Environmental Engineering Reference
In-Depth Information
photoinduced and microbial degradation of allochthonous DOM of plant origin and
Biogeochemical Cycles in Natural Waters
”
). Small algae can carry out 40-95 % of
the bacterivory activity in the euphotic layer of the temperate North Atlantic Ocean
in summer, and 37-70 % in the surface waters of the tropical North-East Atlantic
Ocean (Zubkov and Tarran
2008
). This reveals that the smallest algae have less
dependence on dissolved inorganic nutrients (Zubkov and Tarran
2008
).
The volume of planktonic bacteria increases as water temperature decreases
(Albright and McCrae
1987
; Chrzanowski et al.
1988
; Bjørnsen et al.
1989
), and
thus the occurrence of larger cells in the hypolimnion is linked to its low tempera-
ture (Wiebe et al.
1992
; Callieri et al.
2009
; Bertoni et al.
2010
). Bacterial cells are
often observed to be approximately 30 % larger in the Arctic Ocean and Antarctic
coastal waters than in temperate regimes (Straza et al.
2009
).
The mechanism behind this size shift is presumably that low temperature in
hypolimnion and Arctic or Antactic regions can protect against cell degradation,
whereas microbial assimilations of planktonic bacteria cells can release both nutri-
ents and autochthonous DOM. Correspondingly, high temperatures along with
solar radiation and surface waters mixing by strong waves are effective in pho-
tolytically and microbially releasing nutrients and autochthonous DOM. These
two effects could be responsible for the occurrence of large cells in low tempera-
ture regions including the hypolimnion. The photoinduced and microbial releases
of nutrients, photo-/microbial products, and autochthonous DOM from algae/
phytoplankton (Mostofa et al.
2009
; Zhang et al.
2009
; Tranvik et al.
2009
; Zepp
et al.
2011
; Ma and Green
2004
; White et al.
2010
; Liu et al.
2010
; Mostofa et al.
2005
; Bushaw et al.
1996
; Molot et al.
2005
; Johannessen et al.
2007
; Borges et al.
2008
; Kujawinski et al.
2009
; Lohrenz et al.
2010
; Omar et al.
2010
; Cai
2011
) are
responsible for low photosynthesis in most upper surface layers.
It has also been observed that lower photosynthesis in the shallower epilimnion
(1 m) than in the deeper epilimnion (3 m) (Nozaki et al.
2002
) might be the effect
of higher photoinduced degradation of algae near the water surface. This effect,
coupled with strong wind mixing and turbulence can decrease the size structure
of phytoplankton or algae in the upper epilimnion, thereby decreasing the photo-
synthetic efficiency (Cermeno et al.
2005
; Nozaki et al.
2002
). Note that physical
mixing in the surface mixing zone is an important factor for promoting the pho-
toinduced degradation of DOM (see chapter
“
Complexation of Dissolved Organic
5.11 Effects of Global Warming
Global warming causes an increase in water temperature, lengthens the sum-
mer season, extends the surface water mixing zone and increases the stability of
