PHYSICAL AND CHEMICAL FACTORS IN THE METABOLISM OF LAKES 



21 



mination liave been obstacles in the de- 

 velopment of this important field. Recent 

 improvements in chemical technique liave 

 opened up new possibilities. To cite a 

 special case, Strom (1933) has applied the 

 method used in marine waters by Schreiber 

 (1927). It consists of a direct evaluation 

 of tlie nitrogen and phosphorus in lake 

 waters by their effects on pure algal cul- 

 tures. The method is slow and laborious. 

 Its final utility cannot be predicted but its 

 directness has a strong appeal to the ecol- 

 ogist. 



In field studies it is frequently impossible 

 to have the analyses which might be desired 

 and as Strom (1930) points out we may 

 look for evidence of the nitrogen and phos- 

 phorus factor in its effects, for example, on 

 the oxygen curve. Xaumann (1932) also 

 discusses how the nitrogen and phosphorus 

 standard may be inferred from the phyto- 

 plankton and other indices of the economy 

 in the lake. Sucli inferences were the 

 basis for the original separation of eutro- 

 phic and oliogotrophic lake types. In some 

 cases the inferences may be better than the 

 actual measurement for the amounts pres- 

 ent may differ greatly from those avail- 

 able. Ruttner (1937) shows that in some 

 lakes in the Alps without complete circula- 

 tion there are large amounts of nitrogen 

 and phosphorus which are not available for 

 production. The aforementioned physio- 

 logical scarcity of phosphates is also a case 

 in point. 



Nitrogen and phosphorus are frequently 

 cited as limiting factors in plankton pro- 

 duction and apparently they may be in 

 some ca.ses. In the more exact studies it 

 has often been impossible to show that 

 either was limiting. Atkins (1926) dis- 

 cussing the data from Wisconsin lakes finds 

 "a complete absence of any evidence that 

 in the water of these lakes a deficiency of 

 nitrogen acts as a factor limiting the plank- 

 ton." Wiebe (1931b) concludes that ni- 

 trates and ammonia are not limiting in the 

 Mississippi river. It is of course difficult to 

 decide just when a factor becomes limiting. 

 Rice (1916) suggests that in Winona Lake, 

 Indiana, plants flourished in water with 

 extremely small amounts of nitrates and 



nitrites wlicii conditions for producing 

 tlu'se materials were favorable. 



Phosphorus as we have noted is usually 

 IM'csent in smaller quantities and lias been 

 more frequently considered a limiting fac- 

 tor for iiliyloplaiiktoii. (.(J., by Atkins 

 (1926), Strom (1931), Yoshimura (1932), 

 and Gessner (1934a). However, when 

 Juday ci al. (1928. 1931) investigated the 

 question in a large number of lakes in 

 Wisconsin they found no correlation and 

 only slight reduction of the phosphates in 

 the upper water, although large crops of 

 phytoplaidvton had been produced. Ricker 

 (1937) found similar quantities of phos- 

 phorus and only slight variation in Cultus 

 Lake, British Columbia. 



IRON 



The necessity of iron for plant growth is 

 undoubted though its physiological role is 

 still uncertain. It probably acts as a cata- 

 lyst in the formation of chlorophyll and 

 may be also involved in respiratory activi- 

 ties. Strom (1928) and Ohle (1934) men- 

 tion it as a probable limiting factor for 

 phytoplankton growth in some lakes. Nau- 

 mann (1932) emphasizes its significance by 

 creating a "siderotrophic" water type, a 

 subdivision of the oligotrophic, "in which 

 the iron spectrum reaches an important 

 level." 



The amount of iron present in surface 

 waters of lakes is usually less than 2.0 mg 

 per liter but it may be much more abun- 

 dant, especially in the bottom water. Man- 

 ganese in the same waters usually occurs in 

 smaller quantities, but Ohle (1934) finds 

 that manganese is more abundant than iron 

 in humous lakes. It has been suggested 

 that manganese may under certain condi- 

 tions serve as a partial substitute for iron. 

 Strom (1933) found that in .some of his 

 algal cultures this was not the case. 



Recently Hutchinson ei al. (1938) have 

 shown that in certain lakes of Connecticut 

 ami New York the amount of ferrous ii-on in 

 solution in the hypolimnion determined the 

 value of the redox or oxidation-reduction 

 potential. Moreover, there was a close cor- 

 relation between these potentials aiul the 

 occurrence of the larvae of various genera 



