With identification of species in a particular plant community, it will be possible 

 to determine their optimum needs to attain their best growth and reproductive 

 capacity, or likewise through investigation and research find some means for their 

 control that could be recommended elsewhere. Without the identity of these 

 organisms it would be impossible to accomplish this work. 



Various methods have been used to control aquatic weeds, but undoubtedly 

 the most efficacious though potentially dangerous to the world's life is the use 

 of the many various herbicides. The use of herbicides in the elimination of nuisance 

 aquatic angiosperms occasionally kill fish and desirable organisms. The decay 

 of dead plants, too, can deplete the dissolved oxygen to the extent of killing all 

 aerobic organisms. Often, also, the destruction of one nuisance organism only 

 makes room for invasion of another equally noxious organism. 



The oldest method of combatting aquatic weeds is that of manual and mechani- 

 cal control. This is still practiced, especially where small bodies of water and 

 streamways are involved. These methods include cutting and harvesting the plants 

 by hand, draining and drying out plus bulldozing the water areas to be cleaned, 

 mechanically mowing with cutters along banks or attached to boats, and dragging 

 and dredging the area to be cleaned. In line with these mechanical methods, on 

 Caddo Lake in northeastern Texas an unsuccessful, or rather unprofitable, attempt 

 was made to mechanically harvest the tremendous overgrowth of water plants and 

 to use the dried processed plants as peat or as a soil conditioner. If this activity 

 had been successful this would have been a direct economic way to control aquatic 

 weeds. 



The most idyllic type of aquatic weed control would be biological. Each noxious 

 species, however, would necessitate an individual study to discover in what way it 

 might be controlled — either parasitically by a fungus or insect, or by aquatic 

 herbivores such as certain African and Chinese fish. TTie manatee or sea cow 

 is the classic example of an aquatic herbivore in that it can consume huge amounts 

 of rooting and floating vegetation. Thus far, however, it has proved impractical or 

 biologically impossible to manipulate the manatee as a trained grazer. 



IV. Pollution in Aquatic and Wetland Habitats. 



Certainly there are no greater problems facing our civilization today than 

 those of contending with water and air pollution. Everything that we can learn 

 that will help us ultimately to manage these problems will be to our advantage. 

 It is hoped that the results of this research will provide us with some phase of 

 knowledge that will help us in combatting the corrosive situation of water pollu- 

 tion. 



As has been noted in our Preface, from the very beginning of this research 

 consideration of the environment has had an overwhelming influence upon our 

 interpretation of what plants were to be included in this work. This consideration 

 was long in progress before "environment" and "ecology" became household words 

 in the United States. This consideration of the environment was guided mainly by 

 our initial interest in this project: water as a critical resource in southwestern 

 United States. Since this resource is so critical in this part of the country, and 

 it will doubtless become more so with time, we thought that a knowledge of the 

 plants that are associated with water should be made available to everyone who 

 might be concerned with this vital commodity. We also hoped that our work would 

 encourage more appreciation for water as a vital resource and thus create more 

 respect for and a greater care of this rapidly vanishing and very necessary asset. 



Perhaps one of the most frustrating phases of this project was our not being 

 able to find areas that we could consider as "controls" for each of the ecosystems 



