Environmental Engineering Reference
In-Depth Information
by gradually decreasing the total contents of DOM and nutrients or by reducing
the nutrients at equal DOM. The latter scenario can occur because in waters with
low contents of DOM, as can be found for instance in Lake Biwa and Lake Baikal,
allochthonous DOM usually dominates than autochthonous DOM (Yoshioka et al.
2002
; Mostofa et al.
2005
). The removal of total organic carbon (total internal and
external inputs) is accounted for by respiration (50 %), sedimentation (40 %) and
photo-oxidation (10 %) in acidic lakes (Kopáˇek et al.
2004
).
Production of algae or phytoplankton and the related photoinduced and micro-
bial release of new DOM are greatly influenced by several factors, such as high
precipitation (Zhang et al.
2010
; Freeman et al.
2001
; Tranvik and Jasson
2002
;
Hejzlar et al.
2003
), land use changes that induce high transport of DOC from
catchments to adjacent surface waters (Worrall et al.
2004
; Raymond and Oh
2007
), nitrogen deposition (Pregitzer et al.
2004
; Findlay
2005
), sulfate deposi-
tion (Zhang et al.
2010
; Evans et al.
2006
; Monteith et al.
2007
), drought and
alteration of hydrologic pathways (Zhang et al.
2010
; Hongve et al.
2004
; Knorr
et al.
2005
), and change in total solar UV radiation or increase in temperature due to
global warming (Sobek et al.
2007
; Zhang et al.
2010
; Freeman et al.
2001
; Sinha et
al.
2001
; Rastogi et al.
2010
). Higher temperatures in the tropical zone may acceler-
ate bacterial metabolism, causing a larger fraction of incoming organic carbon to be
respired (Tranvik et al.
2009
). In temperate zones, the additive effect of decreased
water availability and increased primary production may enhance organic carbon burial
through increased autochthonous production and preservation (Cotner and Biddanda
2002
; Downing et al.
2008
). A recent study of DOC concentrations in over 7,500 lakes
in six continents suggests that DOC export is potentially enhanced by global warming
in aquatic ecosystems (Sobek et al.
2007
). It has also been shown that total solar radia-
tion and precipitation can account for 49-84 % of the variation in the long-term DOC
patterns in various catchments (Zhang et al.
2010
). DOC concentrations in Swedish
lakes and streams have substantially increased during 1970-1980, despite a reduction
in temperature, most likely because of higher precipitation (Tranvik and Jasson
2002
).
The uptake of inorganic nitrogen by bacteria during a phytoplankton bloom
occurs particularly in lake or coastal waters where the inputs of terrestrial humic
substances are much higher (Kirchman et al.
1991
; Amon and Benner
1994
).
Photolytically produced ammonium can be assimilated by bacterial populations,
which can enhance the production of autotrophic and heterotrophic biomass in
planktonic environments.
Carbon storage in high-latitude peatlands is estimated to represent one-third
or more of the global soil carbon pool (Post et al.
1982
; Zimov et al.
2006
).
Warming-induced decomposition of soil organic matter, particularly in arctic and
subarctic soils (Anderson 1991), can result in greater transport of allochthonous
DOC to adjacent natural waters. Water bodies that usually received low DOC
inputs such as alpine lakes or those resulting from glacial retreat may be strongly
affected by the altered DOC quality, which causes for instance the replacement of
herbs by less productive shrubs (Shaver et al.
2000
).
Beneath the sea ice in the Central Basin, relatively high values of
p
CO
2
have
been detected, ranging between 425 and 475
μ
atm values. Such values are larger
