WHAT IS WATER QUALITY?
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Before we begin to learn measurement techniques, it is important to understand exactly what we mean by the term "water quality". Most people have an idea of what good and bad water look like, but we need a specific and consistent definition to use in scientific studies and environmental law.
For scientific and legal purposes the following definition is most often used:
Beneficial uses are the ways in which water is used by humans and wildlife; drinking water and fish habitat are two examples. If water supports a beneficial use, water quality is said to be good or unimpaired. If water does not support a beneficial use, water quality is said to be poor or impaired.
A key concept is that different beneficial uses have different needs. Most people believe good water quality means the water is pure and clean. This is partly true, especially when you are using water for drinking. However, fish and wildlife have lots of other requirements. Fish must get all of their oxygen and food from water, and therefore need water that has enough oxygen and nutrients. Thus, good water quality implies that harmful substances (pollutants) are absent from the water, and needed substances (oxygen, nutrients) are present.
The government regulates water quality by setting standards for different kinds (or classes ) of water bodies. All rivers, streams, estuaries, and lakes are assigned to a class based on the beneficial uses they could support if they had good water quality.
Washington environmental laws are defined in the Washington Administrative Code (WAC) and are passed by the state legislature. To develop water quality standards the WAC recognizes the following beneficial uses for state waters:
1. Water Supply - Domestic, Industrial, Agricultural, and Stock Watering
2. Fish and Shellfish:
- -Salmonid spawning, rearing, migration, and harvesting
- -Other fish spawning, rearing, migration, and harvesting
- -Clams, Oyster, and Mussel spawning, rearing, and harvesting
- -Crustaceans and other Shellfish spawning, rearing, and harvesting
3. Wildlife Habitat
4. Recreation
- -Primary Contact (swimming)
- -Secondary Contact
5. Navigation
Based on these beneficial uses, Chapter 173-201 of the WAC defines the following classes:
Class AA: has all beneficial uses to a high degree.
Class A: has all beneficial uses, but not as well as Class AA.
Class B: has all beneficial uses except domestic water supply, salmon spawning, fish harvesting, and primary contact recreation.
Class C: has only a limited set of beneficial uses, including industrial water supply, fish migration, wildlife habitat, secondary contact recreation, and navigation.
Lake: has all beneficial uses, but has hydraulic and water quality characteristics that are different than those of rivers, streams, and estuaries.
Class AA waters have the highest water quality standards, and Class C waters have the lowest. The Skookumchuck and upper Chehalis Rivers are mostly Class AA, while tributaries like the Newaukum River are Class A. Grays Harbor estuary is assigned to Class B.
It is important to understand that a water's class defines water quality goals and standards, not actual water quality. A Class AA water does not necessarily have better water quality than a Class B water; it just has higher standards to meet because it could support more beneficial uses.
Now that we can define water quality in general terms, we need to have parameters we can measure to describe the water quality of a river, stream, or lake. Parameters that are measured include physical, chemical, and biologic properties.
1. Physical Measurements
Physical measurements include water temperature, depth, flow velocity, flow rate, and turbidity. These are all useful in analyzing how pollutants are transported and mixed in the water environment, and can be related to habitat requirements for fish and other aquatic wildlife. For instance, many fish have very specific temperature requirements, and cannot tolerate water that is either too cold or too hot. In the Chehalis River temperatures are often too high for salmon because there are no longer enough trees to shade the riverbank.
2. Chemical Measurements
Chemical measurements include a wide range of chemicals and chemical properties. Most water chemistry tests measure concentration , defined as milligrams of chemical per liter of water (mg/l).
Even the purest water contains countless chemicals, and it would be impossible to measure all of them. Water quality studies therefore focus on the chemicals that are most important for the problem at hand. In agricultural areas, studies measure chemicals found in manure, fertilizers, and pesticides. In an industrial area studies focus on measuring chemicals used by the nearby industries.
The following basic parameters are measured in nearly all studies; petroleum products, metals, industrial chemicals, pesticides, and herbicides are added when needed.
Dissolved Oxygen (DO): Dissolved Oxygen is the concentration of oxygen dissolved in the water, expressed as milligrams oxygen per liter water (mg/l). DO is an important measurement of aquatic health, since aquatic organisms must get all of their oxygen from water. Healthy water bodies usually have DO levels of 8 mg/l or higher.
Biological Oxygen Demand (BOD) : BOD measures how much oxygen is consumed by bacteria as they break down pollution and organic matter in the water. It is measured by observing how much dissolved oxygen levels decrease in a sealed sample over a 5-day period.
Coliform Bacteria: Coliform bacteria are bacteria that grow in the digestive tracts of humans and other warm-blooded animals, and indicate the presence of sewage and other sources of fecal pollution. They are measured by counting the number of bacteria colonies that grow from a 100 milliliter water sample (#/100ml). Sources of coliform bacteria include wastewater discharges, septic tanks, domestic animals, and wildlife. Fecal coliform counts greater than about 200 #/100ml are thought to be unsafe for swimming.
