Variations in chromophoric dissolved organic matter and its influence on the use of pigment-specific fluorimeters in the Great Lakes
2011
Twiss, Michael R.
The variability of colored material (yellow substances, chromophoric dissolved organic matter [CDOM]) in Great Lakes water on the operation of a submersible pigment-based fluorimeter (FluoroProbe) was assessed. The FluoroProbe is designed to account for the influence of ambient CDOM on fluorimetric analysis of natural waters by using background yellow substance content to correct for fluorescence that is not due to phytoplankton. The objective of this study was to assess FluoroProbe performance as well as determine the variability of CDOM that has a bearing on instrument use. This study focused on Lakes Ontario and Huron in spring and summer and employed up to three FluoroProbes for simultaneous comparisons of performance, as assessed by comparing in situ versus extracted concentrations of chlorophyll-a. Conclusions from this study are: FluoroProbes are not equally accurate; yellow substance correction factors obtained by FluoroProbes are instrument specific; there are seasonal differences in yellow substance correction factors between summer and spring and among thermal strata in summer, in Lakes Huron and Ontario.The observed differences among yellow substance correction factors are attributed to chromophoric material that was assessed independently by measuring CDOM using a separate fluorimetric technique and by measuring in situ UV absorption coefficients. These results suggest that the use of FluoroProbes and related instruments for phytoplankton surveillance and monitoring initiatives must account for differences in ambient CDOM.
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