are carried upward; occur usually in arid and semi-arid 

 regions. 



Dynamic Equilibrium 



A system that is maintained in approximately the same 

 condition because of the action of opposing processes or ac- 

 tivities proceeding at about equal rates, cf . Balance of nature. 



Dynamics, Community 



See Community dynamics. 



Dynamics, Population 



See Population dynamics. 



Dysgenic 



Refers to any influence that is detrimental to the genetic 

 properties of a population, cf. Eugenics. 



Dystrophic 



A type of lake or pond which contains brown water with 

 much humic material in solution and with a small bottom 

 fauna characterized by pronounced oxygen consumption. 

 Cf. Eutrophic. 



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