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The Effects of a Spring Resuspension Event on In-situ Optical Parameters and Phytoplankton Light Utilization

This study examines the impact of a spring resuspension event on the optical properties of water and the ability of phytoplankton to utilize light in Southern Lake Michigan. The study uses in-situ measurements and modeling to understand the changes in optical parameters and the composition of the phytoplankton community.

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The Effects of a Spring Resuspension Event on In-situ Optical Parameters and Phytoplankton Light Utilization

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  1. The Effects of a Spring Resuspension Event on In-situ Optical Parameters and Phytoplankton Light Utilization Trisha Bergmann Gary Fahnensteil Steven Lohrenz David Millie Oscar Schofield Coastal Ocean Observation Lab Institute of Marine and Coastal Sciences Rutgers University

  2. 44o.00’ 0 16 32 48 Kilometers N Muskegon, MI 43o.00’ 150 m 100 m 75 m St. Joseph, MI 50 m 42o.00’ Cook, MI 25 m New Buffalo, MI 88o.00’ 87o.00’ 86o.00’ Study Area – Southern Lake Michigan

  3. Optical closure in a variable light environment • Light utilization by phytoplankton communities

  4. 0 0 0 15 15 15 30 30 30 Depth (m) Depth (m) Depth (m) 45 45 45 60 60 60 0 0 0 10 10 10 20 20 20 30 30 30 Range (km) Range (km) Range (km) 1.5 0 Absorption (m-1) Temporal evolution of the sediment plume March 1999 June 1999 April 1999

  5. Optical Properties of the sediment plume 0 0 15 15 Depth (m) Depth (m) 30 30 0 0 5 5 10 10 Range (km) Range (km) atten Plume Non- plume Inverse Meters abs Wavelength 1.5 1 Attenuation (m-1) Absorption (m-1) Absorption (m-1) Attenuation (m-1) 0 0

  6. f a Rrs ratio 490/555 Station a Range (km) Remote Sensing Reflectance (sr-1) a f 0 Station f 15 30 Wavelength (nm) Depth (m) 45 60 Absorption (m-1) 1.5 0 75 20 30 0 10 Range (km) Optical Identification of the plume

  7. Closure Between IOPs and AOPs Measured Kd at 440nm modeled Kd at 425nm Absorption (m-1) Attenuation (m-1) Solving the Radiative Transfer Equation with Hydrolight 4.2 RTE

  8. Downward irradiance (Ed; μW cm-2) Remote Sensing Reflectance (sr-1) measured modeled Depth (m) measured modeled Wavelength (nm) Hydrolight vs. measured data R2 measured vs modeled Rrs Wavelength (nm)

  9. 1:1 line Chlorophyll (μg/L) – calculated from Rrs Chlorophyll (μg/L) - measured Inversion of remote sensing reflectance vs. measured in-water data bb/a at 555nm Remote Sensing Reflectance (sr-1) at 555nm

  10. 2 5 10 16 26 32 Distance offshore 5 10 Depth (m) 40 70 100 Phytoplankton Community Composition II cryptophytes chlorophytes cyanobacteria diatoms

  11. Phytoplankton Distribution 0 0.62 0.58 20 0.54 ) 40 0.50 m ( h 0.46 t p 60 e 0.42 D 0.38 80 0.34 Cryptophyte Relative Abundance Diatom Relative Abundance 0.30 100 March, 1999 March, 1999 0.26 0 5 10 15 20 25 30 0 5 10 15 20 25 30 Distance from Shore (km) Distance from Shore (km)

  12. Phytoplankton Distribution % Chl - Diatoms % Chl - Cryptophytes

  13. surface depth surface depth Available light field Downwelling Irradiance (μmol photons m-2 s-1) Wavelength (nm) Why is the sediment plume important to biology? 5 cryptophytes chlorophytes cyanobacteria diatoms 10 Depth (m) 40 70 100

  14. Single Cell Absorption spectra for Diatoms and Cryptophytes Diatoms Cryptophytes Chl a Chl c2 Single Cell Absorption (m-1) Alloxanthin phycoerythrin Chl a Wavelength (nm-1)

  15. surface Depth (30m) Irradiance (μmol photons m-2 s-1) Wavelength Available Light field and potential absorption Irradiance Ed(λ) (μmol photons m-2 s-1) Irradiance (μmol photons m-2 s-1) Potential Cryptophyte absorption = Ed(λ)* aPH(λ) Potential Diatom absorption = Ed(λ)* aPH(λ) Wavelength

  16. Rates of photon absorption for diatoms and cryptophytes Surface Diatoms Cryptophytes Depth (30m) Photon absorption (photons s-1 nm-1) Photon absorption (photons s-1 nm-1) Wavelength Wavelength Total photon absorption for cryptophytes is 2.5X that for diatoms at depth photon abs. = efficiency of absorption (Qa) * surface area of cell * irradiance (Eo)

  17. Conclusions • parameters calculated from Rrs measurements correlate well with in-water measured values • light availability within the recurrent sediment plume is spectrally restricted, affecting phytoplankton community composition

  18. Acknowledgements Larry Boihem Kimberly Kelly Augie Kutlewski Merrett Tuel Rich Stone the Captain and Crew of the R/V Laurentian Funding provided by NSF (OCE-9727342) and NOAA through the CoOP Great Lakes Initiative.

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