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The Risk of Hypoxia in Narragansett Bay PowerPoint PPT Presentation


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The Risk of Hypoxia in Narragansett Bay. A Synthesis of Available Data. Objectives:. To assess whether hypoxia poses a risk to aquatic life in Upper Narragansett Bay Obtain an estimate of the spatial extent of this risk

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The Risk of Hypoxia in Narragansett Bay

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The risk of hypoxia in narragansett bay l.jpg

The Risk of Hypoxia in Narragansett Bay

A Synthesis of Available Data


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Objectives:

  • To assess whether hypoxia poses a risk to aquatic life in Upper Narragansett Bay

  • Obtain an estimate of the spatial extent of this risk

  • Outline some approaches to integration of existing dissolved oxygen datasets with the EPA saltwater DO criteria (2000)


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Available Data

  • “Insomniac” surveys – Prell, Deacutis, Murray (1999-2003)

  • Nu-shuttle cruises – Berman, Oviatt, Melrose (1998-2004)

  • Monitoring Buoys – Bergondo, Kester (1999-2004)

  • Ambient Aquatic Life Water Quality Criteria for Dissolved Oxygen (Saltwater): Cape Cod to Cape Hatteras

    – EPA (2000)


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Data Types and Limitations


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What do the EPA Criteria Tell Us

  • EPA criteria address both growth and mortality for different life stages:

    • Larvae – growth and mortality effects are incorporated into a larval recruitment model

    • Juveniles and Adults are considered together

  • Both persistent and cyclic/episodic hypoxia are accounted for in the criteria


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2.9 mg/L - Limit for Protection against Larval Mortality

2.3 mg/L Limit for Protection against Juvenile Mortality

Winter

flounder

Tautog

Experimental Mortality Data

  • Plot from the EPA criteria document including protective limits

  • Shows DO concentrations associated with 50% mortality (LC50) for species that commonly inhabit estuaries between Cape Cod and Cape Hatteras


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  • Average bottom DO in most of the Upper Bay is in a range known to cause harm to aquatic life

  • DO divisions based upon larval protection limits


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Where the July and August Insomniac surveys fit into the structure of a hypoxic event at the Bullock’s Reach buoy


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Large regions of the bay show a coherent pattern with DO measured at the Bullock’s Reach Buoy


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  • Deep stations are generally well correlated within a given region of the bay


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  • Cross section of the shipping channel from the Providence River to the south end of Prudence Island

  • Transects show DO (color contours) and density (σt)

  • In this case – the Nu-shuttle cruise occurred 4 days after the Insomniac survey


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Conclusions

  • Aquatic life in Upper Narragansett Bay is at risk from hypoxia - both mortality and growth effects

  • The spatial extent of this risk is large – including almost all areas northward from the south tip of Prudence Island

  • Integration of the existing data can provide information about patterns of hypoxia in Upper Narragansett Bay and guide future monitoring efforts


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Acknowledgements

Many thanks for the free exchange of data and ideas:

Deanna BergondoMark Berman

Dana Kester Chris Melrose

Chris Deacutis Heather Stoffel

Warren PrellHeidi Travers

David MurrayRobin Weber

Don PryorCatherine Walker

Candace OviattPeter August


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Additional Material


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Comparison of Insomniac Summer Averages and Summer Averages from Monitoring Buoys

  • The Insomniacs data and Buoy data are completely independent, yet they give a very similar summer average at the Bullock’s Reach and North Prudence Buoy sites


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Larval Time-to-death Curves from the EPA criteria

  • These time-to-death curves are based upon studies done on larvae

  • Mortality after 24 hours does not increase significantly at a given DO concentration


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Absolute Minimum DO measured at each station in any “Insomniac” Survey.

Note that areas in red are below 1.2 mg/L

(from the EPA VPDO criteria Implementation Guidance document)


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Large regions of the bay show a coherent pattern with DO measured at the Bullock’s Reach Buoy


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  • Deep stations in different regions of the bay are generally very well correlated


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GSO dock does not show on this slide

Roger Williams is a future location


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