Event Title

Impacts on oxygen and DIC of screened municipal wastewater in the Strait of Juan de Fuca

Presentation Abstract

The cities of Greater Victoria share a common sewer system managed by the Capital Regional District (CRD). The system consists of two outfalls located at Clover and Macaulay Points that extend approximately 1.2km offshore and each release an annual average of approximately 45,000 m3 d-1 of screened effluent at just over 60 meters depth. The receiving environments are both highly energetic (with Macauly being slightly less so) and mixing is rapid. As with all sewage outfalls the addition of excess nutrients and organic carbon has the potential to create local zones of hypoxic and acidic water.

To address this the CRD’s monitoring program collects water column oxygen data and in early 2013 collaborated with Ocean Networks Canada to deploy a mooring 125 meters SE of the Macaulay outfall to monitor oxygen levels. At 62 meters depth the Macaulay Point mooring is very near the mean transition depth between seaward flowing surface water and landward flowing deep water, with the landward flow observed to occur 61% of the time. Rising tides bring deep Juan de Fuca water up the Victoria sill to the mooring while ebbing tides can be seen to bring Haro water. These transitions cause oxygen to vary by more than 50umol/kg within a 24-hour period as the different water masses exchange influence. Fluctuations of DIC are much harder to capture with discrete measurement but are expected to follow a pattern similar to oxygen. Discrete samples of DIC and TA that have been analyzed are within the range of other samples from Juan de Fuca and Haro Strait region. This suggests that, like oxygen, any impact the outfall is having on DIC, TA or pH is dwarfed by the large natural variability of the area.

Session Title

Ocean Acidification in the Salish Sea

Conference Track

Climate Change and Ocean Acidification

Conference Name

Salish Sea Ecosystem Conference (2016 : Vancouver, B.C.)

Document Type

Event

Location

2016SSEC

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

Text

Language

English

Format

application/pdf

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Impacts on oxygen and DIC of screened municipal wastewater in the Strait of Juan de Fuca

2016SSEC

The cities of Greater Victoria share a common sewer system managed by the Capital Regional District (CRD). The system consists of two outfalls located at Clover and Macaulay Points that extend approximately 1.2km offshore and each release an annual average of approximately 45,000 m3 d-1 of screened effluent at just over 60 meters depth. The receiving environments are both highly energetic (with Macauly being slightly less so) and mixing is rapid. As with all sewage outfalls the addition of excess nutrients and organic carbon has the potential to create local zones of hypoxic and acidic water.

To address this the CRD’s monitoring program collects water column oxygen data and in early 2013 collaborated with Ocean Networks Canada to deploy a mooring 125 meters SE of the Macaulay outfall to monitor oxygen levels. At 62 meters depth the Macaulay Point mooring is very near the mean transition depth between seaward flowing surface water and landward flowing deep water, with the landward flow observed to occur 61% of the time. Rising tides bring deep Juan de Fuca water up the Victoria sill to the mooring while ebbing tides can be seen to bring Haro water. These transitions cause oxygen to vary by more than 50umol/kg within a 24-hour period as the different water masses exchange influence. Fluctuations of DIC are much harder to capture with discrete measurement but are expected to follow a pattern similar to oxygen. Discrete samples of DIC and TA that have been analyzed are within the range of other samples from Juan de Fuca and Haro Strait region. This suggests that, like oxygen, any impact the outfall is having on DIC, TA or pH is dwarfed by the large natural variability of the area.