Yalgorup National Park
Yalgorup National Park lies on the western edge of the Swan Coastal Plain just south of the new Dawesville Channel near Mandurah. The name Yalgorup is derived from two Nyoongar Aboriginal words; Yalgor, meaning 'a swamp or lake', and up, a suffix meaning 'a place'. It is a very appropriate name as the park protects 10 lakes that run in a chain.
Lieutenant Surgeon Alexander Collie and Lieutenant William Preston, together with a boat party, first came across and named Lakes Preston and Clifton while exploring the coastline between Mandurah and Bunbury in 1829.
In the 1850s, shortly after the introduction of convict labour into the State, the 'Old Coast Road' south of Mandurah was rebuilt by convict road gangs. For most of its length, the road ran through well-timbered, sandy limestone country of little value to agriculture.
Except for a number of small holdings that had been developed by the early 1870s near fishing grounds on the western shore of the Harvey Estuary, settlements near the Old Coast Road were quite scattered. However, only in the early 1970s was Yalgorup National Park formally established to protect the coastal lakes, swamps, and tuart woodland between Mandurah and Myalup Beach. Additions to the park have been occurring ever since.
Soils from the Sea
The soils of Yalgorup National Park originated from the sea. They are largely made up of calcareous material derived from sea shells and other marine organisms. These soils, deposited in a series of dune ridges parallel to today's shoreline, also illustrate past changes in sea level. As the polar ice caps grew during the last ice age (which began approximately 130,000 years ago), the sea level gradually fell, fluctuating as it did so. It reached its lowest point, 130 metres below its present level, about 18,000 years ago. It then rose after the ice age ended some 10,000 years ago, producing the shoreline we see today.
The dune systems within Yalgorup National Park are the result of these changes. The limestone rocks and soils that can be seen at the surface inland from the coast are derived from the older Spearwood system, which formed in the last 10,000 to 140,000 years. The Spearwood system is reflected by leached sands at the surface and creamy yellow to reddish-brown subsoils. The Spearwood beds also extend well offshore. Superimposed over the Spearwood system, for up to two kilometres from the beach, are the sand dunes of the Quindalup Dune System, which have been blown in from the sea or washed ashore over the last 10,000 years.
The lakes that characterise the park lie in the depressions between a series of coastal dunes within the Spearwood system. Reflecting this underlying structure, the ten lakes form three distinctive lines parallel to the coast. Lake Preston is extremely elongated and lies closest to the coast. The lakes behind the next ridge are far more broken, comprising (from north to south): Swan Pond, Duck Pond, Boundary Lake, Lake Pollard, Martins Tank Lake, Lake Yalgorup, Lake Hayward and Newnham Lake. Lake Clifton is the furthest from the coast and the nearest to the Old Coast Road. It too is extremely elongated.
While Yalgorup National Park helps to protect the lakes and the important waterbird habitat they provide, along with attractive coastal vegetation that is diminishing all too rapidly, it is significant for another reason. Some rather special formations on the edge of two of the lakes provide a unique look at what life was like at the dawn of time.
Rock-like structures known as thrombolites can be seen on the edge of Lake Clifton. Like the famous stromatolites of Hamelin Pool, in Shark Bay, the thrombolites are built by micro-organisms too small for the human eye to see. Within the structures of Lake Clifton, are living communities of diverse inhabitants with population densities of 3000 per square metre! Lake Clifton is one of only a few places in Western Australia where living thrombolites survive. These peculiar structures live on the eastern edge of the lake and are most easily seen in March and April. Microbial mounds, which are the remains of thrombolites, can be seen at nearby Lake Preston.
The thrombolite-building micro-organisms of Lake Clifton resemble the earliest forms of life on Earth. The discovery of modern examples helped scientists to understand the significance of micro-organisms in the environment and unravel the long history of life on Earth. These organisms were the only known form of life on Earth from 3500 million to 650 million years ago. The thrombolites and stromatolites they constructed dominated the clear, shallow seas of this period and formed extensive reef tracts rivalling those of modern coral reefs. Similar organisms, for instance, helped to form the rich iron-ore deposits of the Hamersley Range, in the Pilbara's Karijini National Park, some 2000 million years ago. At this time oxygen made up only one per cent of the atmosphere. When there was no more iron to precipitate, the free oxygen leaked into the atmosphere until it formed 21 per cent of atmospheric gases.
Today living examples of these once completely dominant organisms are restricted to only a few places. So why do thrombolites grow at Yalgorup? Scientists have suggested it is perhaps because Lake Clifton is associated with upwellings of fresh groundwater that are high in calcium carbonate. The micro-organisms living in this shallow lake environment are able to precipitate calcium carbonate from the waters as they photosynthesise, forming the mineralised structure that is the thrombolite.
The significance of thrombolites and stromatolites to science is inestimable but they are very fragile and can be degraded by visitors walking over them. To protect the thrombolites, an observation walkway has been built to minimise any impact from visitors wanting to see these fascinating structures.
Animals of the Lake
The Yalgorup lake system is so significant for waterbirds that it is recognised under the international Ramsar Convention (named after the place where it was signed in Iran). The lakes provide important habitat for the international transequatorial waders that migrate from the northern hemisphere. These waders include the bar-tailed godwit, red-necked stint, greenshank, red knot, whimbrel and three species of sandpiper. Other waterbirds that use the lakes include the banded and black-winged stilts, red-necked avocet, hooded and red-capped plovers, Australian pelican and coot.
Surveys carried out in south-western Australia between 1988 and 1992, showed that the Yalgorup lakes consistently supported the highest numbers of musk ducks and, in 1990, supported the most Pacific black ducks of the areas surveyed. The lakes also had the third largest numbers of black swans recorded in 1988 and consistently support high numbers of shelduck in early summer (13,899 at Lake Clifton in November 1988). Black swans also live in high numbers at Lake Pollard, where they graze on extensive growths of stoneworts (musk grasses).
The quacking frog, turtle frog and slender tree frog are among the eight frog species that inhabit the park and the long-necked oblong tortoise is present in Lake Clifton. People are also drawn to Yalgorup National Park. It offers visitors panoramic views of the beaches, dunes and lakes from several high spots. Peaceful settings among the patches of tuart forest and woodland, and sweeping views over the tranquil lakes, give the area a wilderness feel and attract an increasing number of visitors.
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