Municipal wastewater as an ecological trap: Effects on fish communities across seasons
Graphical abstract
Introduction
Municipal wastewater treatment plant (WWTP) effluents, although usually treated, still contain a complex mixture of chemicals, including but not limited to excess nutrients, pesticides, metals, micro- and macroplastics, pharmaceuticals and personal care products (PPCPs), as well as natural and synthetic hormones (Daughton and Ternes, 1999; Kolpin et al., 2002; Ternes et al., 2004; Holeton et al., 2011; McCormick et al., 2016). As a result, effluents from WWTPs are a major source of environmental stressors in aquatic environments, accounting for the largest point source of contamination in Canada, by volume (Environment Canada, 2001; Holeton et al., 2011). Their continuous release into watersheds can significantly impair aquatic environments and ecosystems via chronic exposure of biota to contaminants of emerging concern (CECs), oxygen depletion, eutrophication, and even physical changes to habitats (e.g., alterations in flow, turbidity, and thermal properties; Holeton et al., 2011; Tetreault et al., 2011; Hamdhani et al., 2020).
The impacts of wastewater effluent exposure on aquatic organisms are observed across multiple levels of biological organization. Such impacts include endocrine disruption, represented by severe incidences of intersex, reduced androgen levels, and reduced fertilization success (Bahamonde et al., 2015; Fuzzen et al., 2015). Exposure to wastewater effluents also has metabolic and behavioural effects, demonstrated by an increase in metabolic rate (Du et al., 2018, Du et al., 2019; Mehdi et al., 2018) and irregular courtship and aggressive behaviours (Saaristo et al., 2014; McCallum et al., 2017a; McLean et al., 2019). Comparatively, few studies have examined the impacts of wastewater effluent exposure at higher levels of biological organization, such as population- and community-level responses. This is surprising, given how relevant such impacts are for evaluating risks. For example, one common wastewater constituent, 17α-ethynylestradiol, has been linked to the collapse of a fathead minnow (Pimephales promelas) population and several ecosystem shifts in a whole-lake experiment (Kidd et al., 2007; Kidd et al., 2014). Other studies have also linked wastewater exposure to higher rates of male feminization and reduced breeding success in fishes, implying potential consequences to population sustainability (Jobling et al., 1998; Harris et al., 2011; Bahamonde et al., 2015; Fuzzen et al., 2015). Wastewater effluent can also reduce species richness and promote the dominance of tolerant and/or invasive species (Ra et al., 2007; Yeom et al., 2007; Brown et al., 2011; Tetreault et al., 2012; McCallum et al., 2019). Therefore, population and community disruptions from wastewater effluent may be extensive, but few other studies have examined fish communities in effluent-dominated environments.
In addition to the paucity of studies on fish communities, our knowledge about population- and community-level effects of WWTP effluents is derived solely from research conducted during warmer months of the year. It is unknown if and how the impacts of wastewater are exacerbated or diminished by colder temperatures. This is of vital concern for a number of reasons. First, in many temperate and polar regions of the globe, winter is a dominant season, lasting 4–8 months. Understanding the effects of WWTP effluents during such a prolonged season is of critical importance. Second, WWTPs often produce effluent of poorer quality in the winter; this is partly due to the higher incidence of human ailments that increase usage of PPCPs during the winter, and the reduced effectiveness of biological degradation of contaminants in WWTPs in colder temperatures (Vieno et al., 2005; Sui et al., 2011; Yu et al., 2013; Kot-Wasik et al., 2016). Third, wastewater effluent can be a source of thermal pollution—altering the temperature of receiving environments by as much as 5–10 °C in the winter (Environment Canada, 2001; Kinouchi et al., 2007; Mehdi et al., 2019). These changes in the thermal profile of aquatic environments may significantly alter aquatic communities, as ectothermic organisms (e.g., fish) are attracted to such thermally-enhanced environments, especially during the winter, when temperatures elsewhere may be suboptimal (Coutant, 1987; Cooke et al., 2004). The thermal plumes created by WWTPs may act as ecological traps (Schlaepfer et al., 2002; Battin, 2004) because fishes may use such environments as thermal refugia during the winter, accentuating exposure to contaminants in wastewater effluent.
