simply stated In the negative Is: no phosphates 

 and nitrates, no blooms; hence, no disturbances. 

 We naturally Inquire why, of all the dozens of 

 species of algae In a lake, do only a few respond 

 to a rich supply of nitrates and phosphates by ex- 

 plosive reproductions. From one Montana valley 

 lake, for example, over one-hundred species of 

 algae have been listed; yet only one, Alphanizo - 

 menon flos-aquae developed a bloom. It is diffi- 

 cult, if not impossible, to explain this "selec- 

 tivity" partly because of the multiplicity of spe- 

 cific physiological requirements, the presence or 

 absence of critical trace elements (so far undeter- 

 mined) , the inhibiting actions of antibiotics, and 

 the presence of growth stimulators in the medium. 



Most likely the response of some species by 

 producing bloom populations, and no such response 

 from others, is related in part to the high reproduc- 

 tive rate possessed by particular plants. For ex- 

 ample, when conditions are favorable for both 

 Dinobryon and Synura , they occur together espe- 

 cially in the early spring plankton of hard water 

 lakes. But Dinobryon spp. quickly assume bloom 

 proportions and vastly outnumber Synura because of 

 the rapid, zoospore method of reproduction used by 

 the former. The reproductive rate is usually paral- 

 leled by the speed with which nutrients are ab- 

 sorbed , as with Aphanizomenon , Microcystis and 

 Anabaena among the Cyanophyta which develop 

 superabundant populations in a short time. Also, 

 this group of the algae possesses a more rapid 

 photo synthetic rate than any other. 



Among the blue-green algae there is at least 

 one characteristic which explains why they develop 

 especially well only in waters well-supplied with 

 phosphates and nitrates. The protoplasm of most 

 blue-green species is highly proteinaceous , more 

 so even, than some animal protoplasms. Crude 

 protein analyses (dry weight) show that Micro - 

 cystis aeruginosa is 55.58 per cent protein; Ana - 

 baena flos - aquae is 60 .5 6 per cent and Aphani - 

 zomenon flos - aquae is 62.8 per cent. Hence, 

 their requirement for nitrates for the elaboration 

 of proteins is much greater than that of green algae 

 such as Spiroqyra , for example, which is 23.82 

 per cent protein , or Cladophora 23.56 per cent . 

 Nitrogen alone in Aphanizomenon amounts to 10 .05 

 par cent (dry weight) as compared with 3.81 per 

 cent in Spirogyra . Some other data give inferential 

 evidence to support the thought that phytoplankton 

 depends upon nitrogen for bloom production. Juday 

 (1943) analyzed plankton of Waubesa Lake and 

 found that it was composed of 49 per cent protein, 

 5 per cent fat, 6 per cent pentosans, 4 per cent 

 crude fiber. The total annual plankton yield of 

 this lake was 2592 pounds per acre, which inci- 

 dentally supported 295 pounds of fish per acre. 



It has been demonstrated in laboratory cul- 

 tures and inferred from numerous water and plank- 

 ton analyses that phosphorus is more critical than 



nitrogen in determining phytoplankton production. 



Phosphorus is also important in that it, in turn, 

 facilitates the assimilation of nitrogen. In fertili- 

 zation experiments where attempts are made to in- 

 crease phytoplankton, it has been found desirable, 

 or even necessary, to use a sulphate to fix iron 

 and so prevent this element from taking up the 

 phosphorus and thus lessening the well-known de- 

 sirable effect of phosphate on plankton production. 

 In respect to fertilizers, it is pertinent to mention 

 here that such an operation frequently leads to 

 disastrous upsets in a fish pond because super- 

 abundant growths of algae decay, the oxygen is 

 depleted, and winter-kill results. 



The work of Atkins illustrates the importance 

 of phosphorus . He found that a pure culture of 

 Nitzschia closterium developed a concentration of 

 300,000 organisms per cc . when Miquel's solution 

 was used. All the P was consumed and it was de- 

 termined that 1.12 mg. of P2O5 was used to pro- 

 duce 1 X 109 diatoms during the first phase of 

 growth. One gram of P-pentoxide suffices for 

 9 X 10^1 diatoms. Krumholz (1954) found that Os- 

 cillatoria accumulated P 800 ,000 times that of the 

 medium. These figures are derived from culture 

 studies but it is reasonable to infer that they are 

 applicable in a general way to situations in nature. 

 Atkins (1923, 1925) found that in the sea one liter 

 of water can produce 26.8 million diatoms for each 

 0.03 mg. of P consumed. Here, P2O5 -content at 

 37 mg . per cubic meter, the plankton removed all 

 but 7.4 mg. per cubic meter. It is claimed that in 

 the tropics where phytoplankton development is 

 more uniform throughout the seasons the sea water 

 is persistently low in P2O5 -content. Correspond- 

 ingly, in the Arctic the P2O5 is high in winter and 

 low in daylight periods, paralleling the action of 

 plankton populations in taking up P. In the English 

 Channel P and N are completely exhausted at the 

 peak of phytoplankton production. 



Rice (195 3) and others have demonstrated the 

 use and uptake of P by radioactive-P in laboratory 

 cultures. Hasler (1958) has suggested that strati- 

 fied lakes be given artificial circulation to bring 

 phosphorus from the bottom layers into the photo- 

 synthetic zone so as to increase productivity. 



The disappearance of nitrates and phosphates 

 from standing water in summer and the increase 

 again in winter is taken as evidence that these sub- 

 stances are taken up by phytoplankton. In fact, it 

 appears clear that the exhaustion of P2O4 in a body 

 of water by plankton uptake in late spring or in mid- 

 summer acts as a brake or increment and explains 

 the plateau in population numbers. Therefore, it is 

 only in those lakes which receive a continuous 

 supply of phosphate that tremendous blooms of 

 algae can appear and reappear throughout the en- 

 tire 'growing' season. It has been noted that phy- 

 toplankton increases sharply after the decay of 

 larger aquatic plants whereby substances are 



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