Potential Contribution of Nose Creek Stormwater Discharges to Impacts on Longnose Dace, Rhinichthys cataractae in the Bow River, Alberta

Stormwater runoff is a growing global concern, as urban drainage networks transport complex contaminant mixtures into receiving waters, potentially affecting fish health. Nose Creek, a stormwater-dominated tributary located in southern Alberta, Canada, receives inputs from more than 137 stormwater outfalls, and discharges into the Bow River in Calgary, Alberta. Previous studies on the Bow River have identified physiological impacts in fish collected/caged downstream of the municipal treatment plants, however some responses have also been observed at an upstream site near the Nose Creek confluence. This study aimed to evaluate Nose Creek as a potential contributor to impacts observed in fish in the Bow River. Adult longnose dace (Rhinichthys cataractae) were collected from Nose Creek and from sites along the Bow River upstream and downstream of its confluence, as well as from the downstream reach of the Elbow River, another stormwater-affected tributary. Nose Creek was highly elevated in nutrients, temperature, suspended solids, conductivity, metals and a wide variety of other chemical constituents. There were elevated levels of Escherichia coli (E.coli) and total coliforms in the Bow River downstream of the confluences. Longnose dace collected from two Nose Creek sites had significantly greater condition, liversomatic and gonadosomatic indices, but no differences were observed in whole organism responses in longnose dace collected from downstream Bow River relative to upstream. Whole-transcriptome analysis revealed that Nose Creek fish had markedly different gene expression profiles, with alteration of transcripts involved with steroid biosynthesis and metabolic pathways in female fish, and pathways related to PPAR signalling, metabolism of fatty acid and carbohydrate, and microbial metabolism in male fish. Fish downstream of the confluence showed alteration of the same pathways, although fewer genes were altered (<75) compared to Nose Creek (>140). The similarity of pathways affected in fish downstream of the confluence of Nose Creek suggests that stormwater is contributing to the responses seen downstream of its confluence.