Dissolved Oxygen Dissolved Oxygen’s presence in water is a positive sign, but low levels are a sign of severe pollution. Water with consistently high levels of dissolved oxygen are considered healthy and capable of supporting many different kinds of aquatic organisms. In order for a water body to sustain warm water fish like bluegill, bass, and pike, the dissolved oxygen level must be at least 4 milligrams per liter (mg/L). Dissolved Oxygen in water generally comes from one of two sources. Most Dissolved Oxygen comes from the atmosphere as waves and tumbling water mix atmospheric oxygen. Another source of Dissolved Oxygen comes from plants as they go through photosynthesis.
| Less than 4 mg/L | Bad |
| 4 – 10 mg/L | Good |
| More than 10 mg/L | Excellent |
pH (Potential of Hydrogen) Water (H20) contains both H+ (hydrogen) ions and OH- (hydroxyl) ions. The pH test measures the H+ ion concentration of liquids and substances. Each measured liquid or substance is given a pH value on a scale that ranges from 0 to 14. Any substance measuring below 7 on the pH scale is considered to be an acid. Substances measuring above 7 are basic (alkaline). Normal rainfall has a pH of 5.6 and natural water will range from 6.5 - 8.5. Distilled water's pH value is 7. Water with an extremely high or low pH (9.6 or 4.5) becomes unsuitable for most organisms to survive.
| Less than 6.5 | Low - Acidic |
| 6.5 – 8.0 | Good |
| More than 8.0 | High - Basic |
Total Phosphates Phosphorous is usually present in natural water as phosphate. Although it is essential for life, excessive amounts of phosphorous resulting from the release of human wastes, animal wastes, industrial wastes, soil erosion, and overuse of fertilizers can cause algal growth (blooms) to form in the water. This is a symptom of cultural eutrophication . Cultural eutrophication is the process by which a body of water becomes either naturally, or by pollution, rich in dissolved nutrients (phosphates) and often shallow with a seasonal deficiency in dissolved oxygen. Different species present in clean water are replaced by species tolerant of low dissolved oxygen.
| Less than 1.0 mg/L | Excellent |
| 1.1– 4.0 mg/L | Good |
| 4.1 – 9.9 mg/L | Fair |
| More than 10 mg/L | Bad |
Nitrates/Nitrites To build proteins, all living things need nitrogen. In its molecular form (N2), Nitrogen makes up 79% of the earth's air. Blue-green algae can convert N2 ammonia (NH3 and nitrate (NO-2) that plants can use for growth. Aquatic animals obtain the necessary nitrogen to form proteins by eating plants or by eating other aquatic organisms that feed upon plants. Nitrogen in the form of ammonia and nitrates acts as a plant nutrient so it also causes eutrophication. Unlike phosphorous, nitrogen rarely limits plant growth, so plants are not as sensitive to increases in ammonia and nitrate levels.
Sewage is the main source of nitrates added to rivers by humans. Fertilizers and the runoff from cattle feedlots, dairies, and barnyards are two other sources of nitrates in water. Water containing high nitrate levels can cause methemoglobinemia if it is used for infant milk formula. This condition prevents the baby’s blood from carrying oxygen.
The United States Environmental Protection Agency (US EPA) has set a Maximum Contaminant Level (MCL) goal to maintain Nitrate levels below 10 mg/L.
US EPA has set a MCL goal to maintain Nitrites below 1 mg/L.
Chloride Chloride is composed of a combination of chlorine with a metal. In combination with a metal such as sodium, chloride is essential for life and for normal plant and animal cell production to occur. Chloride is common in areas with deposites of limestone, but is usually not found in other soils. When chloride is found in areas where it doesn't naturally occur, the water may be polluted.
Surface water generally has a chloride level ranging from 45 to 155 mg/L. Water containing chloride levels of 250 to 400 mg/L will have a salty taste. Chlorides are not usually harmful to humans, however, they can contaminate fresh water streams and lakes making conditions impossible for fish and other aquatic life to survive.
Sources of Chloride
Dissloved Oxygen, Phosphate, Nitrate, Nitrite, Chloride, and Sodium Chloride levels are measured in milligrams per liter (mg/L). One milligram per liter is equivalent to one part per million (ppm). Below are some analogies to help better understand how much a milligram per liter is.
one inch in 16 miles one minute in two years one ounce in 32 tons one cent in $10,000 |
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