A critical review of pollution active biomonitoring using sentinel fish: Challenges and opportunities

Water pollution is a significant threat to aquatic ecosystems. Various methods of monitoring, such as in situ approaches, are currently available to assess its impact. In this paper we examine the use of fish in active biomonitoring to study contamination and toxicity of surface waters. We analysed 148 previous studies conducted between 2005 and 2022, including both marine and freshwater environments, focusing on the characteristics of the organisms used as well as the principal goals of these studies. The main conclusions we drew are that a wide range of protocols and organisms have been used but there is no standardised method for assessing the quality of aquatic ecosystems on a more global scale. Additionally, the most commonly used developmental stages have been juveniles and adults. At these stages, the most frequently used species were the fathead minnow (Pimephales promelas) and two salmonids: rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta). Few studies used earlier stages of development (embryos or larvae), mostly due to the difficulty of obtaining fish embryos and caging them in the field. Finally, we identified research gaps in active biomonitoring for water quality assessment which could indicate useful directions for future research and development.

Impacts of wastewater treatment plants on benthic macroinvertebrate communities in summer and winter

Treated effluent from municipal wastewater treatment plants (WWTPs) is a major source of contamination that can impact population size, community structure, and biodiversity of aquatic organisms. However, because the majority of field research occurs during warmer periods of the year, the impacts of wastewater effluent on aquatic communities during winter has largely been neglected. In this study, we assessed the impacts of wastewater effluent on aquatic benthic macroinvertebrate (benthos) communities along the effluent gradients of two WWTPs discharging into Hamilton Harbour, Canada, during summer and winter using artificial substrates incubated for 8 weeks. At the larger of the two plants, benthic macroinvertebrate abundance was higher and diversity was lower at sites downstream of the outfall compared to upstream sites in both seasons. Whereas at the smaller plant, the opposite was observed, abundance increased and diversity decreased with distance from the outfall in both seasons. While the impacts of wastewater on benthic communities were largely similar between seasons, we did detect several general seasonal trends - family diversity of macroinvertebrates was lower during winter at both WWTPs and total abundance was also lower during winter, but only significantly so at the smaller WWTP. Further, benthic macroinvertebrate community composition differed significantly along the effluent gradients, with sites closest and farthest from the outfall being the most dissimilar. Our contrasting results between the WWTPs demonstrate that plants, with different treatment capabilities and effluent-receiving environments (industrial/urban versus wetland), can dictate how wastewater effluent impacts benthic macroinvertebrate communities.

Temperature modulates the impacts of wastewater exposure on the physiology and behaviour of fathead minnow

Municipal wastewater treatment plant (WWTP) effluent is a substantial source of pollution in aquatic habitats that can impact organisms across multiple levels of biological organization. Even though wastewater effluent is discharged continuously all year long, its impacts across seasons, specifically during winter, have largely been neglected in ecotoxicological research. Seasonal differences are of particular interest, as temperature-driven metabolic changes in aquatic organisms can significantly alter their ability to respond to chemical stressors. In this study, we examined the effects of multiple levels of wastewater effluent exposure (0, 25, or 50% treated effluent) on the physiological and behavioural responses of adult fathead minnow (Pimephales promelas) at temperatures simulating either summer (20 °C) or winter (4 °C) conditions. At 20 °C, wastewater exposure posed a metabolic cost to fish, demonstrated by higher standard metabolic rate and was associated with increased haematocrit and a reduction in boldness. In contrast, fish exposed to wastewater at 4 °C experienced no change in metabolic rate but performed fewer social interactions with their conspecifics. Taken together, our results demonstrate that wastewater exposure can lead to metabolic and behavioural disruptions, and such disruptions vary in magnitude and direction depending on temperature. Our findings highlight the importance of studying the interactions between stressors, while also underscoring the importance of research during colder periods of the year to broaden and deepen our understanding of the impacts of wastewater contamination in aquatic ecosystems.

Municipal wastewater as an ecological trap: Effects on fish communities across seasons

Municipal wastewater treatment plant (WWTP) effluents are a ubiquitous source of contamination whose impacts on fish and other aquatic organisms span across multiple levels of biological organization. Despite this, few studies have addressed the impacts of WWTP effluents on fish communities, especially during the winter-a season seldom studied. Here, we assessed the impacts of wastewater on fish community compositions and various water quality parameters during the summer and winter along two effluent gradients in Hamilton Harbour, an International Joint Commission Area of Concern in Hamilton, Canada. We found that fish abundance, species richness, and species diversity were generally highest in sites closest to the WWTP outfalls, but only significantly so in the winter. Fish community compositions differed greatly along the effluent gradients, with sites closest and farthest from the outfalls being the most dissimilar. Furthermore, the concentrations of numerous contaminants of emerging concern (CECs) in the final treated effluent were highest during the winter. Water quality of sites closer to the outfalls was poorer than at sites farther away, especially during the winter. We also demonstrated that WWTPs can significantly alter the thermal profile of effluent-receiving environments, increasing temperature by as much as ~9 °C during the winter. Our results suggest that wastewater plumes may act as ecological traps in winter, whereby fish are attracted to the favourable temperatures near WWTPs and are thus exposed to higher concentrations of CECs. This study highlights the importance of winter research as a key predictor in further understanding the impacts of wastewater contamination in aquatic ecosystems.

Wait and snap: eastern snapping turtles (Chelydra serpentina) prey on migratory fish at road-stream crossing culverts

There is growing evidence that culverts at road-stream crossings can increase fish density by reducing stream width and fish movement rates, making these passageways ideal predator ambush locations. In this study, we used a combination of videography and δ¹³C stable isotope analyses to investigate predator-prey interactions at a road-stream crossing culvert. Eastern snapping turtles (Chelydra serpentina) were found to regularly reside within the culvert to ambush migratory river herring (Alosa spp.). Resident fish species displayed avoidance of the snapping turtles, resulting in zero attempted attacks on these fish. In contrast, river herring did not display avoidance and were attacked by a snapping turtle on 79% of approaches with a 15% capture rate. Stable isotope analyses identified an apparent shift in turtle diet to consumption of river herring in turtles from culvert sites that was not observed in individuals from non-culvert sites. These findings suggest that anthropogenic barriers like culverts that are designed to allow passage may create predation opportunities by serving as a bottleneck to resident and migrant fish movement.