Environmental Engineering Reference
In-Depth Information
one; 1,3,5-trimethyl-1,3,5-triazine-2,4,6-trione; 1,3-dimethyl-2,4-pyrimidinedione;
2-methyl-isoindole-1,3-dione; 5-methoxy-2-methyl-indole; 1,3,5-trimethyl-2,4-py-
rimidinedione; and 3,3-dimethyl-4-[(2-methoxycarbonyl)ethyl]-2,5-dione-pyrro-
lidine (McKnight et al.
1997
; Fimmen et al.
2007
; Laane
1984
; Borowitzka
1988
;
Wershaw
1992
; Xue and Sigg
1993
; Xue et al.
1995
). The aromatic compounds pre-
sent in autochthonous DOM originate from intracellular quinones in the chloroplasts
and mitochondria of algae and bacteria (McKnight et al.
1997
; McKnight and Aiken
1998
; Klapper et al.
2002
).
Algal toxins such as as microcystins and nodularins have high molecular
weight and cyclic peptide structures and are hepatotoxic; anatoxins, cylindrosper-
mopsin and saxitoxins have heterocyclic alkaloid structures. Anatoxins and saxi-
toxins are neurotoxic, while cylindrospermopsin is hepatotoxic (Richardson
2007
).
On the other hand, red tide toxins such as brevetoxins have heterocyclic polyether
structures and are neurotoxic. Note that bacteria, algae and their exudates also
consist of a mosaic of functional groups such as amino, phosphoryl, sulfhydryl
and carboxylic groups. The net charge on the cell wall depends on the pH of the
medium (Filella
2008
). Algae and bacteria have no lignin-like components in their
molecular structure (McKnight et al.
1997
; McKnight and Aiken
1998
; Opsahl and
Benner
1998
), thus the low aromaticity of autochthonous fulvic acids can reflect
the lower content of moieties with
sp
2
-hybridized carbon in cell wall material and
in other components of microbial cells (McKnight et al.
1994
).
Algal- or phytoplankton-derived autochthonous fulvic acids can absorb light to
a lesser extent (by approximately 3-5 times) than allochthonous fulvic acids. They
show a progressive increase in absorbance with decreasing wavelength that is typi-
cal of fulvic acids (McKnight et al.
1991
,
1994
). However, the autochthonous ful-
vic acids (C-like and M-like) of algae or phytoplankton origin can exhibit higher
fluorescence intensity at peak C-region than at peak A-region, which is an opposite
behavior compared to allochthonous fulvic acids (C-like and M-like) of terrestrial
plant origin (Fig.
1
; McKnight et al.
2001
; Mostofa et al.
2009b
). Autochthonous
fulvic acids can persist with ages up to 3,000 yr in the desert lakes in Antarctica
(McKnight et al.
1991
,
1994
).
The stable carbon isotope (
δ
13
C) fractionation of autochthonous DOM of algal
or phytoplankton origin ranges from
−
17.2 to 23.7 ‰ in lake and marine envi-
ronments (Thurman
1985a
; Raymond and Bauer
2001a
; Nissenbaum and Kaplan
1972
). The
δ
13
C values of algae or phytoplankton shows high variation in fresh-
water [
−
(18.3-34.6 ‰)] and sea water [
−
(18-24.2 ‰)] (Mostofa KMG et al.,
unpublished data; McCallister et al.
2004
; McKnight et al.
1997
; Fry and Sherr
1984
; Anderson and Arthur
1983
; Sigleo and Macko
1985
; Yoshioka et al.
1989
;
Currin et al.
1995
; Yoshioka
1997
; Lehmann et al.
2004
). In addition,
δ
13
C shows
high variations between benthic microalgae [
−
(12-18 ‰)]; benthic marsh micro-
algae [
−
(23.7-27.7 ‰)]; C-4 salt marsh plants [
−
(12-14 ‰)]; C-3 freshwater/
brackish marsh plants [
−
(23-26 ‰)]; submerged macrophytes [
−
(21.7-22.2 ‰)];
emergent macrophytes (
−
26 ‰); marsh macrophytes [
−
(23.3-28.9 ‰)]; marsh
OM [
−
(22.3-26.4 ‰)]; and freshwater grass leachate such as
Peltandra virgi-
nica
[
−
(29.6 ‰)] (McCallister et al.
2004
; Raymond and Bauer
2001a
,
c
; Caraco
