86 



PROBLEMS OF LAKE BIOLOGY 



visited. The extreme ease was found in 

 Tieob Lake, 80 meters deep, with no oxygen 

 bek)w 4 meters. Large accumulations of 

 hydrogen sulphide were present in the 

 hypolinniion of most lakes of the islands. 

 Worthington and Ricardo (1936) also have 

 found that the East African lakes do not 

 fit into the old classification. They are 

 eutrophic with high productivity, but oligo- 

 trophic in the sense that oxygen is present 

 in appreciable quantities at all de^Dths. 

 This is contrary to Thienemann 's conclusion 

 that true oligotrophy could not exist in the 

 tropics and that all tropical lakes were 

 eutrophic. High alkalinity was found to 

 be a factor in the unusual conditions in the 

 East African lakes. "Woltereck found that 

 there are eutrophic, mesotrophic, and oligo- 

 trojihic lakes in the tropics which may be 

 very near one another. The extremes, how- 

 ever, are much more pronounced than in 

 temperate lakes. Eutrophy, when it is 

 reckoned throughout the year, is greater, 

 and the same is true of extremelv oligo- 

 trophic lakes such as the great Lake Towoeti 

 in Celebes where the oligotrophy was so 

 great that the Secchi disc was visible at 

 24 1/3 meters below the surface. 



In temperate regions the extreme oligo- 

 trophic lakes tend to be in the northern part 

 of the north temperate zone or in high 

 mountains. Flathead Lake in ]\Iontana 

 which has been studied by Young and others 

 (Young 1935) shows a typical oligotrophic 

 mountain lake with deep cold water and 

 low plankton productivity which is mainly 

 distributed in the upper third or fourth of 

 the lake. Mountain Lake, Virginia, (Hutch- 

 inson and Pickford 1932), is oligotrophic in 

 the chemical composition of the water and 

 mud in the character of its phytoplankton, 

 and also in the poverty of its littoral and 

 bottom fauna. The productivity of the 

 epilimnion, however, is eutrophic due to the 

 shallowness of the lake basin. Hutchinson 

 (1937) in studying the extremely high 

 mountain lakes of Tibet, where the altitude 

 ranged from 4,241 to 5,297 meters (nearly 

 17,500 feet maximum), found that many 

 showed considerable plankton production 

 and were to be considered as mesotrophic. 



The reasons suggested were the greater arid- 

 ity of Tibet, which caused greater concen- 

 tration of nutrient materials in the lakes, 

 and great solar radiation, which also prob- 

 ably increased productivity. 



Plankton productivity of lakes showing 

 unusual conditions has been studied by sev- 

 eral workers in Michigan, particularly. 

 Raymond (1937) found that a marl lake had 

 small plankton production, the plankters 

 being apparently restricted to those which 

 could withstand the conditions present in a 

 marl lake. Large amounts of calcium were 

 believed to be detrimental to plankton pro- 

 ductivity due to the formation of bicar- 

 bonate which robbed carbon dioxide and 

 influenced the pH as a consequence. The 

 deposition of calcium carbonate also formed 

 a type of bottom unsuited for rooted 

 aquatics which would result in an absence 

 of turnover of nutrient materials. Welch 

 (1936a and 1936b) also found low produc- 

 tivity in both acid and basic bog lakes. In 

 the basic bog lake, while the productivity 

 was low, a much larger number of species 

 of plankters was found than had previously 

 been reported for bog lakes. The produc- 

 tivity decreased as the summer progressed. 

 The same conditions were found in a retro- 

 grading bog lake (Welch 1938). Here 

 there were few rooted aquatics, but their 

 number showed some increase with the re- 

 turning alkaline conditions. 



Various indexes of productivity have 

 been suggested. Klugh (1926) proposed 

 that the abundance of rooted aquatics might 

 be an index of productivity, and this con- 

 tention is supported by the work on marl 

 and bog lakes to a considerable extent. 

 Very recently Hutchinson (1938) has found 

 that in some lakes, at least (Green, Mendota, 

 and Black Oak in Wisconsin and Foreso in 

 Denmark), the rate of development of the 

 absolute oxygen deficit in the hypolimnion, 

 per square centimeter of hypolimnion sur- 

 face, is proportional to the mean standing 

 crop of plankton per unit area of lake sur- 

 face. This supports Str0m 's (1932) earlier 

 method in harmonic temperature lakes. 

 This calculation can thus be used as a mea- 

 sure of productivity where gravimetric de- 



