Environmental Engineering Reference
In-Depth Information
Interestingly, the viral lysis of an
Aureococcus anophagefferens
bloom can
release approximately 500 g C L
−
1
that can support bacterial demands for both car-
bon and nutrients (Gobler et al.
1997
). It has been shown that >62 % of a bacte-
rial lysate is metabolized by other bacteria following viral lysis within a few days,
with a correspondent bacterial growth efficiency of 45 % (Middelboe
2003
). Fatty
acids potentially produced by microalgae have been shown to increase permeabil-
ity of the plasma membranes of chlorophytes and cyanobacteria, which might be
connected with an increase of photosynthesis (Wu et al.
2006
). Photoproduction of
biologically labile substrates from CDOM could potentially stimulate the growth of
biomass in Hudson Bay coastal waters (Granskog et al.
2007
).
Bacterial biomass exhibits high values during the summer season and lower
ones during winter in lakes with different water color (Wright
1984
; Arvola and
Kankaala
1989
; Jones
1990
). In winter, the bacterioplankton in humic lakes may
primarily consist of a dormant, substrate-limited community that may sustain only
a small number of microzooplankton grazers (Jones
1992
; Wright
1984
). During
the spring and summer season fresh inputs of labile allochthonous DOM and
autochthonous DOM, possibly with enhanced photoinduced activity, stimulate an
increase in bacterial production (Jones
1992
). In turn, a rapid development is pro-
moted of grazing flagellates until a quasi steady-state is reached, resulting into an
active, grazer-controlled bacterioplankton (Wright
1984
).
Currently, model results reveal that the progressive release of dissolved organic
nitrogen (DON) in the ocean's upper layer during the summer season increases
the regenerated primary production by 30-300 % (Druon et al.
2010
). This in
turn enhances the dissolved organic carbon (DOC) production, mainly deriving
from phytoplankton exudation in the upper layer, and the solubilization of par-
ticulate organic matter (POM) deeper in the water column (Druon et al.
2010
).
A microcosm experimental study on summer carbon metabolism in a humic lake
has shown that DOC is 80-85 % of total carbon, while 75 % of POC is detritus.
Bacterial biomass and production can exceed those of phytoplankton (Hessen et
al.
1990
). It has been shown that most of the zooplankton body carbon (46-82 %)
is apparently derived from direct ingestion of the large detrital carbon pool. The
loop of ingestion and defecation is important, giving a detritus particle turnover
rate of 0.39 d
−
1
, and suggests that carbon cycling in humic lakes is essentially dif-
ferent from that in clear-water lakes (Hessen et al.
1990
).
Finally, both autochthonous and allochthonous DOM contribute to the pro-
duction of photo- and microbial products (CO
2
, DIC, H
2
O
2
and so on) and to
the photoinduced generation of the reactive oxygen species (ROS) such as O
2
•
−
,
•
H
2
O
2
and HO
in photosynthesis. Negative effects of photoproducts on bacterial
growth are linked with phototransformation of algal-derived autochthonous DOM
(Ortega-Retuerta et al.
2007
; Tranvik and Bertilsson
2001
). This can be supported
by the highly photosensitive and photodegradable nature of autochthonous DOM
of algal/phytoplankton origin compared to allochthonous DOM (Mostofa et al.
2009
; Johannessen et al.
2007
). Penetration of sunlight to deep water significantly
depends on the DOM contents, and high-DOM lakes are characterized by shoaling
of the euphotic zone (Laurion et al.
2000
).
