It was intended to compare the response of 

 Bare Lake zooplankton to fertilization with the 

 response of zooplankton to fertilization in 

 similar studies, but little information could 

 be found on the population dynamics of zoo- 

 plankton in a fertilized environment. Waters 

 (1956) followed the dynamics of both the phyto- 

 plankton and the zooplankton populations of 

 two Michigan bog ponds for 3 years after the 

 application of hydrated lime. There are essen- 

 tial differences between applying fertilizer 

 and applying lime to a body of water. In apply- 

 ing fertilizer, nutrient materials are added 

 directly to the water, whereas in applying 

 lime, chemically bound nutrients already pres- 

 ent are released for use by increasing the 

 alkalinity of acid waters. In both cases the 

 purpose is to increase the productivity of the 

 lake, and in this respect both methods pro- 

 duce rapid results. Waters applied the hydrated 

 lime in two applications, one in the summer 

 and the other in the fall of 1953. Immediately 

 after the lime treatment, he observed a partial 

 destruction of some species of the phytoplank- 

 ton population followed closely by a heavy 

 bloom of Mycrocystis aeruginosa, a blue-green 

 alga form. Zooplankton however did not show 

 any response to treatment until 1955, over 2 

 years after treatment had ceased. The Bare 

 Lake zooplankton has exhibited a similar 

 pattern of delayed response that was perhaps 

 further obscured by effective cropping by 

 predators. 



The work of Ricker (1938a, 1938b), Lang- 

 ford (1953), Rawson (1953), Kutkuhn (1958), and 

 many others provide ample guidance for avoid- 

 ing many errors in collecting and analyzing 

 plankton samples. A careful worker should 

 encounter little difficulty in the proper selec- 

 tion of methods to meet his requirements. 

 Although finding the right techniques presents 

 no problem, the vertical and horizontal dis- 

 tribution of the plankton organisms must be 

 considered when selecting the location and 

 number of sampling stations at each new lake. 

 The work at Bare Lake and Pennak's 1944 

 studies of five shallow lakes in Colorado 

 have shown that even in relatively shallow 

 lakes the zooplankton may display a definite 

 variation in depth distribution when considered 

 by species. As has been demonstrated in other 

 zooplankton studies, the vertical distribution 



of the organisms may be a response to the 

 physical or chemical environment of the lake, 

 or it may be a response to a trophic inter- 

 relation, as was suggested for Bare Lake in 

 1957. 



Studies of the trophic rates and relation- 

 ships of fresh-water zooplankters offer much 

 promise in applied as well as theoretical 

 biology. For example, in fish farm pond work 

 in Hungary, various cladocera species are 

 being used to control detrimental phytoplankton 

 blooms in fertilized ponds (Eugene Muzsi, 

 letter, 1959). This type of biological control 

 would offer more benefit to the fish population 

 than the chemical controls now employed in 

 the United States. 



A somewhat cursory examination of the 

 literature regarding lake fertilization studies 

 has revealed that zooplankton studies per se 

 have been largely disregarded by workers 

 in this field. Possibly one reason for this is 

 that phytoplankton life cycles are usually short, 

 and thus their responses to fertilized environ- 

 ments are more accelerated, spectacular, and 

 easily observed. A frequent approach in the 

 analyses of fertilization results has been to 

 proceed directly from the addition of the 

 fertilizer to the waters to the subsequent 

 measurement of the results in terms of fish 

 growth or survival. Frequently the effect of 

 increased nutrient supply on phytoplankton 

 production is also included, and occasionally 

 changes in bottom fauna are recorded. The 

 zooplankton, however, are largely either 

 ignored or lumped with other planktonic forms. 

 The fact that zooplankton are usually one step 

 nearer the fish than are the phytoplankton in 

 the food chain, and, as indicated at Bare Lake, 

 that the effect of fertilization on zooplankton 

 may extend beyond the actual fertilization 

 period, would argue for their importance in 

 any study of this nature. 



Short-term interpretation of zooplankton 

 sampling results is often made difficult by 

 the presence of predator populations. In the 

 Bare Lake study, cropping by predators may 

 have effectively masked the response of the 

 zooplankton to the fertilizer-enhanced environ- 

 ment for a period of time beyond the lag 

 normally expected. The fact that zooplankton 



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