Local environmental conditions determine the footprint of municipal effluent in coastal waters: A case study in the Strait of Georgia, British Columbia

Abstract

To predict the likely effects of management action on any point source discharge into the coastal ocean, it is essential to understand both the composition of the effluent and the environmental conditions in the receiving waters. We illustrate a broadly-applicable approach to evaluating the comprehensive environmental footprint of a discharge, using regional geochemical budgets and nearfield monitoring. We take as a case study municipal effluent discharged into the Strait of Georgia (west coast of Canada), where there has been public controversy over the discharge of screened or primary-treated effluent directly into the ocean. Wastewater contributes ≤ 1% of the nitrogen, organic carbon and oxygen demand in the Strait and is unlikely to cause eutrophication, harmful algal blooms or hypoxia in this region. Metals (Hg, Pb, Cd) are controlled by natural cycles augmented by past mining and urbanization, with 0.3-5% of the flux contributed by wastewater. Wastewater contributes ~5% of PCBs but ≤ 60% of PBDEs and is likely also important for pharmaceuticals and personal care products. Effects of high organic flux on benthos are measurable in the immediate receiving environment. The availability of particle-active contaminants to enter the food chain depends on how long those contaminants remain in the sediment surface mixed layer before burial. Secondary treatment, slated for completion in Vancouver in 2030, will reduce fluxes of some contaminants, but will have negligible effect on regional budgets for organic carbon, nitrogen, oxygen, metals and PCBs. Removal of PBDEs from wastewater will affect regional budgets, depending on how the sludge is sequestered.

A Global Perspective on Microplastics

“…Even in affluent countries such as the U.S., waivers allowing primary‐only treatment have been issued to facilities discharging into open or fast‐moving marine waters, for example, in California, Hawaii, Guam, Virgin Islands, Alaska, and Puerto Rico. Cities in several Canadian provinces also discharge to the ocean following only crude treatment (e.g., Johannessen et al, ). As another example, Antarctica is largely pristine.…”

Vulnerability of a semienclosed estuarine sea to ocean acidification in contrast with hypoxia

“…The FR-plume end-member contains the most carbon during high freshet years (raised mixing lines, Table S6). The FR carries significant DIC (∼900 μmol kg −1 ) [Moore-Maley, 2014] and organic carbon [Johannessen et al, 2003[Johannessen et al, , 2015, part of which will remineralize to DIC somewhere in the system. The relative roles of FR carbon input, natural and anthropogenic, and high local organic matter production coupled with long retention times in the SoG require further investigation.…”

Diversity of Escherichia coli found in the Salish Sea

“…Seventy-nine WWTPs are in the United States and twenty on the Canadian side (2019). WWTPs near Vancouver and Vancouver Island, British Columbia, dump partially treated wastewater into the Salish Sea (Johannessen et al, 2015). In the counties which border the Salish Sea (Whatcom, Skagit, Snohomish, King, Pierce, Thurston, Mason, Jefferson, and Clallam), pasture and hay make up the most agricultural land use behind shellfish harvesting (Agricultural Land Use | Washington State Department of Agriculture) (See map 1).…”