why is the sea salty but lakes are not?

Answer 1

Everyone who has been to the beach knows that seawater is salty. Everyone also knows that fresh water in rain, rivers, and even ice is not salty. Why are some of Earth’s waters salty and others not? There are two clues that give us the answer. First, “fresh” water is not entirely free of dissolved salt. Even rainwater has traces of substances dissolved in it that were picked up during passage through the atmosphere. Much of this material that “washes out” of the atmosphere today is pollution, but there are also natural substances present.

As rainwater passes through soil and percolates through rocks, it dissolves some of the minerals, a process called weathering. This is the water we drink, and of course, we cannot taste the salt because its concentration is too low. Eventually, this water with its small load of dissolved minerals or salts reaches a stream and flows into lakes and the ocean. The annual addition of dissolved salts by rivers is only a tiny fraction of the total salt in the ocean. The dissolved salts carried by all the world’s rivers would equal the salt in the ocean in about 200 to 300 million years.

A second clue to how the sea became salty is the presence of salt lakes such as the Great Salt Lake and the Dead Sea. Both are about 10 times saltier than seawater. Why are these lakes salty while most of the world’s lakes are not? Lakes are temporary storage areas for water. Rivers and streams bring water to the lakes, and other rivers carry water out of lakes. Thus, lakes are really only wide depressions in a river channel that have filled with water. Water flows in one end and out the other.

The Great Salt Lake, Dead Sea, and other salt lakes have no outlets. All the water that flows into these lakes escapes only by evaporation. When water evaporates, the dissolved salts are left behind. So a few lakes are salty because rivers carried salts to the lakes, the water in the lakes evaporated and the salts were left behind. After years and years of river inflow and evaporation, the salt content of the lake water built up to the present levels. The same process made the seas salty. Rivers carry dissolved salts to the ocean. Water evaporates from the oceans to fall again as rain and to feed the rivers, but the salts remain in the ocean. Because of the huge volume of the oceans, hundreds of millions of years of river input were required for the salt content to build to its present level.

Rivers are not the only source of dissolved salts. About twenty years ago, features on the crest of oceanic ridges were discovered that modified our view on how the sea became salty. These features, known as hydrothermal vents, represent places on the ocean floor where sea water that has seeped into the rocks of the oceanic crust, has become hotter, and has dissolved some of the minerals from the crust, now flows back into the ocean. With the hot water comes a large complement of dissolved minerals. Estimates of the amount of hydrothermal fluids now flowing from these vents indicate that the entire volume of the oceans could seep through the oceanic crust in about 10 million years. Thus, this process has a very important effect on salinity. The reactions between seawater and oceanic basalt, the rock of ocean crust, are not one-way, however; some of the dissolved salts react with the rock and are removed from the water.

A final process that provides salts to the oceans is submarine volcanism, the eruption of volcanoes under water. This is similar to the previous process in that seawater is reacting with hot rock and dissolving some of the mineral constituents.

Will the oceans continue to become saltier? Not likely. In fact the sea has had about the same salt content for many hundred of millions if not billions of years. The salt content has reached a steady state. Dissolved salts are being removed from seawater to form new minerals at the bottom of the ocean as fast as rivers and hydrothermal processes are providing new salts.

We can summarize this discussion. Wherever water comes into contact with the rocks of Earth’s crust, either on land or in the ocean or within the oceanic crust, some of the minerals in the rock dissolve and are carried by the water to the ocean. The salt content of seawater does not change because new minerals are forming on the sea floor at the same rate as salt is added. Thus, the salt content of the sea is at steady state.







LAKES

A lake is the opposite of an island; it’s a body of water completely surrounded by land. However, widened portions of rivers and coastal bodies of water that are connected to the sea are sometimes called lakes, also. For example, Louisiana’s Lake Pontchartrain was formed by the Mississippi River. (Fronting New Orleans, it’s also very near the sea.) Venezuela’s “Lake” Maracaibo is sometimes described as South America’s largest lake, though it’s actually an extension of the Caribbean Sea.

The study of lakes is called limnology. Lacustrine is an adjective that describes things related to lakes. Thus, animals adapted to a lacustrine habitat live in lakes.

