Water Resources Glossary
In a Word: Terms for Water Quality Smarts
Algae: One-celled or multi-celled plants that are either suspended
in water or attached to rocks or other materials. Their abundance is measured
by the amount of chlorophyll
in water samples. Algae are essential parts of aquatic ecosystems,
providing the food base for most organisms, including aquatic invertebrates
and fish. However, too much algae can degrade water quality by diminishing
or, when it decomposes, lowering
Aquatic invertebrates: Aquatic animals without internal skeletal
structures, such as insects, mollusks, and crayfish.
Biomass: Amount of plant or animal matter, the total of which
indicates the degree of a lake’s eutrophication
Blue-green algae: Algae that often cause problems in lakes because
some produce chemicals that are toxic to animals, including humans.
They often form thick floating mats of blue-green scum as they die.
Chlorophyll a: Green pigment present in all plant life
and necessary for photosynthesis.
The amount in water samples depends on the amount of algae
and is therefore used as a common indicator of water quality.
Conductivity: Measure of the ability of water to conduct electrical
current. It is directly related to the total dissolved substances
in the water.
Dissolved oxygen: Oxygen in water that is produced by aquatic
plants and is mixed from the air. Used by fish and other organisms
to live, dissolved oxygen (DO) is measured either as a weight concentration
per volume of water (milligrams per liter) or as parts per million (ppm).
Ice and snow cover blocks sunlight and air contact with waterbodies during
many Eagan winters, lowering DO in shallow lakes and ponds. When
DO concentrations fall below 5 ppm, sensitive aquatic organisms are at
an increased risk of mortality.
Drainage basin: Total land area that drains to a lake or pond.
Eutrophication: Natural process by which waterbodies are enriched
with nutrients, increasing the production of algae
Urbanization can accelerate this process when lakes, ponds, and wetlands
are incorporated into the stormwater
Filamentous algae: Algae that forms filaments or mats that are
attached to sediment,
weeds, piers, etc.
Gun Club Lake Watershed Management Organization: A public agency
comprised of the respective governmental units of the cities of Eagan,
Inver Grove Heights, and Mendota Heights. Because it comprises most
of the Gun Club Lake watershed, the City of Eagan coordinates the
activities of the organization. The general purpose of the organization
is to regulate the natural water storage and retention of the Gun Club
Lake watershed to: 1) protect, preserve, and use natural surface and ground
water storage and retention systems; 2) minimize public capital expenditures
needed to correct flooding and water quality problems; 3) identify and
plan for means to effectively protect and improve surface and ground water
quality; 4) establish more uniform local policies and official controls
for surface and ground water management; 5) prevent erosion of soil into
surface water systems; 6) promote ground water recharge; 7) protect and
enhance fish and wildlife habitat and water recreational facilities; and
8) secure the other benefits associated with the proper management of surface
and ground water.
Impervious surface: Exterior covering that does not allow rainwater
or snowmelt to infiltrate into the soil but rather causes it to run off
and enter the stormwater
system via street drains. Rooftops, driveways, sidewalks, and streets
are common impervious surfaces in cities.
Macrophytes: Multi-celled plants that grow in or near water.
Generally, macrophytes are beneficial to lakes and ponds because they produce
oxygen and provide habitat for aquatic
invertebrates and fish. However, overabundance of
such plants, especially problem species (e.g., curlyleaf
pondweed) is related to shallow water depth and high levels
of nutrients, such as phosphorus.
Nutrient removal rates: Essentially, estimates of the proportion
of the nutrients entering a stormwater treatment basin that are retained
and not exported to a receiving waterbody. In 1987, W. W. Walker
developed for the U.S. Environmental Protection Agency’s (EPA)
National Urban Runoff Program computer models that are used by the City
to design and define the dimensions of such treatment basins.
pH: Within a scale from 1 to 14, a measure of acidity, where
low numbers are more acidic than high numbers and 7 is neutral.
Phosphorus: Key nutrient influencing plant growth in most lakes
and ponds, where it is the least available nutrient and therefore limits
the growth of algae
and aquatic vegetation. Phosphorus is abundant in plant and animal
matter and attaches to fine soil particles. Stormwater
transports phosphorus, increasing levels in waterbodies and causing algae
populations to increase. This in turn causes a decline in water transparency
and can accelerate eutrophication.
With very high phosphorus concentrations, intense "blooms" of algae may
occur, coloring the water green and releasing strong odors when they decay.
Photosynthesis: Process by which green plants convert carbon
dioxide to sugar and oxygen using sunlight for energy. In lakes and
ponds, photosynthesis is essential to producing a food base, and is an
important source of oxygen.
Respiration: Process by which aquatic organisms convert organic
material into energy. It is the reverse reaction of photosynthesis.
Respiration consumes oxygen and releases carbon dioxide. It also
takes place as organic matter decays.
Runoff: See Stormwater.
Secchi disk: An 8-inch diameter plate (usually all-white or with
alternating black and white quadrants) used to measure transparency.
Attached to a length-calibrated cord, the disk is lowered into the lake
until it disappears. It is then raised until it becomes visible.
The average of these depths is the Secchi disk reading. About 30
citizen lake monitors regularly collect Secchi disk readings as part of
the Eagan citizen lake monitoring program. Invented by an astrophysicist
and scientific advisor to the Pope, the first disk was lowered into the
Mediterranean Sea by Fr. Pietro Angelo Secchi on April 20, 1865.
Sediment: Accumulated organic and inorganic matter on the bottom
of a waterbody. It includes decaying algae and weeds and soil and
organic matter from the drainage
Stormwater: Rainwater and snowmelt that runs off impervious
surfaces rather than infiltrate into the soil. Through
a drainage system of underground pipes, stormwater carries nutrients, fine
soils, plant debris, drippings from vehicles, and other substances from
the drainage basin.
Most of Eagan lakes, ponds, and wetlands are connected to the stormwater
Suspended solids: Algae,
dirt particles, grass clippings, and other material that floats in water
or is carried in stormwater without dissolving.
Transparency: The extent to which lake water is clear, indicating
the amount of light penetration into a lake. Transparency is typically
referred to as a depth measured with a Secchi
disk. Water transparency tells a lot about a lake's
water quality. It provides an indirect measure of the amount of suspended
material in the water, which in many cases includes algae.
Long-term transparency monitoring helps detect signs of degradation to
a lake. Generally, the sooner water quality problems are detected,
the easier and less expensive it is to restore the lake to its previous
Trophic State Index: A water quality index developed by R. E.
Carlson in 1977 that uses three parameters (total phosphorus,
to characterize nutrient levels of waterbodies on a scale from 1 to 100.
The index is widely used because data collection for it is easy and economical,
there is a relatively large existing database, and it takes into account
both algae growth
and suspended solids.
Watershed: See Drainage
Wetland: Land that is transitional between terrestrial and aquatic
systems where the water table is usually at or near the surface or the
land is covered by shallow water. According to Minnesota law, a wetland
is defined by the presence of: 1) soils with characteristics developed
under wet conditions, 2) surface or subsurface water, and 3) vegetation
that is growing where at least periodically deficient oxygen exists as
a result of excessive water content.
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