THE RESPIRATION OF AN INLAND LAKE 343 



creasingly ineffective, and during the summer its action is confined to 

 the upper warmed layer of the lake, and the lower, cooler, water is 

 wholly shut off from the direct influence of the wind currents. 



These facts show that an inland lake has an extremely inefficient 

 apparatus for absorbing and distributing oxygen, and the net result is 

 that in many lakes the amount and character of the higher life which 

 the lake will support is conditioned by the amount of oxygen which 

 the lake contains rather than by the amount of food which it can 

 produce. The oxygen in the lower and cooler water of the lakes can 

 not be renewed between spring and fall. This amount would be in- 

 deed ample to sustain a large amount of animal life in full activity. 

 But its use can not be confined to the necessities of ordinary life. The 

 processes of decomposition draw upon it much more heavily than does 

 the animal or the ordinary vegetable life. All the plants and animals 

 of the upper water, which die and sink into the deeper strata, the 

 leaves blown into the lake, and the material washed in from the shore, 

 decompose in the cooler water and in the process of decomposition use 

 up a great amount of oxygen. This depletion of the stock of oxygen 

 goes on with a rapidity which varies with the amount of decompos- 

 ing matter dropping into the lower water, which to some extent regu- 

 lates the rapidity of decomposition, and, with the depth of the water, 

 on which depends the quantity of oxygen contained in it. Each of 

 these factors may and does differ in different lakes, but the result is 

 that in a very large proportion of our inland lakes the bottom water 

 loses its stock of oxygen comparatively early in the season and becomes 

 uninhabitable for higher animals. This fact excludes from our lakes 

 a good many kinds of animals which they might otherwise support, and 

 very greatly limits the quantity of the higher life which the lake is 

 able to maintain. A lake which loses its bottom oxygen, for example, 

 can not support a fish such as the lake trout, which must retire to the 

 deeper and cooler water during the summer. To causes such as this 

 may probably be attributed a considerable number of our failures in the 

 planting of fish in our inland lakes. From causes such as these, the 

 whole of the lower water, containing half, or more, of the volume of 

 the lake, may become uninhabitable during the season when life is most 

 abundant; and the quantity of life which the lake supports may be 

 correspondingly limited. 



Still further, since the rapidity with which the oxygen is exhausted 

 depends on the amount of material which is deposited in the lower 

 water, those lakes whose upper water contains the greatest quantity 

 of vegetable life and which can therefore support the greatest amount 

 of animal life, use up the oxygen of the lower water most rapidlv. It 

 looks, therefore, as if we were in a somewhat unfavorable situation as 

 regards the possibilities of higher life in the lower water of inland 



