Environmental Engineering Reference
In-Depth Information
Despite the constant low temperature (4 °C) during the summer and winter sea-
sons in lake sediment pore waters, high variations in methane production in sum-
mer compared to winter are suggested to be caused by algal biomass blooms in
surface waters (Schulz and Conrad
1995
). In this case, the effect of temperature
would not be significant in the microbial formation of methane from acetate in
the sediment pore waters. The effect of temperature on methanogenesis mostly
depends on the nature of organic sediments, presence of microorganisms and the
fermentation or degradation products in water.
4.4 pH
The pH is an important factor that influences the rate of methanogenesis as well
as the CH
4
production pathway and the methanogenic archaeal community in
sediment waters. The methanogenesis is typically inhibited at low pH, where
microbial turnover rates are slower, although significant methane production is
still observed in acidic peat lands (Kotsyurbenko et al.
2007
; Horn et al.
2003
;
Dunfield et al.
1993
; Hornibrook et al.
2000
; Goodwin and Zeikus
1987
; Bräuer
et al.
2004
,
2006
). Acetate as a major carbon source for methanogenesis may
be unavailable to the methanogens at low pH because of the inhibitory effect of
non-dissociated acetate toward methanogenesis (Fukuzaki et al.
1990
). Low pH
conditions may also reduce the microbial processes of H
2
production and con-
sumption in anaerobic environments (Goodwin et al.
1988
). An isolate from a
landfill is able to grow at pH 5 (Lapado and Barlaz
1997
) and an isolate from a
peat land grows at pH 5.3 but generates some methane down to pH 3.1 (Williams
and Crawford
1985
). Acidotolerant hydrogenotrophic methanogenic consortia
have been enriched from a peat bog at pH 4 (Sizova et al.
2003
), and molecular
analysis of an acidic peat bog reveals the presence of
Methanomicrobiaceae
and
Methanosarcinaceae
at pH 4.5 (Kotsyurbenko et al.
2004
).
In acidic mining lakes, sulfate reduction often occurs when the pH in the sed-
iment is almost neutral (Meier et al.
2004
). An increase with depth of pH from
2.6 up to 6 enhanced the production of CH
4
and CO
2
in the sediment cores of
Lake Caviahue (Koschorreck et al.
2008
). In the most acidic surface layer of the
sediment (pH < 4), methanogenesis is inhibited as suggested by a linear CH
4
con-
centration profile. In contrast, methanogenesis is highly active below 40 cm depth
at high pH (>4). The carbon isotope composition of CH
4
is between -65 and
-70 ‰, which is indicative of the biological origin of methane in Lake Caviahue.
Therefore, it is suggested that the high biomass content of the sediment may
induce high rates of sulfate reduction, which presumably raises the pH and creates
favorable conditions for methanogens in deeper sediment layers (Koschorreck et
al.
2008
). On the other hand, the ratio of
δ
13
CO
2
to
δ
13
CH
4
increases from 1.053
at pH 6 up to 1.072 at pH 3.8, indicating a relative increase of hydrogenotrophic
methanogenesis at low pH values (Hornibrook et al.
2000
; Whiticar
1999
). The
genus
Methanobacterium
contains two alkaliphilic and one moderate acidophilic
