REDUCTION OF DISSOLVED-OXYGEN CONCENTRATION IN WISCONSIN STREAMS DURING SUMMER RUNOFF

It is commonly beleived that runoff from heavy rainfall is not detrimental to the O content of rural streams free from industrial and municipal discharges. However, evidence is presented of low dissolved O (DO) concentrations during high flows (caused by agricultural runoff during summer rainstorms) in southern Wisconsin streams. Continuous monitoring of streams with in situ oxygen meters indicated a rapid decrease in dissolved oxygen with a rise in the hydrograph. The cause of the oxygen reduction may be due to one or more factors such as (i) inflow of large volumes of runoff with low DO concentrations, (ii) the influx or resuspension of O demanding materials as a result of the storm water input, (iii) decreased O solubility caused by increased water temperature, and (iv) possible reduced photosynthetic productivity. Loss of DO is important because it appears to be associated with fish kills and declining sport fish populations in streams in the region.