Risks of hypoxia and acidification in the high energy coastal environment near Victoria, Canada's untreated municipal sewage outfalls

Abstract

Wastewater disposal often has deleterious impacts on the receiving environment. Low dissolved oxygen levels are particularly concerning. Here, we investigate the impacts on dissolved oxygen and carbon chemistry of screened municipal wastewater in the marine waters off Victoria, Canada. We analyzed data from undersea moorings, ship-based monitoring, and remotely-operated vehicle video. We used these observations to construct a two-layer model of the nearfield receiving environment. Despite the lack of advanced treatment, dissolved oxygen levels near the outfalls were well above a 62 μmol kg hypoxic threshold. Furthermore, the impact on water column oxygen at the outfall is likely <2 μmol kg. Dissolved inorganic carbon is not elevated and pH not depressed compared to the surrounding region. Strong tidal currents and cold, well-ventilated waters give Victoria's marine environment a high assimilative capacity for organic waste. However, declining oxygen levels offshore put water near the outfall at risk of future hypoxia.

Pharmaceuticals and Personal Care Products in Municipal Wastewater and the Marine Receiving Environment Near Victoria Canada

“…However, the city is unique among its North American and European counterparts for its lack of even primary sewage treatment (Environment and Climate Change Canada, 2012;European Environmental Agency, 2013;OECD, 2015). The city of nearly 350,000 inhabitants (Statistics Canada, 2012) fine screens (6 mm) its wastewater to remove large debris (CRD, 2015) before discharging it through two deep-sea outfalls into the cold fast moving waters of Juan de Fuca Strait (Krogh, 2017). The two pump stations are located at Macaulay (MAC) and Clover (CLO) Points (Figure 1) and each outfall extends over a kilometer offshore to approximately 65 m depth.…”

“…The residual nontidal currents in the bottom of the water column are toward the south-east at the MAC outfall (Krogh, 2017) and toward the east at the CLO outfall (Chandler, 1997). These residual currents are driven by the large estuarine circulation of the Fraser River (Krogh, 2017). Water temperatures are cool (8-12 • C) and oxygen levels are high (200 µmol kg −1 , Krogh, 2017).…”

“…These residual currents are driven by the large estuarine circulation of the Fraser River (Krogh, 2017). Water temperatures are cool (8-12 • C) and oxygen levels are high (200 µmol kg −1 , Krogh, 2017). Of the two outfalls MAC has lower flows, but the effluent typically has higher concentrations of contaminants, and the receiving environment is generally considered to be more vulnerable to negative impacts as current speeds are lower than around CLO (Dinn et al, 2012).…”

“…Of the two outfalls MAC has lower flows, but the effluent typically has higher concentrations of contaminants, and the receiving environment is generally considered to be more vulnerable to negative impacts as current speeds are lower than around CLO (Dinn et al, 2012). The seabed around MAC is made up of a mixture of sediment size classes ranging from fines to gravel while CLO is rocky (Markovic, 2003;CRD, 2015;Krogh, 2017). Past sediment quality assessments from MAC show that elevated concentrations of many sewage derived compounds extend out to 800 m in the dominant down current direction (south-east) (Dinn et al, 2012;CRD, 2015).…”

Antibiotic Resistance of Bacteria in Two Marine Mammal Species, Harbor Seals and Harbor Porpoises, Living in an Urban Marine Ecosystem, the Salish Sea, Washington State, USA

“…The sampling regions represented areas with variable anthropogenic activities and human population density. Tourists heavily visit the northern portion during the summer months, but less so the rest of the year; however, currents may transport untreated wastewaters down from the cities of Vancouver and Victoria, British Columbia into this region [27]. The lower half of the northern region contains two military bases (Naval Air Station Whidbey Island and Naval Station Everett), heavily visited Whidbey and Camano Islands, as well as agricultural areas on these islands and the mainland at corresponding latitudes.…”