Stagnation in Cycles 303 



tinually being added to the ocean by run-off and river discharge— a 

 process constituting a loss of nutrient material from the land. These 

 nutrients enter the marine cycle and the major portion of them is 

 eventually distributed to the huge reservoir of nutrients in the deep 

 sea. These critically important materials are thus being drained 

 away inexorably from the land environment and being added to the 

 accumulation in deep water which is unavailable, except for that por- 

 tion brought to the surface again by vertical circulation. 



Stagnation in Cycles. Materials move from the environment into 

 the bodies of plants and animals as they grow, return to the environ- 

 ment when they die and decompose, and in some instances undergo 

 complicated transformations and translocations in the environment 

 before they are again taken up by living organisms. The study of 

 the geographical distribution of materials used by plants and animals 

 and their cycles is known as biogeochemistrij . A further discussion 

 of these circular causal systems in ecology is presented by Hutchin- 

 son (1948). Materials are not equally abundant in the different 

 phases of these cycles, nor do the various steps take place at uniform 

 rates. Biogeochemical investigations show that materials of critical 

 concern to plants and animals have accumulated in certain places and 

 represent points of stagnation in the cycles. The gradual augmenta- 

 tion of nutrient materials in the deep sea is an instance of this phe- 

 nomenon. Nutrient substances may thus be withdrawn from circula- 

 tion for longer or shorter periods. 



A relatively temporary stagnation is represented by the organic 

 matter in the soil or on the bottom mud of natural water bodies. The 

 nutrient minerals contained in this organic matter are unavailable for 

 plant growth until the material decomposes. In many soils this re- 

 tardation of the cycle is beneficial because, as explained earlier, the 

 formation of humus in the soil has valuable physical effects besides 

 providing a slow, steady release of nutrients. Guano deposits, such 

 as those on the islands off Peru, illustrate a long-term accumulation 

 of nutrient materials (Hutchinson, 1950). The many cubic miles of 

 peat, lignite, and coal buried in the earth's crust represent stagnation 

 in the carbon cycle for hundreds of millions of years. A similar 

 stagnation in the calcium cycle is represented by the deposits of chalk, 

 limestone, and coral material. 



Great differences exist in the total supply of the various building 

 materials needed by plants and animals as well as in their availability. 

 When stoppages occur in cycles of elements likely to be scarce in 

 available form, such as nitrogen and phosphorus, critical conditions 

 may arise. An inexhaustable supply of nitrogen exists in the earth's 



