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Glossary of lake terms

Glossary of lake terms

King County, Washington

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Aerobic: Living in the presence of oxygen. Most organisms are aerobic and must have oxygen available in order to survive.

Algae: Single celled nonvascular plants occurring singly or in groups (colonies). They contain chlorophyll-a, used to produce their own food by means of photosynthesis. Algae form the base of the food chain in aquatic environments.

Algal Bloom: Heavy growth of algae in and on a body of water, often a result of high nutrient concentrations.

Alkalinity: The acid neutralizing capacity of a solution, usually related to the amount of carbonates present; buffering capacity.

Anaerobic: Living in the absence of oxygen. Some bacteria can survive and grow without oxygen present.

Anoxic: No oxygen present in the system; see anaerobic.

Average: (see “Mean”) 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 which hosts the community of organisms (benthos) that live in or on the sediment.

Biovolume: Space occupied by organic matter.

Bluegreen algae: See cyanobacteria.

Catchment Basin: See “Watershed.”

Chlorophyll-a: A green pigment in plants which is used to capture light energy and convert it, along with water and carbon dioxide, into food or organic material.

Chlorophyte algae: Bright green algae that occur in lakes as plankton, as well as forming tangled masses of filaments coming up from the lake bottom or near shorelines. This group does especially well in warm water and bright light and is usually abundant in summer. The species are very diverse, including several that look more like grassy aquatic plants than algae. Another species, Botryococcus, turns bright orange under certain conditions, but is not toxic like the marine red tides.

Chrysophyte algae: Golden algae that are common members of the plankton in small lakes. They can be solitary or make colonies with large numbers of individuals. Some species make a protective silica sheath around the cells or have a covering of siliceous scales that preserve in lake sediments and have been used for reconstruction studies of past lake environments.

Concentration: The amount of one substance in a given amount of another substance, such as the weight of a chemical in a liter of water.

Conductivity: The measure of water’s capacity to convey an electric current. Increasing the numbers of dissolved ions also increases the conductivity.

Cryptophyte algae: Algae with a characteristic brown color, which are solitary and mobile, with two whip-like appendages (“flagella”). They are common residents of the plankton in lakes and are known as excellent food items for planktonic animals, thus supporting healthy food chains.

Cyanobacteria: Bacteria living in lakes and streams that make their own food instead of decomposing dead organisms and are very similar to freshwater algae in lake ecosystems. Many cyanobacteria grow especially well in lakes with high phosphorus content and are sometimes used as indicators of change due to human impacts through watershed development. Several species can make toxins dangerous to humans and other mammals if ingested. High concentrations of these cells in the water can result in closure of lakes to recreation or domestic use of water, although this has been relatively rare in occurrence historically.

Diatoms: Golden-brown algae that make intricate siliceous shells, which are found in lake plankton and attached to wood and rocks along shorelines. Many diatoms grow in cool water and low light, and are often abundant in winter and early spring in temperate lakes. Diatoms are nutritious food for planktonic animals and are important components of a healthy food chain in lakes. The shells preserve well in sediments and can be used in studies of lake history.

Dissolved Oxygen: The oxygen gas that is dissolved in water as O2

Ecosystem: Any complex of living organisms along with all other factors that affect them and are affected by them.

Epilimnion: The warmer, less dense, upper layer of a lake lying above cooler water (metalimnion and hypolimnion) in some seasons of the year.

Euglenophyte algae: Algae often found in ponds and smaller water bodies, particularly in the warm seasons of the year. They may be bright green, orange or brown. Euglenoid algae are mobile, using a whip-like appendage (“flagellum”) to move through the water. Some make an organic shell that encloses the cell, with the flagellum inserted through a pore.

Eutrophic: Waters in which algae grow into large populations and biovolumes, generally related to nutrient supply. Trophic state indicators above 50 are classified as eutrophic.

Eutrophication: The physical, chemical, and biological changes associated with enrichment of a body of freshwater due to increases in nutrients and sedimentation.

Fall Turnover: The mixing of thermally stratified waters that commonly occurs during early autumn. The sequence of events leading to a turnover includes: cooling of surface waters leading to a density change in surface water that produces convection currents from top to bottom, and circulation of the total water volume by wind action. Turnover generally results in uniformity of the physical and chemical properties of the water.

Green algae: See chlorophyte algae.

Humic Substances: Organic substances incompletely broken down by decomposers such as bacteria. Humic acids are large molecular organic acids that are present in water, often giving the water a yellow or brown color.

Hypolimnion: The colder, dense, deep water layer in a thermally stratified lake, lying below the metalimnion and removed from surface influences.

Lake Level – Water level of a lake in centimeters relative to a given point established when the first King County lake level gauge was installed at the lake.

Level I sampling: An annual volunteer monitoring program managed by the King County Lake Stewardship Program. The program involves daily measurements of precipitation and lake level, as well as weekly measurements of surface water temperature and water clarity, and observations on aquatic plant growth, lake use, and numbers of geese throughout the year.

Level II sampling: A seasonal volunteer monitoring program managed by the King County Lake Stewardship Program. The program involves biweekly measurements of surface water temperature and water clarity, collecting water samples for laboratory analysis, and observations on aquatic plant growth, lake use and numbers of geese from late April through October.

Limiting Nutrient: Essential nutrient for algae that is available in the smallest amount in the environment, relative to the needs of the organisms.

Limnology: The study of lakes and inland waters as ecosystems.

Littoral: The shallow region in a body of water which can be inhabited by rooted aquatic plants. This is somewhat dependent on the ability of light to penetrate the water. Specific animal groups also inhabit this zone.

