Nutrients & Dissolved Oxygen

Jonathan PennockUniversity of New Hampshire

Marine Program, NH Sea Grant & Jackson Estuarine Laboratory

EutrophicationPositive Versus Negative Effects

Oligotrophic MesotrophicEutrophic Dystrophic

Phytoplankton

Zooplankton

Pelagic Fish

Bottom Oxygen

Benthos

Benthic Fish

NOAA Estuarine Eutrophication Assessment

Bricker 1999

Environmental Protection Agency

Nitrogen in Great Bay

Have nitrogen concentrations in Great Bay changed significantly over time?

Yes. The total nitrogen load to the Great Bay Estuary increased by 42% in the past 5 years. Dissolved inorganic nitrogen concentrations have increased in Great Bay by 44% in the past 28 years.

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Nitrogen Loads to Great BayTotal N Load

2002-2004

1,097 tons/yr

2006-2008

1,558 tons/yr

Percent Change

42%

•Data Source: PREP

WWTFs

484.64 tons/yr

31%

Groundwater

31.28 tons/yr

2%

Atmospheric

27.92 tons/yr

2%

Tributaries and Runoff

1014.00 tons/yr

65%

Dissolved Nitrogen

Dissolved Inorganic Nitrogen

44% increase over 28 years

Ru Morrison

Chlorophyll-a & Suspended Solids

Suspended Solids

123% increase over 28 years

Chlorophyll-a

28% increase over 28 years

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Chlorophyll-a

0 1 2 3 4 5 Kilometers

N

Chlorophyll-a

0.1 - 2 ug/L%2 - 5 ug/L%5 - 10 ug/L%10 - 20 ug/L%20 - 60 ug/L%

Sample Size

N >=10 Results#SN <10 Results#S

Chlorophyll Concentration

Dissolved Oxygen

How often do dissolved oxygen levels in the estuary fall below state standards?

Rarely in the bays and harbors but often in the tidal rivers.

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Oxygen Depletion at Datasondes

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#S #S MinimumDissolvedOxygen

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Minimum Dissolved Oxygen

8 - 10 mg/L%6 - 8 mg/L%5 - 6 mg/L%4 - 5 mg/L%3 - 4 mg/L%

Sample Size

N >=10 Results#SN <10 Results#S

Dissolved Oxygen Concentration

Dissolved Oxygen Concentration

Ru Morrison

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Dissolved Oxygen Diel Variability

Phil Trowbridge

Data Gaps

• Additional Sampling Stations in the Bay are Needed to Provide Better

Insight and Averages for the Bay Proper…

• A Robust Nutrient Loading/Sink Model is Needed to Determine Specific

Nutrient Loading and Ultimate Fate of Nutrients in the System…

• There are No Data on Phytoplankton Production in the Estuary…

• …

Thank You!