Glossary

The following explanations of the water quality technical terms typically used in the reports that are contained at this website have been obtained from: King County Lake Volunteer Monitoring Report 1998. King County Water and Land Resources Division, Seattle, WA, October 1999.

Aerobic
Condition characterized by the presence of oxygen.
 
Algae
Single or multi-celled, non-vascular plants containing Chlorophyll a. Algae form the base of the food chain in aquatic environments.
 
Algal bloom
Heavy growth of algae in and on a body of water as a result of high nutrient concentrations.
 
Alkalinity
The acid combining capacity of a (carbonate) solution, its buffering capacity.
 
Anaerobic
Condition characterized by the absence of oxygen.
 
Anoxic
Depleted of oxygen.
 
Average
The sum of a group of numbers divided by the total number of values in the group.
 
Bathymetric map
A map showing the bottom contours and depth of a lake.
 
Benthic
Bottom area of the lake that hosts the community of organisms (benthos) that live in or on the sediment.
 
Biomass
The total organic matter present.
 
Chlorophyll a
The green pigments of plants.
 
Concentration
The amount of specific substance in a unit amount of another substance, such as a specific weight of a chemical in a given volume of water.
 
Conductivity
The measure of water’s capacity to convey an electric current. The amount of dissolved ions affects the conductivity of water. Increasing amounts of ions causes the conductivity to increase.
 
Dissolved Oxygen
The oxygen gas that is dissolved in water.
 
Ecosystems
Any complex of living organisms together with all the other biotic and abiotic (non-living) factors that affect them.
 
Epilimnion
The warmer, less dense, superficial layer of a lake lying above the metalimnion.
 
Eutrophic
Waters with a good supply of nutrients and hence a rich organic production.
 
Eutrophication
The physical, chemical, and biological changes associated with enrichment of a body of freshwater due to increases in nutrients and sedimentation.
 
Fall turnover
A natural mixing of thermally stratified waters that commonly occurs during early autumn. The sequence of events leading to a fall turnover includes: 1) cooling of surface waters, 2) density change in surface water that produces convection currents from top to bottom, and 3) circulation of the total water volume by wind action. The turnover generally results in a uniformity of the physical and chemical properties of the water.
 
Humus substances
Organic substances only partially broken down, which occur in water mainly in a colloidal state (humus colloids). Humic acids are large-molecule organic acids that dissolve in water.
 
Hypolimnion
The colder, deep layer of a lake lying below the metalimnion and removed from surface influences.
 
Limiting nutrient
Essential nutrient which is the most scarce in the environment relative to the needs of the organism.
 
Limnology
The study of freshwaters (lakes and streams).
 
Littoral
The shallow, shoreward region of a body of water sometimes inhabited by aquatic plants.
 
Loading
The total amount of material (sediment or nutrients for example) entering a water body via streams, overland flow, precipitation, direct discharge, or other means over a specific time period (often annually).
 
Mean
The sum of a group of numbers divided by the total number of values in the group.
 
Median
The middle measurement in a set of data.
 
Metalimnion
The layer of water in a lake between the epilimnion and hypolimnion in which the temperature exhibits the greatest difference in a vertical direction.
 
Monomictic
A lake water mixing pattern which occurs once a year.
 
Nitrogen
One of the elements essential for the growth of organisms. Nitrogen is most abundant in the form of N2 and comprises 80% of atmospheric constituents.
 
Nonpoint pollution
Pollution from a diverse set of undefined sources that are often difficult to identify and control. Examples of "sources" include erosion, on-site septic systems, farm practices, forest practice, and residential/urban land use.
 
Nutrient
Any chemical element, ion, or compound required by an organism for the continuation of growth, reproduction, and other life processes.
 
Oligotrophic
Waters that are nutrient poor and have little organic production.
 
pH
The negative logarithm of the hydrogen ion activity.
 
Pheophytin
A pigment resulting from Chlorophyll a degradation found in dead algae or suspended organic matter.
 
Phosphorus
One of the elements essential for the growth of organisms. Phosphorus is also commonly the limiting or least available nutrient for plant growth in freshwater ecosystems. The primary source of phosphorus is from the earth in the form of phosphate rock.
 
Photic zone
The area of a lake which is lighted and where photosynthesis takes place.
 
Photosynthesis
Production of organic matter (carbohydrate) from inorganic carbon and water in the presence of light.
 
Phytoplankton
Free floating microscopic plants (algae).
 
Productivity
The rate of formation of organic matter averaged over a certain time period (day, week, or year).
 
Residence time
The average length of time that water or a chemical constituent remains in a lake.
 
Secchi disk
A 20-cm (8-inch) diameter disc painted white and black in alternating quadrants. It is used to measure light transparency in lakes.
 
Sediment
Solid material deposited in the bottom of a basin.
 
Stratification
Layering of water caused by differences in water density.
 
Thermocline
Zone of temperature decrease. See metalimnion.
 
Transparency
Water clarity of a lake as measured using a Secchi disk.
 
Trophic state
Term used to describe the productivity of the lake ecosystem and classify it as oligotrophic, mesotrophic, or eutrophic.
 
Turbidity
Cloudiness of water caused by the suspension of tiny materials (soil, algae, or pollen) in the water.
 
Turnover
The mixing of lake water from top to bottom. Typically occurs in the fall and is caused by cooling of surface waters and wind mixing.
 
Watershed
The area drained by, or contributing to, a stream, lake, or other water body.
 
Watershed management
The management of the natural resources of a drainage basin for the production and protection of water supplies and water-based resources.
 
Water year
Generally a year which divides the flood season or wet-weather season from one year to the next. The US Geological Survey uses the water year October 1 through September 30 for data publication.
 
Zooplankton
Microscopic animals with limited powers of locomotion that feed on bacteria, algae, and organic material found in the water column of a lake.