What is the difference between salt water and freshwater?
Salt water is water that contains a certain amount of salts. This means that its conductivity is higher and its taste much saltier when one drinks it. Salt water is not suited to be used as drinking water, because salt drains water from human bodies. When humans drink salt water they risk dehydration. If we want to drink seawater, it needs to be desalinated first. Salt water can be found everywhere on the surface of the earth, in the oceans, in rivers and in saltwater ponds. About 71% of the earth is covered with salt water. Freshwater is water with a dissolved salt concentration of less than 1%. There are two kinds of freshwater reservoirs: standing bodies of freshwater, such as lakes, ponds and inland wetlands and floating bodies of freshwater, such as streams and rivers. These bodies of water cover only a small part of the earth’s surface, and their locations are unrelated to climate. Only about 1% of the earth’s surface is covered with freshwater, whereas 41% of all known fish species live in this water. Fresh water zones are usually closely connected to land; therefore they are often threatened by a constant input of organic matter, inorganic nutrients and pollutants.
Where is Groundwater?
Groundwater is water that is under the ground. Humans get most of its water from groundwater sources. There is more groundwater under the surface of the Earth than in all the lakes and streams put together. Unfortunately, groundwater is also polluted more than any other source of fresh water.
How Does It Get there?
Groundwater starts life on the surface. When it rains and the water moves through the soil, it’s called infiltration. There are spaces between the dirt and rocks that allow the water to flow through easily. Eventually the water makes it to rocks where scientists say it percolates deeper into the Earth (yes, like a coffee pot). The area where the water winds up is called the zone of saturation. Different from the soil, the zone of saturation has very small spaces between the rocks. The spaces are so small they may even be the size of large molecules. When the water can go no deeper, it creates an aquifer. An aquifer is an underground reservoir inside the rocks. When a farmer digs a well, they are digging into an underground aquifer. After they drill to the water table (the highest level of the aquifer), they are able to pump the water to the surface. As farmers pump too much water out of an aquifer, they find that the water table dips in that specific area. That dip in the water table is called a cone of depression.
We’re talking about humans pumping water out of an aquifer. There are two kinds of aquifers. One type you need to pump the water out of and another type in which the water is under pressure and moves towards the surface by itself. The pumping type is called unconfined. It has a layer of permeable (water can pass through) rock on top and non-permeable (nothing can pass through) rock on the bottom. The water does not build up any pressure because it can expand and contract. The second type of aquifer is confined and called pressurized. It is sandwiched between two non-permeable layers of rock. There is nowhere for the water to go when new water comes in and the pressure builds. The water eventually pushes up to the surface and creates springs and a type of freshwater called artesian water.
Freshwater marshes are flooded for most of the year. Winter brings seasonal rains and snows that raise water levels for the remainder of the year. You will find many grasses and reeds as the major plant type in these biomes. Animals above water include birds, insects, and mammals such as mice or raccoons. Below the water’s surface, you will find small fish, crustaceans, and a variety of worms working their way through the dead vegetation. Sometimes freshwater marshes dry out during long or excessively hot summers. During these dry times you will still find small pools of water that are home to larvae and small plants. Even if the surface is dried out, there may still be a great deal of water below the surface in a muddy environment that is home to many bacteria and microscopic organisms.