Image by John-Morgan via Flickr
A salt lake or saline lake is a landlocked body of water which has a concentration of salts (mostly sodium chloride) and other minerals significantly higher than most lakes (often defined as at least 3,000 milligrams of salt per liter). In many cases, salt lakes have a higher concentration of salt than sea water.
Salt lakes form when the water flowing into the lake, containing salt or minerals, cannot leave because the lake is endorheic or terminal. The water then evaporates, leaving behind any dissolved salts and thus increasing its salinity, making a salt lake an excellent place for salt production. High salinity will also lead to a unique flora and fauna in the lake in question.
If the amount of water flowing into a lake is less than the amount evaporated, the lake will eventually disappear and leave a salt flat or playa (sometimes also referred to as salt pan).
Difference between Fresh Water and Saline Water
Value of Salt Concentration
The term salinity needs careful definition to avoid confusion with the oceanographic definition: for limnologists, salinity is the sum total of ions! A conventional value, now widely accepted, and with at least some physico-chemical and biological basis, is 3 g/L or 3 o/oo. This salinity is near, i
) the calcite branch point,
ii) the low points between modes when the frequency distribution of salinity of all lakes over 100 sq.km area is plotted logarithmically,
iii) the salinity at which most humans first begin to taste salt, and
iv) the salinity below which biota typical of higher salinities are not found and above which the freshwater biota begins quickly to disappear or not extend.
- Salt lakes are a good deal more varied in many physico-chemical features than freshwater lakes. Salinities are between 3 and >300 g/L (not <1-3>300 g/L) or secular basis or, as in freshwater lakes, scarcely at all; and major ions may show a variety of patterns of dominance (most freshwater lakes are dominated by the divalent cations and bicarbonate).
- Most saline lakes are also defined by endorheic drainage basins, so that most slat lakes represent the termini of inland drainage basins in which there is a balance between inputs and outputs. Since all inflows contain significant concentrations of salts and evaporating water none, salts accumulate in the lake itself.. Coastal marine embayments, although saline and often lake-like, are not the termini of inland drainage basins and have many physico-chemical and biological features closer to marine (thalassic) than inland (athalassic) environments. A few inland salt lakes, mostly in temperate areas, are not within endorheic basins; their high salinities derive from underground or local salt sources, often associated with mining. On the other hand, solar salt ponds drawing water from the sea, and in which this water is progressively concentrated, do have many similarities to salt lakes.
- Salt lakes may contain water permanently, intermittently or episodically; water levels may be constant or fluctuate widely on a seasonal or secular basis, often in accord with salinity fluctuations; and they range from deep to shallow, small to extremely large, round to dendritic in shape.
GLOBAL IMPORTANCE
Major values and threats
Economically, salt lakes are important as a source of minerals (especially halite, but including also uranium, zeolites, lithium, borax and many other minerals), water (by diversion of inflows), fish, biochemical products (e.g. glycerol and β-carotene from Dunaliella, protein from Spirulina), and foodstuffs for aquaculture (especially Artemia cysts). Many are of cultural significance (e.g. the Dead Sea). A large number has high aesthetic values both as naturally attractive environments (e.g. Mono Lake, California), and as habitats for certain biota (notably flamingos).
Threats
Perhaps threats to salt lakes are even greater than to freshwater lakes because of a general perception that salt lakes are less valuable than other sorts of inland water. Best known examples of severely damaged slat lakes are undeniably the Dead Sea, the Aral Sea, and Mono Lake. In each case, levels have dropped tens of metres and salinity risen by many g/L in the relatively recent past. For the Aral Sea, the total effects have been catastrophic to the local human population, agricultural production, and the environment in general.
- Not the least of threats are those likely from global climatic change, given the sensitivity of salt lakes to climatic events, and increased levels of UVB radiation, given that many salt lakes are shallow, already exposed to high levels of solar irradiation, and have fewer refuges from light than many freshwater lakes.
- Pollution of salt lakes is yet another anthropogenic activity of widespread importance, as is the ad hoc spread of exotic biota, especially Artemia.
Global Distribution
Salt lakes are widespread, occur on all continents, and are often present not far from centres of population. They are not abundant in very dry areas though, in true deserts where annual precipitation is <25 class="blsp-spelling-error" id="SPELLING_ERROR_14">drylands. Within each continent, they are also widely dispersed and extensive
SHALLOW LAKES AND THEIR VEGETATION
Shallow lakes have abundant aquatic plant growth due to high nutrient content (phosphorus, nitrogen, and minerals) and the high sunlight availability in shallow water. Stands of emergent and floating-leaved aquatic plants such as cattails (Typha spp.), bulrush (several genera), ater lily (Nymphaea spp.) and reeds (severalgenera), as well as submerged plants, such as coontail, are usually present throughout the entire basin, creating an extended littoral zone. These plants provide excellent food and habitat for zooplankton, insects, fish, waterfowl, and other wildlife. Aquatic vegetation also anchors sediments, maintaining water clarity (Conroy 2005). Sediment and nutrients in shallow lakes, unlike in deeper lakes, are constantly mixing. Shallow lakes lack temperature stratification, and wind–wave action easily penetrates to the bottom of the shallow basin. Shallow lakes can often benefit from periods of low water that stimulate beneficial aquatic plant growth. Persistent and high water levels restrict plant growth and reduce water quality, allowing significant algal growth. Low water conditions can help set the stage for winterkills that can decrease or eliminate populations of rough fish species, such as carp and black bullhead. While shallow lakes can support populations of game fish, low levels of dissolved oxygen and winterkills tend to limit their numbers.
Chemical, nutrient, and sediment inputs from agricultural practices and runoff from impervious sources, such as roads, parking lots, and roofs, can seriously degrade shallow lake habitats. Due to the low volume of water, shallow lakes can be more susceptible to such runoff than deep-water lakes. Surface water use can sometimes be as important as land use management in maintaining a healthy shallow lake. Aquatic vegetation can suffer from too many docks, boats, and outboard motors on a lake.
Shallow lakes are well recognized for their importance as breeding areas for waterfowl species, migratory birds for their re-generation etc.
cOURTESy --http://www.pib.nic.in/release/release.asp?relid=32200
