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from 3.8 to 9.9 (Kotelnikova et al. 1998 ; Worakit et al. 1986 ; Patel et al. 1990 ).
The pH is thus one of the important factors that can control the methanogenesis in
sediment.
4.5 Sediment Depths
It is shown that the degradation of organic matter is mostly occurring in the upper
sediment layer (1-10 cm depths) in lakes or in soil (Nakane et al. 1997 ; Li et al.
unpublished data; Roden and Wetzel 1996 ; Schulz and Conrad 1995 ). However,
the methanogenesis may also occur in deeper sediment layers under favorable con-
ditions, either in peatlands or in sediment pore waters (Koschorreck et al. 2008 ;
Nakagawa et al. 2002 ; Galand et al. 2005 ). In the sediments of Lake Caviahue the
CH 4 concentration is steadily increased from 0 to 6.0 mM from 1 to 30 cm sedi-
ment depths (Fig. 9 ) (Koschorreck et al. 2008 ). The concentration of CH 4 typi-
cally reaches saturation (~1 mM) at 3-40 cm below the top few centimeters in
unvegetated sediments. In vegetated sediments CH 4 concentrations are very low
(0.0-0.1 mM) until 20 cm, after which they increase at ~1 mM level at 40 cm
(Roden and Wetzel 1996 ). In humic bog lakes the deeper parts of the water col-
umn favor microdiversification of methanogens, whilst the periodically disturbed
water column of shallower dimictic lakes promotes genetically more diverse
methanogen communities (Milferstedt et al. 2010 ). In peatlands, hydrogenotrophic
methanogenesis is the predominant pathway of CH 4 formation, accounting for 50
to 100 % of total CH 4 production, particularly in the deeper layers (Nakagawa
et al. 2002 ; Galand et al. 2005 ). Therefore, sediment depths play an important role
in the production of methane in sediment waters.
Fig. 9 Vertical profiles of pH ( a ), dissolved gases CO 2 ( b ) and CH 4 ( c ) in different sediment
cores from Lake Caviahue. The pH is measured in KCl extracts during the field work in 2003 (
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