Ecological effects of a bleached kraft pulp mill effluent on benthic biota of the Athabasca River
Podemski, Cheryl Linda
The effects of nutrient enrichment and contaminant toxicity from a bleached kraft mill effluent (BKME) on the benthic biota of the Athabasca River were assessed using an integrated assessment approach. Components of the research included a stream mesocosm experiment, field observations, and chronic and behavioral laboratory bioassays using mayfly species from the receiving environment. Effluent and nutrient additions to stream mesocosms resulted in a 7-fold increase in periphyton biomass (Chl'a'), a doubling of insect abundance, approximately 30-100% increase in individual dry weight of some grazing insect taxa, and altered diatom and insect community composition. In all cases, responses to 1% BKME and an equivalent nutrient addition were remarkably similar, indicating that the primary effect of this discharge was nutrient enrichment. These findings were corroborated by observations in field samples from reference and exposed river reaches. Laboratory bioassays addressed the effect of exposure to BKME in water alone, or both water and food, on feeding behavior of the mayfly ' Ameletus subnotatus'. BKME in water had no effect on feeding, but exposure through both food and water resulted in 26-33% reduced consumption in BKME treatments. Contrary to expectations, when given a choice, mayflies preferentially fed on diatoms exposed to 1-7% BKME. Exposed diatom cultures contained more bacteria than control algae, and total lipid content of the diatoms ranged from 11.7% in the controls to 16.9% in 7% BKME. These observations, combined with results from feeding bioassays, indicated that exposure to effluent increased algal food quality. Chronic toxicity of the effluent was assessed for 'A. subnotatus ' and 'Baetis tricaudatus'. In both taxa, exposure to effluent in food and water increased size (total length) by 10-30%, supporting the conclusion that BKME exposure increased food quality of algae. First instar 'B. tricaudatus' were sensitive to BKME, with >= 50% mortality at concentrations above 1%, while mortality in older nymphs increased by at 7% BKME. Effluent-exposure had no effect on hatching success of 'B. tricaudatus. A subnotatus' exhibited increased mortality at 1%. Increased mortality with faster growth may indicate that these insects do not expend metabolic resources on defense. This research demonstrates a new approach for assessing the environmental effects of BKME release, and has resulted in new understanding of the impacts of this industry on the benthic community of this and perhaps other, northern rivers.