Relationships of Phytoplankton 

 to Lake Productivity 



One of the more interesting problems confronting the aquatic bi- 

 ologist, and one of great practical importance, is that of productivity. 

 By this term is meant the quantity and quality of plant and animal 

 life which a body of water is capable of supporting. Limnology com- 

 prises such a heterogeneity of fields of inquiry that limnological 

 studies often seem to lack correlation. Nevertheless, the chief aim of 

 the limnologist is to devise methods of evaluating productivity of 

 aquatic habitats for both purely scientific and practical purposes. 

 Many of the problems that arise in shellfish culture, fish management 

 programs, and similar projects are problems of productivity. Consid- 

 erable progress in both the Old and New Worlds has been made 

 in deteiTnining index characters by which productivity of aquat- 

 ic environments can be evaluated and predicted; that is, a set 

 of characteristics or standards by which a lake may be measured in 

 respect to the quantity and kinds of plants and animals it can pro- 

 duce. Physical-chemical factors, however, seem to defy analysis be- 

 cause they interlock and interact in bewildering complexities. Since 

 they are never quite the same in any two lakes, they give each body 

 of water a distinct individuality. Thus limnologists find great diffi- 

 culty in determining a productivity index which can be generally 

 applied. A brief consideration of a few biological and physical- chem- 

 ical factors involved in the relationships of the algae to productivity 

 in lakes is in order here. 



No more graphic outline of the factors involved in production 

 is at hand than a diagram prepared by D. S. Rawson (1940). Re- 

 ferring to this diagram ( reproduced here, Fig. 7 ), it is of interest to 

 check through the factors, noting which ones have a direct bearing 

 upon the quantity and quality of the algae and other plant life, 

 factors which also influence animal life, of course, either directly or 

 indirectly. As complex as this chart may appear, it is, of necessity, a 

 simplified presentation of the multitudinous factors involved and 

 shows none of the ramifying and anastomosing interactivities of the 

 components. If the contributing agents shown in this chart were to 

 be analyzed further, the diagram would become very much in- 



[34] 



