Many species of plants have a beneficial effect upon water in contrast to those 

 that have a deleterious effect. For instance, it is realized that depletion of vegeta- 

 tion with accelerated stream-channel erosion decreases or entirely prevents fish 

 production through the reduction of available food and cover, the increasing of 

 water temperatures, and through sedimentation of spawning beds. To maintain a 

 continuity of fish and wildlife, generally, it is essential to know how to maintain 

 their habitat and to determine the biological requirements and relationship of 

 each species, especially in regard to cover and food for its normal growth. 



Another function of plant life in relation to water is its restraining action upon 

 rapidly moving streams so as to prevent excessive erosion of their banks. Only 

 those species that can tolerate having their roots submerged or that can grow in 

 saturated soils can survive on the margins of streams and lakes. Without such 

 species to exert control there would be no limit to the amount of erosion that 

 might occur. The knowledge to be gained from the study of aquatic and wetland 

 vegetation can thus be directed to the control of channel- and bank-erosion to 

 improve fish habitats and their food supply. 



In 1970, Boyd published a paper in which he pointed out the apparent poten- 

 tial of using aquatic angiosperms for the wholesale removal of nutrients from 

 effluents and natural waters. He further suggested that because of their food 

 qualities aquatic angiosperms could be harvested, dried and used as a feedstuff. 



Boyd found that the most suitable species for possible nutrient removal from 

 water were water hyacinth {Eichhornia crassipes), alligator weed (Alternanthera 

 philoxeroides) , water willow (Justicia americana) and cat-tail (Typha ladfolia). 

 All of these plants could be harvested by relatively simple means and they had a 

 relatively high nutritive value for use as feedstuff. A series of small holding ponds 

 into which effluents would be directed and in which plants would be grown for 

 nutrient removal were thought to be more satisfactory than just one large body 

 of water. 



There are problems in this proposed use of these aggressive aquatic angio- 

 sperms, foremost of which is the fact that, with the possible exception of Justicia 

 americana, they can become pernicious weeds. 



It is entirely possible that with more research man will be able to manipulate 

 native vegetation, even more than he does at present, for his welfare. The most 

 obvious and a long-standing practice has been the use of plants in erosion control. 

 There are many and various uses that might be made of aquatic angiosperms. 



There are numerous troublesome aquatic weeds throughout the world, and 

 there is no question whatsoever about the necessity to control the rampant growth 

 of many of these noxious vascular hydrophytes. The main question revolves around 

 how this should be done. Anyone who has seen a waterway that was once open 

 and clear but is now essentially dessicated and clogged by water-hyacinth {Eich- 

 hornia crassipes) or alligator weed {Alternanthera philoxeroides) must realize 

 that such is a situation that should and must be corrected. 



An improper balance of the flora and fauna, frequently caused by the undue 

 aggressiveness of such plants as Alternanthera and Eichhornia, can result in pollu- 

 tion and/or stagnation. Observations on the tolerance and aggressiveness of indi- 

 vidual species must be undertaken so as to understand better why some species are 

 limited in distribution while others are widely distributed. A detailed study of 

 the reproduction by seeds and vegetative means of some hitherto neglected species 

 will supplement that which is already known about other species. Mobility, aggres- 

 siveness, and various methods of distribution, such as the requirements needed for 

 dissemination, and the viability of seeds under different conditions should be 

 studied so as to better understand some of the yet unanswered problems of the 

 specialized adaptation of these plants to their environment. 



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