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Dissolved Oxygen (DO) and Dissolved Organic Carbon (DOC) in the Cape Fear River Estuary. Lauren Thompson Chemical and Physical Analysis of Seawater Fall 2008. Why DO?. Frequently measured analyte General water conditions Oxic, suboxic, anoxic implications to fish health - PowerPoint PPT Presentation
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Dissolved Oxygen (DO) and Dissolved Organic Carbon (DOC) in the Cape Fear River Estuary
Lauren ThompsonChemical and Physical Analysis of
SeawaterFall 2008
Why DO?
• Frequently measured analyte
• General water conditions– Oxic, suboxic, anoxic– implications to fish health
• Important marker of biological activity of the water body
• Indicates Redox conditions
Four Main Controls of DO• Physical-
– Temperature– Salinity
– Most DO in cold, fresh water.
• Biological– Photosynthesis: produces of DO
• CO2+ H2O CH2O+ O2
– Respiration: use of DO
• CH2+ O2 CO2+ H2O
YSI
• Measured in situ with a YSI meter• Cathode Reaction
– Reduction- 02+ 4e- 202-
• Anode Reaction– Oxidation- 4Ag 4Ag+ 4e-
• Overall Reaction– 4Ag 4Ag+ +4e-
• DO measured is proportional to current flow of the meter.
Physical Controls
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M18 M23 M35 M42 M54 M61 HB
DO
(m
g/L
)
Cruise 1
Cruise 2
Cruise 1 Temp: 22.4oC
Cruise 2 Temp: 16.5oC
DO Comparison
Cruise 1
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5.00
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M18 M23 M35 M42 M54 M61 HB
DO
(m
g/L
)
Class Average Cruise 1
Cruise 1, 2008
LCFRP
DO Comparison
Cruise 2
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1.00
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M18 M23 M35 M42 M54 M61 HB
DO
(m
g/L
)
Class Average Cruise 2
Cruise 2, 2008
LCFRP
What about DOC?
Dominant control of DO in Cape Fear is utilization.
CH2 + O2 CO2 + H2O
DOC causes a decrease in %O2 saturation as salinity increases.
Cruise 1
y = -0.0371x + 100.38
R2 = 0.9123
0
20
40
60
80
100
0 200 400 600 800 1000 1200 1400
DOC (µM)
% S
atu
rati
on
Cruise 2
y = -0.0316x + 101
R2 = 0.8316
0
20
40
60
80
100
0 200 400 600 800 1000 1200
DOC (µM)
% S
at
What is DOC?
• Dissolved Organic Carbon– Operational definition- material that passes
through a filters 0.2-0.7µM
• Cape Fear is an input to the Oceans– 0.2 x 1015 g C yr-1
• Biological Production – Excretion and Cell Lysis– Sloppy Feeding– Release from Fecal Matter
Surface vs. Deep
Cruise 1
0
200
400
600
800
1000
1200
1400
m18 m23 m35 m42 m54 m61 hb
DO
C (
uM
)
Surface
Deep
Cruise 2
0
200
400
600
800
1000
1200
m18 m23 m35 m42 m54 m61 hb D
OC
(u
M)
Surface
Deep
More DOC in surface.
Salinity EffectsDOC vs Salinity
0
200
400
600
800
1000
1200
1400
0.0 10.0 20.0 30.0 40.0
Salinity
DO
C (
µM
)Cruise 1
Cruise 2
Conservative mixing
Increased Salinity, Decreased DOC
y = -29.751x + 1190.8
R2 = 0.8664
0
200
400
600
800
1000
1200
1400
1600
1800
0 5 10 15 20 25 30 35Salinity
[DO
C]
µM C
Long-term Trend
Class Data from previous 6 years!
Chl-a
Increased levels of Chl-a with decreasing DOC concentrations. Optical clarity of water ?
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0 500 1000 1500
DOC (µM)
Ch
l-a
Cruise 1 Surface
Cruise 2 Surface
Cruise 1 Deep
Cruise 2 Deep
Conclusions
• Cruise 2 was colder than Cruise 1 by 5.9 ºC– Higher Levels of DO for Cruise 2 at all sites.
• Cruises 1 & 2 showed Correlation to salinity, but it was reverse of what is expected.– Not main controlling factor.
• Both Cruise 1 and Cruise 2 DOC vs. % saturation produced an inverse relationship– Surface typically had higher numbers when compared to deep.
• Except Cruise 2 M18-35.
– DOC has inverse relationship to Salinity
• Also, inverse to chl-a. – More production with decreased DOC.
• Main Control is Utilization.
