Environmental Engineering Reference
In-Depth Information
past changes in tree-line position and TOC of another
lake. However, they emphasized that this work was
just a fi rst step in developing DRIFTS into a new
paleolimnological tool and that future research was
needed to include many more lakes to assess further
the uniformity of reconstructions among different
types of lake.
Gallé
et al.
(2004) applied DRIFTS to follow the
sediment composition of a mountainous river during
changes in its hydrological life cycle for one and a
half years. A set of 57 sediment samples collected on
a weekly basis were wet-sieved down to less than
63
3.4 Final considerations
Mineralogical characterization of particles obtained
using electronic microscopy and X-ray diffraction
techniques in combination with information of par-
ticle size distribution from laser diffraction and func-
tional groups enables advances in understanding of
sediments. Understanding the reactivity of particles
that are found in sediment and their capacity to
interact with the environment, either in water or
organisms, is the greatest benefi t of such studies of
sediment characterization.
m, freeze-dried, and homogenized before analy-
sis. All samples were ground and mixed with KBr
before DRIFS analysis. Usually, a drawback is the
presence of inorganic carbonate in the sediment
samples submitted to FTIRS analysis, because it gives
rise to a broad signal around 1650 cm
−1
that can
mask the asymmetric COO
−
/C-C stretches bands.
However, the sediment samples studied by Gallé
et al.
(2004) were practically free from inorganic
carbonate. Therefore, the refractory organic matter
contribution to the overall C
org
was easily detectable
in the DRIFTS spectra, without the removal of
inorganic carbonates by chemical methods.
Gallé
et al.
(2004), observed that during or shortly
after fl ood events particulate organic matter content
in sediments was reduced and sediments poor in C
org
content gave rise to DRIFTS spectra enriched in car-
boxylic and aromatic signals. These signals were con-
sidered characteristic of terrestrial oxidized vascular
plant debris (humic substances). The reduction in
organic matter content during fl ooding was attrib-
uted to the fact that, at higher fl ow velocities, the
loosely organized upper parts of biofi lms were
removed from the particle, with only diatoms or
cyanobacteria remaining attached directly to the
surface. Although often damaged, these algae and
bacteria can serve as inocula for the recolonization of
the particle surface. DRIFT spectra obtained during
low-fl ow conditions showed growth of bands corre-
sponding to -OH, -CH
3
, -CH
2
, and secondary amide
-C O stretches and the -NH band. According the
authors, these bands are considered to be the most
prominent features of microbial (bacterial) spectra.
Therefore, the DRIFTS results seem to indicate that
low-fl ow conditions allow the recolonization of the
sediment particle by bacteria, which are rich in
amide, aliphatic, and polysaccharide moieties.
μ
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