Puget Sound Pollution: Linking Nutrients & Dissolved Oxygen Copyright © 2011, Facing the Future

South Puget Sound Dissolved Oxygen Study Published by Washington State Department of Ecology, December 2008 study area Copyright © 2011, Facing the Future

Why focus on dissolved oxygen (D.O.)? An easily measurable indicator of effects of some types of runoff and whether we’re using water sources sustainably. Aquatic species get oxygen from the water. Low levels of dissolved oxygen can stress aquatic species. For example: Dissolved Oxygen LevelImpact on Salmon 9 mg/LOptimal 7-8 mg/LAcceptable mg/LPoor Below 3.5 mg/LStressful or fatal Copyright © 2011, Facing the Future

How has low D.O. impacted Puget Sound? “Fish kills,” typically in late summer/fall, including: – Fish (rockfish, ratfish, flatfish, ling cod, sole) – Prawns – Crabs Bottom fish move to surface to get more oxygen (may run out!) Animals move slower than usual, therefore more susceptible to other issues Deaths of Dungeness crabs have been linked to periods of low oxygen in South Puget Sound. Copyright © 2011, Facing the Future

How do nutrients contribute to low D.O.? Limiting factor for plants is often nutrient availability. (That’s why fertilizer makes plants grow – removes the limiting factor.) Copyright © 2011, Facing the Future Excess nutrients (nitrogen & phosphorous) in water can cause excess growth of algae. When the plants eventually die, the decomposition process uses up oxygen in the water. The result is hypoxia, or oxygen depletion. Brainstorm and discuss: How do excess nutrients get into water sources? Think about point and nonpoint sources. Note: some/most nitrogen from natural sources…humans are only part of the issue…

What contributes to hypoxia? Discuss, and be ready to explain this graph. Both rivers and wastewater treatment plants (WWTPs) bring nutrients (in this case, dissolved inorganic nitrogen) into Puget Sound. Copyright © 2011, Facing the Future

What areas in South and Central Puget Sound have the highest nitrogen inputs from rivers and WWTPs? (Compare this to the human population density we discussed yesterday…) Copyright © 2011, Facing the Future

Sustainability of DO How could humans in the Puget Sound Ecosystem make DO levels more sustainable over time? What could YOU do? What are the constraints, if any, for your solutions to the above question? What are some potential consequences (unintended or intended) for your solutions? Brainstorm with your neighbor, record in your notebook, and be ready to share. Note: DO and nutrient pollution are just ONE case study example of issues/terms we discussed yesterday… Copyright © 2011, Facing the Future

Stop here Keep next few slides for reference… Copyright © 2011, Facing the Future

Factors other than nutrient pollution lead to hypoxia. For example: Why is dissolved oxygen lower: in summer months? in stagnant water? at greater depths? Copyright © 2011, Facing the Future

What scientific questions would you ask to determine how to address hypoxia in Puget Sound? Questions being researched by the UW School of Oceanography’s ORCA program: Are human-derived nutrient inputs currently small relative to natural (physical and biological) fluxes? Will increases in nutrient inputs (eutrophication) as population and industrialization increase adversely impact water quality in South Puget Sound? What are the key factors in the cause of hypoxia in southern Hood Canal? On Monday: How does nonpoint source pollution affect salmon spawning in Puget Sound streams? Copyright © 2011, Facing the Future