Increased sewage pollution beginning c. 1910 



After approximately 1910, as the pollution load increased, criti- 

 cally low dissolved oxygen levels in the water and putrescent conditions 

 in the bottom muds occurred farther and farther downstream with detri- 

 mental effect on food organisms and fish (Richardson, 192Lb) . Richardson 

 believed that in the 1915-1920 period the area in which the bottom fauna 

 was drastically reduced or obliterated was expanding downstream at the 

 rate of 16 miles per year. By 1920, the bottom fauna in the river and 

 bottomland lakes as far downstream as Browning (mile 97.0) had been 

 affected. The aquatic plants ( Potamogeton , Ceratophyllum , Scirpus , and 

 Vallisneria ) which once covered up to 50 percent of the total surface 

 acreage of bottomland lakes near Havana and several square miles of 

 Peoria Lake had practically disappeared. The weed fauna (aquatic insects 

 and snails which inhabit aquatic vegetation) had disappeared with the 

 aquatic plants. (Richardson 1921b) reported the following changes in the 

 bottom fauna of Peoria Lake: 



"(1) Disappearance of most species and genera and of 

 several families of small Mollusca, along with important 

 average decrease in numbers of the more tolerant forms 

 still surviving; (2) enormous increase in larval midges 

 (Chironomidae) , with invasion of several more or less 

 distinctly pollutional species, and similar or even 

 greater increase in sludge-worms (Tubif icidae) ; and 

 (3) disappearance throughout Peoria Lake, except im- 

 mediately along shore or in the short, half-mile, 

 stretch of swifter water in Peoria Narrows, of all 

 "other insects" (Ephemeridae, Odonata, Phryganeidae, 

 Corixidae, etc.), as well as of planarians and leeches, 

 Amphipoda, Isopoda, sponges, and Bryozoa." 



In the river channel upstream from Havana, he noted these changes 

 (Richardson, 1921b) : 



"While the average weight of the channel haul here 

 was over 5,000 pounds per acre in 1915, in 1920 it 

 was less than 250 pounds — a net loss of 95.3 percent 

 In the 4 — 7ft. zone for the same five-year period 

 the average haul showed a shrinkage of 95.9 percent, 

 or from 2,122 pounds to only 87 pounds per acre. 



•4 7 



