Students know:

·       that the health of a water system is determined by the balance between physical, chemical and biological variables. Physical variables include temperature, turbidity, and water movement. Chemical variables include dissolved oxygen and other gases, pH, nitrates, and salinity. Both natural and man-made forces are constantly changing these variables. Freshwater systems are of particular concern because they are the source of most of the potable water consumed by humans. Testing for the occurrence of chemicals and other factors that can influence water quality, such as nutrients and pesticides in water resources is a normal part of public health maintenance and stewardship of freshwater resources. Water that is safe to drink is called potable water, or drinking water, in contrast to safe water, which can be used for bathing or cleaning. In the United States, the Environmental Protection Agency sets maximum levels for the 90 most commonly occurring contaminants.

·       that the temperature of water in rivers and lakes determines the kinds of organisms that can survive there. Particular aquatic species have preferred water temperature ranges within which they will live and thrive. Warm water dissolves more of a solid substance as it gets warmer, but it also dissolves less of important gases like oxygen and carbon dioxide. Very warm water may not contain enough dissolved oxygen for aquatic life to survive.

·       that measuring dissolved oxygen is an important factor in determining water quality. Dissolved oxygen (commonly called DO, pronounced dee-oh) is oxygen that is dissolved in water. Dissolved oxygen (DO) is a measure of the amount of oxygen in water that is available for chemical reactions and for use by aquatic organisms. In the aquatic ecosystem, dissolved oxygen balance in water is important for the survival of certain microorganisms and higher organisms such as zooplankton and fish. Normally oxygen in water gets there through diffusion with the air and as a waste product of photosynthesis by aquatic plants. Dissolved oxygen in surface water is used by all forms of aquatic life; therefore, it is measured to assess the "health" of lakes and streams. Dissolved oxygen levels vary with seasons, and over 24 hour cycles. When dissolved oxygen levels in a body of water decline, sensitive animals may move away, weaken, or die. High DO levels in potable water usually make it taste better.

·       that pH is a measure of how acidic or basic water is. pH is important because it controls many chemical and biological processes that occur in the water. pH is measured on a scale that ranges from 0 to 14, with 7 considered neutral. Values of pH less than 7 are acidic, while values higher than 7 are basic. The pH scale ranges from 0 (high concentration of positive hydrogen ions, strongly acidic) to 14 (high concentration of negative hydroxide ions, strongly basic). In pure water the pH measures exactly 7. Students know that the pH of a body of water is important because pH has a synergistic effect. This means that the impact of other materials in a body of water - such as

iron, aluminum, ammonia, or mercury - is amplified or diminished depending on the pH of the water. For example, when acidic waters come into contact with certain chemicals and metals, it makes these chemicals and metals more poisonous than normal. This has special significance in water treatment processes, because specific water treatment processes require specific pH ranges.

·       that nitrogen and phosphorous are essential plant nutrients. The nitrates and phosphates derived from them are chemicals that pose possible health risks to humans if their presence in drinking water is not controlled. The major sources of nitrates in surface water include runoff contaminated with fertilizers, septic tank leakage, sewage, and erosion of natural deposits. Phosphates, on the other hand, usually enter waterways from human and animal waste, laundry, cleaning and industrial effluents.

·       that turbidity is a measure of how clear water is. The more suspended solids there are in a water sample, the less transparent it is. Turbidity is considered a good measure of water quality. In drinking water, high turbidity is generally not considered a favorable sign because it can be associated with organic pollution that might include pathogenic materials. In surface bodies of water, high turbidity can lead to increased water temperatures, low dissolved oxygen, and even physical impairment of aquatic organisms.

·       that the water quality of a body of water can also be assessed by using bioindicators (macroinvertebrates). The presence, condition, and numbers of the types of fish, insects, algae, plants and other aquatic life provide accurate information about the health of freshwater, coastal and marine waters. Bioindicators include living macroinvertebrates. Macroinvertebrates are easy for people to collect and identify. Because many macroinvertebrates are sensitive to pollution in water, they are a good indicator of whether or not a body of water is livable. Good water quality is indicated by a variety of macroinvertebrates. Poor water quality is indicated by a few of one type of macroinvertebrates in one place.

8.E.1.4

Students know:

·       that water quality is a term used to describe the chemical, physical, and biological characteristics of water. Scientifically, an array of chemical, physical, and biological measurements is used to define water quality. Water quality is also described in terms of the purpose for which water is intended to be used. Water that is safe to drink is called potable water, or drinking water, in contrast to safe water, which can be used for bathing or cleaning. In the United States, the Environmental Protection Agency sets maximum levels for the 90 most commonly occurring contaminants.

·   that water quality standards outline the water quality pollution control program that is mandated and regulated by local, regional and federal agencies. Standards outline the goals for a body of water by identifying its uses, establishing how to protect those uses and establishing provisions to protect and preserve the water bodies in the long term. Point and non-point environmental stressors such as urban and/or agricultural runoff, industrial inputs and over-fishing can impact a variety of aquatic and land-based populations. Because the water

quality of a given water body is so closely linked to the surrounding environment and land use, monitoring and regulation at local, regional, and national levels is important.

·         clear water may contain odorless, tasteless, and colorless harmful contaminants. Water must be tested for specific contaminants such as bacteria, nitrates, arsenic and others. Natural supplies of potable water are very limited and do not exist in sufficient quantities to meet human needs. Because of this, humans have developed water treatments that process water so that it can be used for a particular purpose. Drinking water treatment requires some basic steps:

o    Water collection

o    Coagulation, during which lime and alum are added to the water, causing particulates to clump together.

o    Next, the water is shaken to form larger clumps, called flocs.

o    During the sedimentation process water stands for approximately 24 hours, which allows the clumps to settle to the bottom.

o    The water is then filtered, disinfected (usually with chlorine) and aerated.

The substances removed during the drinking water treatment process include suspended solids, bacteria, algae, viruses, fungi, minerals, and chemical pollutants.

that water is essential to life. Water quality determines the sustenance of ecosystems, human activity such as agriculture, fishing, and recreation, as well as public health of human societies. Water quality supports healthy environments in which rich and varied communities of organisms can be found. The importance of monitoring and maintaining water quality cannot be overstated.  Cultivating an awareness of their connection to North Carolina’s hydrologic system is the first step towards developing stewardship skills and dispositions in students.