American Fisheries Soeieti/ 225 



doe.'^ not Ijreatlio at all and duriiiii- the sninmcr lias only a vrrv 

 shallow and imperfect respiration. As the lake cools in the tall 

 the te.]ii|:eratnre becomes uniform from to]) to bottom at a date 

 which will vary from late Septemhei- to late \o\H'nd)er or early 

 December, according to the area and the di'])th of the lake and 

 the consequent temperature of the l)ottom water, the ^■olunle 

 of water to be cooled, and the vij^or of the cooling' ])rtx-esses. 

 When the temperature has thus become uniform, the water of the 

 lake is readily moved throughout its entire dejitb hy tlu' wind. 

 It is turned over and all ])arts of it are brouglit into contact with 

 the atmosi)hei-e. As a result, inland lakes, even those wliose 

 de[)th is two hundred feet or mort>, beconu' almost, or ([uile. 

 saturated with oxygen at a Icmiieratun' l)iit litllc above the 

 freezing point. This quantity amounts to ahoul 10 cc. ]nT litci'. 

 or about 1 per cent by volume; nearly twice as much as xhv 

 water will hold at the liighest summer temperature. In this con- 

 dition as regards oxygen the lake goes into winter quarters, be- 

 comes covered with a sheet of ice in our latitudes, and is. there- 

 fore, shut ofl: until spring from all further dii'cct connection with 

 the atmosphere. During this period the stock of oxygen is used 

 u{) to some extent, especially in the water adjacent to the bottom. 

 But as the vital processes of both ])lants and animals, and also 

 those connected with decay, go on slowly at the low tcmpi'raturc 

 of the water in winter, the amount ot oxygen thus consuiucfl is 

 comparatively small, and most lakes contain an abundance for 

 all forms of life at all depths, exce])t ])erhaps in the strata very 

 close to the bottom. This statement, though generally true, -will 

 not hold universally: In some ponds which are shallow and 

 contain a large amount both of living oj-ganisms and of de- 

 conijiosing matter, the oxygen heiieath the ice may become 

 wholly used u]). \\\' all know of lakes, which become so ])oor 

 in oxygen that if a hole is cut through the ice in late w'uter. 

 the fish will crowd to it tor air so eagerly and in such num- 

 bers as to be forced out on the ice. 'I'here are on record cases 

 when' an unusual exhaustion of the oxygen below the ice of 

 a lake has caused tlu' death (d' most of tlu' fish. Such cases, 

 however, are not common, and in the great majority of lakes 

 the consumption of oxygen in winter does not go far euimgb to 

 affect unfavorably their living inhaliitants. 



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