Place of Decomposition 



301 



loss of mineral salts takes place under the best of conditions. How- 

 ever, serious amounts of these valuable nutrients are leached from 

 soils that are acid and subject to excessive rainfall or that exist un- 

 der other unfavorable circumstances. Farm or forest practices that 

 permit soil erosion to take place have resulted in accelerated and often 

 irreparable loss of mineral nutrients and humus from the land. 



Respiration 



Carbon dioxide 

 in air and natural waters 



*-C0o-« 



Respiration 



^v- ' -^ — /^ 



f^nima/s 



Ingestion Digestion 

 Absorption Metabolism 



Carbon (organic) 

 compounds in the 



environment 



in dead organisms 



and their 



remnants 





Fig. 8.7. Diagram of the carbon cycle, showing the principal components and 



processes. Compounds not included in circles are free in the environment. 



( From Principles of Modern Biology by Marsland and Plunkett. By permission of 



Henry Holt and Co., Copyright, 1945.) 



In the water environment dead organisms tend eventually to sink 

 even though they may have a period of buoyancy. After the or- 

 ganism's substance has gone into solution, no further tendency to sink 

 exists. During the period of sinking the decomposing material may 

 have been displaced horizontally by currents for considerable dis- 

 tances. By the time that the organic matter has been decomposed 

 and transformed, the resulting nutrient materials may be very far re- 

 moved both horizontally and vertically from the spot originally in- 

 habited by the organism from whose body they were derived. 



In deep areas of lakes or of oceans the bodies of many dead plants 

 and animals sink to depths below the euphotic zone before they 



