EFFECTS OF BIOLOGICALLY TREATED BLEACHED KRAFT MILL EFFLUENT ON COLD WATER STREAM PRODUCTIVITY IN EXPERIMENTAL STREAM CHANNELS

Large-scale outdoor experimental streams were used in a series of effluent addition studies to determine the compatibility of biologically treated bleached kraft mill effluent with satisfactory production of salmonid fishes. Results are reported for 9- to 10-month studies at effluent concentrations representing from 0.5 to 2.0 mg/L of effluent 5 d biochemical oxygen demand (BOD5) addition (1.3-5.1% v/v), as well as for an extended 3.5-year study at 0.5 BOD5 addition (1.5% v/v). The series of studies indicated a pattern of greater rainbow trout (Oncorhynchus mykiss) cumulative production and average weight in streams receiving effluent and better survival in the control streams. The final long-term study also indicated that successful maturation, spawning, hatching, larval development, and juvenile growth could take place during conditions of continuous effluent exposure. Measurements of the supporting food web suggest that effluent can increase periphyton production at low concentrations through nutrient additions but that higher effluent concentrations may reduce periphyton production due to the effect of color on underwater light transmittance. Macroinvertebrate populations increased in the streams receiving effluent.