PHYSICAL AND CHEMICAL FACTORS IX THE METABOLISM OF LAKES 



23 



nncolored lakes, i.e., those with little allocli- 

 thonoiis materials, the percentag'e was as 

 high as 23. AVe may point to this as a 

 demonstration of dystrophy as a disturbing 

 element in the metabolism of lakes. It ents 

 across the normal gradation from eutrophy 

 to oliogotrophy and thus shonld not be con- 

 sidered as indicating a third lake type. It 

 has been suggested that these organic ma- 

 terials of alloehthonoiis origin not only fail 

 to support production but they ma.y ac- 

 tively inhibit production by adsorbing in- 

 organic materials, e.g., phos]ihorns, of nutri- 

 tive importance. 



The comparative constancy of dissolved 

 organic materials in lakes is in striking 

 contrast with the high variability of the 

 same elements in their inorganic state. 

 Birge and Juday (1927) found little cor- 

 relation between amounts of the two groups 

 of substances except in lakes where both 

 were present in veiy small quantities. A 

 part of this constancy may be apparent 

 rather than real since the quantities of 

 organic materials are much larger than the 



inorganic and the metabolic exchanges 

 make lesser inroads into this large capital. 

 The immediate temptation is to hope that 

 the dissolved organic matter will provide 

 an index to productivity. This could only 

 be considered in lakes wiiere the dystrophic 

 factor is known to be at a minimum. Even 

 in these cases we still face the objection that 

 productivity must be determined not by the 

 amount of organic capital but by the rate 

 of turnover. Our final statement is that 

 which Birge and Juday have made on vari- 

 ous occasions. We do not know the func- 

 tion of the dissolved organic matter in the 

 biological economy of the lake. 



Concluding Remarks 



Our discussion began with an attempt to 

 organize the ph.ysical and chemical factors 

 in the metabolism of a lake and a chart 

 (Fig. 1) is presented to suggest these inter- 

 relations. As a second step we have con- 

 sidered a number of these factors sum- 

 marizing and attempting to evaluate pres- 



In doing so we 



ent knowledge in this field. 



Fig. I. Okologisches Totalspekfrum (Theoretlsches Schema). 

 Oben: Milieu eines Biotops 



a) zur Zelt der Vollilrkulatlon, 



K\ ..Hv.. A A . c . ., (a) Epillmnlsche Kurve, 



b) wahrend der Sommerstagnation. | ^ Hypollmnlsche Kurve. 



MMc: Vatcaupcktram dacs aatotrophcn planktlschen Organlsmus. — Unten: Belde Spektra (Milieu wShrend der SommerstagnatioD) 



komblnlert — Welterej s. Tcxtl 



Fig. 6. The eeolog-ienl total spectniin of Groto (19.34). 



