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Living in the presence of oxygen. Most organisms are aerobic and must have oxygen available in order to survive.
Mostly aquatic, non-vascular plants that float in the water or attach to larger plants, rocks, and other substrates. Also called phytoplankton when floating In the water, these individuals are usually visible only with a microscope. They are a normal and necessary component of aquatic life, but excessive numbers can make the water appear cloudy and colored, which may discourage human use.
Heavy growth of algae in and on a body of water, often a result of high nutrient concentrations when occurring frequently through the year, although blooms are a normal occurrence in spring in many area lakes.
The acid-neutralizing or buffering capacity of water. It is primarily a function of the carbonate, bicarbonate, and hydroxide content in water. The lower the alkalinity, the less capacity the water has to absorb acids without lowering pH, becoming more acidic.
A nitrogen-containing substance which may indicate recently decomposed plant or animal material.
Living in the absence of oxygen. Some bacteria can survive and grow without oxygen present.
No oxygen present in the system; see anaerobic.
The sum of a group of numbers divided by the total number of values in the group.
A map showing the bottom contours (shape) and depth of a lake.
Bottom area of the lake which hosts the community of organisms (benthos) that live in or on the sediment.
See Invertebrates.
The communities of aquatic life which dwell in or on the bottom sediments of a water body.
Space occupied by organic matter.
See Cyanobacteria.
See Watershed.
A green pigment found in plants that make their own food, including algae. It plays an important part in the chemical reactions of photosynthesis. A measurement of chlorophyll-a (one type of chlorophyll) is commonly used as way to estimate the abundance of algae in water.
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. One chlorophyte species, Botryococcus, turns bright orange under certain conditions, but is not toxic like the marine red tides.
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, which been used for reconstruction studies of past lake environments (paleolimnology).
Discharges of combined sewage and stormwater into water bodies during very wet or storm weather. These discharges occur to relieve the sewer system as it becomes overloaded with normal sewer flow and increased storm run-off. The term is also used to denote a pipe that discharges those overflows.
The amount of one substance in a given amount of another substance, such as the weight of a chemical in a liter of water or the number of animals in a cubic meter of space.
A measure of water's capacity to convey an electric current. It is related to the total amount of dissolved charged substances in the water. Therefore, it can be used as one general indicator of water quality. It is often used as a surrogate for salinity measurements.
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 natural food chains.
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.
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.
Oxygen that is dissolved in the water. Certain concentrations are necessary for life processes of aquatic animals. The oxygen is supplied by the photosynthesis of plants, including algae, and by aeration through contact of the surface water with the atmosphere and mixing. Oxygen is consumed by animals and plants at night when photosynthesis cannot take place, as well as bacterial decomposition of dead organic matter (plant matter and animal waste).
Any complex of living organisms, along with all other factors that affect them and are affected by them. This includes plants, animals, the nutrients that sustain them, and all of the other environmental conditions necessary for successful maturation and reproduction.
Liquids discharged from sewage treatment plants, septic systems, or industrial sources to surface waters.
The warmer, less dense, surface waters of a lake that are thermally separated from the colder (hence denser) water at the bottom of the lake (metalimnion and hypolimnion) when a lake is stratified by temperature.
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.
Waters in which conditions are right for algae to maintain large populations and biovolumes, generally related to nutrient supply. Trophic state indicators above 50 are classified as eutrophic.
The physical, chemical, and biological changes associated with enrichment of a body of freshwater due to increases in nutrients from a variety of sources.
The mixing of thermally stratified waters that destroys the stratification of the water column 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.
Bacteria from the intestines of warm-blooded animals. Most of the bacteria are not in themselves harmful, but they are measured or counted as indicators of the possible presence of harmful bacteria.
See chlorophyte algae.
Water located and moving beneath the surface of the earth. The water in the ground is supplied by the seepage (percolation) of rainwater, snowmelt, and other surface water into the soil. Some groundwater may be found far beneath the earth surface, while other groundwater may be only a few inches from the surface. Groundwater discharges into lowland streams at a relatively constant rate, which maintains their baseflow during periods of dry weather such as Pacific Northwest summers.
