Abstract Title

Session S-01A: Current Salish Sea Water Quality

Keywords

Marine Water Quality

Start Date

30-4-2014 10:30 AM

End Date

30-4-2014 12:00 PM

Description

EPA and the Washington Department of Ecology reviewed available science regarding dissolved oxygen impacts in Hood Canal at the request of the Hood Canal Coordinating Council. This review encompassed all relevant studies of Hood Canal by researchers from the University of Washington, U.S. Geological Survey, Pacific Northwest National Laboratory, and Mason County. The Puget Sound Institute organized an independent peer review of our report by outside experts. There is a consensus among researchers that: (1) Marine water upwelling delivers most of the nitrogen to the photic zone in Hood Canal, (2) Shoreline onsite sewage systems represent the dominant human source of nitrogen, and (3) Relative human impacts are highest in Lynch Cove. At the same time, there are a range of estimates of the scale of human impact on dissolved oxygen, particularly around the southern areas of the Great Bend and Lynch Cove. Sediment cores indicate that oxygen levels in central Hood Canal were lower before 1900 than between 1900 to 2005, contrary to the pattern expected if human contributions of nitrogen are significant. Water column data collected in the 1950s and 2000s indicated no consistent trends in dissolved oxygen concentration across Hood Canal over that time. We concluded that human nitrogen loadings are not contributing substantially to low dissolved oxygen in central Hood Canal, including the Hoodsport region where episodic fish kills have occurred. Episodic fish kills occur from a cascade of natural factors, including upwelled water from the Pacific Ocean that intrudes into Hood Canal, pushing low-oxygen water at depth to the surface, where southwesterly winds can suddenly displace the thinning cap of freshwater. We reviewed model-based impact assessments for Lynch Cove in detail. We could not determine conclusively whether human nitrogen loadings cause Lynch Cove dissolved oxygen levels to violate Washington water quality standards. While we estimated that humans contribute 0.03 to 0.3 mg/L of oxygen depletion in Lynch Cove, the external peer review concluded that the marine flux methodology used by researchers was problematic. The wide range of marine nitrogen flux values led to the high uncertainty in the impact estimates. The project report, “Review and Synthesis of Available Information to Estimate Human Impacts to Dissolved Oxygen in Hood Canal”, was published in March 2013 and is available at https://fortress.wa.gov/ecy/publications/SummaryPages/1303016.html.

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Apr 30th, 10:30 AM Apr 30th, 12:00 PM

Review and Synthesis of Available Information to Estimate Human Impacts to Dissolved Oxygen in Hood Canal

Room 615-616-617

EPA and the Washington Department of Ecology reviewed available science regarding dissolved oxygen impacts in Hood Canal at the request of the Hood Canal Coordinating Council. This review encompassed all relevant studies of Hood Canal by researchers from the University of Washington, U.S. Geological Survey, Pacific Northwest National Laboratory, and Mason County. The Puget Sound Institute organized an independent peer review of our report by outside experts. There is a consensus among researchers that: (1) Marine water upwelling delivers most of the nitrogen to the photic zone in Hood Canal, (2) Shoreline onsite sewage systems represent the dominant human source of nitrogen, and (3) Relative human impacts are highest in Lynch Cove. At the same time, there are a range of estimates of the scale of human impact on dissolved oxygen, particularly around the southern areas of the Great Bend and Lynch Cove. Sediment cores indicate that oxygen levels in central Hood Canal were lower before 1900 than between 1900 to 2005, contrary to the pattern expected if human contributions of nitrogen are significant. Water column data collected in the 1950s and 2000s indicated no consistent trends in dissolved oxygen concentration across Hood Canal over that time. We concluded that human nitrogen loadings are not contributing substantially to low dissolved oxygen in central Hood Canal, including the Hoodsport region where episodic fish kills have occurred. Episodic fish kills occur from a cascade of natural factors, including upwelled water from the Pacific Ocean that intrudes into Hood Canal, pushing low-oxygen water at depth to the surface, where southwesterly winds can suddenly displace the thinning cap of freshwater. We reviewed model-based impact assessments for Lynch Cove in detail. We could not determine conclusively whether human nitrogen loadings cause Lynch Cove dissolved oxygen levels to violate Washington water quality standards. While we estimated that humans contribute 0.03 to 0.3 mg/L of oxygen depletion in Lynch Cove, the external peer review concluded that the marine flux methodology used by researchers was problematic. The wide range of marine nitrogen flux values led to the high uncertainty in the impact estimates. The project report, “Review and Synthesis of Available Information to Estimate Human Impacts to Dissolved Oxygen in Hood Canal”, was published in March 2013 and is available at https://fortress.wa.gov/ecy/publications/SummaryPages/1303016.html.