24 



PROBLEMS OF LAKE BIOLOGY 



have in some measure answered our ques- 

 tions as to which are most important and 

 to what extent their separate eifeets can 

 be recognized. We may now ask what gen- 

 eral conclusions or picture of the whole 

 field can be offered. 



The number of environmental factors in- 

 volved makes it difficult to bring them into 

 a single picture. However, Grote (1934) 

 has made a noteworthy attempt to do this 

 in his ecological total spectrum (Fig. 6). 

 It will be noted that he lists the factors and 

 attempts to show the condition with respect 

 to each at the time of vernal circulation and 

 during summer stagnation. In the central 

 section he indicates the optimum and limit- 

 ing conditions for an autotrophic plankton 

 organism. In the lower section he super- 

 imposes the upper curves. The procedure 

 is highly theoretical but it merits careful 

 consideration. However, it is our conten- 

 tion that these factors do not act indepen- 

 dently and w^e must look to another field for 

 a natural synthesis of our conclusions. 



A proper scheme of lake types should 

 provide a logical grouping of lakes with 

 respect to these factors. On a basis of the 

 material discussed above we feel that there 

 are only two valid lake types, eutrophic and 

 oligotrophic, and these intergrade. Dys- 

 trophy is considered as a disturbing fac- 

 tor which may affect the natural grada- 

 tion from eutrophy to oliogotrophy at any 

 point. Certain features such as shallow- 

 ness, smaller area, V-shaped bottom con- 

 tour, higher temperature, and plentiful 

 supplies of nitrogen, phosphorus and cal- 

 cium have been indicated as conducive to 

 eutrophy while greater depth, larger area, 

 U-shaped bottom contour, lower tempera- 

 ture and lesser supplies of nitrogen, phos- 

 phorus and calcium tend to produce oligo- 

 trophy. If in any lake, all factors are 

 favorable (harmonious), extremes of eutro- 

 phy or oligotrophy will result. In most 

 lakes the degree of eutrophy or oligotrophy 

 represents the balance of certain favorable 

 factors over others of an unfavorable (dis- 

 harmonious) nature. 



In a survey such as this, it is considered 

 fitting to suggest problems or fields in 

 which there is urgent need for research. 



This has already been done, to some extent, 

 by reference to the numerous unsolved 

 problems and it may be ]iresumptuous to 

 make more specific suggestions. Personally 

 we are impressed with the need for studies 

 of the various activities of lake bacteria, 

 the role of organic matter in lake water and 

 the question of deep water currents. No 

 doubt these and other gaps in our knowl- 

 edge are evident to most limnologists who 

 merely await the opportunity to attack the 

 problems involved. 



Emphasis might be placed on the desir- 

 ability of certain attitudes in research in 

 this field. Strom and others have urged 

 the need for a more dynamic view, to con- 

 sider the time factor and rates of produc- 

 tion rather than static conditions and abso- 

 lute amounts. Such an attitude is par- 

 ticularily needed in that most difficult of all 

 limnological problems, productivity. 



Eeferences Cited 



Alsterberg, G. 1927. Die Sauerstoffschichtung 



der Seen. Bot. Notiser. 

 . 1929. tJber das aktuelle und al)solute 



Oo-Def3zit der Seen im Sommer. Bot. Notiser. 

 . 1930. Die thermisehen und eliemischen 



Aiisgleiche in den Seen zwisclien Boden- und 

 Wiisserkontakt sowie ilire biologische Bedeutung. 

 Int. Ecv. Hydroh., 24. 



Antonescu, C. S. 1931. uber das Yoi-kommen 

 eines ausegepragten metalimnisclien Sauerstoff- 

 niinimums in eineni norddeutsclien See. Arch. 

 Hi/droh.. 22. 



Atkins, W. E. G. 1926. A Quantitative Consid- 

 eration of Some Factors Concerned in Plant 

 Growth in Water. J. Conseil. Int., 1. 



Birge, E. a. 1916. The Heat Budgets of Ameri- 

 can and European Lakes. Trans. Wis. Acad. Sci., 

 18. 



Birge, E. A., and Juday, C. 1911. The Inland 

 Lakes of Wisconsin. The Dissolved Gases of the 

 Water and Their Biological Significance. BuU. 

 Wis. Geol. Nat. Hist. Survey, 22. 



— . 1927. The Organic Content of the 



Water of Small Lakes. Froc. Am. Phil. Soc, 66. 



. 1934. Particulate and Dissolved Or- 



ganic Matter in Inland Lakes. Ecol. Monog., 4. 

 Brehm, v., and Ruttner, F. 1926. Die Biocono- 



sen der Lunzen Gewasser. Int. Rev. Hydroh., 16. 

 Einsele, W\ 1936. Vber die Beziehungen des 



Eisenkreislaufs zuni Phosphatkreislauf im eutro- 



phen See. Arch. Hydroh., 29. 

 . 1938. Uber cheniisehe und kolloidchem- 



ische Vorgange in Eisen-Phosphat-Systemen unter 



limnochemischen und limnogelogischen Gesichts- 



punkten. Arch. Hydroh.. 33. 



