ALGAE — MEIER 417 



Meterological conditions were responsible for the tragedy. The 

 weather had been extremely warm and the temperature of the water 

 at the surface was 82° F. The humidity was high enough to prevent 

 evaporation from the surface. There was so little wind that the 

 lake was as calm as a mirror. The algae tended to rise to the sur- 

 face and form a scum there. Concentrated at the surface, their 

 food material became exhausted as, owing to the warm weather and 

 the intense summer sunlight, the algae had developed to such an 

 extent that there was not enough carbonic acid in the lake to supply 

 them. The majority of algae flourishing at this time of year are the 

 blue-greens, which are much less powerful oxygenators than the green 

 forms. The lake was overstocked with fish, which, lacking a suffi- 

 cient supply of oxygen, died of suffocation. 



A short time after the death of the fish, a breeze sprang up, then 

 a heavy wind, restoring oxygen to the lake, especially to the end 

 toward which the wind was blowing. With the decay of the blue- 

 green algae, which to a large extent were Anabaena and Clathrocystis^ 

 the type of algae changed to the green forms such as Scenedesinus 

 and Raphidium. These latter forms contain chlorophyll and are 

 strong oxygenators. They developed with such rapidity that the 

 oxygen in the water was increased beyond the point of saturation. 

 Plenty of carbonic acid was then derived from the decay of the car- 

 bonaceous material at the bottom of the lake, for when the water is 

 in circulation the carbonic acid manufactured by the bacteria at the 

 bottom of the lake is distributed through the water, giving food to 

 the algae. There are always less blue-green algae in water that is in 

 constant circulation. 



Just as an acre of land will support a certain plant population, a 

 given volume of water will support only a certain number of plants. 

 Intense light is bad for algae, but the blue coloring matter in the 

 blue-green algae helps protect their green pigment, so that more 

 blue-green algae are found on the surface of a lake on the hot, sunny 

 days of summer, and the green algae are farther below the surface. 

 Deep cold lakes of the north rarely are covered with water bloom. 



In Alberta, a report was made of cattle being killed by the water 

 from a lake covered with water bloom. The owner thought that his 

 slough had been poisoned with paris green when he saw the water 

 covered with the oily green masses of GloeotricMa pisum, which 

 gives the water an opalescent or iridescent appearance. As in other 

 districts, the horses, cattle, hogs, poultry, and even wild birds were 

 seemingly poisoned by the water from these lakes, the aborigines 

 called them poison lakes. The algae may be the indirect cause of 

 the death of the animals as seen from the example of the fish given 