Nitrate (NO3) and Phosphate (PO4): Nitrates and phosphates are nutrients that come from both natural sources and human activities (fertilizers, detergents, wastewater). These nutrients determine the productivity of a water body, and are needed at some level to provide good aquatic habitat. However, pollution from manure, fertilizer, and wastewater can cause excessive nutrient levels. Too much nitrate or phosphate causes algae to grow out of control, reducing light and oxygen for fish.
pH : pH is a measure of the acidity of water, and is important in understanding the chemical balance of the water. pHs below 7 indicate acid conditions, while pHs above 7 indicate alkaline conditions. pH is a strong determinant of the solubility and availability of both nutrients and pollutants. Most natural water bodies will have pHs close to 7, depending on the local geochemistry. Very low pHs (less than about 6) can come from acid rain, industrial sources, or mine drainage.
3. Biologic Indicators
Our understanding of the needs of aquatic wildlife is incomplete, and water chemistry testing does not tell us everything about the suitability of a water body as habitat. An alternative approach is to measure the abundance, diversity, and health of different kinds of aquatic plants and animals. This data is then analyzed to come up with an indicator of water quality.
The simplest biologic approach is toxicity testing . This involves placing a group of small animals in a water sample and observing how many die or become sick. This is most often done with water fleas and small fish. Toxicity testing provides useful but difficult-to-interpret data. Conditions in a laboratory sample are quite different from field conditions, and at the end of the test you only know that the animal died - you don't know what killed it. Still, toxicity testing is a useful check on chemical test results, especially if there is a toxic pollutant in the water that you did not include in your water chemistry analysis.
Another biologic approach is to measure the numbers and types of macroinvertebrates found in a stream. Macroinvertebrates are aquatic insects, insect larvae, crustaceans, and other smaller animals that spend their lives in water. We know that different species can tolerate different levels of pollution, and can use this knowledge to measure water quality. For instance, a stream that has lots of stone fly and mayfly larvae would have very high water quality, while a stream that has only water striders and aquatic snails might have poor water quality. Like toxicity testing, this method doesn't tell you why animals are present or absent, but it can help you identify what problems to investigate.
Putting all of this together, the Department of Ecology has developed water quality standards for different classes of water. These standards are based on scientific studies of the needs for different beneficial uses. Standards for pollutants and harmful substances are defined as maximum levels (for example, coliform bacteria must be less than 50 #/100ml). Standards for needed substances like dissolved oxygen are defined as minimum levels (for example, dissolved oxygen must be greater than 9.5 mg/l). Other parameters like pH have standards defined as a range (for example, pH must be between 6.5 and 8.5).
The following are state water quality standards for some common parameters (freshwater only):
| Standard for Classes | ||||
| PARAMETER | AA | A | B | C |
| Minimum Dissolved Oxygen (mg/l) | 9.5 | 8.0 | 6.5 | NA |
| Maximum Coliform Bacteria (#/100ml) | 50 | 100 | 200 | NA |
| Maximum Temperature (degrees C) | 16 | 18 | 21 | NA |
| pH range | 6.5-8.5 | 6.5-8.5 | 6.5-8.5 | NA |
| Maximum Turbidity (NTU) | 5 | 5 | 10 | 10 |
Using information from the "What is Water Quality" unit, try to answer the following questions:
1. What is the legal definition of water quality?
2. Based on its assigned Class, what beneficial uses are not appropriate for Grays Harbor? Why do your think Grays Harbor is assigned a different class than the rest of the Chehalis River basin?
3. Which two beneficial uses do you think need the cleanest water? Which two uses can tolerate the most pollution? (Hint: look at the definitions for Class B and Class C waters)
4. What are some sources of nitrates and phosphates in water? Why can these be a problem for fish?
5. The following are the results for a water quality sample from a Class AA stream:
According to State water quality standards, does this look like good water quality?
6. Part of the water sample from question 5 was taken to a laboratory for toxicity testing. After a short period of time most of the animals in the sample died. What does this tell you about the water? What should the investigators do next?
7. Dissolved Oxygen in a water sample was measured as 8 mg/l. The sample was then placed in a sealed container for 5-days. After 5 days the Dissolved Oxygen in the sample was 5 mg/l. What is the Biological Oxygen Demand (BOD) for this sample? Why did the dissolved oxygen in the sample drop from 8 to 5 mg/l?
Go to: A General Definition
- | - Beneficial Uses For Different Classes Of Waters
- | - Parameters That Describe Water Quality
- | - Water Quality Standards
- | - Exercises or
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This water quality course material created by Rob Schanz. Send comments to Rob Schanz
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Send comments or questions to the: Chehalis River Council