. Bulletin. Natural history; Natural history. 320 Illinois Natural History Survey Bulletin Vol. 31, Art. 8 ri80. 1 1100 1200 1300 CENTRAL STANDARD TIME OXYGEN = 0 OsuRFACE A—A mid-depth nbottom |barge passage •—•turbidity Fig. 1.—Dissolved oxygen concentrations and turbidity in the middle of the navigation channel of the Illinois River at mile , during passages of towboats on 7 November, 1963. Symbols for dissolved oxygen are circles for at the surface, triangles for at mid-depth, and squares for at the bottom. Turbidity is indicated with black dots. The time at which each towboat passed m
. Bulletin. Natural history; Natural history. 320 Illinois Natural History Survey Bulletin Vol. 31, Art. 8 ri80. 1 1100 1200 1300 CENTRAL STANDARD TIME OXYGEN = 0 OsuRFACE A—A mid-depth nbottom |barge passage •—•turbidity Fig. 1.—Dissolved oxygen concentrations and turbidity in the middle of the navigation channel of the Illinois River at mile , during passages of towboats on 7 November, 1963. Symbols for dissolved oxygen are circles for at the surface, triangles for at mid-depth, and squares for at the bottom. Turbidity is indicated with black dots. The time at which each towboat passed mile is marked by an arrow. occasions on 7 November, 1963. It took approximately T-k hours for the tur- bidity to return to background levels following passage of towboats. A Natural History Survey crew took a few dissolved oxygen readings in midchannel on 6 and 7 November, 1963, before, during, and after tow- boats had passed (Fig. 1 and 2). One might expect turbulence from move- ment of the hulls and from the pro- pellers to aerate the water. Surpris- ingly, oxygen levels at the surface de- clined and then recovered following passage of a towboat on 6 November. On 7 November, oxygen levels at both the surface and bottom declined. The dechnes are significant; oxygen levels at the surface on 6 November and at the bottom on 7 November declined by mg/1, and the standard deviation of the method used (azide modification of the Winkler method) is mg/1, even in the presence of appreciable interference. The decline in dissolved oxygen and the increase in turbidity are both attributable to the resuspension of sediment caused by towboats mov- ing in the relatively shallow naviga- tion channel ( m deep). Sediments in the Illinois River exert an appreciable oxygen demand, and the demand in- creases 7-fold to 10-fold when the sedi- ments are disturbed. For example. Butts (1974:12) reported an oxygen demand of g/mVday for sediment at mile , under quiescent
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