DEFINITION OF TERMS

Specialized technical terms related to streamflow, water-quality, and other hydrologic data, as used in this report, may be accessed at http://water.usgs.gov/ADR_Defs_2004.pdf .  Terms such as algae, water level, and precipitation are used in their common everyday meanings, definitions of which are given in standard dictionaries.  Not all terms defined in this alphabetical list apply to every State.  Definitions specific to the USGS Illinois Water Science Center are listed below.  See also table for converting English units to International System (SI) units.  Other glossaries that also define water-related terms are accessible at  http://water.usgs.gov/glossaries.html.

Chlorophyll--The green pigment found in photosynthetic organisms that harnesses the energy in sunlight to synthesize carbohydrates from carbon dioxide and water.

Dew point--(Or dew-point temperature.)  The temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur.

Langley per hour--(Lg/hr) is the amount of energy measured in calories arriving at an area of 1 square centimeter in 1 hour.  One Langely per hour is equivalent to 0.08598 watt per square meter.

Nephelometric turbidity unit--(NTU) is the measurement for reporting turbidity that is based on use of a standard suspension of formazin.  Turbidity measured in NTU uses nephelometric methods that depend on passing specific light of a specific wavelength through the sample.

Periphyton--Algae attached to an aquatic substrate; also known as benthic algae.

Recoverable from bed (bottom) material--is the amount of a given constituent that is in solution after a representative sample of bottom material has been digested by a method (usually using an acid or mixture of acids) that results in dissolution of readily soluble substances.  Complete dissolution of all bottom material is not achieved by the digestion treatment and, thus, the determination represents less than the total amount (that is, less than 95 percent) of the constituent in the sample.  To achieve comparability of analytical data, equivalent digestion procedures would be required of all laboratories performing such analyses because different digestion procedures are likely to produce different analytical results.