Billy White, age 12, of San Lorenzo, Calif., for his question:
Do the fresh rivers make the sea less salty?
Every day the great rivers of the world empty millions of gallons of water into the sea. And river water is fresh water at least it is fresh compared with the salty water of the sea. Gallons of fresh rain water also fall into the ocean every day, and melting icebergs add. More fresh water to the sea. yet the ocean is getting saltier all the time.
It is reasonable to think that the rivers dilute the salty Sea with their streams of fresh water, but this is far from true. Amazing as it may seem, the so called fresh water from the rivers adds more and more salt to the salty sea. This is how the ocean has built up its massive supply of dissolved salts, and this has been going on since the earth began.
Falling raindrops are made from the freshest water in nature. On their way down, they may collect a few scraps of dust and perhaps dissolve a few molecules of carbon dioxide gas. This fresh water strikes the ground and touches rocks and soil which are made of minerals. Some of these minerals are very eager to dissolve in water, and even the most stubborn stone eventually can be worn away and dissolved by running water.
Gushing streams wash over the stones, and ground water sinks through the rocks. All this moving water is dissolving chemicals from the earth and carrying them, along as it goes. The so called fresh water of streams and rivers bears an invisible load of dissolved salts and other chemicals. It carries its loot to the rivers, and the rivers dump this water into the ocean.
A bucket of river water contains but a fraction of the chemicals dissolved in a bucket of sea water. But every year more than 6000 cubic miles of river water is emptied into the sea, and this so called fresh water contains several billion tons of dissolved chemicals. Meantime the beaming sun evaporates water from the face Of the sea. Tons of gaseous vapor escape up into the air, but the dissolved chemicals do not evaporate. They stay behind, and year by year the rivers of so called fresh water add more salty chemicals to the ocean.
The rivers do not dilute the salty sea. Instead, their traces of dissolved chemicals add to the salts already in the ocean. A few fragments of the sea's salt may escape into the air and be wafted aloft to the clouds, and rain may carry them back to the land.. But the ocean hoards most of the salts it has been collecting from the rivers through the ages which is why the salty sea is getting saltier with every year.