TRIBUTARY CONTRIBUTIONS OF NUTRIENT LOADS AND SUSPENDED  SOLIDS  TO
THE ILLINOIS RIVER SYSTEM

Jeff L. Arnold and Dustin W. Gallagher.
Long Term Resource Monitoring Program, Havana Field Station, 704 North Schrader 
Avenue, Havana, IL 62644.  

Recently, considerable attention has been focused on hypoxia in the Gulf of Mexico. 
Excess nutrient loading from the Mississippi River basin is being blamed for this 
situation.  Due to liberal fertilizer application and intensive agricultural practices, 
Illinois contributes large amounts of nutrients and sediments to the Illinois and 
Mississippi River systems.  Beginning in 1989, the Illinois Natural History Survey's 
Long Term Resource Monitoring Program began monitoring various limnological 
parameters on the La Grange reach of the Illinois River.  Water passing through this 
reach is derived from a basin area of approximately 24,648 miż.  In 1993, monitoring 
effort was expanded to include the five Illinois River tributaries of Quiver (261 miż), 
Mackinaw (1,140 miż), La Moine (1,315 miż), Spoon (1,860 miż), and Sangamon 
(5,420 miż) Rivers with a total drainage area of 10,031 miż.  Monthly and annual 
nitrogen, phosphorus, and suspended solids loads were calculated for each tributary. 
Preliminary results indicate that, on average, Sangamon River contributed the highest 
nitrogen and phosphorus loads with a maximum load occurring in 1993.  At this time, 
the annual nitrogen load was calculated at 60,000 metric tons and the annual 
phosphorus load was calculated at 4,000 metric tons.  However, when comparing 
nutrient loads in relation to basin size, the Mackinaw and Spoon Rivers contributed 
more nitrogen and phosphorus.  In 1993, the Mackinaw River emptied approximately 
16 metric tons/miż/year of nitrogen and 1.8 metric tons/miż/year of phosphorus into 
the Illinois River while Spoon River discharged approximately 12 metric tons/miż/year 
of nitrogen and 2.0 metric tons/miż/year of phosphorus.  By comparison, the 
Sangamon River emptied approximately 10 metric tons/miż/year of nitrogen and .6 
metric tons/miż/year of phosphorus into the Illinois River.  Spoon River was also the 
primary contributor of suspended solids into the Illinois River system.  In 1993, 
approximately 9,500,000 metric tons/year of suspended solids entered La Grange 
reach from the entire river basin.  Of this total, nearly 4,500,000 metric tons/year 
originated from the Spoon River basin.  

Keywords:  Illinois River, hypoxia, nutrient loads, suspended solids, nitrogen
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