Gabor, Baker, McKnight, and Miller
322
H and an increase in O-containing functional groups (Figure 9.10). The HIX EM showed a
stronger correlation to these changes in chemical characteristic than the HIX SYN . Bu et al.
(2010) also saw a correlation between the two indices when investigating the water-extractable organic matter from soils taken from different vegetation areas along an elevational
gradient. They found that surface soil OM had a greater degree of humification than deeper
8
portion of aromatic H
(% of total H of DOM)
portion of aromatic H
(% of total H of DOM)
DOC mineralization
(% of total DOC)
10
12
14
10 15 20 25 30
portion of O-containing functional groups
(mainly carbohydrate; % of total H of DOM)
portion of O-containing functional groups
(mainly carbohydrate; % of total H of DOM)
35 40 45 50
10 15 20 25 30 35 40 45 50
6
4
8
1 0
1 2
1 4
6
4
10
15
group 1
group 2
group 3
25
20
30
5
0
0
20
40
60
80
100
(a)
(d)
(b)
(e)
(c)
(f)
0
5
10
HIX
em (humification index,
emission mode)
HIX em (humification index,
emission mode)
20
25
15
r
2 = 0.80
r
2 = 0.53
r
2 = 0.09
r
2 = 0.81
r
2 = 0.87
DOC mineralization
(% of total DOC)
1.0 1.4
group 1
group 2
group 3
2.2
1.8
2.6
0.6
0.2
0
20
40
60
80
100
HIX syn (humification index,
synchronous mode)
r
2 = 0.39
30
0
5
10
20
25
15
30
0.0
0.4
0.8
HIX
syn (humification index,
synchronous mode)
HIX
syn (humification index,
synchronous mode)
1.6
2.0
1.2
2.4
2.8
0.0
0.4
0.8
1.6
2.0
1.2
2.4
2.8
HIX
em (humification index,
emission mode)
Figure 9.10. Comparison of the HIX SYN and HIX EM for a set of samples extracted from maize straw,
forest floors, peats, and agricultural soils. Samples were incubated for 90-days to determine the
impact of biodegradation on the DOM character and fluorescence signature. Group 1 samples were
considered to have high biodegradation (measured as mineralization to CO 2 ) after 90 days, group
2 intermediate biodegradation, and group 3 low biodegradation. Graphs (a) and (b) show the logarithmic (solid line, r
2
) as well as linear (dashed line) regressions using the average value from each
group, showing the decrease in both HIXs with increased biodegradation. HIX EM (c, d) and HIX SYN
(e, f) are also plotted vs. portion of aromatic H- (c, e) and O-containing functional groups (d, f). In
both cases the HIX EM has a stronger linear relationship. (From Kalbitz et al., 2003.)