systems which collect nutrients from the water. 



Species designated as weeds are not necessarily 

 such in all places and at all times. For example, 

 many submersed, floating, and emersed plants that 

 normally interfere with boating, swimming, and 

 fishing are regarded as desirable growths in water- 

 fowl refuge areas. Rooted plants with floating 

 leaves, such as water lillies and watershield, and 

 those that float upon the surface, such as water 

 hyacinth, elodea, parrotweed, alligatorweed, and 

 duckweed, are considered highly objectionable for 

 many water uses. In clear water areas, however, 

 where artificial or natural fertilization is moderate, 

 the removal of these surface-shading plants may 

 permit sunlight to penetrate to the bottom muds 

 and submersed plants soon will occupy these 

 waters. These submersed plants generally are more 

 objectionable in an area than the original surface- 

 covering plants. 



Most emersed, marginal, and a few submersed 

 plants and filamentous algae produce growths that 

 provide a suitable habitat for the development of 

 anopheline and other pest-type mosquitoes as well 

 as a hiding place for snakes. They are excellent 

 habitats for damselflies and some aquatic beetles. 



Most rooted and floating aquatic plants can 

 seriously interfere with navigation of small rec- 

 reational craft and large commercial boats in in- 

 fested areas. Such problems are prevalent in 

 intercoastal waterways and in some streams in 

 the Gulf States area. Water shortages due to con- 

 sumption by undesirable aquatic plants or reduc- 

 tion in carrying capacity of an irrigation or drain- 

 age canal through excessive vegetation can result 

 in decreased crop quality, yield, or even crop 

 failure. 



Submersed and emersed weeds consume nutri- 

 ents, either available or added, that could other- 

 wise be used to grow desirable planktonic algae 

 in impounded waters. Thus, the presence of ex- 

 cessive rooted plants may reduce total fish pro- 

 duction in the infested body of water. Extensive 

 growth of weeds provides dense cover that allows 

 the survival of excessive numbers of fish resulting 

 in overcrowding and stunting as well as interfer- 

 ing with harvesting the fish by hook and line or 

 other methods. There is evidence that rank growths 

 of submersed, emersed, or floating weeds may de- 

 plete the dissolved oxygen supply in shallower 

 water and that fish tend to leave these areas if 

 there are open-water areas available of better 

 quality. Although they carry on the process of 

 photosynthesis, their multicellular structure often 

 makes them less effective in re-oxygenating the 

 water. 



All the elements essential for plant growth are 



yet to be determined. Some of the elements known 

 to be important are nitrogen, phosphorus, potas- 

 sium, magnesium, calcium, manganese, iron, sili- 

 con (for diatoms), sulfur (as sulfates), oxygen, 

 and carbon. In many habitats, abundance of the 

 first two elements, N (nitrogen) and P (phos- 

 phorus), promotes vegetative production if other 

 conditions for growth are favorable. Most algae 

 also require some simple organics, such as amino 

 acids and vitamins, and many trace elements, such 

 as manganese and copper. Not only are the various 

 factors important, but their relative abundance and 

 combined affect can be of even greater importance. 

 Limited laboratory studies made to date indicate 

 that different species of algae have somewhat dif- 

 ferent phosphorus requirements with the range 

 of available phosphorus usually falling between 

 0.01 and 0.05 mg/1 as phosphorus. At these levels, 

 when other conditions are favorable, blooms may 

 be expected. As has been pointed out by the Sub- 

 committee on Water Quality Criteria for Public 

 Water Supply, the total phosphorus is of outstand- 

 ing importance. While there is no set relationship 

 between total and available phosphorus (because 

 the ratio varies with season, temperature, and plant 

 growth), the total phosphorus is governing as it 

 is the reservoir that supplies the available phos- 

 phorus. It is believed that allowable total phos- 

 phorus depends upon a variety of factors; e.g., 

 type of water, character of bottom soil, turbidity, 

 temperature, and especially desired water use. Al- 

 lowable amounts of total phosphorus will vary, 

 but in general it is believed that a desirable guide- 

 line is 100 lUg/l for rivers and 50 ;Ug/l where 

 streams enter lakes or reservoirs (recommended 

 by the Public Water Supply Subcommittee). 



The nitrogen-phosphorus ratio is also of impor- 

 tance. The ratio varies with the water, season, tem- 

 perature, and geological formation, and may range 

 from 1 or 2:1 to 100:1. In natural waters, the 

 ratio is often very near 10:1, and this appears to 

 be a good guideline for indicating normal condi- 

 tions. 



The major sources of nitrogen entering fresh 

 waters are atmospheric (approximately 5 lbs/ 

 acre/year), (Hutchinsen, 1957), domestic sewage 

 effluents, animal and plant processing wastes, ani- 

 mal manure, fertilizer and chemical manufacturing 

 spillage, various types of industrial effluents, and 

 agricultural runoff. 



The major sources of phosphorous entering 

 fresh waters are domestic sewage effluents (in- 

 cluding detergents), animal and plant processing 

 wastes, fertilizer and chemical manufacturing spill- 

 age, various industrial effluents, and, to a limited 

 extent, erosion materials in agricultural runoff. 



462-246 0-72-5 



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