Untitled Document
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
2 Department of Theoretical Physics,
, Research School of Physical Sciences & Engineering
and
Mathematical Sciences Institute, Australian National University, Canberra,
ACT 0200, Australia
3 Coastal Environment Laboratory, Department of Socio-Cultural Environmental
Studies, Graduate School of Frontier Sciences, The University of Tokyo,
Japan
4 Department of Microbiology, University of Western 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.
Subtidal Stromatolites, Hamelin Pool
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.