by a Mandurah resident has had a devastating impact on the water quality, biota and microbial communities of the Lake Research is being undertaken on the nature of possible remedial action that might be implemented.
Freshwater aquifer depletion - It appears that the construction of the Dawesville Cut involved pumping of the groundwater aquifer and discharge of the fresh groundwaters into the sea. This channel was constructed as an ecologically questionable engineering solution aimed at dealing with the environmental degradation of the Peel Harvey Estuary. The coincidence between the excavation of the Dawesville Cut and elevated salinity of Lake Clifton lake water suggests that this groundwater pumping severely impacted the fresh groundwater aquifer running along the eastern boundary of Yalgorup Lakes. This may account for the salinisation of the aquifer, the reduction in carbonate and fresh water input into Lake Clifton, and the death of stands of Tuart Trees along the eastern Boundary of the Lake System. This may therefore be the result of not properly assessing the environmental impact of Groundwater pumping. Possible remedial action is under consideration.
Burne R.V. (1991-92): Lilliput's Castles: Stromatolites of Hamelin Pool. Landscope V.7 No.2 Summer ed. p. 34-40
Burne, R.V., Moore, L.S. (1987) Zircons from Syros, - Microbialites: Organosedimentary deposits of benthic microbial communities. Palaios, 2:241 - 254
Moore, L.S., Burne, R.V. (1994):-The modern thrombolites of Lake Clifton, Western Australia. in Phanerozoic Stromatolites II .(Bertrand Sarfati, J., & Monty C. L., Editors), Kluwer Academic, Pages 3 - 29.