

The poor oxygen content in the La Grange Pool in 

 the summers of 1964 and 1965 (Fig. 3 and Table 1) 

 probably reflects the eflfects of additional wastes coming 

 into the river from the Peoria-Pekin area. Conditions 

 were particularly bad during the summer of 1965. This 

 has been a problem of some duration. Roruff & Buswell 

 (1929:54) in reviewing their own and other studies of 

 the BOD (biological oxygen demand) of the river prior 

 to 1928, stated: "Physical conditions, especially below 

 Peoria and Pekin and below this latter city for some 

 miles, tend to show each summer season signs of an 

 increasing pollution load. The extra load that is being 

 added to the river is due to the increased population of 

 the Pekin and Peoria districts, as well as to the veiy 

 marked increase in industrial wastes." BorufT (1930:5) 

 found that the dissolved oxygen content of the water 

 below Peoria and Pekin remained at a low level. 



Our present study of the bottom fauna (Starrett & 

 Paloumpis, unpublished) and of the fishery indicates 

 that some improvement in conditions occurs below the 

 mouth of the Sangamon River at Beardstown. The pos- 

 sible influence of this tributary at times is clearly shown 



in the cross-section oxygen readings made in 1964 (Fig. 

 4). In the entire cross section of the Illinois River at 

 Mile 89.3, just above the mouth of the Sangamon, dis- 

 solved oxygen was at a value of 2.4 ppm. The cross 

 section at Beardstown at Mile 88.6, also shown in Fig. 

 4, disclosed a high oxygen content on the left bank below 

 the Sangamon's confluence through Muscooten Bay, and 

 a low content on the right or opposite side. However, 

 our 1965 data do not reflect such beneficial effects from 

 the Sangamon River as were noted in 1964. Tiie longi- 

 tudinal section (Fig. 4) below the Sangamon's mouth 

 shows that the mixing of the high-oxygen Sangamon 

 water in 1964 did not reach midstream until about 

 Mile 88. 



BOTTOM FAUNA 



The bottom fauna ( benthos j consists of the macro- 

 scopic animals which spend all or a part of their lives 

 living on or in the bottom sediments. Certain benthic 

 organisms, such as insect larvae, fingernail clams, and 

 snails, are important food items for larger animals such 

 as fish and ducks (Starrett & Paloumpis, unpublished; 



2.4- 



CF?OSS SECTION 



Left MILE 89.3 RigM 



Bonk 1047 CST Bank 



DISSOLVED OXYGEN- ILLINOIS RIVER 



3 FEET BELOW SURFACE 



16 JULY 1964 



9,0 



80- 



7,0- 



6.0 



5.0 



4.0 



3.0- 



2.0 



6.0 



5.0- 



4.0- 



3.0- 



2.0- 



CROSS SECTION 



HIGHWAY 

 BRIDGE 



Left MILE 88.6 RigM 

 B(»ik 1000 CST Bonk 



MILE 89 3 



RAILROAD 

 BRIDGE 



ILLINOIS 

 RIVER 



BEARDSTOWN 



88.0 



LONGITUDINAL SECTION 

 BELOW MOUTH OF SANGAMON RIVER 



87.0 



Fig. 4. — A continuous 

 scries of dissolved oxygen read- 

 ings made in the Illinois River 

 with a galvanic oxygen ana- 

 lyzer near the mouth of the 

 Sangamon River. The graphs 

 reflect the increase and mixing 

 of dissolved oxygen in the Illi- 

 nois River resulting from the 

 effects of a major tributary 

 having a higher dissolved oxy- 

 gen content. Cross section at 

 Mile 89.3 is above the mouth 

 of the Sangamon River, and 

 cross section at Mile 88.6 is 

 below. ( Illinois Natural His- 

 tory Survey data.) 



MILES FROM 



RIVER 



11 



