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Water Quality Parameters

How Water Quality is Measured



Water quality measurements include chemical, physical and biological parameters. The following is a brief description of some commonly used parameters.
Chemical

Chlorophyll

Chlorophyll is the pigment that allows plants, including algae, to convert sunlight into organic compounds through photosynthesis. Measuring chlorophyll a concentrations in water is a surrogate for an actual measurement of algae biomass. Excessive amounts of chlorophyll a indicate the presence of blooms, which usually consist of a single species of algae - typically one that is not desirable for consumption by fish and other predators. Unconsumed algae sink to the bottom and decay, depleting deeper water of oxygen.

Suspended Minerals

Suspended minerals is a measure of the amount of sediment moving along in a stream. It is highly dependent on the flow of water and usually increases during and immediately after rain events. As the sediment settles out of the water, aquatic habitats are often destroyed.

Colored Dissolved Organic Carbon

Colored dissolved organic carbon, also referred to as fulvic acid and humic acid, contributes to the brownish tan color of a waterway. Tannins are one example of such compounds. In a nutrient-poor environment, it can serve as a nutrient allowing for the growth of algae whereas in a nutrient-rich environment, it can be given off as a byproduct from the decay of algae.

Turbidity

Turbidity is a measure of the amount of particulate matter that is suspended in water. Water that has high turbidity appears cloudy or opaque. High turbidity can cause increased water temperatures because suspended particles absorb more heat and can also reduce the amount of light penetrating the water.

Secchi Depth

Secchi depth is the depth to which one can see into a lake and is an indication of water clarity. This measurement is obtained by lowering a black and white disk into the water and recording the depth at which it is no longer visible.

Dissolved Oxygen

Although water molecules contain an oxygen atom, aquatic organisms rely upon a small amount of oxygen that is actually dissolved in the water. In general, rapidly moving water contains more dissolved oxygen than slow or stagnant water and colder water contains more dissolved oxygen than warmer water. Bacteria consume oxygen as organic matter decays. As a result, an oxygen-deficient environment can develop in lakes and rivers with excess organic material. These conditions can eventually lead to fish kills.
Physical

Temperature

Water temperature affects the ability of water to hold oxygen, the rate of photosynthesis by aquatic plants and the metabolic rates of aquatic organisms. Causes of temperature change include weather, removal of shading streambank vegetation, impoundments, discharge of cooling water, urban storm water, and groundwater inflows to the stream.

pH

pH is a term used to indicate the alkalinity or acidity of a substance as ranked on a scale from 1.0 to 14.0. Acidity increases as the pH gets lower. A pH of 7.0 is neutral. Aquatic organisms differ as to the range of pH in which they flourish.

Streamflow

Streamflow, or discharge, is the volume of water that moves over a designated point over a fixed period of time. It is often expressed as cubic feet per second (ft3/sec). The flow of a stream is directly related to the amount of water moving off the watershed into the stream channel. It is affected by weather as it increases during rainstorms and decreases during dry periods, and also varies by season.
Biological



Benthic Macroinvertebrates

Macroinvertebrates are organisms that are large (macro) enough to be seen with the naked eye and lack a backbone (invertebrate). Benthic refers to the bottom of a waterway. Examples of benthic macroinvertebrates include insects in their larval or nymph form, crayfish, clams, snails, and worms. Most live part or most of their life cycle attached to submerged rocks, logs, and vegetation. The basic principle behind the study of macroinvertebrates is that some are more sensitive to pollution than others. Therefore, if a stream site is inhabited by organisms that can tolerate pollution and the more pollution-sensitive organisms are missing a pollution problem is likely.


Submerged Aquatic Vegetation

Submerged aquatic vegetation (SAV) provides invaluable benfits to aquatic ecosystems. It not only provides food and shelter to fish and invertebrates but also produces oxygen, traps sediment and absorbs nutrients such as nitrogen and phosphorus. Whereas SAV are dependent upon the transmission of sunlight through the water, the location of individual species depends upon a variety of factors such as salinity, depth and bottom sediment.