Environmental Engineering Reference
In-Depth Information
The described processes (Fig.
5
) are more important in waters having high con-
tents of DOM, naturally or because of pollution, and can lead to further eutrophi-
cation of DOM-rich waters. The process would be enhanced by the extension of
the summer season and of the euphotic zone that is expected to take place because
of global warming. Total contents of DOM and global warming together thus
severely affects on foodwebs, primary productivity, and nutrients cycles in fresh-
water environments which ultimately impact on drinking water quality, sustainable
uses of agriculture and industrial purposes as well as the whole water ecosystem
(Mostofa et al.
2009b
; Li et al.
2008
; Larsen et al.
2011
; Hessen et al.
1990
; Ask
et al.
2009
; Karlsson et al.
2009
). The importance of the described processes would
be much lower in DOC-poor (oligotrophic) systems. In such cases other phenom-
ena could play a more important role, and the enhanced photoinduced DOM degra-
dation could even lead to a further oligotrophication of DOC-poor systems.
The photoinduced degradation of DOM generally takes place through redox reac-
tions that can lead to supply (
+
) or consumption (
−
) of energy in natural waters.
Energy changes (
±
) also occur during photosynthesis (Komissarov
1994
,
1995
,
2003
). DOM with its content of organic C and N is a thermodynamic anomaly
that provides a major source of energy to drive aquatic and terrestrial ecosystems
(Wetzel
1984
,
1992
; Salonen and Vähätalo
1994
; Tranvik
1992
; Hedges et al.
2000
).
Therefore, any changes in energy during the photoinduced degradation of DOM are
thermodynamically vital for all the living organisms and for the aquatic environments.
The photoinduced degradation of DOM is interlinked free radical production,
microbial processes, photosynthesis, autochthonous DOM, nutrients, end pho-
toproducts and their utilization as food for microorganisms in natural waters. A
conceptual schematic diagram for the global warming effects on photoinduced and
microbial processes of DOM and POM, photoproducts and their importance in the
aquatic environment is depicted below (Fig.
5
):
Finally, it can be concluded that any changes in nature are absolutely inter-
linked with other changes in the natural ecosystem.
5.1 Remedial Measures for Controlling Algal Blooms
due to Global Warming
The possible remedial measures for controlling the lake algal blooms that are severely
affecting the water quality because of global warming are listed below: (i) The total
DOM contents in lake waters should be reduced by applying coagulation processes
that can reduce the regeneration of photoproducts, microbial products and nutrients.
Such measures would thus reduce photosynthesis and, as a consequence, the primary
production (algae or phytoplankton) in natural waters. During the algal blooms, algae
or phytoplankton should be removed using fine, small-mesh nets. Such a procedure
could reduce the further photoinduced and microbial release of DOM and nutrients
from primary production. The consequence would be a significant reduction of fur-
ther photosynthesis and, thus, of primary production. (ii) The sediments in the lake
