Limitation by Nutrients in Nature 283 



per cent in their phosphorus content (Ketchum and Redfield, 1949). 

 Some cultures multipHed threefold in deficient media and contained 

 only Vs the normal amount of phosphorus. These algae not only 

 could make up their deficiency in one day when again supplied with 

 phosphate, but also would absorb more of this material than neces- 

 sary if excess phosphate were available. 



Although a certain degree of flexibility exists in the use of nutri- 

 ents by plants, in their ability to produce some growth under deficien- 

 cies, and in the possible partial substitution of one nutrient for an- 

 other, an ultimate minimum is eventually reached for the availability 

 of the required elements. If the plants or the nutrients are mobile, 

 the lack of nutriment will affect the whole population at about the 

 same time. 



Urban sewage and certain other pollutants discharged into rivers 

 and lakes provide extra nutrients that frequently cause the growth 

 of excessive quantities of algae that are unsightly and odoriferous. 

 Practical application of the law of the minimum has been suggested 

 in controlling this objectionable growth. Since the treatment of all 

 the sewage effluents is costly, consideration has been given to the 

 removal of one essential nutrient only. After the elimination of phos- 

 phate from the sewage in pilot tests in Wisconsin the growth of algae 

 was greatly curtailed, although all other nutrients were present in 

 great abundance. The feasibility of using this procedure on a large 

 scale is being investigated. 



Pollution from duck farms bordering Great South Bay, New York, 

 cause the water of the bay to be rich in reduced nitrogen compounds 

 and to furnish a low ratio of nitrogen to phosphorus. This unusual 

 situation in regard to the nutrient factor, in combination with other 

 special environmental conditions, has resulted in the suppression of 

 the usual type of phytoplankton in Great South Bay and the produc- 

 tion of tremendous quantities of small green algae (Ryther, 1954a). 

 This alteration in the phytoplankton population appears to have pre- 

 vented the oysters in the bay from feeding and growing normally, 

 with consequent serious reduction in the oyster fishery. 



Limitation by Nutrients in Nature. In the terrestrial environment 

 nutrients exert a control over the growth and distribution of plants 

 primarily as a result of deficiencies, although excessive quantities of 

 harmful substances occasionally exclude plants from particular areas. 

 Availability of suitable nutrients is, of course, only one aspect of the 

 soil that determines whether a given species can grow successfully; 

 physical texture, moisture, pH, and other chemical aspects of the 

 environment, as well as the climate, must also be suitable. Emphasis 



