Salt Lake

Microbes exist within all parts of the globe. Where it was once thought that conditions were too extreme to sustain life, microscopic organisms have been found that call it their home and have adapted to such an extreme that they are incapable of survival anywhere else. Salt lakes like the Great Salt Lake in Utah or the Dead Sea along the border of Jordan and Israel are two of the saltiest bodies of water in all of the Earth. These places often accumulate such a high amount of salt and minerals because water runoff towards the lake carries minerals into the lake and when the water evaporates, the salts are left behind and leave the lake even more saline each time. With salt concentrations as much as ten times that of the ocean, these places still manage to maintain microbial life. The organisms that survive use a wide array of strategies to manage the water’s harsh conditions. In order to adapt to the salty environment, halophiles prevent cellular water loss by increasing the intracellular solute concentration in order to reach equilibrium with the extracellular surroundings by adjusting the intracellular concentrations to primarily use potassium as the main cation and synthesizing glycerol to balance the extracellular salt concentration and maintain their membrane stability.

Description of Niche

The Great Salt Lake

Imagine the sun setting over dark wine colored waters. As day turns to night, you marvel at the stillness of your surroundings. While there seems to be very little life, the Great Salt Lake actually teems with all sorts of organisms above and below its surface. This lake has been nicknamed “America’s Dead Sea,” and while there are some obvious similarities between America’s Dead Sea and the Dead Sea, there are far more differences (1). Upon examining both bodies of salty water, there is the realization that there is more to these waters than meets the eye.

The Great Salt Lake is the fourth largest terminal lake in the world (2). It is also the second saltiest lake in the world; it lacks an outlet so when water enters the lake and evaporates, the salt is left behind (2, 3). Before the construction of a railroad built in 1959, the salt concentration had been fairly homogeneous (2, 4). Upon completion, this railroad separated the Great Salt Lake into two distinct ecosystems with differing organisms and salinity (5, 6, 4). For example, the number of brine shrimp cysts (eggs) in the south arm has decreased while the number of brine shrimp in the north arm has become somewhat unproductive (7).

The South Arm

The south arm has a pH of 8.2 and has a variable salinity due to the various amounts of freshwater entering it (7, 5). It receives ninety percent of the freshwater entering the Great Salt Lake (8). This is important because it affects the salinity and thereby determines the survivability of a number of species in the south arm (5). Recent studies have found that there has been an overall decrease in salinity and an increase in the variety of organisms (4).

The North Arm

One of the most striking features about the north arm is its reddish hue caused by flourishing halophilic Archaea. For this reason, the north arm has been nicknamed the Red Sea (7). Although they are parts of the same lake, physical properties of the north arm and south arm vary by drastic amounts. The north arm has a pH of 7.7 and has fairly stable salinity because it is saturated with salt (7, 5). The north arm is much saltier than the south arm because only ten percent of all the freshwater that enters the Great Salt Lake flows into the north arm (8, 7). Another reason for such high salinity is that the water in the north arm evaporates faster than it enters (3). Because the south arm flows into the north arm, the number of minerals in the south arm has been reduced while the number of minerals in the north arm has been increased (7). The increased salinity has limited the diversity of microbial life capable of surviving (4).

Effects of Salinity Changes

A clear way to describe the effects on ecology of the lake’s changing salinity would be this: the higher the salinity, the fewer species present (3). With the conditions more extreme, fewer species are suited to succeed and grow. The changes in salt levels affect the organisms that live there in many ways and completely transform the ecosystem. High salinity causes brine shrimp to be smaller, reach maturity more quickly and develop a longer abdomen than brine shrimp in less salty water (9). Adult brine shrimp have a maximum salt tolerance around 30% salinity. Cyst (egg) production has optimal levels at around 14% to17%. Interestingly, cysts have evolved to have the following adaptation to their surroundings: they have a lower density in water of 16% to 28% salinity than those in water of 10% to 14% salinity. Cysts break prematurely below these optimal levels (at low salt concentrations). In such conditions, other organisms enter previously uninhabitable areas and consequently affect the ecosystem (9). One example involves the insect Trichocorixa verticalis entering the Great Salt Lake during periods of low salinity (10). At the same time, the number of brine shrimp decreased and three other kinds of zooplankton invaded the area. With the number of brine shrimp decreased, protozoans flourish to fill their role (10).

Heavy Metal Accumulation

Arsenic, copper, cadmium, gold, lead, magnesium, mercury, molybelenum, selenium, silicon, silver and zinc are some common heavy metals found in the Great Salt Lake (11). Such metals enter the lake via streams, rivers and precipitation. Since the Great Salt Lake is a terminal lake, these heavy metals gradually accumulate. The exact impact that the heavy metals have on the ecosystem is unknown, but recent studies on mercury concentrations show that the brine layer in the lake has methylated the mercury (11, 12). While inorganic mercury is toxic, the methylated mercury is even more toxic to organisms because its lipophilic properties allow it to pass the blood-brain barrier. Such methylation allows microorganisms to absorb the heavy metals. Since these microorganisms are at the bottom of the food chain, the organisms higher upon the food chain are also affected (11). High concentrations of selenium and mercury are found in birds such as the common goldeneye, green winged teal and northern shoveler (13). The finding that there is such a high concentration of mercury in the lake is so alarming that even the mainstream media has taken notice, as evidenced by The New York Times article “Studying Great Salt Lake’s High Mercury Levels.”

The Dead Sea

The Dead Sea is another body of water with extremely high levels of salinity. These places often accumulate such a high amount of salt and minerals because water runoff towards the lake carries minerals into the lake and when the water evaporates, the salts are left behind and become more concentrated each time.

Located between Jordan and Israel, this lake is named for its lack of fish and other forms of macroscopic life. With a salt concentration ten times greater than the ocean, the organisms that live there must use unique adaptive measures to survive. Ones that have survived the intense salt levels include species of archaea, bacteria, fungus, and even algae.

References

Edited by [Alan Wong, Gary Porter, Kate Graham, Nicolle Ma] students of Rachel Larsen