Effect of an industrial ammonia discharge on the dissolved oxygen regime of the Willamette river, Oregon

Studies completed by the Department of Environmental Quality demonstrate that an industrial discharge of 7000–10,000 kg day −1 ammonia nitrogen can exert a very great impact on the oxygen regime of the lower Willamette River, Oregon through the microbially mediated process of nitrification. This conclusion is based upon the following evidence: (1) inorganic nitrogen mass flow data; (2) measured reductions in Willamette River dissolved oxygen during ammonia discharge as compared to non-discharge conditions; (3) the presence of nitrifying bacteria in mud and attached to aquatic vegetation and river cobbles; (4) verification of a dissolved oxygen model based upon nitrification as a primary ammonia sink and a dominant deoxygenation process; and (5) 15N heavy isotope tracer studies indicating significant conversion of ammonia to nitrate. An analysis of the data indicates that the observed average increase of 15% in dissolved oxygen saturation of the lower river during the period 1973–1979 is primarily a result of a drastic reduction of an industrial ammonia discharge in a relatively shallow surface active reach of the lower Willamette River, Oregon, U.S.A.