Geoscience Reference
In-Depth Information
(a)
1.41
(b)
1.41
r
2
= 0.81
p<0.001
r
2
= 0.69
p<0.001
1.36
1.36
1.31
1.31
1.26
1.26
y = 0.0032 x + 1.36
y = 0.0031 x + 1.24
1.21
1.21
0510 15 20 25
Continuous cropland in riparian zone (%)
30
35
40
45
012
Wetland in riparian zone SQRT (%)
3456 78
(c)
0.68
(d)
0.68
r
2
= 0.67
p<0.001
r
2
= 0.50
p<0.001
0.64
0.64
0.60
0.60
0.56
0.56
0.52
0.52
y = 0.1119 x + 2.4
y = 0.0027 x + 0.54
0.48
0.48
0510 15 20 25
Continuous cropland in riparian zone (%)
30
35
40
45
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
Log TDN (
µ
g
1
)
Figure 9.14. Relationship between McKnight et al. (
2001
) fluorescence index (FI)
(a, b)
and fresh-
ness index (
β
/
α
)
(c, d)
to characteristics of land cover and nutrients for 34 watersheds. FI correlated
positively with % of continuous cropland in the riparian zone
(a)
and negatively with % wetland in
the riparian zone (square root transformed)
(b)
whereas (
β
/
α
) correlated positively with both % of
continuous cropland
(c)
and log total dissolved nitrogen (TDN)
(d)
. These results support the ability
of fluorescence indices to respond to changes in catchment and stream characteristics. (Adapted from
Wilson and Xenopoulos,
2009
.)
values being associated with lower C/N ratios. This relationship is consistent with those
determined from studying humics isolated from natural waters, with humics derived from
microbial sources generally having a lower C:N, reflecting the absence of lignin precursors
(McKnight et al.,
1997
).
9.3.4 Understanding DOM Changes in Estuaries
Huguet et al. (
2009
) compared the HIX
EM
, the BIX (the modified
β
/
α
ratio of Parlanti et al.,
2000
) and McKnight et al. (
2001
) FI when applied to dissolved organic matter in an estu-
arine environment. The McKnight et al. (
2001
) FI demonstrated low values, and no trends
seasonally or with salinity through this estuarine transect. In contrast, the HIX
EM
and BIX
ratios presented trends with salinity and appeared to provide differing information in an
estuarine environment (
Figure 9.16
). HIX
EM
and BIX are related in that they look at very
