Lakes fluorescence index

Figure 7. CDOM fluorescence of water from two lakes (Hargreaves, unpublished) emission scans for excitation at 370 nm (Shimadzu 551 fluorometer), before and after subtraction of water blank. Samples deionized water (DIW), L. Giles water (ca. 1 g m DOC), L. Lacawac water (ca. 5 g m DOC) The Raman scattering peak at 417 nm represents a shift in wavenumber by 3400 cm from the excitation wavenumber. The broad peak is contributed predominantly by the fulvic acid fraction of DOM. The peak wavelength and fluorescence index ratio for these samples (L. Giles, 452 nm peak and ratio = 1.5 L. Lacawac, 455 mn peak and ratio = 1.4) suggest a slight difference in CDOM...

Figure 9.7. Two components of the Cory and McKnight (2005) PARAFAC model that have spectral properties similar to semiquinones (SQl and SQ2) explain the variation in the McKnight et al. (2001) fluorescence index (FI). The SQ2 component is resolved in a model using only samples from Antarctic lakes, indicating it is likely microbial in origin. As the portion of SQ2 to the total of SQl -i-SQ2 falls, so does the FI, and a lower FI is associated with less microbially derived material. (From Cory and McKnight, 2005.)...

Figure 9.13. Seasonal variation in (a) chlorophyll a, (b) DOC, (c) percentage fulvic acid, (d) whole water (solid line) and fulvic acid (dashed hue) McKnight Fluorescence Index (FI), and (e) whole water redox index (RI) at the outlet to Green Lake 4, an alpine lake in the Colorado Rocky Mountains. The vertical dashed lines indicate the sustained rain event, and the shaded areas represent the timing of the peak in chlorophyll a at the outlet. PLFA represents the FI of the Pony Lake fulvic acid, a microbial end member, and SRFA represents the FI of the Suwannee River fulvic acid, a terrestrial end member. (Adapted from MiUer et al., 2009.)...

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