Geoscience Reference
In-Depth Information
Table 4.1.
Changes in the fluorescence intensity of tryptophan-like fluorescence
(excitation of 225-230 nm and an emission range of 335-350 nm) and humic-like
fluorescence (excitation of 230-245 nm and an emission range of 395-430 nm) with
filtration in six freshwater samples
Percent decrease from initial tryptophan-like fluorescence
Treatment
Sample
Raw water
1.2 µm filtered
1.2 and 0.2 µm filtered
1
0
-5
-32
2
0
-32
-68
3
0
-71
-79
4
0
-7
-32
5
0
-52
-86
6
0
-43
-50
Percent decrease from initial humic-like fluorescence
Treatment
Sample
Raw water
1.2 µm filtered
1.2 and 0.2 µm filtered
1
0
-2
-8
2
0
2
-4
3
0
-11
-14
4
0
-22
-30
5
0
-9
-13
6
0
-12
-9
Source
: Modified from Baker et al. (2007).
also show a removal of tryptophan-like fluorescence between the 1.2 µm filtered water
and the 0.2 µm filtered water. However, in the majority of samples a greater decrease in
tryptophan-like fluorescence was observed between the unfiltered and the 1.2 µm filtered
rather than between the 1.2 and 0.2 µm filtered waters. The authors suggest this means a
significant portion of tryptophan-like fluorescence derives from particulate and the larger
colloidal material as well as that a fraction of tryptophan-like fluorescence is found in the
<0.2 µm fraction. The majority of the samples in the study also showed for the humic-
like fluorescence a decrease between the unfiltered water and the 1.2 µm filtered water
(2-22% decrease, mean = 10%;
Table 4.1
) and the unfiltered water and the 0.2 µm filtered
water (4-30 % decrease, mean = 13%;
Table 4.1
). These results suggest that although some
humic-like fluorescence is in the particulate and colloidal fractions the majority is truly dis-
solved in the <0.2 µm fraction (Lead et al.,
2006
; Baker et al.,
2007
; Seredynska-Sobecka
et al.,
2007
). One clear outcome from this study is that filter pore size impacts unevenly
on fluorophores and thus emphasizes the need to standardize filter size within individual
