||Lake Eyre Floods, South Australia |
Heavy rain in early March 2011 produced the comparatively unusual event of water entering Lake Eyre. The southernmost and deepest lobes, Belt Bay and Lake Eyre South, were filled first. In this northeast-looking view from the International Space Station, water can be seen in the southern basins of Lake Eyre, especially in Belt Bay where it appears green, and in Madigan Gulf where it appears in shades of pink and red. Despite some cloud, water is also apparent in narrow Jackboot Bay and at the estuary where Cooper Creek, one of the most important inflow rivers, fills a small, dark green lake.
The varying water colors result from the effects of water depth and resident organisms. The green coloration of Belt Bay is likely related to its depth, which was reported in early December 2011 to be just less than 1 meter. The red color of Madigan Bay on the other hand, appears to be related to salt-loving bacteria. At half the depth of Belt Bay (0.4 m), evaporation had apparently raised salt concentrations high enough to allow salt-loving bacteria to flourish when this image was taken. In Australian lake waters with salinities from about 30% upwards the majority of microbes are haloarchaea (family Halobacteriaceae, domain Archaea). The density of microbes that live in Australia's salt lakes can reach 107 - 108 cells/ml--so dense in fact, that the pink-red carotenoid pigments in the cell membranes appear to color the water.
By August 2011 more than half the lake floor was covered by shallow water, with local creeks continuing to deliver water to the lake. Lake Eyre is an internal drainage basin, which means that all the water accumulates in the lake since it has no outlet to the sea. Any water that reaches the lake evaporates in the course of subsequent months. Water levels were reported to be falling everywhere in late 2011, when this image was acquired. The bright white salt of the floor of Lake Eyre South shows that this lake is entirely dry.