Geoscience Reference
In-Depth Information
Quality of Dissolved Organic Material (DOM) varies with source
1.8
LTER Sites
AND
ARC
BNZ
CAP
FCE
HBR
JAK*
LUQ
NWT
PIE
SBC
SEV
VCR
WWC*
*other sites
1.7
Dom from microbes
1.6
1.5
1.4
1.3
Dom from plants and soil
1.2
1.1
0
20
40
60
80
C:N ratio
100
120
140
160
Figure 9.15. Relationship between the McKnight et al. (
2001
) fluorescence index (FI) and the C/N
ratio for DOM samples from a variety of freshwater and marine sites studied in the LTER network
and elsewhere. Higher FI DOM, attributed to predominately microbial precursor material, generally
had a lower C/N ratio, whereas lower FI DOM, attributed as predominately terrestrial precursor
material, had a higher C/N. This also shows the value of using proper measurement and correction
techniques so results and indices can be compared between labs and sites. (Adapted from Jaffé et al.,
2008
.)
similar ratios of emission but with contrasting excitation wavelengths: HIX
EM
with excita-
tion at 254 nm and BIX at 310 nm. However, the processes affecting the HIX
EM
index in an
estuarine environment are poorly understood; Huguet et al. (
2009
) interpret HIX
EM
values
as differentiating humic/terrestrial organic matter from recent/autochthonous organic mat-
ter. Excitation at 254 nm and emission at 300-345 nm would detect peak T and peak B
fluorescence. Emission measured at 435-480 nm would detect peak A fluorescence. So for
estuarine samples where peak T and peak B fluorescence is autochthonously sourced, this
interpretation is valid. However, where the terrestrial input to the estuary has a high peak
T intensity, this simple mixing model would not apply. The extent to which HIX
EM
directly
measures DOM character or is measuring the interactions of peaks A, B, and T with a chan-
ging matrix (increasing salinity) and associated chemical effects (flocculation) is yet to
be determined. Thus the use of HIX
EM
for aquatic samples requires careful consideration.
In contrast, the BIX ratio, measuring the peak M to peak C intensity ratio, is more likely
