Water quality monitoring is performed to help determine the causes of water quality degradation. There are several methods of assessing stream quality.

Water Chemistry

Water samples can be collected from streams and analyzed for chemical composition. Parameters measured may include dissolved oxygen, pH, nitrogen, phosphorus, bacteria, biological oxygen demand, heavy metals and hydrocarbons.

Dissolved oxygen is necessary for biological organisms (fish and insects) to live. When dissolved oxygen levels fall too low, organisms become stressed and can die.

pH measures the relative acidity in the water. Fish, in particular, are extremely sensitive to changes in pH. The pH of a stream may be affected by acidic rainfall, and certain chemicals, such as deicing materials.

Nitrogen and phosphorus are nutrients that, when present in excess, cause algae to grow too rapidly. When the algae dies, the decomposition process consumes oxygen, often causing oxygen levels to fall too low to support aquatic life. Sources of nutrients include sewage treatment plant effluent, lawn and agricultural fertilizers and septic tanks.

Elevated bacteria levels can indicate contamination from fecal materials from warm-blooded animals. This can include improperly-funtioning septic systems, pet waste and wildlife.

Biological oxygen demand is a measurement of the rate at which oxygen is consumed in the water.

Heavy metals and hydrocarbons indicate impacts from development and from automobiles.

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Biological Monitoring

Sampling the biological community of the stream is another method of assessing the relative health of the stream system. Aquatic insects are collected, counted, sorted and identified. The diversity of species, abundance of insects, and the presence of pollution-sensitive species are measurements of biological health. In addition to insect communities, fish communities can also be sampled. The presence of a diverse biological community is an excellent indicator of a healthy stream system. Development can impact the biological community by altering the chemical composition of the water or altering the habitat value of the stream.

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Physical Monitoring

The physical characteristics of the stream can also be measured. Measurements include width and composition of the streamside buffer, channel width and depth, substrate (channel bottom) composition, and presence of pool and riffle areas. These parameters indicate the habitat value of the stream system. Increased impervious surfaces (roads, driveways, rooftops) allow stormwater to flow into streams at a much faster rate than it would if the watershed were forested. This change in flow often causes streambanks to become unstable and erode. Rapidly eroding banks, sediment-laden stream beds, and channelized streams with no pool and riffle areas, are indications of poor biological habitat. Biological organisms require both good water quality and a suitable habitat to survive.