returned in a soluble form to a lake. 



It follows that lakes which have been en- 

 riched by various kinds of pollution from human 

 habitats, run-off from agricultural lands, wastes 

 from farm animals, etc. are the ones in which 

 blooms appear. Accordingly, blue-green algae fol- 

 low man about as he colonizes and pioneers, cre- 

 ating situations favorable for his worst aquatic 

 pests. It is common knowledge that virgin lakes 

 and lakes in unsettled areas rarely, if ever suffer 

 from blooms and have no fish deaths caused by 

 algae. Also, it is well-known that oligotrophic 

 lakes are spared algal blooms since they are low in 

 electrolytes, nitrates, and phosphates. Such lakes 

 have a high Na2 - K2O ratio (3.2) and support a 



CaO - MgO 

 desmid and planktonic chlorophycean flora together 

 with such Pyrrhophyta as Peridinium Willei . Un- 

 contaminated lakes, therefore, are not enriched, 

 have a flora that is 62 .4 per cent desmids and a 

 diatom flora of 11 .1 per cent; blooms do not de- 

 velop. When the Na/Ca ratio is low (1 .1) eu- 

 trophic conditions and a predominant blue-green 

 flora exist. Two English lakes, for comparison, 

 were found to have: 



Lake Postherne - Nitrates .012; 



Hardness 18.0 



Chlorine 3.45; 



Flora Myxophyceae 



Lake Katrina - Nitrates .001; 

 Hardness 9 .0 

 Chlorine .85; 

 Flora Desmids 



Eutrophic lakes, on the other hand, by their 

 chemical nature may be veritable garden spots for 

 blue-green algae when phosphates and nitrates are 

 plentifully supplied. Here at Pymatuning Lake, 

 Tryon and Jackson (195 2) have shown that blue- 

 greens predominate in summer months, with 90 per 

 cent of the plankton consisting of Microcystis , the 

 remaining 10 per cent being made up of Chloro- 

 phyta and Pyrrhophyta . In their middle lake station 

 HCO3 varied from 35 to 20 ppm.; CO3 from 15 to 

 25 ppm. This is the situation found, in general, in 

 all basic, eutrophic lakes with a high pH. 



It is purely conjectural, but at least worthy 

 of mention, that trace-elements and/or growth 

 stimulators are present in water where peak popu- 

 lations of a single species explode. In our igno- 

 rance it appears possible that there is an unde- 

 tectable agent (or agents) present — some ingredient 

 coupled with animal excretory matter, possibly Bi2- 



Numerous other studies and analyses, both 

 marine and fresh-water, in the field and in the lab- 

 oratory, have demonstrated the importance of N 

 and P in plankton production . Reference might be 

 made to numerous researches on this problem. 

 Harvey (1940), for example, determined in labora- 

 tory studies that phytoplankton used 10.5 times 



more nitrogen than phosphorus, but of course this 

 does not mean that a maximum amount of P is criti- 

 cal. Hasler and Einsele (1948) found that for every 

 1000 Kg of N in lake water, 20,000 Kg. of plankton 

 material was possible but that P to the amount of 

 10 per cent of the available N was necessary before 

 the N could be used. 



As mentioned above, lakes well-supplied with 

 bicarbonates provide a CO2 reserve that makes 

 blooms possible. The demand for carbon dioxide by 

 such a mass of vegetation during photosynthetic 

 hours is tremendous. Obviously CO2 from respira- 

 tion provides for some photosynthesis, but addi- 

 tional amounts from bicarbonates can support a 

 mass of vegetation when, or if the dissolved CO2 

 is reduced or depleted. Photosynthesis has been 

 shown to be proportional to concentrations of bi- 

 carbonates. In distilled water, free, from car- 

 bonates, which has been saturated with CO2 photo- 

 synthesis occurs but very little. Two- thousand 

 six-hundred and fifty-four units of blue-green algae 

 per cc . of lake water were found at the upper one- 

 foot zone of a lake where carbonic acid was 1 ppm. 

 Whereas, at the 23-foot depth where carbonic acid 

 was 8 ppm., only 756 units per cc . were found. At 

 46 feet with carbonic acid at 16 ppm. there were 

 only 120 units of algae per cc . 



As Birge and Juday (1911) have pointed out, 

 an ample supply of dissolved carbonates benefits 

 aquaUc plants in two ways: 1) by supplying CO2 

 from the half-bound carbonates , and 2) in that 

 mono-carbonates take on a greater amount of CO2 

 from the atmosphere than would be absorbed other- 

 wise. Further, they also take up and hold CO2 of 

 respiration in the water and thus retain the gas for 

 subsequent use by the plants. 



Plankton population in eutrophic lakes where 

 electrolytes are abundant are characteristically 

 greater than in oligotrophic where electrolytes and 

 C02-content are low. For example, Rawson (195 3) 

 measured 10 to 40 Kg. of plankton per hectare in 

 Canadian oligotrophic lakes as compared with 100 

 Kg . per hectare in eutrophic lakes . He refers to 

 Lake Mendota (Wisconsin) in which Birge and Juday 

 measured 177 Kg. of plankton per hectare. 



An attending phenomenon in lakes which are 

 well-supplied with calcium carbonate is the pre- 

 cipitation of lime on stems of submerged plants, 

 stones, and other objects. When carbon dioxide 

 is withdrawn by photosynthesis , mono-carbonates 

 are formed. Lime may also be formed by oxidation 

 of calcium bicarbonates. Hence, dense blooms of 

 algae may lead to the formation of a thick layer of 

 lime which directly or indirectly has a profound 

 effect upon the limnology and the biology of an 

 aquatic habitat. This layer becomes inhabited by 

 lime-precipitating, benthic blue-green algae and 

 the deposition is accordingly amplified. Marl 

 weights down vegetation, thus forming bottom 

 layers of dead and decaying vegetation and so 



24 



