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A Decade of Research on the Environmental Impacts of Pulp and Paper Mill Effluents in Canada (1992-2002)

4.3 Mesocosms

The use of mesocosms to assess the effects of PME on aquatic biota has permitted studies of algae, invertebrates and fish, exposed under natural temperature and lighting conditions (Figure 3). Mesocosm studies have shown that PME increases the periphyton biomass and shifts the diatom community structure (Glozier et al., 2002). These effects are usually related to increased carbon and nutrient loads from the effluent, which may increase algal and bacterial growth (Culp et al., 1996). The increased algal and bacterial biomass results in growth-enhancing effects on invertebrates. Increased benthos abundance downstream of these PMEs was seen in many environmental effects monitoring surveys (Ellis & Lowell, 2001; Grapentine et al., 2001; Lowell et al., 2001, 2003).

Mesocosm studies have exposed mummichog for 28 d to control water or 3 % effluent from the bleached kraft mill located in Saint John NB (Dubé et al., 1997). The mesocosm pilot study, exposing juvenile fish and adult males and females, proved successful at this site (Dubé et al., 1997). Mesocosm studies have been used to track the steroid-reducing effects in bleached kraft pulp mill waste streams (Dubé & MacLatchy, 2000a, 2001b). Dubé and MacLatchy (2001a) have shown that installation of reverse osmosis (RO) treatment of evaporator condensates can reduce the potency of effluent to reduce plasma sex steroids and in vitro ovarian and testicular steroid production. Adult mummichogs, captured from a nearby reference site, were exposed to final BKME or to RO-feed and RO-permeate for 27 to 57 days. Exposure to 1 % effluent reduced steroids in 1997, but after installation of RO by the mill in 1997-1998, the effluent was not as potent at causing steroid depression (Dubé & MacLatchy, 2000a, b, 2001a) (See Characterization of Bioactive Chemicals).