Field Work in Support ofEcological Models

Warren Prell - Historical Hypoxia based on benthic forams

Candace Oviatt - Water Column MetabolismWarren Prell - Sediment Oxygen Demand

Scott Nixon/Wally Fulweiler - Denitrification Gradient

Historical Hypoxia Based on

Benthic Forams

Warren Prell

Objective: Develop a reliable historical record (pre-settlement to present) of the degree of NNB hypoxia based on benthic foraminifera populations in surface sediments and sediment cores.

Benthic Foraminifer Survey

• Completed sampling for mid-bay to lower bay

• Both abundance (#/g) and diversity tend to increase downbay

• AE (hypoxia?) Index increases at low abundance

• Abundance is 4 to 11 times the 1950 abundance in mid-Bay locations

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1400

0 50 100 150 200 250 300 350

# Benthic foraminifers per gram

Site # Providence Mid-Bay

Abundance (#/gram)• Lower in Providence

River, Greenwich Bay and embayments

• Higher in mid and upper Bay

• Reflects both environment and substrate

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2

4

6

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14

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Foraminifer Abundance (#/g)

Diversity vs. Abundance

Diversity

•Increases down Bay

•Low in Providence River and embayments

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0.4

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0.8

1

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Foraminifer Abundance (#/g)

AE Index vs. Abundance

AE Hypoxia Index

•High in Providence River and embayments. Consistent with low DO

•AE Index increases at lower population abundance

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UpperWest

Passage

GreenwichBay

UpperBay

Upper East

Passage

79 132

13 3 3

x4x9

x8 x11

UpperWest

Passage

Abundance 1950 vs. 2003

UpperWest

Passage

GreenwichBay

UpperBay

Upper East

Passage

79 132

13 3 3

x4x9

x8 x11

UpperWest

Passage

Abundance 1950 vs. 2003

Comparison of abundance (#/g) from 1950 to 2003 shows increases of 4 to 11 fold in upper Bay and upper East and West Passages and Greenwich Bay.

Water Column Metabolism

Candace Oviatt

Project Goal

To estimate primary productivity and respiration along a gradient in

Narragansett Bay to test the impacts of water column metabolism on hypoxic

events.

Sampling Design Sampling 6 stations

Conimicut Point North Prudence Mount View Bullocks Reach Quonset Point GSO Dock

3 depths at each station Surface Chlorophyll Max Bottom

Water collected monthly

http://www.nbnerr.org/propertieshome.htm

Water Column Assessment Methods

14C Primary Productivity Incubations

O2 Primary Productivity Incubations

Respiration Incubations

Surface Primary Productivity6/28/06

North Prudence 14C

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Irradiance (μ E m-2 s-1)

Productivity( mg C m

-3 h

-1)

North Prudence O 2

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1000

0 500 1000 1500

Irradiance (μ E m-2 s-1)

Productivity( mg O

2 m-3 h

-1)

Respiration Rates

-0.11

-0.06

-0.01

0.04

6/15/2006 6/29/2006 7/13/2006 7/27/2006

Bottom

Chl Max

Surface

North Prudence-0.17

-0.12

-0.07

-0.02

0.03

6/15/06 6/29/06 7/13/06 7/27/06 8/10/06 8/24/06 9/7/06 9/21/06

Date

mgO2/l/hr

Conimicut Point

-0.11-0.06-0.010.04

6/15/20066/29/20067/13/20067/27/20068/10/20068/24/20069/7/20069/21/2006

Date

mgO2/l/hr

Primary Production June & July

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1 2 3 4

Date

mg C/O

2 d

-1 m

-2

Conimicut C-14

Cominicut O2

No Prud C-14

No Prud O2

Sediment Oxygen Demand

Warren Prell

Objective:

Measure the spatial variability of sediment oxygen demand (SOD) in the shoal parts of NNB and to relate SOD to the benthic environment (grain size and organic carbon content).

We will use simple benthic chambers with YSI CTD-DO sensors to measure bulk oxygen demand in sediments and the 0.2 m water column in the chamber.

Preliminary chamber tests exhibit a smooth and systematic draw down of oxygen over a few hours. We will use existing maps of organic carbon as a guide to likely areas of high SOD and coordinate with the spatial surveys of DO and estimates of water column respiration. We plan to make measurements within each of the initial-phase spatial elements of the hybrid model.

Denitrification in Upper Narragansett BayCHRP MEETING

Robinson W. FulweilerScott W. NixonOctober 2, 2006

Graduate School of Oceanography University of Rhode Island

240 g C m-2 y-1

520 g C m-2 y-1

560 g C m-2 y-1

PP data Oviatt et al. 2002

Denitrification Rates in Narragansett Bay (6-13ºC)

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N2-

N, μ

mol

m-2 h

-1N

2-N

, μm

ol m

-2 h

-1

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60

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40

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120N

2-N

, μm

ol m

-2 h

-1

1979 1986 2005/06

Denitrification Rates in Narragansett Bay (6-13ºC)