American Fisheries Sociefij -^^T 



fiU-tui'tMl in tlic lake as the result of (leeoniiiositioii and these iiia\- 

 lie utilized as food liy tlie ii'i'een plants. Thus there is k('i)t u]) in 

 the lake a sort of internal eireulation of carhon d'oxidc; tli" 

 stoek of the cireulatinu- nu'dinrn bein^u' iiU'reased and I'cpli'nislicd 

 1)V additions from the outside. The aeti\'ities of aninuds and the 

 prceesses of deconiposit 'on liberate tlie ,uas. which is taken up 

 and uianufactureil by tlu' jilants into or^anie substances; and 

 these in tui'n serve as food and as material for lU'W deeompo-i- 

 tion ; while from the air the water may be absorbin^y- new sup- 

 |)lies of carbon dioxide to make good the losses of this ju'ocess. 

 Thus under normal conditions, the lake would return little (U' no 

 carl)on dioxide to the atmosphere, Ijut would utilize within 

 itself all that it manufactured or absorbed, at h'ast until tli/ 

 ])lant life becanu' so abundant as to be limited by othei' causes 

 than that of food supply. 



If this were all. the story would lie (piite sim])le and quite to 

 the advanta,ue of the lake. -But it is by no means all the stoi'y ; 

 on the othei- hand, so far from being forced to solve probitmis as- 

 sociated with an o\t'rsupply of carhon dioxide, the lake has to en- 

 countei- many ddliculties in secui'in*i- an adiMpiate sujiply of that 

 ii'as, and is able to meet them only \ery jiartially and ini])erfectly. 

 Since the ])lants are able to utilize carbon dioxide in the manu- 

 facture of starch only during the hours of sunlight, consider- 

 able (piantities may escape into the atmosphere during the night. 

 Rut this is not the only disadvantage as regards the su])])ly of 

 carl)on dioxide, with which the jilants of the up])er water have to 

 contend. By no means all. <u' even the greater [)art of the or- 

 ganic matter which tlu'y manufacture decomposes in the upper, 

 warmer stratum of the lake. As the plants and animals die, 

 they sink into the lower and cooler water before any great part 

 of the decomposition has been completed. The carbon dioxide 

 which is there produced is discharged into this bottom water. 

 It cannot l)e used there l)y plants on account of lack of light : and 

 the same imperfections of transportation Avhich ])revent the ac- 

 cess of oxygen to the cooler water in summer make it impossible 

 to transport the carbon dioxide ])roduced there to the upper 

 stratum, where it can lie utilized. In certain lakes, indeed, a 

 small portion of this gas may he used in the cooler watei'. as I 

 indicated above, but, in general, the upper \\ater, as a result of 



