2-M 



Thhhi-sivlh Aninnil Mrrli,,;/ 



lo tlic imiiici'oiis factois wliicli iiiv aircctin- llic -iippiv of ow.izvii 

 ill the ii|)|)ci- water of the lake in suidiikt. If 1 lie ox v>icii of tliis 

 rc,uion i.- studied, it rarelv happens lliat the (|iiant!l\- foiiiid is llie 

 amount wliicli would he t heoret icallv expected, aeeordiii-i- to tlie 

 hiws of the ahsorption of ,yases hy water at dilVeivnl teiiipvra- 

 inres. It is soiiietiiiies hir.uvly in ex.-ess of the theoretical 

 aiuount. and sonietiines is eonsderahl v deth-ienl. Tile fact is 

 that the amount of ow'-vu in the upper water of (he hike is tlie 

 result of wrv numerous and \ariahle lorco. 'I'he lake mav or 

 may not he ahsorhiiii;- oxy.iicii from the air. If saturaied. it will 

 ,U-i\'e oil' oxygen to the air as the watir warms, oi' will take it in 

 as it cools. Moth of Ihese pi-,„vsses -o on somewhat slowlv. a> 

 the oxyucii 's not .ui\en olT or ahsorhed as rapidly as the I'aie 

 of cooliiiii' .-md warniin<:- \aries. Into the water the ,iireen plaiit> 

 are dischar.uiii.ii' oxy,i;-eii duriii.u' the hours when the li.u'ht is suf- 

 lieieiitly slrou^i': from tlie water hoth ])laiits and animals are 

 takiii.i;- oxy,nvii to assist tlieir vital oiierations: and the proci'ss 

 of decomposkioii is aidin<i' to exhaust the stock of oxygen. Thus 

 the amount present at any <i'i\-en moment will depend on the 

 relative value of these forces; ^ome of them positive; other- 

 iiepiti\(': and all \aryiiiu- not only from day to dav hut from 

 houi' to hour. .\or do these factors exhaust the list. The wind 

 has somethiu.u- to do here. |)uriii<;- a calm period the oxygen 

 content of the upper water may differ from that of a stoniiv 

 period. The \ital coiid'tion of the siiccessixf crops of algae, a- 

 they come and go. may determine for the time, the predom- 

 inance of the manufacture of starch, with accom))anying lihei'a- 

 liou of oxygen, or deconqiosit ion. with ]iartial exhaustion of 

 oxygen. Thus tlie ahility of tlie gi'cen plant to set fvrr oxygen 

 into the upper water may he of great \'aliie in maintaining tlie 

 supply of the lake. 



This power may he far more important in the lower water. 

 If the transparency of llu' water and tlie thickness of the warm 

 layer are such that a good deal of light can penetrate to the 

 cohh 1- water, algae will he ahle to maiiufacture starch in the 

 upper part o\' this stratum. 'Idiiis in the reg'on which is prac- 

 tically cut oir from access to the atmosphere, large amounts of 

 oxygen may he set I'vvr. There may he enough not only lo serve 

 the ordinar\' needs of the stratum, hut the water mav l)e satur- 



