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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
-0.2
-0.1
0
0.1
0.2
0.3
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
01/03/2011 02/03/2011 03/03/2011 04/03/2011 05/03/2011 06/03/2011 07/03/2011 08/03/2011 09/03/2011
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
01/03/2011 02/03/2011 03/03/2011 04/03/2011 05/03/2011 06/03/2011 07/03/2011 08/03/2011 09/03/2011
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
01/03/2011 02/03/2011 03/03/2011 04/03/2011 05/03/2011 06/03/2011 07/03/2011 08/03/2011 09/03/2011
NO
3-N
(mg/
L)
Nitrate Concentration
Downstream Flume – 15 minute sample interval
0
0.5
1
1.5
2
2.5
01/03/2011 02/03/2011 03/03/2011 04/03/2011 05/03/2011 06/03/2011 07/03/2011 08/03/2011 09/03/2011
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
01/03/2011 02/03/2011 03/03/2011 04/03/2011 05/03/2011 06/03/2011 07/03/2011 08/03/2011 09/03/2011
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
01/03/2011 02/03/2011 03/03/2011 04/03/2011 05/03/2011 06/03/2011 07/03/2011 08/03/2011 09/03/2011
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)