Date of Award

5-2005

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Oceanography

Advisor

Mark L. Wells

Second Committee Member

Emmanuel Boss

Third Committee Member

Larry Mayer

Abstract

Chromophoric dissolved organic matter (CDOM) plays an essential role in the biogeochemical cycling of organic matter, microbial ecology and regulating optical properties in marine surface waters. Coastal waters in particular exhibit large spatial and temporal variations in CDOM abundance and spectral signature. A significant amount of variability in the optical properties of CDOM might be due to changes in the abundance and optical characteristics of colloidal (>I kDa) material. Our primary goal was to investigate the relationship between chromophoric dissolved organic matter (CDOM), colloidal organic matter and phytoplankton biomass in marine waters of the Damariscotta River Estuary, Maine using flow field-flow fractionation (flow FFF) interfaced with a long-pathlength liquid core waveguide (LCW). The application of LCWs for CDOM measurements is a new development in the field of oceanography. We initially conducted an analytical intercomparison of Type I and Type I1 LCWs to assess the agreement of data collected with the two instruments as well as determine the effect of salinity variations and colloidal material on absorbance measurements. While no statistical differences between absorbance measurements from the two instruments were observed for a dissolved holmium wavelength calibration standard and molecular weight standards (MWS) sized 14,45 and 150 kDa, discrepancies were found for MWS of 1 kDa and filtered seawater samples. Additionally, the 1 kDa MWS caused an apparent increase in absorption within both liquid core waveguides. These data will enable the quantitative intercomparison of our CDOM measurements with the Type I1 LCW with previous work conducted with the Type I LCW. Seasonal changes in colloidal size and associated optical properties of CDOM were investigated at a coastal site over a period of two years. We observed changes in colloidal size spectra and CDOM optical properties related to phytoplankton bloom dynamics. In particular, the (r2 = 0.772). Neither colloidal absorbance, nor CDOM absorption co-varied with phytoplankton biomass (chlorophyll a). However, consistent patterns of increasing colloidal absorbance, CDOM absorption and spectral slope were observed with temporal progression of the phytoplankton bloom. Absorption spectra slopes of colloidal CDOM(0.2 pm) seawater and large variations in spectral slope were observed between colloidal size fractions. These observations indicate that changes in the colloidal fraction may contribute significantly to the variability in CDOM optical properties.

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