A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z


Aft: towards, at, or near the back end of a ship. 

Atrazine: atrazine is an organic compound widely used as an herbicide, and can be found in drinking water sources due to runoff from herbicide use on row crops. When present in drinking water in excess of the maximum contaminant level (MCL), atrazine poses health risks including reproductive difficulties and cardiovascular system problems for people with long-term exposure.


Ballast water: water that is carried on a ship to provide extra weight for balance and stability during movement and when load/unloading heavy materials. The ballast water is typically held in tanks near the bow and stern of the ship, and helps keep the ship upright.

Biomagnification: an increase in concentration of a particular substance, such as a toxic chemical, within the tissues of organisms at higher levels of the food web. Many pollutants introduced to the lake environment settle on the bottom sediments and are ingested by benthic organisms. Those benthic organisms accumulate toxins and are then eaten by animals higher up the food web, further concentrating these chemicals. For this reason, animals near the top of the food web (i.e. predatory fish such as lake trout and walleye, birds, and marine mammals) are most affected by the accumulation of chemical pollutants.

Benthic: relating to the bottom of a sea or lake; in reference to bottom-dwelling organisms such as plants and animals (i.e. benthic invertebrates; benthos).

Boom: pole used to hoist equipment; the lifting arm of a crane.

Bow: front end of a ship.


Chloride: chloride is a salt compound that forms when a metal combines with chlorine gas. When concentrated in water, chloride yields a noticeable odor and salty taste. Chloride also has corrosive and staining properties in water.

Cod end: the narrow end of a tapered trawl net.

Conductivity: conductivity measures the ability of an electrical current to pass through water. This ability is affected by factors like temperature (warmer water yields greater conductivity) and presence of inorganic dissolved solids (variable affect on conductivity based upon the charge of their ions). While bodies of water have varied conductivity based upon the geology of the materials it flows through, baseline measurements can be recorded for any body of water so that any observed changes can then be used as a indicator of discharges/pollution to the water body.


DDT: (dichloro-diphenyl-trichloroethane) developed as a synthetic insecticide in the 1940s, DDT's persistence in the environment and adverse health effects on wildlife caused the EPA to issue a cancellation order in 1972 prohibiting its use domestically. DDT is classificed as a probable human carcinogen. For more information, visit the EPA website:

Dissolved Oxygen: (DO) a measure of the relative amount of oxygen that is dissolved within water. Standard units are milligrams per liter (mg/l) or parts per million (ppm).


Elutriation: a process used to separate materials, in particular to wash away very fine particles of sediment. This process is used to wash a sample (i.e. from the PONAR grab) so that fine particles are rinsed off and the larger components (i.e. benthic organisms) are strained for collection and further analyses.

Epilimnion: the uppermost layer in a thermally stratified lake. Due to its close proximity to the surface, the epilimnion receives the most sunlight and is more prone to gas exchange with the atmosphere and mixing from wind. For these reasons the water in the epilimnion is typically warmer, has a higher pH, and a higher dissolved oxygen concentration than the water in layers lying below (within the hypolimnion and thermocline).


Flame retardant: refers to a range of chemicals added into plastic, textile, and foam products to decrease the ignitability of materials and inhibt the combustion process. Studies have demonstrated that certain flame retardant chemicals can persist in the environment, bioaccumulate in people and animals, and have been shown to cause adverse developmental effects in animals. 


Hypolimnion: the bottom layer of a thermally stratified lake, nearest to the lake floor. This layer is typically the coldest in the summer and warmest in the winter. The lack of sunlight reaching this layer results in very limited (if any) photosynthetic organisms dwelling within the hypolimnion.


Lake of focus: Each year research efforts are intensified for one Great Lake, on a rotating basis. This means each Great Lake is the "lake of focus" once every five years. For example, in 2015 the lake of focus was Lake Michigan, in 2016 it is Lake Superior, 2017 is Lake Huron, 2018 is Lake Ontario, 2019 is Lake Erie. In 2020 the rotation starts over with Lake Michigan.

Legacy contaminants: toxic chemicals that persist in the enviroment long after they are introduced (often through industry) and biomagnify within the ecosystem.


Mysis: a shrimp-like crustacean in the Great Lakes that is a crucial component of the base of the food web in deep, cold waters. Mysis migrate within the water column each day, moving downwards towards areas with less sunlight during the day, and returning to higher depths at night— which is when mysis samples are collected from the Lake Guardian.


