Lake Alexandrina

Lake Alexandrina is a lake in South Australia, Australia, adjacent to the coast of the Southern Ocean, about 100 kilometres south-east of Adelaide.

Lake Alexandrina is located north of Encounter Bay and east of Fleurieu Peninsula. The Murray River is the major river to flow into Lake Alexandrina. Others include the Bremer, Angas, and Finniss Rivers, all from the eastern side of the southern Mount Lofty Ranges. The lake is shallow and contains a number of islands near the southern end. The lake empties into the sea near Goolwa (the channel is known as the Murray Mouth), but when the river flow is low the entrance is often blocked by a sand-bar. Originally subjected to tidal and storm inflows of seawater the lake is now maintained as fresh water by a series of barrages across the islands near the Murray Mouth. This has produced an annual requirement for more than 1 million megalitres of fresh water to replace losses from evaporation that once came from sea water. Though connected to the ocean historically the fresh and salt water flows mixed very little, with the lake area remaining fresh over 95% of the time with normal river inflow. Salt water inflows from the ocean would result in relatively little mixing of fresh and salt water, either vertically in the water column or laterally across the flow stream. Hindmarsh Island is reputed to be the largest island in the world with salt water on one side and fresh water on the other. Lake Alexandrina is connected by a narrow channel to the smaller Lake Albert to the south-east.

The lake was named after Princess Alexandrina, niece and successor of King William IV of Great Britain and Ireland. When the princess ascended the throne and took the name Queen Victoria there was some talk of changing the name of the lake to Lake Victoria, but the idea was dropped.^[1]

In Australian Aboriginal Dreamtime the lake is inhabited by a monster known as the Muldjewangk.

The lake is a habitat to numerous species of water bird, including migratory species from the northern hemisphere, pelicans, black swans, and a number of other birds who enjoy the insects, plants and water available from the lake. These include wrens, willie wagtails (a flycatcher), swallows and magpies. Raptors including eagles and hawks may often be seen over the lake and surrounding land. Turtles live in the lake, with lizards and snakes present along the shoreline. Insect species include dragon flies, a range of moths and butterflies and large numbers of beetles (coleoptera). Freshwater fish inhabit the lake, including the introduced European carp. The soils around the lake are relatively low in organic carbon although good barley and vegetable crops may be produced. Non-wetting soils are present along the south eastern bounds of Lake Albert and in areas around Lake Alexandrina.

In 2008, water levels in Lake Alexandrina and Lake Albert became so low that large quantities of acid sulphate soils threatened to form. The soils on the lake beds are naturally rich in iron sulfides. When exposed to the air, such as may occur in a time of severe drought, the sulfides oxidize, producing sulfuric acid. The barrages now prevent seawater inflows that have prevented this phenomena in every drought since the last ice age ^[2]. A weir has been proposed near Pomanda Island to protect upriver water supplies should it become necessary to open the barrages.

References

1. ^ "Alexandrina, Lake". Place Names of South Australia. State Library of South Australia. http://www.slsa.sa.gov.au/manning/pn/a/a5.htm#alexandrina. Retrieved 2007-01-12. 
2. ^ "Catalyst - Fire, Flood and Acid Mud". http://www.abc.net.au/catalyst/murraydarling/. Retrieved 2008-05-07. 

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