Salt evaporation pond

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San Francisco Bay salt ponds
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San Francisco Bay salt ponds
Salt evaporation pond in Ile de Ré, France.
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Salt evaporation pond in Ile de Ré, France.

Salt evaporations ponds, also known as saltern ponds, are shallow man-made ponds designed to produce salt from sea water. The seawater is fed into large ponds and water is drawn out through natural evaporation which allows the salt to be harvested. The ponds also provide a fertile resting and feeding ground for more than 70 species of waterbirds, including several endangered species. The ponds are usually separated by levees.

Due to variable algal concentrations, vivid colors, from pale green to bright red, are created in the evaporation ponds. The color indicates the salinity of the ponds. Micro-organisms change their hues as the salinity of the pond increases. In low to mid-salinity ponds, green algae is predominant. In middle to high salinity ponds, an algae called Dunaliella salina shifts the color to red. Millions of tiny brine shrimp create an orange cast in mid-salinity ponds. Other bacteria such as Stichococcus also contribute tints. These colors are especially interesting to airplane passengers or astronauts passing above due to their somewhat artistic formations of shape and color.

Notable salt ponds include the San Francisco Bay salt ponds in the United States, and the Dead Sea salt ponds in Israel and Jordan.

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