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BULLETIN OF THE BUREAU OF FISHERIES 
In the first place many of the smaller organisms will not be retained by the plankton 
net, and in the second place some organisms pack much more closely in the centrifuge 
tube than others. For the centrifuge plankton counts, half a liter of water was run 
through the Foerst centrifuge. The algse in the centrifuge plankton were enumerated 
in the usual manner. 
Most of the chemical results are expressed in parts per million (p. p. m.) in the 
text. The organic matter of the net plankton also called the organic matter or in 
some cases the net loss on ignition has been expressed in milligrams per liter. In the 
tables the expression milligrams per liter alone has been used. The hydrogen-ion 
concentrations are as a matter of convenience expressed in terms of pH values rather 
than in terms of the actual hydrogen-ion concentration. According to this notation 
the maximum hydrogen-ion concentration corresponds to the minimum pH value. 
The transparency is expressed in inches. 
The volumetric net plankton determinations are expressed in cubic centimeters 
per 10 liters of water. The algae of the centrifuge plankton are expressed in numbers 
per liter of water. 
The expressions ammonia-nitrogen, nitrate-nitrogen, and nitrite-nitrogen when 
used in this paper have the same meaning as they have in Standard Methods of 
Water Analysis. The values for phosphorus are stated in terms of the element rather 
than in terms of P0 4 or P 2 0 5 . 
ACKNOWLEDGMENTS 
The writer wishes to express his gratitude to Prof. C. Juday, of the University of 
Wisconsin, and to Dr. H. S. Davis, of the United States Bureau of Fisheries, for helpful 
advice and criticism. The writer wishes also to acknowledge his indebtedness to 
those members of the staff at Fairport who have cooperated in the carrying out of this 
investigation. 
C POND EXPERIMENTS 
DESCRIPTION OF PONDS 
The C ponds are a series of six small cement ponds, all of the same size and shape. 
Their arrangement with respect to one another is shown in Figure 1. These ponds are 
50 feet long and 8 feet wide and each has an area of 378 square feet. The ends are 
in the form of a semihexagon, which accounts for the reduced area. The depth of the 
water in these ponds was 14 inches at the upper end and 20 inches at the lower end. 
This would give each pond a volume of water of approximately 530 cubic feet. 
PURPOSE OF THIS EXPERIMENT 
The series of experiments in the C ponds was carried on to determine the effective- 
ness of soybean meal, shrimp bran, and superphosphate as pond fertilizers. Accord- 
ingly C 1 was fertilized with superphosphate, C 2 with soybean meal, and C 3 with 
shrimp bran. C 4 was used as a control without any fertilizer. An analysis of the 
soybean meal gave the following results: Total phosphorus 1.2 per cent, nitrogen 
(exclusive of nitrate nitrogen) 24 per cent, and total organic matter 60.9 per cent. A 
similar analysis of shrimp bran gave the following results: Total phosphorus 1.9 per 
cent, nitrogen (exclusive of nitrate nitrogen) 7.1 per cent, and total organic matter 
52.6 per cent. The superphosphate is the 16 per cent acid phosphate. 
The amounts of fertilizer used and the dates on which it was applied are shown in 
Table 1. 
