355 



though the invasion resulted in the enrichment of the lake by 

 the decay of vegetation and dead animals. It may also have 

 "seeded" the lake w^ith organisms whose subsequent multipli- 

 cation caused these temporary increases in production. These 

 same floods are attended by depressions in production in the 

 main stream, so that these two pulses in Quiver Lake lie in 

 these depressions, intercalated between summits of the curve 

 of production in channel water (cf. PI. IX. and XXVI.). The 

 inference is suggested that the run-off of this plankton-breeding 

 impounded water of Quiver Lake and similar reservoirs else- 

 where may have contributed to the increased production in 

 channel waters following the flood. 



The plankton content of Quiver Lake water on July 26 

 (.71) and Sept. 6 (1.57) thus exceeds that in theriver on July23 

 and Sept, 6 (.68 and .99), and its contributions to the stream, if 

 any were made, serve to enrich the channel plankton. In three 

 other cases the lake production exceeds that of the river; on 

 Feb. 23 (lake, .03, river, .01), April 9 (1.42 and .52), and Dec. 28 

 (.29 and .01). In the flrst instance there was stagnation under 

 the long continued ice-sheet in both river and lake, as wasshown 

 by the great mortality of fish in the latter. The plankton, how- 

 ever, did not reach the degree of extermination in lake water that 

 it did in the channel, since there was less sewage, more veg- 

 etation, and access of spring water. In the April instance 

 the silt burden of the channel waters (4.67 cm.^ PI. IX.) 

 is much greater than that in the lake (1.43), and suggests the 

 intercalation of storm water in the former, resulting in the 

 slight rise in levels (PI. IX.) and the lessened plankton content 

 of the channel waters as compared with those of the less dis- 

 turbed lake. The great contrast on December 28 is also due 

 to the flushing action of the great winter flood which depleted 

 the channel plankton but increased the impounding function, 

 and therefore breeding capacity and productivity, of the lake. 

 Each of the three instances of greater production in lake than 

 in river waters occurs with rising river levels, when the rising 

 river checks the relative outflow from the lake or otherwise 