The primary source of lake water is precipitation (rain and snow). In fact, precipitation that falls on some 40% of Earth’s land surface flows into lakes. Rain may fall directly into lake basins, or it may flow into lakes as runoff from surrounding higher ground or through underground springs.

Most water leaves lakes through transportation or overflow. Lake Superior has a water retention/replacement time of 191 years. In other words, water that enters the lake, on average, stays in the lake for nearly 200 years.

Water temperature varies within a lake and between seasons. The surfaces of lakes located at high latitudes or altitudes may freeze in winter. Ponds are generally small, shallow lakes that have a more even temperature.

Most lakes are “freshwater;” that is, they are not salty like the sea. Salt and bitter lakes are most common in dry areas where water evaporates faster than it can be replaced, leaving high amounts of mineral salts. The most famous such lakes are Asia’s Caspian Sea, the Dead Sea and Utah’s Great Salt Lake. Tanzania’s Lake Natron is one of several “soda lakes” that lie in Africa’s Great Rift Valley. Their salty condition is caused by volcanic gases or fluids.

Lakes are important sources of drinking water, electricity and water for irrigation. Some lakes also support commercial fishing or are valued for recreation. North America’s Great Lakes serve as an important transportation system.

Answer 2

Basically the lakes are simply large temporary holding spots in the path of a river, creek, bayou or stream. The water flows out at the same rate the water flows in. So whatever is the salinity of the water supply will be the salinity of the lake/pond. Whenever there is a blockage (dam) and the water cannot flow out the water will evaporate leaving whatever minerals, etc to gradually increase in the lake ... think Great Salt Lake in Utah and the Dead Sea in the middle east.

Oceans are the final destination of the water in the rivers and over time behaves simply as a huge lake.

Answer 3

Because the ocean is the ultimate "holding pot" or destination for water before it is evaporated. Lakes or ponds are just relatively ephemeral visiting spots until water from them reaches the ocean. Depending on the salinity of the water, the pond/lake will have some saltwater, but won't have much because the oceans are the catch all of all rivers that carry salt (NaCl) to them. As sea water evaporates, all the salt is left behind in the ocean. The only natural way that NaCl is present in land water is by erosion of minerals that contain NaCl or Halite; consequently, as water runs over the NaCl, it becomes mixed with water and is on its way back to the ocean... perhaps taking a brief visit at a pond or lake along the way - but usually not in high concentrations. Many areas are NaCl deficient.

Answer 4

The Dead Sea is a lake fed by the River Jordan and believe me, it is salty! Much saltier than the sea.

Rivers are unsalty because they are fed by rainwater (which is pretty pure), salts are leached out of the soil as they flow to the sea. So the salt tends to accumulate in the oceans.

Answer 5

Lakes are made of rain water, rain is water mainly evaporated from the sea (which is salty from all the rocks that the waves crush up) and the salt stays behind during the evaporation making rain pure water.

Answer 6

It is thought that the salt in the oceans stems from erosion of bedrock near ocean basins; big lakes and rivers are formed by evaporation and subsequent precipitation/runoff of ocean water, and by melting of freshwater ice. Since evaporated water can't "take the salt with it", even big lakes are generally made of freshwater, whereas the oceans are made of saltwater.

People don't really know what happens to the salt concentration (or salinity) of the oceans over time; Accurate salinity maps of oceans are hard to produce since oceans are so big. As the Earth's temperature rises in the future (both from natural and human effects) - two things will happen to the salinity. First, increased evaporation over oceans will tend to make the salinity rise. Second, increased melting at the poles will bring more freshwater into the oceans, which will decrease the salinity. Which of these two effects dominates the water cycle in the future will determine the change in salt concentration.

Answer 7

Lake Merritt in Oakland (as in A's) California is a Salt water lake. It has a tidal feed from the Oakland Estuary that connects with the San Fransisco Bay.

(and it has been known to get rather smelly in the summer) It has fish (and occationally too much algae)

Answer 8

Some lakes are salty. Some lakes are more salty than the ocean.

Answer 9

The lakes are fresh water.

Answer 10

I love it !! Someone asks why are lakes not salty, and someone answeres because lakes are fresh water. Top of tha class for that one.