Siderophores
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SALINE LAKES Carol D. Litchfield George Mason University, Manassas, VA, USA
Synonyms Salt Lakes Definition Salt: chloride, sulfate, phosphate, carbonate, bicarbonate salts of primarily sodium, magnesium, calcium, and potassium. Lake: an enclosed body with or without water entering it from a stream, rain, or snow melt. Ephemeral lake: a lake formed only following rain or snow melt, which dries up during the rest of the year. Thalassohaline: salts in a lake derived from the evaporation of seawater with the dominant ions of sodium and chloride as found in the ocean. Athalassolhaline: salts in a lake derived from rocks and geological weathering and dominated by magnesium, calcium, and sulfate. Alkaliphilic lake: also called soda lake. A lake in which the dominant ions are sodium and bicarbonate and carbonate. This causes the lake to have an alkaline pH. General description of saline lakes Saline lakes are a natural worldwide phenomenon. They can be found on all continents and in most countries, and they are frequently recognizable by their name – for example, Salt Lick, Salt Lake, Salt Pond, and Salt Marsh. They range in salinity from just above the salt content of sea water (>3.2% salts) to hypersaline lakes (>20% and up to saturation with respect to salts). Examples of saline lakes include, at the lower end, salt lakes in Antarctica, the Caspian Sea, which borders five countries and has
a salinity slightly less than that of seawater, and the Salton Sea in California. At the upper end in salt concentrations are the Dead Sea bordering Israel and Jordan, the soda lakes of North Africa, and Quinghai Lake in China. A general characteristic of saline lakes is that they are terminal lakes, which means that although rivers may flow into them, they have no significant outflow. Therefore, as the water evaporates, the lakes become more salty and in some cases may dry up completely forming salt basins or playas especially in extremely arid environments. In Australia, for example, occasional rains may cause the dry salt basins to become lakes, and these then are called ephemeral salt lakes. Saline lakes are typically divided into two main types: athalassohaline and thalassohaline. The former refers to lakes which have a different chemical ratio of the main cations from what is found in seawater, while the latter refers to lakes with the cation ratio similar to seawater. Table 1 lists the sodium + potassium ion to calcium + magnesium ion ratios and summarizes the chemical composition of a variety of saline lakes thus showing the wide range of lake types possible. The data in Table 1 indicate that a subset of the athalassohaline lakes exists. These lakes have a high concentration of carbonate and therefore a high pH. These are the soda lakes or alkaline lakes. They, too, are found worldwide and are described below. No Antarctic lakes are listed in Table 1 because the surface waters are generally only very slightly saline (less than seawater) and it is only with depth, often greater than 10 m, that true saline waters are found. In
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