Nutrient and Contaminant Effects of Bleached Kraft Mill Effluent on Benthic Algae and Insects of the Athabasca River

Pulp mill effluents may result in both inhibitory (chemical toxicity) and stimulatory (through nutrient enrichment) effects on aquatic ecosystems. In September 1993, we conducted an experiment to determine if there were differences in the response of benthic algae and insects to an addition of effluent versus the addition of similar levels of bioavailable phosphorus and nitrogen. This experiment was conducted in an artificial stream system constructed on-site at a bleached kraft pulp mill located in Hinton, Alberta. The stream system was stocked with a natural community of algae and invertebrates from the Athabasca River, collected just upstream of the mill’s discharge. The 28 d experiment consisted of three treatments: (1) a control, (2) a 1% dilution of treated bleached kraft mill effluent (BKME) and (3) the addition of nitrogen and phosphorus (NP) to match levels of soluble reactive phosphorus and nitrogen in the forms of nitrate/nitrite and ammonium (N-NO₃+NO₂ and N-NH₄) in the effluent. The addition of effluent or nutrients resulted in a dramatic and significant increase in the chlorophyll a (ChlJ content of periphyton on both natural and artificial substrates, compared to control streams. There was no difference in periphyton Chl_a content in effluent and nutrient addition steams. Composition of the invertebrate community was not affected by the addition of effluent, suggesting no effect on survival. Insect growth, as measured by differences in mean thorax length, increased with the addition of effluent. Growth of Ameletus (Ephemeroptera, Siphloneuridae) and capniid stoneflies (Plecoptera, Capniidae) was similarly increased in streams receiving a nutrient addition. Growth of baetid mayflies was not affected by the addition of effluent or nutrients. Our results suggest that the primary effect of 1% BKME addition to the Athabasca River is to stimulate primary productivity. If there were any inhibitory effects of the effluent on insect growth, these appear to have been mitigated by the concurrent increase in food resources.