at its mouth near St. Charles, Missouri (Mississippi River mile 195.0) 

 (Hooker, 1897, in Galtsoff, 1924: 371). The influence of the highly 

 turbid waters of the Missouri River on the lower Mississippi River was 

 also noted by Townsend (1915 in Galtsoff, 1924: 370); 



The amount of sediment in the lower Mississippi depends 

 almost exclusively on the proportion of water from the 

 Missouri. In comparison with the Missouri, the upper 

 Mississippi is a clear stream and the amount of sediment 

 carried by it is insignificant. 



Water clarity is influenced by factors other than suspended sedi- 

 emnt, such as the quantity of plankton. However, Galtsoff (1924: 372) 

 felt that in the Mississippi River, water transparency depended prin- 

 cipally on the amount of sediment in suspension. He reported that 

 the upper Mississippi in 1921 was "muddy" even during low water and 

 progressively more turbid downstream (Galtsoff, 1924: 371). Water 

 clarity readings (measured by a round white disk, 25 cm diameter) 

 during the 1921 survey ranged from a maximum of 102 cm at the outlet 

 of Lake Pepin (Mississippi River mile 763.5) to 22 cm at Fairport, 

 Iowa (Mississippi River mile 463.0) (Galtsoff, 1924: 371). 



Platner (1946: 16) also reported an increase of turbidity in a 

 downstream direction in the Mississippi River. His only comments on 

 the methods he used were: "... turbidity was recorded in parts per 

 million based on readings calculated from a previously standardized 

 Fuller's earth curve" (1946: 16) and "The percentage of sedimentation 

 was recorded in a 100 ml capacity mine-waste tube, one hour after 

 collection of the sample" (1946: 16). He found average turbidity values 

 during low water at 40 ppm in the upper reaches of the river, 300 

 ppm in a middle section, and 1,880 ppm below the mouth of the Missouri 

 River (Platner, 1946: 16). Both Galtsoff (1924: 371) and Platner 

 (1946: 16) noted that turbidity levels increased with an increase in 

 river water levels. Turbidity levels during high water averaged 40 

 percent greater than during low water (Platner, 1946: 16). 



In 1955, Dorris et al. (1963) sampled several limnological parameters 



134 



