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Definition of Terms

Here is a list of water-related terms, gathered from a number of web-based sources, to help you better understand our site.

Hydrology- the study of water including it properties, distribution and cycles
within the earth and its atmosphere. It may be subdivided into surface water, marine water and groundwater. The water cycle is a model that help show storage and movement of water.

Geology- the study of the solid earth, the rocks of which it is composed of, and the physical, chemical, and biological processes that the earth has undergone or is undergoing. It provides insight into the history of Earth.

(Image courtesy of U.S Geological Survey)    

- the study of life and of living matter in all its forms. It includes the structure, function, evolution and commonalities with other living matter. There are many subcategories of biology.

Ecology- the branch of biology dealing with the relations and interactions between organisms and their environment, including other organisms. (The study of living and non living interactions.)

Watershed- an area of land where water drains downward on the landscape and joins a larger body of water. This can be a small stream that leads to the mouth of a river, a lake, wetland or even the ocean. A watershed can be defined by drawing a line along the highest elevations (often a ridge) between two areas on a map. Large watersheds are made up of several smaller ones. The Gallatin Watershed, for example, is part of the Missouri Watershed which is part of the larger Mississippi Watershed.

Groundwater - water that is stored beneath the surface of the Earth, within the geologic material. It is supplied by infiltration of rainwater, snowmelt and other surface water. It generally and slowly flows from high areas to low areas, just like surface water tends to flow. Groundwater is used to supply springs and wells. Groundwater can be considered part of a watershed.

Nonpoint Source Pollution - water pollution that is discharged over a wide land area and not from one specific location or point. This is pollution caused runoff of excessive sediment, nutrients, organic and toxic substances that originated from land-use activities and carried to a body of water.

Point Source Pollution- water pollution that comes from a specific location or single point. Examples would be a sewage-outflow pipe, or storm runoff drainage pipe.

Water quality- the physical, chemical and biological characteristics of water in relationship to a set of standards. Common measurements of water quality include the following terms listed below.

- a measure of how much hydrogen (H+) is in a solution. A solution with a pH of 7 is neutral. Lower pH levels, from 1-6.9, indicate acidic solutions. Higher pH levels, from 7.1-14, indicate basic or alkaline solutions. To the right: a pH scale with household items to help you get better aquainted with acidic and basic solutions.

                                                                                           (Image courtesy of

Dissolved Oxygen (DO)- the amount of oxygen gas dissolved in a body of water.  DO is an indication of the degree of health of the water and its ability to support a balanced aquatic ecosystem. DO is often expressed in percent saturation, since the amount of oxygen water can hold changes drastically with temperature. For most organisms around the Gallatin, specifically aquatic insects and fish, thrive when DO saturation is higher than 80%. 

(Image courtesy of

-is a form of nitrogen that is usable by plants and animals. Just like adding nitrogen (e.g fertilizers) to a garden helps vegetables to grow, it also adds nitrogen to a stream and can cause increased plant growth in the form of aquatic algae.  Excessive algal growth can have negative impacts, including low dissolved oxygen, unsightly conditions, and poor habitat conditions for fish and other aquatic organisms.  Sources of streamwater nitrate include organic matter, the atmosphere, geology, human and animal waste, and fertilizers.  Nitrate is measured in miligrams per liter as Nitrogen (mg/L-N).

Temperature- a measure of the warmth or coldness of an object or substance with reference to some standard value. Temperature can effect aquatic life populations like fish, macroinvertebrate (bugs) and algal masses.  At 0 degrees C, water freezes. At 100 degrees C, water boils. To the right: Temperature comparison of Celcius to Farhrenheit. (The image is borrowed from

Turbidity- a measure of the amount of solid particles suspended in water which results in how cloudy or opaque the water is. The units for turbidity are Nephelometric Turbidity Units (NTU). Turbidity is often low in the winter resulting in clear rivers, but take notice how the river turns brown during snowmelt. This is because the melting snow will
                                                           carry soil with it to the river. Particles that contribute to cloudiness includes algae, silt and clays. To the left: Examples of different turbidity levels ranging from 10- 250.
(Above image courtesy of

Escherichia coli-(commonly E. coli;) is a bacterium that is commonly found in the lower intestine of warm-blooded animals. Most E. coli strains are harmless, but some can cause illness, especially in young children and the elderly.

Total coliform
- the most basic test for bacterial contamination of a water supply. Both e.Coli and Total Coliform are measured in the same test. Coliform bacteria themselves are not toxic but the level at which they occur in water can indicate possible contamination of other bacteria that are more difficult and more expensive to test.

Bacteria is measured in colony forming units per 100 mililiters (cfu/100mL). This is number of dots that appear on a petridish for every 100mL of water used, as pictured to the right. The red dots are total coliform units, the blue are E. Coli and the green are               
salmonella. **Note: Pictured sample is not from
 the Gallatin River. **                                                        (Courtesy of )

Algal biomass
- describes the amount of algae in a body of water at a given time. Algal mainly refers to aquatic eukaryotic organism. Their size ranges from microscopic single-celled forms to multicellular forms of 100 ft. (30 m) or more long. Algae is distinguished from plants by the absence of true roots, stems, and leaves and by a lack of nonreproductive cells in the reproductive structures.  Algae growth is natural but an excessive amount, due to an excessive amount of nitrogen, can increase turbidity, decrease dissolved oxygen, and increase temperatures. Therefore, too much algae can stress fish and other aquatic organisms.

Aquatic Benthic Macroinvertebrates
- large aquatic organisms that have no skeleton. They live on and under the rocks and within the substrate of a stream. These organisms or "macros" are a great indication of water quality as some are very sensitive to different types of pollution. When collecting macros the BWTF looks for the presence of sensitive species such as mayflies, stonfiles and caddisflies. The picture below displays numerous types of macros.

                                              (Image courtesy of

Conductivity- Electrical conductivity (EC) estimates the amount of total dissolved salts (TDS), or the total amount of dissolved ions in the water. Although salinity, measured as electrical conductivity, can be naturally high in some systems, waters with elevated salinity levels are usually the result of both nonpoint (non-traceable) and point (traceable) source pollution and can adversly impact aquatic ecosystems.  High levels of EC can inhibit plant and animal life. 

Total Maximum Daily Load (TMDL)- Under section 303(d) of the Clean Water Act, states, territories, and authorized tribes are required to develop lists of impaired waters. These are waters that are too polluted or otherwise degraded to meet the water quality standards set by states, territories, or authorized tribes. The law requires that these jurisdictions establish priority rankings for waters on the lists and develop TMDLs for these waters. A Total Maximum Daily Load, or TMDL, is a calculation of the maximum amount of a pollutant that a waterbody can receive and still safely meet water quality standards.

These definitions were borrowed from, and 
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