Environmental Engineering Reference
In-Depth Information
et al.
2006
). N
2
O may be consumed in the hypolimnion, whilst shallow sediments con-
tribute to N
2
O emissions to the atmosphere (Huttunen et al.
2003b
; Wang et al.
2006
).
3.6 Photoinduced and Microbial Degradation of OM
in Plants and Soil Environments
Photoinduced and microbial processes can directly degrade the organic matter
(OM) in terrestrial plants and in soil environments, releasing CO
2
to the atmos-
phere (Brandt et al.
2009
; Rutledge et al.
2010
). Photodegradation contributes
19 % of the annual CO
2
flux from peatland and almost 60 % of the dry-season
CO
2
flux from grassland. The respective fractions of the summer mid-day CO
2
fluxes are up to 62 and 92 % (Rutledge et al.
2010
). Photodegradation may be
important in a wide range of ecosystems with exposed OM (Rutledge et al.
2010
).
Plant litter can be exposed outdoors to natural solar radiation. It has been shown
that in clear sunny days, close to the summer solstice at mid-latitude, UV radiation
(280-400 nm) accounted for 55 % of the photolytically induced CO
2
production,
while shortwave visible radiation (400-500 nm) accounted for the remaining 45 %
(Brandt et al.
2009
). Abiotic mineralization to CO
2
is the primary mechanism by
which C is lost from litter during photodegradation. It is estimated that annual
CO
2
production via photodegradation could be between 1 and 4 g C m
−
2
a
−
1
in
arid ecosystems in the southwestern United States (Brandt et al.
2009
).
4 Impacts of Global Warming on Natural Waters
Global warming may severely affect various physical, chemical and biological
processes that involve DOM in natural waters. The main effects are the following:
(i) Changes in the light cycle and increase of water temperature; (ii) Increase of
the photoinduced activity of natural waters; (iii) Changes in the microbial activ-
ity in natural water; (iv) Changes in photosynthetic processes in natural waters;
(v) Changes in the primary production and disorders in the chlorophyll
a
maxima;
(vii) Changes in the DOM dynamics and in the global carbon cycle. (viii) Changes
in the nutrients cycle.
4.1 Changes in the Light Cycle and Increase
of Water Temperature
Global warming could cause changes in the seasonal light cycle and an increase
in water temperature, which affects the light distribution in the euphotic zone
