Environmental Engineering Reference
In-Depth Information
4.2 Sources of DOM and its Fermentation Products
The methanogenesis depends on the sources of organic matter such as vascu-
lar plants or algal biomass, the fermentation or degradation products of which are
greatly varied in soil, peatland or sediment pore waters. For example, the disintegra-
tion or fermentation of vascular plant materials by aerobic and anaerobic bacteria
can produce humic substances (fulvic and humic acid), structural polysaccharides,
polyphenols, proteins, amino acids, carbohydrates and inorganic components in
soil environments (Mostofa et al.
2009a
; Malcolm
1985
; Chefetz
2002
; Cadillo-
Quiroz et al.
2010
; Hur
2011
; Peña-Méndez et al.
2005
). In contrast, among the
DOM components that originated from algal or phytoplankton biomasses, one can
find autochthonous fulvic acid, protein, amino sugars and labile polysaccharides
(Mostofa et al.
2009a
; Zhang et al.
2009
; Li W et al., unpublished data; Parlanti
et al.
2000
; Benner and Kaiser
2003
). The changes of the DOM by microbial
processes significantly depend on its sources and composition and/or the mixing
ratios of the individual original source materials in natural water (Hur
2011
).
It is shown that fulvic and humic acids are composed of diverse functional groups
such as -COOH, carboxyl, methoxyl, alcoholic OH, carbohydrate OH and phenolic
OH. Low aromaticity is observed in fulvic acid (17 % of aromatic C and 63 % of
aliphatic C) compared to humic acid (30 % and 47 %, respectively) (Malcolm
1985
;
Steelink
2002
). Carbon distribution by solid-state CPMAS
13
C NMR shows about
24 % of C-O, 3 % of anomeric C, 12 % of C
=
C, 5 % of
ϕ
-O (
ϕ
=
other elements
except C), 16 % of COOH, 4 % of C
=
O. Elemental analysis showed 38 % of O,
0.87 % of N, 0.74 % of S and 0.62 % of P (Malcolm
1985
). Although the chemi-
cal structure of autochthonous fulvic acid of algal origin is still unclear, the mate-
rial is likely to be a macromolecule because of the similarity of its EEM spectra to
standard Suwannee River Fulvic Acid (Fig.
1
d,e, and f) (Mostofa et al.
2009b
). This
might be the reason of the effective degradation of the autochthonous fulvic acid of
algal origin, which is observed in the EEM images in the lake sediment pore waters
Li W et al. (unpublished data). Therefore, it is not surprising that functional groups
bound to either fulvic and humic acids of terrestrial origin or autochthonous fulvic
acid of algal origin are affected by microbial processes in the sediment waters.
Depending on the presence of either terrestrial plant material or algal or phy-
toplankton biomass, different fermentation products can be found in a variety of
sediment waters. In a similar way, the contribution of H
2
to CH
4
production in
different methanogenic sediments is quite variable: 32-46 % in Kichier Lake,
36-46 % in Lake Mendota, 15-39 % in Lake Washington, 17-31 % in anoxic
paddy soil, 8 % in Colne Pt. Salt marsh, 4 % in Knaack Lake, 0 % in Lake
Constance, 97 % in Kuznechika lake, 74-86 % in Octopus Spring mat, 76-82 %
in Blelham Tarn, 71-80 % in Cape Lookout Bight, 100 % in Kings Lake Bog,
95-97 % in Bunger Hills (Antarctica), and 99-100 % in Lake Baikal deep sedi-
ments (Schulz and Conrad
1996
; Ivanov et al.
1976
; Winfrey and Zeikus
1979
;
Sandbeck and Ward
1981
; Jones et al.
1982
; Banat et al.
1983
; Crill and Martens
1983
; Phelps and Zeikus
1984
; Kuivila et al.
1989
; Lansdown et al.
1992
;
Rothfuss and Conrad
1992
; Galchenko
1994
; Namsaraev et al.
1995
). It is shown