Loading: The total amount of material (sediment or nutrients) entering a water body via streams, overland flow, precipitation, direct discharge, or other means over time (usually considered annually). Recycling of nutrients among sediment, organisms and water is sometimes referred to as “internal loading.”

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Mean: (see “Average”) The sum of a group of numbers divided by the total number of values in the group.

Median: The datum in a set of numbers that represents the exact center of the group: half of the numbers are smaller and the other half are larger.

Mesotrophic: Waters that promote algae growth at rates intermediate between eutrophy and oligotrophy. Trophic state indicators between 40 and 50 are classified as mesotrophic.

Metalimnion: The layer of water in a lake between the epilimnion and hypolimnion in which the temperature, and thus density, change rapidly over a short distance.

Monomictic: A water pattern of lakes in which thermal mixing and stable stratification alternate once per year.

NH3-N – The ammonia nitrogen portion of total nitrogen in a sample. Increases in the absence of oxygen.

NO2-3 – Nitrite and nitrate portions of total nitrogen in a sample.

Nitrogen: One of the elements essential for the growth of organisms. Nitrogen is most abundant on the earth in the form of N2, comprising 80% of the atmosphere, but is usually taken up by plants in the forms NO3, NO2 and NH3.

Nonpoint Source Pollution: Pollution from diverse sources difficult to pinpoint as separate entities and thus more complicated to control or manage. Examples of “nonpoint sources” include area-wide erosion (as opposed to landslides or mass wasting), widespread failure of septic systems, certain farming practices or forestry practices, and residential/urban land uses (such as fertilizing or landscaping).

Noxious weeds: A legal definition of by the State of Washington that lists specific non-native, invasive plants known to destroy habitat for other plants or animals, or documented as having caused serious agricultural problems. A list of names is published each year by the Department of Ecology which lists the level of threat posed by the plants and the legal responsibilities of owners who find them growing on their properties. Individual counties may modify the list to fit specific distributions within the county. King County Noxious Weed Control Program.

Nutrient: Any chemical element, ion, or compound required by an organism for growth and reproduction.

Oligotrophic: Waters that are nutrient poor and which, as a result, have little algal production. Trophic state indicators below 40 are classified as oligotrophic.

Orthophosphate (OPO4) – The dissolved portion of phosphorus that is available for biological uptake.

pH: The negative logarithm of the hydrogen ion concentration in a solution. This is a measure of acidity. pH decreases as acidity increases. Values below 7 are considered acidic.

Precipitation – Rain or snow. Volunteer lake monitors record daily rain in millimeters (or snow measured in millimeters of water equivalent).

Pheophytin: A pigment compound resulting from the degradation of chlorophyll a, usually found in algal remains, suspended organic matter, or bottom sediments.

Phosphorus: One of the elements essential for growth and reproduction. Phosphorus is often the limiting or least available nutrient for plant growth in temperate freshwater ecosystems. The primary original source of phosphorus is from the earth in the form of phosphate rocks.

Photic Zone: The upper water in a lake in which light penetrates enough to enable plants to carry out photosynthesis.

Photosynthesis: The production of organic matter (carbohydrates) from inorganic carbon and water, utilizing the energy of light.

Phytoplankton: Free floating microscopic organisms that photosynthesize (algae and cyanobacteria).

Productivity: The production and accumulation of organic matter, usually measured over a certain period of time.

Pyrrhophyte algae: These algae, also called dinoflagellates, are solitary and mobile, with two appendages (“flagella”) that move the cell through water using whiplike motions. In marine waters, certain species are known for making toxic “red tides” that can render shellfish poisonous for humans. Freshwater dinoflagellates are not known to produce toxins and, while they may color the water brown or red when abundant, have never been considered dangerous.

Residence Time: The average length of time that water or a chemical within the water, such as phosphate, remains in a lake.

Secchi Disk: A 20-cm (8-inch) diameter disk painted white and black in alternating quadrants. It is used to measure the transparency of the water in lakes.

Sediment: Solid material deposited in the bottom of a lake over time.

Stratification: The separation of water into nearly discrete layers caused by differences in temperature and subsequent water density differences.

Thermocline: The zone of rapid temperature decrease in a vertical section of lake water. (See metalimnion.)

Transparency: Water clarity of a lake as measured with a Secchi disk.

Trophic State: A term used to describe the productivity of a lake ecosystem classifying it as one of three increasing categories based on algal biomass: oligotrophic, mesotrophic, or eutrophic. Trophic state indicators are calculated on the basis of total phosphorus, chlorophyll-a and secchi transparency measurements.

Turbidity: Cloudiness in water caused by the suspension of tiny particles (algae or detritus).

Turnover: The mixing of lake water from top to bottom after a period of stable stratification. This typically occurs in fall and is caused by wind and seasonal cooling of surface waters.

UV254 – A measure of water color; measures water sample’s absorbance of ultra violet rays at a wavelength of 254 nanometers.

Van Dorn Sampler: A water sampling device that allows collection of a water sample from a desired depth without contaminating the sample with water from other depths.

Watershed: The geographical area that contributes surface and groundwater flow to a stream, lake, or other body of water. This can also be referred to as the “catchment basin” or “drainage basin.”

Watershed Management: The planning and carrying out of actions, legal requirements and protective measures taken by agencies and citizens to preserve and enhance the natural resources of a drainage basin for the production and protection of water supplies and water-based resources.

Water Year (WY): A division of the earth year based on the general pattern of annual wet and dry periods rather than by calendar months. The U.S. Geological Survey uses the water year of October 1 through September 30 for data analysis.

Zooplankton: Small animals found in the water of lakes that possess limited powers of locomotion, and which feed on bacteria, algae, smaller animals, and organic detritus present in the water.

For questions about lakes in King County, please contact or call the Water and Land Resources Division front desk at 206-477-4800.