photosynthesis fails to occur because of ineffective light 

 penetration. 



EuRYTOPic Organisms — Organisms with a wide range of 

 tolerance to a particular environmental factor. Ex- 

 amples are sludgeworms and bloodworms. 



EuTROPHiCATioN — The intentional or unintentional en- 

 richment of water. 



EuTROPHic Waters — Waters with a good supply of nu- 

 trients. These waters may support rich organic pro- 

 ductions, such as algal blooms. 



Facultative Aerobe — An organism that although fun- 

 damentally an anaerobe can grow in the presence of 

 free oxygen. 



Facultative Anaerobe — An organism that although fun- 

 damentally an aerobe can grow in the absence of free 

 oxygen. 



Fall Overturn — A physical phenomenon that may take 

 place in a body of water during the early autumn. 

 The sequence of events leading to fall overturn in- 

 clude: (1) Cooling of surface waters, (2) density 

 change in surface waters producing convection cur- 

 rents from top to bottom, (3) circulation of the total 

 water volume by wind action, and (4) vertical tem- 

 perature equality, 4 C. The overturn results in a uni- 

 formity of the physical and chemical properties of the 

 water. 



Fauna — The entire animal life of a region. 



Flatworms (Platyhelminthes) — Nonsegmented worms, 

 flattened from top to bottom. In all but a few of the 

 flatworms, complete male and female reproductive sys- 

 tems are present in each individual. Most flatworms 

 are found in water, moist earth, or as parasites in 

 plants and animals. 



Floating Aquatic Plants — Plants that wholly or in 

 part float on the surface of the water. Examples are 

 water lilies, water shields, and duckweeds. 



Flora — ^The entire plant life of a region. 



Fry (Sac Fry) — ^The stage in the life of a fish between 

 the hatching of the egg and the absorption of the 

 yolk sac. From this stage until they attain a length 

 of 1 inch, the young fish are considered advanced fry. 



Fungi (Fungus) — Simple or complex organisms without 

 chlorophyll. The simpler forms are one-celled; the 

 higher forms have branched filaments and complicated 

 life cycles. Examples of fungi are molds, yeasts, and 

 mushrooms. 



Fungicide — Substances or a mixture of substances in- 

 tended to prevent, destroy, or mitigate any fungi. 



Game Fish — Those species of fish considered to possess 

 sporting qualities on fishing tackle. These fish may 

 be classified as undesirable, depending upon their use- 

 fulness. Examples of fresh water game fish are sal- 

 mon, trout, grayling, black bass, muskellunge, walleye, 

 northern pike, and lake trout. 



Green Algae — Algae that have pigments similar in color 

 to those of higher green plants. Common forms pro- 

 duce algal mats or floating "moss" in lakes. 



Herbicide — Substances or a mixture of substances in- 

 tended to control or destroy any vegetation. 



Herbivore — An organism that feeds on vegetation. 



Heterotrophic Organism — Organisms that are depend- 

 ent on organic matter for food. 



Higher Aquatic Plants — Flowering aquatic plants. 

 (These are separately categorized herein as Emergent, 

 Floating, and Submerged Aquatic Plants.) 



HoLOMicnc Lakes — Lakes that are completely circu- 

 lated to the deepest parts at time of winter cooling. 



Hypolimnion — ^The region of a body of water that ex- 



tends from the thermocline to the bottom of the lake 

 and is removed from surface influence. 



Insecticide — Substances or a mixture of substances in- 

 tended to prevent, destroy, or repel insects. 



Invertebrates — Animals without backbones. 



LDm (see Median Lethal Dose). 



Lenitic or Lenitic Environment — Standing water and 

 its various intergrades. Examples of lenitic environ- 

 ments are lakes, ponds, and swamps. 



Life Cycle — The series of stages in the form and mode 

 of life of an organism: i.e., the stages between succes- 

 sive recurrences of a certain primary stage such as 

 the spore, fertilized egg, seed, or resting cell. 



Limnetic Zone — The open-water region of a lake. This 

 region supports plankton and fish as the principal plants 

 and animals. 



Limnology — The study of the physical, chemical, and 

 biological aspects of inland waters. 



Littoral Zone — The shoreward region of a body of 

 water. 



LoTic Environment — Running waters, such as streams 

 or rivers. 



Macro-organisms — Plants, animal, or fungal organisms 

 visible to the unaided eye. 



Median Lethal Dose (LD.-„) — The dose lethal to 50 

 percent of a group of test organisms for a specified 

 period. The dose material may be ingested or in- 

 jected. 



Median Tolerance Limit (TLm)— The concentration of 

 the tested material in a suitable diluent (experimental 

 water) at which just 50 percent of the test animals 

 are able to survive for a specified period of exposure. 



Meromictic Lakes — Lakes in which dissovled sub- 

 stances create a gradient of density differences in 

 depth, preventing complete mixing or circulation of 

 the water. 



Microorganism — Any minute organism invisible or 

 barely visible to the unaided eye. 



MoLLUSciciDE — Substances or a mixture of substances in- 

 tended to destroy or control snails. Copper is com- 

 monly used. 



MoLLUSK (Mollusca) — A large animal group including 

 those forms popularly called shellfish (but not includ- 

 ing crustaceans). All have a soft unsegmented body 

 protected in most instances by a calcareous shell. 

 Examples are snails, mussels, clams, and oysters. 



Moss — Any bryophytic plant characterized by small, 

 leafy, often tufted stems bearing sex organs at the 

 tips. 



Motile — Exhibiting or capable of spontaneous move- 

 ment. 



Mycology — The study of fungi. 



Nekton — Swimming organisms able to navigate at will. 



Nematoda — Unsegmented roundworms or threadworms. 

 Some are free living in soil, fresh water, and salt 

 water; some are found living in plant tissue; others live 

 in animal tissue as parasites. 



Neuston — Organisms resting or swimming on the sur- 

 face film of the water. 



Osmole — The standard unit for expressing osmotic pres- 

 sure. One osmole is the osmotic pressure exerted by 

 a one-molar solution of an ideal solute. 



Oceanography — The study of the physical, chemical, 

 geological, and biological aspects of the sea. 



Oligotrophic Waters — Waters with a small supply of 

 nutrients; thus, they support little organic production. 



Organic Detritus — The particulate remains of disin- 

 tegrated plants and animals. 



108 



