Coble, Spencer, Baker, and Reynolds
80
exhibits some variability. For this reason, it is useful to specify a humic-like C component
that includes both peaks.
Humic-like C component is the predominant type found in soils, most freshwater samples, rivers, and the deep ocean. The range in composition across these environments is
reflected in the wide range of excitation and emission wavelengths given in Table 3.1 for
the peak C maximum. Environments dominated by humic substances leached from soils
tend to be the most complex pool observed. Across the range of environments, the position
of the overall fluorescence maximum from the humic-like C component varies, with older
or more terrestrial material showing the most red-shifted excitation and emission maxima
(Figure 3.2). Some researchers working in peaty waters have designated subregions of peak
Emission Wavelength (nm)
Fluorescence (QSE)
300
0
500
1000
1500
2000
2500
300
350
400
450
3000
3500
350
400
450
500
550
650
700
600
Exc (nm)
Emission Wavelength (nm)
Fluorescence (QSE)
300
0
300
Exc (nm)
350
400
450
50
100
150
350
400
450
500
550
650
700
600
Figure 3.1b. EEMS for quinine bisulfate (top) and Columbia River water (bottom) shown in threedimensional view.