Platner (1946: 74), in his 1944 water quality survey of the upper 

 Mississippi River, found that total nitrogen values were less than 1.0 

 ppm in midwinter, averaged 1.7 ppm during low water and 5.5 ppm in 

 high water. The 1944 phosphate levels of the Mississippi River ranged 

 from .05 to .22 ppm during midwinter, .20 to .35 ppm during high water, 

 and .22 to .45 during low water (Platner, 1946: Figure 13). 



Colbert et al. (1975: 39) reported that 1974 nutrient concentrations 

 in Pools 24, 25, and 26 were comparable to those found by Platner (1946) 

 in 1944. Nutrient concentrations in 1974 were higher during a high 

 stage than during an average stage (Colbert et al. , 1975: 38). This 

 was also observed by Platner (1946: 74). Ammonia-nitrogen levels (main 

 channel) in Pools 24, 25, and 26 in 1974 averaged 0.12 mg/1 during an 

 average stage and 0.70 mg/1 at a high stage (Colbert et al. , 1974: D-3) . 

 Total phosphorus levels the same year averaged 0.18 mg/1 and 1.2 mg/1 

 during average and high stages, respectively (Colbert et al. , 1975: D-3). 

 Colbert et al. (1975: 38) attributed the increase in nutrient concentra- 

 tions during high water to the resuspension of nutrients from bottom 

 sediments and to land runoff. 



Due to lack of early data, it was impossible to evaluate pre- and 

 post-construction changes of nutrient concentrations in the upper Mis- 

 sissippi River. 



Heavy Metals and Pesticides . The analytical methodology to measure 

 trace materials in water was in its infancy in the period preceding 

 construction of the nine-foot navigation system. Therefore, no data on 

 heavy metals or pesticides were obtained for this period. 



A few trace elements (iron, manganese, zinc, and fluorine) were 

 measured by Platner (1946). Recent (1974) heavy metal data for Pools 

 24, 25, and 26 can be found in Colbert et al. (1975). 



In general, one would expect the concentration of toxic materials 

 in sediments to increase in the downstream direction in each pool, due 

 to the physical distribution of sediment according to particle size and 

 weight. For the same reasons, one would also expect a lateral distribution, 

 with higher concentrations in slackwater areas than in the main channel. 



137 



