Key Points
Key Points will give you the main information you should know to teach the activity.

• Water quality is the chemical, physical and biological properties of water that affect the living things able to use the water. It can be determined by looking at many factors including temperature, salinity, pH and dissolved oxygen content.
• pH is a measure of how acidic or how basic a water solution is. It is measured on a scale of 0 to 14 with numbers below 7 being acidic and numbers above 7 being basic.
• Salinity is a measure of how much salt is dissolved in the water. It is usually measured in parts per thousand (ppt). For example, the ocean has a salinity of 35ppt. This means there are 35 mL of salt dissolved in every 1000 mL of ocean water.
• Dissolved oxygen content refers to the amount of oxygen molecules dissolved in water. It is expressed as a percentage. Water with 100% dissolved oxygen is completely saturated with oxygen and water with 0% dissolved oxygen has no oxygen.

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Detailed Information
Detailed Information gives more in-depth background to increase your own knowledge, in case you want to expand upon the activity or you are asked detailed questions by students.

Water quality includes the chemical, physical and biological properties of water. The water quality of a body of water affects the type of life found there.

A water molecule, H₂O, is composed of two hydrogen atoms and one oxygen atom. When water dissociates or separates it forms H⁺ and OH^-.This process is known as ionization. The hydrogen ion, H⁺, has a positive charge because it lost an electron, while the hydroxide ion, OH^-, has a negative charge due to its gaining an electron. When another substance that ionizes is added, acids and bases are formed. An acid is created when excess hydrogen ions are present while a base is formed due to extra hydronium ions. To determine if a substance is acidic or basic, the pH should be determined.

pH is a measure of the hydronium concentration in a water solution. The pH range is 0 to 14. If the solution contains more H⁺ ions it is acidic while one containing more OH^- ions is basic. 

0-----------------------	-----------7------------	---------------------14
most acidic	neutral	most basic
(H+>OH-)		(H+<OH-)

pH can be measured using a variety of methods. pH paper is often used and is simple. There are indicators like phenolphthalein and bromthymol blue, as well as, foods that change colors in the presence of acids and bases.

The pH is one attribute that determines the biotic characteristics of a body of water. Most plants can tolerate a pH range of 6.5 to 13 while a large variety of animals prefer 6.5 to 7.5. For this reason, when the pH drops below the ideal level, many plants and animals become stressed and may die.

Temperature is another attribute that determines the biotic characteristics of aquatic habitats. The temperatures of mountain streams are dramatically different when compared to reservoirs and rivers in other regions of the state. Animals have adapted to different habitats and have specific temperature needs. For example, brook trout prefer water temperatures between 54 and 60 degrees Fahrenheit while menhaden prefer salt water with a temperature range of 59 to 68 degrees. If temperatures vary from the ideal, animals can become stressed.

Salinity is the third attribute that has a profound affect on plants and animals. Salinity is the amount of dissolved salts in water and soil. It is measured as the concentration of dissolved salt in milligrams per liter and may be expressed in parts per thousands (ppt or ⁰/₀₀). The average salinity of the ocean is 35 ⁰/₀₀. The salinity varies near the mouths of rivers where there is the presence of freshwater. It also varies in areas of increased evaporation.

Students frequently ask how salt enters the ocean. As the rivers flow across the land, they pick up salt from the rocks and soil they pass over and carry it until it is then deposited into the ocean. Salt is also added from the sea floor. As evaporation occurs, freshwater is removed leaving salts behind which increase the salinity.

Plants and animals living in the estuaries and salt marshes of South Carolina can tolerate dramatic changes in salinity due to tidal changes that occur throughout the day. Organisms that live in the deep ocean have adapted to a salinity range that is more constant than that of estuaries. Salinity is measured using a hydrometer or a refractometer. Hydrometers may be purchased at local aquarium supply stores and are relatively cheap. The refractometer is somewhat more expensive and may be purchased from a scientific supply company.

Dissolved oxygen, the percentage of oxygen in water, is the fourth attribute that can affect organisms in aquatic habitats. The range varies dramatically, some rivers contain 100 ⁰/₀ dissolved oxygen while others are almost devoid of oxygen. The organisms living in the aquatic habitats are dependent on the oxygen. Without it, they cannot survive. Dissolved oxygen can be measured in a variety of ways; dissolved oxygen kits and dissolved oxygen meters are commonly used. Both items can be purchased through a scientific supply company.

The biotic factors within an aquatic environment are also influenced by current speed, the rate at which the water flows, and water clarity. Current speed can be determined through the use of a biodegradable substance, such as an orange, being placed in the water and measured over a set distance. The speed or velocity can be calculated by dividing the distance the object traveled by time it took. Water clarity is related to the current speed. The fast moving streams of the Mountains and Piedmont carry larger sized sediments. When the water slows, the sediment falls out. The rivers in the Coastal Plain and coastal regions of South Carolina carry a greater sediment load, smaller particle size, than do those of the Mountains and Piedmont. The water clarity decreases as the sediment load increases. To measure the water clarity, a secchi disk may be used or you can make a light penetration apparatus using a glass jar, black construction paper and flashlight.

You may ask, how do temperature, salinity and dissolved oxygen influence each other. The temperature influences salinity and dissolved oxygen. When the air temperature is high, evaporation increases creating a higher salinity. This is evident around the equator. The salinity is generally higher in the polar regions also, due to pure water freezing, leaving a higher salt concentration in the water underneath. Temperature also influences dissolved oxygen. Cool water normally has a higher concentration of dissolved oxygen. The mountain streams of South Carolina are cool, fast moving, highly oxygenated bodies of water. Warmer water has the tendency to have a lower concentration of dissolved oxygen.

All of these factors together influence the water quality of a body of water. What the water quality is determines what organisms will live around the body of water. As water quality changes, the animals that live around the water will change as well.

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