Phosphorous entering an ecosystem may produce 

 a high oxygen demand. It has been pointed out 

 that 1 milligram of phosphorous from an organic 

 source demands about 160 milligrams of oxygen 

 in a single pass through the phosphorus cycle to 

 complete oxidation. Thus the oxidation of organic 

 matter, the growth of which has been induced by 

 adding phosphorus, may bring about a great reduc- 

 tion of oxygen in a lake or stream. 



Dissolved carbon in the form of simple organic 

 compounds can be utilized by many kinds of algae. 

 These types of carbon compounds are also used 

 directiy as a source of food by many animals. 

 Varying amounts of simple organic compounds 

 containing carbon are found in sewage and several 

 types of industrial wastes. Other more complex 

 forms of organic carbon can be utilized by bac- 

 teria. The most common nuisance growth that 

 becomes very abundant in the presence of very 

 small amounts of carbon is Sphaerotilus. Patrick 

 (unpublished data) has shown that the addition 

 of 0.05-0.1 mg/I of glucose, without changing 

 other ecological conditions, may produce nuisance 

 growths. 



Knowledge of the nutrient requirements of fungi, 

 phytoplankton, and filamentous algae is more ex- 

 tensive than for rooted aquatic plants. Laboratory 

 data on nutrient requirements must be used with 

 caution, however, because the maintenance of 

 most long-term cultures has required that extracts 

 of soil be incorporated into the inorganic culture 

 medium. Analyses of field grown algae have indi- 

 cated a wide divergence in elemental composition 

 among various species and among the same species 

 from different localities. Excessive growths often 

 seen to be triggered by small amounts of so-called 

 minor or trace elements and vitamins, particularly 



One of the most obvious effects of increases or 

 imbalances in nutrients is the change in the kinds 

 and abundance of species composing the algal 

 flora. Historical studies of Lake Erie show a 

 change from an Asterionella dominance in the 

 spring and a Synedm dominance in the fall of 

 1920 to a Melosira dominance in the spring and 

 a Melosira, Anabaena, Oscillatoria dominance in 

 the fall of 1962. Between 1919 and 1934, the 

 number of cells per ml, with two exceptions, al- 

 ways were less than 4,000/ml. Since 1934, the 

 cell count, with one exception, has always been 

 greater than 4,000/ml. In 1944, it reached 11,032 

 cells/ml. It should be pointed out that blue-green 

 algae are a poor source of food for most aquatic 

 life. 



Benthic forms also indicate the increase in nu- 

 trients in an ecosystem. Various species of Clado- 



phora become abundant in lakes and rivers when 

 nutrients are abundant and replace the original 

 diverse benthic flora. 



This demand for a wide variety of nutrients 

 is also characteristic of many of the rooted 

 aquatic plants. Their affinity for numerous metals, 

 however, does not appear to be comparable to 

 that of the algae. 



Extensive data exist on the concentration of 

 nitrogen and phosphorus in fresh waters through- 

 out the United States. (Allee, et al., 1949; Ellis, 

 1940; Engelbrecht and Morgan, 1961; Juday, 

 et al., 1927; Lackey, 1945; USDHEW, 1962a) 

 In evaluating these data, it must be remembered 

 that algae and most other aquatic plants are capa- 

 ble of utilizing any available N and/or P in a very 

 short time providing other growth conditions are 

 favorable. Thus, analyses of filtered water would 

 not provide an evaluation of all elements existing 

 in the original water sample. A more meaningful 

 figure would result if all materials in an original 

 water sample were digested and then analyzed. 

 Often, the dissolved or available phosphorus may 

 be very low, while the total amount in the orga- 

 nisms and organic matter may be quite large. Not 

 only does this determination of total phosphorous 

 give a better estimate of the existing nutrient load 

 of an area, but it also provides an index to the 

 potential release that would occur if these plants 

 should all die within a short period of time. 



This information would also point out the fact 

 that in many freshwaters, various species of rooted 

 aquatic plants are excellent receptors for this nu- 

 trient load. Their use in effluent treatment might 

 be one of the cheaper waste-treatment procedures. 

 The chemical composition of several species of 

 plants is given in table III-4. Indications are that 

 the N-P content of freshwaters in the United 

 States is quite varied, and their presence in fairly 

 large amounts may or may not produce algae 

 blooms. 



It must be remembered that factors other than 

 plant nutrients also are operative in the establish- 

 ment and maintenance of aquatic plant growths. 

 There must be sufficient light reaching the plant 

 for photosynthesis to occur. If turbidity from 

 muds, dyes, other materials, or even phyto- 

 plankton is too great, plants at lower depths can- 

 not grow. These same plants, however, if estab- 

 lished in an area, can trap large amounts of 

 intermittent silt and other materials and clear the 

 waters for downstream uses. 



Another factor that might be operative in pre- 

 venting aquatic plant growth would be the lack 

 of free CO, and bicarbonate ions in a particular 



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