Niskin bottles: a modified version of the Nansen bottle, the Niskin bottle is a sampling device designed by Shale Niskin. It is used to collect a sample of water from a specific depth. The Niskin bottle is actually a cylindrical tube, usually made of plastic to minimize sample contamination, that allows water to flow through as it descends until it reaches the desired depth. At this point the bottle is shut and sealed with the sample inside, to be returned onboard for laboratory analyses. Typically, several Niskin bottles are carried on a rosette sampler so water samples can be collected from many, different depths.


PCBs: PCBs (Polychlorinated Biphenyls) are a group of man-made organic chemicals that were domestically manufactured starting in 1929 for commercial applications including: electircal, heat transfer, and hydraulic equipment; plasticizers in paints, plastics, and rubber products; and pigments, dyes, and carbonless copy paper. Their use in US industry was banned in 1979 due to environmental toxicity and detrimental health effects to animals and humans. For more information, visit the EPA website:

PFCs: (perfluorochemicals) chemicals of emerging concern that are found in non-stick and stain-resistant products, that have been shown to persist in the environment and cause health issues in humans. PFCs are used in a variety of consumer products such as surface coating for packaging products, cookware, and carpets.

Phosphorus: phosphorus and nitrogen are both vital nutrients in the aquatic food web. Phosphorus is typically a limiting factor in the growth of aquatic plants and animals, and therefore even a slight increase in phosphorus levels can have major implications including increased plant growth, algal blooms, decreased dissolved oxygen concentration, and thus the death of aquatic animals, invertebrates, and fish.

Phytoplankton: small photosynthesizing plants that float freely within a body of water. Phytoplankton and zooplankton are crucial to the lake ecosystem, as they make up the base of the foodweb.

PONAR: the PONAR grab was named after Great Lakes scientists, Charles E. Powers, Robert A. Ogle, Jr., Vincent E. Noble, John C. Ayers, and Andrew Robertson. This device is used to collect a sample of benthic sediments and organisms from the lake bottom.

Potable water: water that is safe for human consumption; i.e. drinking water.


R/V: research vessel; a ship designed and equipped to carry out scientific sampling and analyses at sea.


Stern: the rear or aft-most part of the ship.

Stratification: the separation into layers. Specifically in lake stratification, also known as thermal stratification, this refers to three layers identifiable by distinct water properties: the epilimnion (top), the thermocline (middle), and the hypolimnion (bottom). These properties vary by season, and lend to a habitable environment for plankton and other aquatic organisms.

Survey: a survey typically involves assessing chemical, biological, and physical properties of water, air, sediments, and aquatic organisms at 8-20 predetermined stations within each lake. Common analyses performed to samples collected include conductivity, temperature and depth (CTD) tests, testing water properties from various depths within the water column, studying contaminants within organisms collected in a plankton tow, and assessing benthic communities within a sediment sample.


Thermocline: the thermocline, sometimes referred to as the metalimnion, is the layer in a lake that separates the epilimnion near the surface from the hypolimnion near the bottom. The thermocline is characterized by the rapid change in temperature observed in this layer.


Vertical profile: the vertical profile for a water column is derived when a seabird (CTD) cast gives instantaneous data as it descends in the lake. This data is transmitted to a computer onboard the ship, providing a cross-sectional view of how various parameters (i.e. temperature, conductivity, pH, transparency) change with depth from the surface of the lake down to the bottom.


Water column: the water column is a conceptual concept representing a vertical cross-section in a body of water, from the lake’s surface to its bottom. This is useful in understanding how various parameters change from top to bottom in a lake (i.e. thermal stratification).

Winch: a machine used to lift or lower heavy objects, using containing a drum with a rope/chain/cable coiled around for lifting and lowering equipment.


Zooplankton: small animals that drift, float, or weakly swim within a water body. Zooplankton and phytoplankton are crucial to the lake ecosystem, as they make up the base of the foodweb.

The R/V Lake Guardian sails on behalf of the USEPA Great Lakes National Program Office, gathering environmental data to gauge the health of Great Lakes.

What's Happening?

The 2018 sampling season has begun! See the full schedule here »

Read about the Lake Guardian and Captain Mallard in the Illinois-Indiana Sea Grant newsroom »

Check out a social media recap of the 2016 Summer Survey »

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