•^•^(i 



'I'linhi-sLrlh A II mini Mrrlimj 

 ■ pjll-liill (■\li;lli>l 



A>S()ci;ili'(l with lliis I 

 1 increase iliiriiii:- wiiilei- (if llie 

 aiii ijaseDiis iiroilucl ol' i-esnii-al 



n\' oxvucii. ll)ei-(' is 

 111 of carlioii (lioxiil. — the 

 riiis is iini inTseiii ill any 



nl)ser\al)le (|iianlity in llie ialsc at the liiiic of IV, v/.iiiu- iuil il in- 

 ci'casrs (liii-iii.L:' tile winter and the (iiiantily at the liotldiii may 

 heeonie \ei-y coii^idcralile. 'I'lie aiiKHinl will lir. in i^ciieral. pi'o- 

 jMij-tionai 1(1 the amount of ().\y,i:'eii used np. 



!n llie spriiiu'. wlieii the iee lia> melted, the water of the lake 

 is mice more niiirdmi in tein|»ei'at nre. It i> pnt into motion om-i' 

 more liy the w'nd and all parts of the water are hi'oiiLiht into 

 eentaet with the air. 'Idle earhon dioxide. wlii(di has hecn ae- 

 enninlalin.i:' dnriim- the winter, is diseharp'd and the lake aijain 

 heeomes nearh' saturated with ox\\i;('ii. lint. a> the tein|ierat lire 

 in s|iriii,i;- is hi,i;her than n tlie iiiitunin, the aiiMinnt of oxxuvn 

 taken in is less; and <inee the teni|iei'at lire of ihr water eon- 

 Tinues to rise, the stock of oxyiicn is heiiii:- dimini^hed from this 

 eau^e (juite ' nde|iendently of any use in;ide of the li'as hy the 

 or_u-anisins of the lake. 



Tlie i)eri()d of full oxyu-eii saturation in the s|n'in_i;- is a \ci-y 

 ])rief one in our (dimate. 'I'lie season advaiui's I'apidly and the 

 su]-face water soon ac(|uii'es a liiiiliev temperature than that at the 

 liottom. 'Idiis wai'med water is, of course. Huiiter than tlie cooler 

 watei- helow and tends to float upon it. The ditTcl-eilce in delisiiy 

 tlius cause(l makes it increasingly ditticult for tlu' wind to create 

 and maintain a conij^lete circnilal ion of tlie watei'. For a time 

 the action of the wind may continue to mix eacli successi\-e 

 stratum of water witli that helow it. the mixture extending to 

 tlie hoitom of the lake. But this action is a veiw dilVerent thing 

 from the complete o\ci'turning of the wafer, and wliile it results 

 in raising the temperatui'c of the lower water, it does not cai'i'V 

 freelv oxygen to the hottom. Thus, when the surface liecome- 

 decidedU" wanner than the water Ixdow it. the hoitom watei, 

 though it continues to warm, is withdrawn fi-om direct contact 

 with the air and is theivfore at a d isad\antage in the matt''r if 

 gaining a new supply of oxygen. 



As the season adxances this si rat ilicat ion of water dependeni 

 on lemperature heeomes accentuated, and. in the way of wliiidi I 

 s))()ke last yeai' and iic^mI not now repeat, the lake heeomes sep- 

 arati'd into two parts: an upper warm stratum of nearl\- uniform 



