354 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
VIII.— EFFECT OF PHOSPHATE DREDGING UPON THE OYSTER WATERS. 
It lias been claimed that dredging for phosphate rock (one of the most important 
industries of the State) pollutes the waters and renders whole regions totally unlit 
for oyster-culture, and it seems natural that the extent of the industry would exercise 
some effect upon the life of neighboring waters. In the Ooosaw River, for example, a 
dozen dredgers in the space of 3 miles collect daily about 1,000 tons of washed phos- 
phate rock. This continued work might affect the neighboring water in two ways : 
(1) chemically, by causing substances, gases, acids, or salts that have been imprisoned 
in rock or marl, to be taken into solution by the water ; or (2) mechanically, by churn- 
ing or creating a marked muddiness of the water, the material in suspension becoming 
gradually deposited wherever carried by the currents. 
In the first case, to determine any noteworthy chemical changes, a number of 
water specimens were specially collected; several from the neighborhood of dredgers 
on either side of Ooosaw River, one at the mouth of Parrott Creek, and all of bottom 
water. The following are the results: 
(1) That the salty constituents of the water appear in no way abnormal. 
(2) That the ammonias are increased in a marked way, doubtless from the churned- 
up organic matters which may at once be detected by the microscope, perhaps in part 
from the dissolved salts of the marl or phosphates. The free ammonia in the imme- 
diate neighborhood of dredgers shows as great a proportion as ^ parts per 1,000,000, 
ten times as great an amount as shown at Port Royal. This ammoniated condition of 
the water can hardly be regarded as of serious danger to neighboring life. 
(3) That the phosphoric ingredient of the water exists in so slight a degree as to 
be altogether innocuous. No better biological proof is needed than the presence of 
large gorgonias, sponges, and bryozoans anchored to the fragments of the phosphate 
rock itself. Water from the neighborhood of Ooosaw Dredge No. 5 * shows ^ parts 
per 1,000 of phosphoric acid, the highest result obtained. Off the mouth of Dale 
Creek, about half a mile distant, the phosphoric acid contained is but jf „ parts per 
1,000. The alkaline ingredients of the water render impossible the presence of phos- 
phoric acid in an unprecipitated condition, save perhaps as a trace. The amount of 
phosphate present, slight as it is, is doubtless due to the suspended particles of the 
phosphate rock. Chemically, therefore, the neighboring waters are not dangerously 
polluted by the dredging of phosphate. 
The injury that would befall life in the neighborhood of dredging is due almost 
entirely to the mechanical formation and deposit of sediment. The murkiness of the 
water, the heavy character of the fine, gray silt, and the continual current shiftings of 
bottom are the causes that render the entire neighborhood for miles about practically 
unfit for oyster-culture. Particular note was made in the shallow water of the char- 
acter of the depositing sediment and of the entire absence of living oysters. The daily 
amount of waste sand, mud, and marl that is sifted out into the stream by the washing 
processes is almost incalculable. One great dredger, for example, before reaching the 
phosphate rock, cuts through a dozen feet of overlying material. 
* Then in Coosaw River, 1 mile above the mouth of Parrot. Creek, 1,000 yards from right shore. 
