Biological Oxygen Demand
The amount of oxygen required by aerobic microorganisms to decompose the organic matter in sample of water. Used as a measure of the degree of water pollution.

Biological Oxygen Demand, Five-Day (BOD5)
The amount of oxygen required by aerobic microorganisms to decompose organic matter in a water sample, based on the maximum rate of O2 consumption in a water sample over a five-day period in the dark at 20 degrees C. It is used to estimate the total amount of “biodegradable” organic matter in the system and therefore serves as a measure of the degree of water pollution.

Chlorophyll a
Photosynthetic pigment found in all green plants, and the main pigment in algae. The concentration of chlorophyll a is used to estimate the amount of algae (all phytoplankton in a given area) in surface water. Measured in micrograms per liter (µg/L). While it is normal to find algae in streams and lakes, high levels of algae can lead to low levels of dissolved oxygen in a water body.

Cubic feet per second (cfs): a cfs is equal to 0.0283 cubic meters per second (cms).

Channel: an open conduit either naturally or artificially created that may convey water.

Confluence: the point at which two streams converge.

Discharge
The volume of water that passes through a given cross section per unit time. Discharge is commonly measured in cubic feet per second (cfs) or cubic meters per second (cms). It is also referred to as flow. (MDNR)

Fecal Coliform Bacteria
A group of bacteria found in the intestinal tract of humans and animals, and also found in soil. While harmless in themselves, coliform bacteria are commonly used as indicators of the presence of pathogenic organisms and other disease-causing bacteria, such as those that cause typhoid, dysentery, hepatitis A and cholera. Measured in number of bacteria per 100 milliliters of water. Failing septic systems and runoff from feedlots are common sources of fecal coliform in water samples.

Field Turbidity
A measurement that provides an estimate of the muddiness or cloudiness of the water due to clay, silt, fine organic and inorganic matter, soluble colored organic compounds, plankton, and microscopic organisms. It is an indication of the degree to which light is scattered in water by suspended particles and soluble colored compounds. Measured in Nephelometric Turbidity Units (NTU) or Formazin Turbidity Units (FTU).

Floodplain
Lowland areas adjoining lakes, wetlands, and rivers that are susceptible to inundation of water during a flood. For regulatory purposes, the floodplain is the area covered by the 100-year flood or the area that has a 1 percent chance of flooding every year. It is usually divided into districts called the floodway and flood fringe. Areas where the floodway and flood fringe have not been determined are called approximate study areas or general floodplain. Local units of government administer ordinances that guide development in floodplains. (MDNR)

Hydrograph: a description of flow versus time or a description of stage versus time. (MDNR)

Hydrologic Cycle
The continuous process of water movement between the oceans, atmosphere, and land.The hydrologic cycle is a process that occurs within the earth?s atmosphere in which water molecules move and are transformed from liquid to vapor and back to liquid again. The cycle begins when an unending circulation of water begins as energy from the sun which evaporates enormous quantities of water from the oceans. Atmospheric winds transport the moist air to other regions, where it condenses into clouds, some of which produce rain and snow. If the precipitation falls into an ocean, the water is ready to begin its cycle again. If the precipitation falls on a continent, a great deal of the water makes its way back to the ocean in a complex journey over land and underground. (MDNR)

Hydrology
The study of water. Hydrology generally focuses on the distribution of water and interaction with the land surface and underlying soils and rocks. (MDNR)

Infiltration: the movement of water from the land surface into the soil.

Nephelometric Turbidity Units (NTUs)
The unit used to describe turbidity. Nephelometric refers to the way the instrument, a nephelometer, measures how much light is scattered by suspended particles in the water. The greater the scattering, the higher the turbidity. Therefore, low NTU values indicate high water clarity, while high NTU values indicate low water clarity.

Nitrate and Nitrite Nitrogen
Nitrate (NO3) plus nitrite (NO2) as nitrogen. In lakes, most nitrate/nitrogen is in NO3 form. It is measured in milligrams per liter (mg/L). Elevated levels of nitrates/nitrogen are often caused by over application of fertilizers that leach into waterbodies.

Peak: the highest elevation reached by a flood wave. Peak is also referred to as the crest.

Peak flow: the point of the hydrograph that has the highest flow.

Phosphate: An essential nutrient containing phosphorus and oxygen. Phosphate is often a critical nutrient in lake eutrophication management.

Phosphorus: A nutrient essential to the growth of organisms, and is commonly the limiting factor in the primary productivity of surface water bodies. Total phosphorus includes the amount of phosphorus in solution (reactive) and in particle form. Agricultural drainage, wastewater, and certain industrial discharges are typical sources of phosphorus, and can contribute to the eutrophication of surface water bodies. Measured in milligrams per liter (mg/L).

Rating curve: the relationship between stage and discharge. (MDNR)

Reach: a segment of a stream channel. (MDNR)

Secchi Depth
The depth in a lake, measured in meters, to which a Secchi disk can be observed, as a measure of light penetration in water. The Secchi disk is lowered into a section of shaded water until it can no longer be seen and then lifted back up until it can be seen once again. Averaging the two depths gives the clarity of the water

Temperature
A specific degree of hotness or coldness as indicated on or referred to a standard scale.

Total Kjeldahl Nitrogen
The sum of organic nitrogen and ammonia in a water body. Measured in milligrams per liter (mg/L). High measurements of TKN typically results from sewage and manure discharges to water bodies.

Suspended Solids
Very small particles remaining dispersed in a liquid due to turbulent mixing that can create turbid or cloudy conditions. Measured in milligrams per liter (mg/L).

1. A measure of the material suspended in wastewater. Total suspended solids (TSS) cause: a) interference with light penetration, b) buildup of sediment and c) potential reduction in aquatic habitat. Solids also carry nutrients that cause algal blooms and other toxic pollutants that are harmful to fish.

2.Very small particles remaining dispersed in a liquid due to turbulent mixing exceeding gravitational sinking that can create turbid or cloudy conditions.

pH (pH) Field pH
A measure of the relative acidity or alkalinity of water. The pH scale ranges from 1 to 14, with 1 being the most acidic and 14 the most alkaline. Pure water is neutral with a pH of 7. The pH scale is a measure of acidity, with 7 being neutral. Numbers under 7 are acidic and numbers over 7 are alkaline.

Volatile Suspended Solids
Volatile solids are those solids lost on ignition (heating to 500 degrees C.) They are useful because they give a rough approximation of the amount of organic matter present in the water sample. ‘‘Fixed solids’’ is the term applied to the residue of total, suspended, or dissolved solids after heating to dryness for a specified time at a specified temperature. The weight loss on ignition is called ‘‘volatile solids.’’ Source: American Public Health Association

Source: Minnesota Pollution Control Agency unless otherwise noted.