Gabor, Baker, McKnight, and Miller
328
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 estuarine 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
1.21
0
5
10 15 20 25
Continuous cropland in riparian zone (%)
30
y = 0.0031 x + 1.24
y = 0.0032 x + 1.36
35 40 45
0
5
10 15 20 25
Continuous cropland in riparian zone (%)
30 35 40 45
0
1
2
Wetland in riparian zone SQRT (%)
3
4
5
6
7
8
0.48
0.52
0.56
0.60
β /α
β /α
0.64
0.68
0.48
0.52
0.56
0.60
0.64
0.68
y = 0.0027 x + 0.54
y = 0.1119 x + 2.4
2.4
2.6
2.8
Log TDN (µg
1
)
3.2
3.0
3.4
3.6
3.8
1.26
1.31
Fluorescence index (FI)
1.36
(a)
r
2 = 0.81
p<0.001
r
2 = 0.69
p<0.001
r
2 = 0.50
p<0.001
r
2 = 0.67
p<0.001
1.41
1.21
1.26
1.31
Fluorescence index (FI)
1.36
(b)
(c)
(d)
1.41
Figure 9.14. Relationship between McKnight et al. (2001) fluorescence index (FI) (a, b) and freshness 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.)
328
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 estuarine 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
1.21
0
5
10 15 20 25
Continuous cropland in riparian zone (%)
30
y = 0.0031 x + 1.24
y = 0.0032 x + 1.36
35 40 45
0
5
10 15 20 25
Continuous cropland in riparian zone (%)
30 35 40 45
0
1
2
Wetland in riparian zone SQRT (%)
3
4
5
6
7
8
0.48
0.52
0.56
0.60
β /α
β /α
0.64
0.68
0.48
0.52
0.56
0.60
0.64
0.68
y = 0.0027 x + 0.54
y = 0.1119 x + 2.4
2.4
2.6
2.8
Log TDN (µg
1
)
3.2
3.0
3.4
3.6
3.8
1.26
1.31
Fluorescence index (FI)
1.36
(a)
r
2 = 0.81
p<0.001
r
2 = 0.69
p<0.001
r
2 = 0.50
p<0.001
r
2 = 0.67
p<0.001
1.41
1.21
1.26
1.31
Fluorescence index (FI)
1.36
(b)
(c)
(d)
1.41
Figure 9.14. Relationship between McKnight et al. (2001) fluorescence index (FI) (a, b) and freshness 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.)