!)() 



PROBLEMS OF LAKE BIOLOGY 



Fig. 2. Bt-in-li on the iiortli sliore of Day Lake, Vilas County, Wisconsin. 



110 eonstant correlation between the amount 

 of organic material in the sand and the 

 populations of oroanisms. However, a 

 beach having less than 0.5 mg per 10 cc of 

 sand will support only a small population. 

 On the other hand, in outer regions of some 

 beaches where quantities of humus become 

 mixed with the sand, few organisms are 

 found, even though plenty of interstitial 

 water might be present. 



Chemical Factors 



A small amount of work has been done 

 on tlie chemistry of the capillary water con- 

 tained in the uppermost 8 cm of the sand. 

 For these studies sufficient quantities of 

 water were sucked out of the sand with a 

 25 cc volumetric pipette having a small 

 piece of silk bolting cloth over the lower 

 end to prevent the entrance of sand par- 

 ticles. Because the interstitial air intro- 

 duced bubbles into the samples, determina- 



tions of dissolved gases could seldom be 

 made on water samples taken beyond 100 

 cm from the edge of the lake. It would be 

 valuable to devise methods of sampling the 

 small amounts of water present between 

 100 and 300 cm where a large portion of 

 the organisms are found. 



From the point of view of life in the 

 sand dissolved oxygen is an important fac- 

 tor. Studies have shown that the greater 

 the distance from the lake the lower the 

 oxygen content. In several instances no 

 oxygen could be demonstrated in the capil- 

 lary water at the 100 cm stations. Also, in 

 a number of beaches the sand at distances 

 of 200 and 250 cm, at depths of 4 cm and 

 lower, contained ferrous compounds, indi- 

 cating anaerobic conditions. Such situa- 

 tions are w^ell known in sea beaches. 



The free carbon dioxide in the capillary 

 water had considerable variation, depend- 

 ing upon prevailing chemical, physical, and 



