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Dissolved Oxygen (DO) and Dissolved Organic Carbon (DOC) in the Cape Fear River Estuary

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

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Dissolved Oxygen (DO) and Dissolved Organic Carbon (DOC) in the Cape Fear River Estuary

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  1. Dissolved Oxygen (DO) and Dissolved Organic Carbon (DOC) in the Cape Fear River Estuary Lauren Thompson Chemical and Physical Analysis of Seawater Fall 2008

  2. 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

  3. 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

  4. 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.

  5. Physical Controls Cruise 1 Temp: 22.4oC Cruise 2 Temp: 16.5oC

  6. DO Comparison

  7. DO Comparison

  8. 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.

  9. 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

  10. Surface vs. Deep More DOC in surface.

  11. Conservative mixing Increased Salinity, Decreased DOC Salinity Effects

  12. Long-term Trend Class Data from previous 6 years!

  13. Chl-a Increased levels of Chl-a with decreasing DOC concentrations. Optical clarity of water ?

  14. 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.

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