Why aren’t rivers/estuaries/lakes etc salty like the sea ?
In: Planetary Science
Freshwater bodies- rivers, lakes, etc have teeny tiny amounts of salt in them. They’re not salt free. The salt is dissolved from minerals in the rocks they pass over.
Once they reach the ocean, both the water and salt they contain is dumped into the ocean.
The water eventually evaporates back into the atmosphere, is transported over land, comes down as precipitation, and starts the cycle anew.
But the salts cannot evaporate. They just build up in the ocean until they start getting deposited on the bottom (salt mines are old ocean salt deposits!).
So rivers act as conveyor belts for water and salt to get to the ocean. In the case of water, it’s a loop- the water evaporates from the ocean and rains back down on land, keeping the river going. But in the case of salt, it’s a one-way process.
Thus the oceans have a balance of water- incoming from streams versus losses to evaporation. But for salts a river is a one way street into the ocean- the oceans maintain a rough equilibrium of salt concentration through sedimentary processes- salts get turned into rock on the sea floor at the same rate they enter the ocean from streams.
This is why there are salt lakes like the Great Salt Lake in the USA and the Dead Sea in the Middle East- the same processes are at work, just with different equilibrium points for the salt concentration.
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