Geoscience Reference
In-Depth Information
(a)
(d)
100
100
group 1
r
2
= 0.87
r
2
= 0.39
group 1
80
80
60
60
40
40
group 2
group 3
group 2
20
20
group 3
0
0
0
5
10
15
20
25
30
0.2
0.6
1.0
1.4
1.8
2.2
2.6
HIX
em
(humification index,
emission mode)
HIX
syn
(humification index,
synchronous mode)
(b)
(e)
30
30
r
2
= 0.81
r
2
= 0.80
25
25
20
20
15
15
10
10
5
5
0
0
4
6
8
portion of aromatic H
(% of total H of DOM)
10
12
14
10 15 20 25 30
portion of O-containing functional groups
(mainly carbohydrate; % of total H of DOM)
35
40
45
50
(c)
(f)
2.8
2.8
r
2
= 0.53
r
2
= 0.09
2.4
2.4
2.0
2.0
1.6
1.6
1.2
1.2
0.8
0.8
0.4
0.4
0.0
0.0
4
6
8
10
12
14
10
15
20
25
30
35
40
45
50
portion of aromatic H
(% of total H of DOM)
portion of O-containing functional groups
(mainly carbohydrate; % of total H of DOM)
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 loga-
rithmic (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
.)
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 gradi-
ent. They found that surface soil OM had a greater degree of humification than deeper soil
