Environmental Engineering Reference
In-Depth Information
carbon in lake sediments exhibits a strong positive relationship with temperature,
which suggests that increasing temperature would lead to increased mineraliza-
tion of OM in natural waters (Gudasz et al.
2010
). As already seen, the distribution
of DOC concentrations for various lakes (7500 lakes from 6 continents; Fig.
2
)
(Sobek et al.
2007
) does not show a simple relationship between DOC and tem-
perature, because the DOC values are affected by both temperature and the sur-
rounding vegetation. However, autochthonous DOM is often higher in lake waters
where the water temperature (WT) is higher. For example, WT in the surface water
of Lake Baikal is generally lower (4-16 °C: summer period) compared to Lake
Biwa (10-28.7 °C: summer period), although the DOC levels are almost similar:
88-114
μ
M C at 0-1400 m depth and 76-135
μ
M C at 0-80 m at central basins,
respectively, during the summer stratification period (Weiss et al.
1991
; Mostofa
et al.
2005a
; Yoshioka et al.
2002a
; Goldman et al.
1996
). However, autochtho-
nous production in Lake Biwa is significantly higher (3-82 %) than in Lake Baikal
(6-35 %) (Table
2
) (Mostofa et al.
2005a
; Yoshioka et al.
2002a
; Sugiyama et al.
2004
). Autochthonous production is not observed in a region where the WT is very
low (ca.
≤
0 °C) and, at the same time, chlorophyll
a
(Chl
a
) production does not
occur in the upper water column (Bussmann and Kattner
2000
) However, a little
increase in WT may produce a little amount of Chl
a
with a corresponding increase
in autochthonous DOM in natural waters (Wheeler et al.
1996
,
1997
; Bussmann
and Kattner
2000
; Melnikov and Pavlov
1978
; Tremblay et al.
2006
). Low WT
may affect the DOM contents by several pathways (Mostofa et al.
2009a
): (i)
Photoinduced degradation of surface DOM is less effective due to low solar effects
at low WT and air temperature. This may result in low contents of photoprod-
ucts, such as DIC, CO
2
, H
2
O
2
, LMW organic substances and so on, which subse-
quently decreases photosynthesis and primary production. The result is a decrease
of autochthonous DOM production in natural waters. (ii) Mineralization of DOM
by photoinduced degradation becomes significantly low at low WT, which may
preserve the DOM in natural waters and lead to increased allochthonous DOM
contents.
An increase in air temperature can significantly enhance DOC export from soil
to surface water by increasing soil respiration and mineralization of plant organic
material (Mostofa et al.
2005a
,
b
; Monteith et al.
2007
; Raymond and Saiers
2010
;
Gielen et al.
2011
; Evans et al.
1999
,
2002
; Gudasz et al.
2010
; Newson et al.
2001
). This can lead to DOM leaching from groundwater to stream or riverbeds
or lakes, and the DOC concentrations are linearly increased with increasing tem-
perature in natural waters. Coherently, the DOC leaching from forest catchments
to streams is significantly enhanced during the summer season. It has been shown
that releases of DOM in upstream waters of forest mountainous origin are much
higher (28-84 %) during summer than in winter season. This has been estimated
during monthly samplings in four upstream rivers and the releases were highest
(52-84 %) in forest soils at upstream sites of Kurose River than in forest gran-
ite mountain (28-31 %) in Lake Biwa watershed (Mostofa et al.
2005a
,
b
). It is
suggested that increased temperature during the summer season can lead to higher
microbial activity and enhanced decomposition of organic matter or peat, which
