Continuously monitoring flow, carbon, and nitrogen in a

restored North Carolina salt marsh

J. Randall Etheridge, Michael R. Burchell II, François Birgand

Site Location

Nor

th

Riv

er

N

Restoration Goals

• Improve water quality in the North River

• Restore habitat• Provide design

guidance for future salt marsh projects in coastal North Carolina

N

300 ft

Construction

Restoration Research Objectives

• Quantify the ability of a restored salt marsh to dissipate excess nutrients

• Quantify the timing and kinetics of nutrient dissipation and/or release

• Correlate the dissipation and/or release of nutrients to the type of organic matter

Method

• Continuous nutrient mass balance between inlet and outlet

• Sediment-water interface process kinetics experiments

• Qualify nature of organic matter using fluorescence measurements

Method

• Continuous nutrient mass balance between inlet and outlet

• Sediment-water interface process kinetics experiments

• Qualify nature of organic matter using fluorescence measurements

Upstream/Downstream Monitoring

P

P

300 ft

N

PNew Flume

New WQ Probe

Flow Control Fence

Flow Monitoring in a Tidal Stream• Cannot use normal

rating curve due to bi-directional flow

• Flumes serve as a constant cross section – cross section area measurement creates the most error in flow monitoring

Downstream flume between tides

Downstream flume at high tide

Flow CalculationsQ = V x A

– Q: flow– V: velocity– A: cross-section area

A

A

Continuous Flow Monitoring

• Doppler velocity meter records velocity and water depth in flume

• Average velocity and water depth recorded every 15 minutes

• Use manual stream gagingto relate Doppler velocity to actual flow in the flume

Doppler velocity meter in the flume bottom

Manual Stream Gaging

Flow Calibration

y = 0.9889xR² = 0.9856

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0 0.2 0.4

Vmea

n (m

/s)

Vcenter (m/s)

Vi Vc

40% of the depth

Doppler meter

Flow Monitoring in a Tidal Stream• One challenge presented in

the marsh: high tide or water level above the flumes

• Solution: direct flow through the flume using impermeable fence

Downstream Flume

-0.5

-0.4

-0.3

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-0.1

0

0.1

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0

0.1

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0.9

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Velo

city

(m/s

)

Stag

e (m

)

Stage and VelocityLevelVelocity

Downstream Flume Flow

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

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Flow

(m3 /s

)

Continuous Water Quality MonitoringParameter Max (mg/L) Resolution

(±mg/L)NO3

-N 70 0.1TOC 150 0.2DOC 90 0.2

• Monitored using UV-visual spectrophotometer placed in the stream

• Absorption spectrum and parameters measured every 15 minutes

Continuous Water Quality Monitoring

0

50

100

150

200

250

300

350

200 300 400 500 600 700Wavelength (nm)

Absorption Spectra

High NO3-NLow NO3-N

Downstream Flume – Daily Sample

0

0.5

1

1.5

2

2.5

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NO

3-N

(mg/

L)

Nitrate Concentration

Downstream Flume – 15 minute sample interval

0

0.5

1

1.5

2

2.5

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NO

3-N

(mg/

L)

Nitrate Concentration

Downstream Flume

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0

0.5

1

1.5

2

2.5

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Flow

(m3 /s

)

NO

3-N

(mg/

L)

Nitrate Concentration and FlowNO3-NFlow

Downstream Flume

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

5

10

15

20

25

30

35

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Flow

(m/s

)

DO

C (m

g/L)

DOC Concentration and FlowDOCFlow

Challenges of Continuous Water Quality Monitoring

• Calibration• Preventing/reducing

window fouling• Solar power

Future Research

• Continuously monitor:– pH– Conductivity/Salinity– Dissolved Oxygen– DOM Fluorescence

Future Research

For more information on our future work with organic matter see this poster:Mikan et al., Chromophoric Dissolved and

Particulate Organic Matter Cycling Through a Tidally Influenced Restored Marsh Ecosystem in Eastern North Carolina

Acknowledgements• North Carolina Coastal Federation• United States Environmental Protection Agency• North Carolina Sea Grant/North Carolina Water Resources Research

Institute• North Carolina Ecosystem Enhancement Program• NSF Graduate Research Fellowship Program• Equipment Installation:

– Spencer Davis– Brad Smith– Guillaume Lellouche

• Collaborators:– Dr. Chris Osburn – NCSU Marine, Earth, & Atmospheric Sciences– Molly Mikan

• Others:– Phil Harris (Electronics)– Kris Bass (Installation and site design)– Evan Corbin (Previous research)