662 Ecology 



epilimnion, is rich in oxygen but relatively high in temperature. Below 

 the thermocline is the hypolimnion which is relatively cold and low in 

 oxygen. These physical relationships influence the distribution of the 

 organisms within the lake. 



LATE SPRING 



AUTUMN 



Fig 215— Temperature relationships in a small lake during a yearly cycle. 

 The direction of the water currents is indicated by arrows. Temperature relation- 

 ships are only approximate. 



