David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.
After completing this lesson, you'll be able to define surface water as well as describe some of its properties and understand why those properties are important.
What Is Surface Water?
Surface water is any water that collects on the surface of the earth. This includes oceans, seas, lakes, rivers, or wetlands. Fresh surface water is maintained by rainfall or other precipitation, and it's lost through seepage through the ground, evaporation, or use by plants and animals. Man-made bodies of water are not considered surface water since they generally rest on artificial surfaces, not the ground itself.
Properties of Surface Water
There are many important properties of surface water, including temperature, saltiness (also called salinity), turbidity, and levels of dissolved nutrients, such as oxygen and carbon dioxide. These factors all affect climate and the biodiversity in and around a body of water.
Temperature, scientifically, is the average kinetic energy of the molecules in a substance. The temperature of surface water is warmest at the top, and it gets cooler as you go deeper. The deep oceans, for example, are extremely cold, dark places. Surface water temperature varies much more by season as well. So, when we look at temperature, we tend to look at averages.
While we're talking about temperature, an interesting fact is that sea water doesn't freeze at 0 degrees Celsius: the salt in the water allows it to get colder before it does. Also, warmer water tends to have less oxygen, which can make it harder for some species of marine life to survive.
Salinity is the saltiness of water. It measures the amount of dissolved sodium, potassium, and other salts in the water. Higher salinity leads to denser water, which has an impact on water currents around the world. Areas with a lot of evaporation have higher salinity and denser water, because when water evaporates, it leaves the salts behind. Here's a representation of sea surface salinity around the globe.