In this study, we examined the influence of seasonality by assessing the impacts of wastewater effluent on fish communities near two WWTPs during the summer and winter. The two WWTPs chosen are located on the eastern- and western-most ends of Hamilton Harbour, one of 43 Areas of Concern under the Great Lakes Water Quality Agreement (Great Lakes Water Quality Agreement, 2012). Wastewater contamination is a stressor that is of particular concern in Hamilton Harbour, as it is estimated that ~50% of its inflow comes from wastewater (Government of Canada, 2017). We examined various fish community indices along a distance- and therefore contamination-gradient from the two plants to assess the impacts of wastewater exposure on the integrity of these respective ecosystems. In addition, water quality parameters and the concentrations of various PPCPs and other anthropogenic compounds in the final treated effluent were characterized to assess the abiotic impacts of wastewater contamination. We predicted that wastewater inputs would have significant effects on the physical habitat of effluent-receiving environments, thus affecting fish communities in these impacted sites. We expected this to be more apparent during the winter, when the quality of the effluent is expected to decline. If fish seek thermal refuge near WWTP outflows, then we predicted these sites would be highest in fish abundance, species richness, and species diversity, and be most compositionally distinct from sites farther away, particularly during the winter.
Section snippets
Dundas WWTP
The Dundas WWTP is located on the western tip of Cootes Paradise Marsh, the largest wetland west of Lake Ontario. The treatment facility is rated as a conventional activated sludge plant with tertiary filtration. The facility treats the majority of wastewater from the Dundas population (~30,000 people) and has a capacity of 18.2 million litres per day (City of Hamilton, 2019). The plant's effluent is discharged into the Desjardins Canal, an old shipping corridor located on the western-most end
Dundas WWTP
At the Dundas WWTP sampling sites, 2388 fish were collected (2112 in the summer and 276 in the winter) consisting of 23 unique species (Supplementary Table 8). Overall, fish were less abundant (based on CPUE) in the winter than in the summer (PLMM, t = −4.63, p < 0.01; Fig. 2A). In the winter, abundance declined with distance from the outfall (t(Winter) = −3.13, p < 0.01; Fig. 2A); however, no such decline was observed in the summer (t(Summer) = 0.83, p = 0.39; Fig. 2A). Similarly, species
Discussion
Our study explored the impacts of wastewater contamination on fish communities between the summer and winter. Fish communities were sampled along contamination gradients generated by two WWTPs in Hamilton, ON, Canada during both seasons. In the winter, sites closer to the effluent outfall generally had higher fish abundance, higher species richness, and higher species diversity compared to sites farther away. This trend, however, was not as apparent in the summer. Wastewater plumes are a
CRediT authorship contribution statement
Hossein Mehdi: Conceptualization, Methodology, Formal analysis, Investigation, Writing - original draft, Writing - review & editing, Visualization. Samantha C. Lau: Investigation, Writing - review & editing. Caitlyn Synyshyn: Investigation, Writing - review & editing. Matthew G. Salena: Investigation, Writing - review & editing. Erin S. McCallum: Investigation, Formal analysis, Writing - review & editing. Melissa N. Muzzatti: Investigation, Writing - review & editing. Jennifer E. Bowman:
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We are extremely grateful to the numerous students, volunteers, technicians, and others who helped with field and laboratory work. We especially appreciate Brittney Borowiec, Jonathan Hamilton, Catherine Ivy, Markelle Morphet, and Kirsten Nikel for their unyielding dedication to this project. A special thank-you is also dedicated to Chelsea Airstone, Mark Bainbridge, Shagufta Bi, Jacqueline Bikker, Kate Brouwer, Katrina Cantera, Andrea Court, Lien Dang, Hadi Dhiyebi, Alexandra Green-Pucella,
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2022, ChemosphereCitation Excerpt :It would be imperative to validate these findings in the field in future studies, and to consider the potential interactive effects of seasonal differences in temperature and effluent quality, as wastewater in the winter is often of poorer quality than in the summer (Mehdi et al., 2021). We believe that our findings will strengthen our understanding of ecotoxicology during the winter, a season that is rarely studied in ecotoxicological research (Larocque et al., 2020; McMeans et al., 2020; Mehdi et al., 2021). Hossein Mehdi: Conceptualization, Methodology, Formal analysis, Investigation, Writing – original draft, Writing – review & editing, Visualization., Markelle E. Morphet: Investigation, Writing – review & editing., Samantha C. Lau: Investigation, Writing – review & editing., Leslie M. Bragg: Conceptualization, Methodology, Formal analysis, Investigation, Writing – review & editing, Mark R. Servos: Conceptualization, Methodology, Writing – review & editing, Supervision., Graham R. Scott: Conceptualization, Methodology, Writing – review & editing, Supervision, Funding acquisition., Sigal Balshine: Conceptualization, Methodology, Writing – review & editing, Supervision, Project administration, Funding acquisition.