Organic substances incompletely broken down by decomposers such as bacteria, often due to cool, wet conditions that hamper decomposition rates. Humic acids are generally large molecular organic acids that persist in water, often giving the water a yellow or brown color.
The science dealing with the properties, distribution and circulation of water. The term usually refers to the flow of water on or below the land surface before reaching a stream or lake.
The colder, dense, deep water layer in a thermally stratified lake, lying below the epilimnion and metalimnion, and isolated from surface influences.
 Animals without internal skeletons. Some require magnification to be seen, while others such as worms, insects, and crayfish are relatively large. Benthic invertebrates are an important link in the food chain for fish and can be used as an excellent indicator of stream and river water quality. In general, higher numbers of species present in invertebrate communities indicate water bodies with good environmental conditions.
Having to do with lakes, similar to the term marine for oceanic systems.
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.
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.
The nutrient that is in lowest supply relative to the demand. The limiting nutrient will be the one that is exhausted first by algae, which require many different nutrients and light to grow. Increasing the amount of the limiting nutrient will result in increased algal production, but as soon as the limiting nutrient is exhausted, growth stops. Phytoplankton growth in lake waters of temperate lowland areas is generally phosphorus limited.
The study of lakes and inland waters as ecosystems.
The shallow region in a body of water which can be inhabited by rooted aquatic plants. This is dependent on the ability of light to penetrate the water. Specific animal and algae groups also inhabit this zone.
The portion of a water body extending from the shoreline lakeward to the greatest depth occupied by rooted plants.
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 within a lake among sediment, organisms and water is sometimes referred to as “internal loading.”
The rate at which of a substance is added to a water body. For example, streams add nutrients to lakes at various loading rates as in "500 kilograms per year (500 kg/yr)" or "227 pounds per year (227 lb/yr)."
rooted and floating aquatic plants, larger (macro-) than the phytoplankton and most often belonging to the higher, vascular plant groups
(see Average) A representative value for a group derived by summing a group of numbers and dividing by the total number of values in the group.
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.
Waters that promote algae growth at rates intermediate between eutrophy and oligotrophy. Trophic state indicators between 40 and 50 are classified as mesotrophic.
The layer of water in a lake between the epilimnion and hypolimnion in which the temperature, and thus water density, change rapidly over a short distance.
A lake which has one mixing and one stratification event per year. If a lake does not freeze over in the winter, the winter winds will mix the waters of the lake throughout the season. In summer, the lake resists mixing and becomes stratified because the surface waters are warm (light) and the bottom waters are cold (dense). Deep lakes in the Puget lowlands are monomictic lakes.
Two types of nitrogen compounds. These nutrients are forms of nitrogen that algae may use for growth.
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.
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 lawns or landscaping).
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
Any chemical element, ion, or compound required by an organism for growth and reproduction.
A condition of lakes characterized by low concentrations of nutrients and algae and resulting high water transparency. An oligotrophic lake has smaller amounts of nutrients than a mesotrophic or eutrophic lake. Trophic state indicators below 40 are classified as oligotrophic.
Microorganisms that can cause disease in other organisms or humans, animals, and plants. Pathogens include bacteria, viruses, fungi, or parasites found in sewage, in runoff from farms or city streets, and in water used for swimming. Pathogens can be present in municipal, industrial, and nonpoint source discharges.
Deep, open water area of a lake away from the edge of the littoral zone towards the center of the lake.
Measure of the acidity of water on a scale of 0 to 14, with 7 representing neutral water. A pH less than 7 is considered acidic and above 7 is basic, also sometimes called alkaline.
A pigment compound resulting from the degradation of chlorophyll a, usually found in algal remains, suspended organic matter, or bottom sediments.
One of the elements essential as a nutrient for the growth of organisms. In western Washington lakes, it is usually the nutrient in shortest supply relative to the needs of the algae (also referred to as the limiting nutrient). Phosphorus occurs naturally in soils, as well as in organic material. Various measures of phosphorus in water samples are made, including total-phosphorus (TP) and the dissolved portion of phosphorus-containing molecules (orthophosphate).
