Why are lakes freshwater and oceans saltwater? (Smithsonian.com)
Why are lakes freshwater and oceans saltwater?
Lexile

It has something to do with this leaky faucet. You see, rain falls on the land as fresh water. As this water flows downward, it ever so slightly erodes the rocks and soil. This causes an ever so slight amount of salt and minerals to dissolve in the water and continue downstream. Eventually, all the dissolved minerals get dumped into the ocean.

Meanwhile water on the ocean's surface evaporates into the air, ditching all those salts and minerals. It then falls back on land as fresh water, replenishes the lakes and rivers, and the cycle continues. In lakes and rivers, theres enough turnover that the water stays fresh. But in the oceans, the salts pretty much stay there for millions of years.

Worldwide, it's estimated that rivers dump about 4 billion tons of salts into the oceans each year. But even with all that new salt, the oceans are so big, that their salinity stays fairly constant, at about 3.5%.

Critical thinking challenge: How is the water cycle like a bicycle?

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COMMENTS (102)
  • CASSIDYK-ZDE
    6/04/2014 - 08:18 a.m.

    The cycle of water turning into salt water is a different story from the rest. The water cycle is a unique article because its not reporting on a story. The cycle of fresh to salt water is interesting and very informative.

  • KateL-4
    6/04/2014 - 04:53 p.m.

    Often people wonder why oceans have salt water and lakes have fresh water. Oceans are made up of the water from streams and lakes, and when this water travels down into the ocean it carries salts and minerals with it. Then, the salts and minerals end up in the ocean. When water evaporates it leaves salts and minerals behind. So, when it rains the water remains fresh in lakes and streams. The cycle goes on forever. I thought this article was very interesting. I have always thought about why the ocean has salt in it, and never thought the answer would be that obvious.

  • SHANELLEH-ZDE
    6/04/2014 - 06:26 p.m.

    This is very valuable information because Im sure plenty of people have wondered why are oceans are so salty but probably never have put these two things together. It's nice to know that goddess or fairytale creatures aren't dumping salt into the ocean, all along it's been nature itself.

  • BENJAMINO-ZDE
    6/04/2014 - 07:56 p.m.

    With all the salt and minerals being dumped the ocean has to be really massive to keep its solidity the same. Its so massive we know less about it than we know about anything else. It's full of mystery's and things we haven't seen nor imagined.

  • DEYVINV-ZDE
    6/04/2014 - 08:47 p.m.

    I find this fact intersting because I did not know that it all started in rivers and lakes,I thought the ocean was already like that.

  • SHILOH-ZDE
    6/04/2014 - 09:17 p.m.

    i was never really interested in why but this article caught my eye to see why the ocean is salty and lake are ready about everything he said but rarely do they ever go in to detail nor do i put two and two together.

  • squish4343
    6/05/2014 - 09:01 a.m.

    I find this cool because I actually had no idea that it was a cycle that involved rain water going into the ocean. I just thought that it was there...

  • Sierraf-3
    6/05/2014 - 10:48 a.m.

    This article is about freshwater and saltwater. Rain falls on the ground as freshwater but as it goes down drains and toward the ocean, it collects rocks and soil which has the slightest bit of salt and minerals in it. The salt from the ocean evaporates, but then comes back down to the ocean in the rain, like a cycle. Rivers dump about 4 billion tons of salt into the ocean each year. I thought this article was interesting because I didn't know that that was the cause of why the ocean is salty.

  • jaden5k1
    6/05/2014 - 12:10 p.m.

    i think the water cycly is like a bicacal becusa a bike wheel is round and the water cycle is to it evaporats into clouds then it rains (half of the cycle/circle) then the water gose into the ochon to make a complet cicle.

  • MorganWright1170030
    6/05/2014 - 01:52 p.m.

    This is an article that did not really intrest me. only thing about it is that the water on the pictures is very pretty. that is why chose it.

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