The upper water in a lake in which light penetrates enough to enable plants to carry out photosynthesis.
The production of organic matter (carbohydrates) from inorganic carbon and water, utilizing the energy of light. In general, plants are equipped to carry out this process, while animals cannot.
Free floating microscopic organisms that photosynthesize (includes both algae and cyanobacteria).
An input of pollutants into a water body from discrete sources, such as municipal or industrial outfalls.
The first stage of wastewater treatment involving removal of debris and solids by screening and settling.
The production and accumulation of organic matter, usually measured over a certain period of time.
A structure used to move wastewater uphill, against gravity.
These algae, also called dinoflagellates, are solitary and mobile, with two appendages (“flagella”) that move the cell through water using whip like 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 not been considered dangerous.
A structure that controls the flow of wastewater from two or more input pipes to a single output. Regulators can be used to restrict or halt flow, thus causing wastewater to be stored in the conveyance system until it can be handled by the treatment plant.
The average length of time that a molecule of water or a chemical within the water, such as phosphate, remains in a lake.
Salmon, trout, char and whitefish species of fish belonging to the taxonomic family Salmonidae.
Measure of transparency of water obtained by lowering a 10 inch black and white (or all white) disk into water until it can no longer be seen. The Secchi depth is the length of line let out by the observer between when the disk disappears from view and then re-appears with lowering and raising through the water column.
Following primary treatment, bacteria are used to consume organic wastes. Wastewater is then disinfected and discharged through an outfall. Nutrient concentrations are not decreased with secondary treatment.
Solid material deposited in the bottom of a lake over time, carried in by wind and water inputs, as well as that produced in the lake by plants and animals.
A method for controlling combined sewer overflow whereby the combined sewer is separated into both a sanitary sewer and a storm drain, as is the practice in new development.
That portion of wastewater that is composed of human and industrial wastes from homes, businesses, and industries.
A legally established allowable limit for a substance or characteristic in the water, based on measurable criteria. Enforcement actions by the appropriate agencies can be taken against parties who cause violations.
Water that is generated by rainfall and is often routed into drain systems.
A layering effect produced by the warming of the surface waters in many lakes during summer. Upper waters are progressively warmed by the sun and the deeper waters remain cold. Because of the difference in density (warmer water is lighter), the two layers remain separate from each other: upper waters "float" on deeper waters and wind induced mixing occurs only in the upper waters. Oxygen in the bottom waters may become depleted. In autumn as the upper waters cool, the whole lake mixes again and remains mixed throughout the winter, or until it freezes over, when a wintertime stratification may persist beneath ice layers on the surface.
Depth in a stratified lake where the greatest change in temperature occurs. Separates the epilimnion from the hypolimnion (see metalimnion).
Particles, both mineral (clay and sand) and organic (algae and small pieces of decomposed plant and animal material), that are suspended in water.
Causing death, disease, cancer, genetic mutations, or physical deformations in any organism or its offspring upon exposure, ingestion, inhalation, or assimilation.
A measure of the clarity of water in a lake, which is measured by lowering a standard black and white Secchi disk into the water and recording the depth at which it is no longer visible. Transparency of lakes is generally affected by the color of the water and the amount of material suspended in it. In colorless water bodies of the Puget lowland, the transparency of the water in summer is determined by the amount of algae present in the water. Suspended silt particles may also have an effect, particularly in wet weather.
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 the relationships derived between total phosphorus, chlorophyll-a or secchi transparency measurements and algal biovolume in a study conducted by Robert Carlson in 1977.
Cloudiness in water caused by the suspension of tiny particles (algae or detritus).
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.
A water sampling device that allows collection of a water sample from a desired depth without contaminating the sample with water from other depths.
Total flow within the sewage system. In combined systems, it includes sewage and stormwater.
Water in a lake between the surface and the bottom sediments. Used in vertical measurements taken to characterize lake water.
Legal term from the state Shoreline Management Act, which recognizes particular bodies of water and sets criteria and standards for their protection.
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.
The surrounding 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.”
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.
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.