Environmental Engineering Reference
In-Depth Information
untreated surface sediments (8.4 wt% organic
carbon) from the Peru Margin. The NMR spectrum
showed resonance of alkyl, carbohydrate, aromatic,
and carboxyl structures. This kind of marine sedi-
ment was accumulating in coastal regions, away
from strong river discharges, and was predominantly
composed of opal or carbonate. Iron metal was
almost absent in this case, because there was no ter-
restrial input of sediments. Therefore the NMR
analysis could be performed without pretreatment
for paramagnetic impurity removal.
Dickens
et al.
(2006) used solid-state
13
C-NMR
spectroscopy, along with elemental stable carbon
isotopic (
organisms. Phosphorus availability in aquatic systems
is regulated by the conversion of particulate phos-
phorus to dissolved forms and organic phosphorus
to inorganic orthophosphate. There is relatively little
information about concentrations, transport, and
fate of particulate phosphorus in aquatic environ-
ments which primarily results from the current limi-
tations in phosphorus analytical techniques. Most of
the knowledge of phosphorus in sediment has been
obtained from several sequential extraction proce-
dures and is related to phosphorus in its inorganic
form. In contrast, organic phosphorus concentra-
tions in particulate and dissolved samples are deter-
mined indirectly by the difference between total
phosphorus and soluble reactive phosphorus (SRP).
SRP is the fraction that reacts to form a blue-colored
phosphomolybdate complex under slightly acidic
conditions (Cade-Menun
et al.
2005). Although the
degradation of organic phosphorus compounds in
environmental samples, including sediments, may be
an important source of bioavailable phosphorus,
little is known about the chemical forms of organic
phosphorus (Nanny & Minear 1997; Ahlgren
et al.
2006a). Therefore, new analytical methods are
required to study phosphorus in environmental
systems. In this context,
31
P-NMR spectroscopy is a
powerful tool that can identify inorganic phosphorus
forms such as orthophosphate, pyrophosphate, or
polyphosphate and organic forms such as ortho-
phosphate monoesters, orthophosphate diesters, or
phosphonates (Paytan
et al.
2003). In addition,
information on degradation and mineralization can
be obtained using
31
P NMR in monitoring changes
to P composition promoted by these processes
(Ahlgren
et al.
2006a).
31
P-NMR spectroscopy is widely used in the
investigation of organic phosphorus speciation in
terrestrial ecosystems; however, there are few
studies of aquatic phosphorus using this technique
(Cade-Menun
et al.
2006). This is probably because,
in environmental samples, the phosphorus concen-
tration of the sample is below the lower limit of
NMR detection, which therefore requires a concen-
tration procedure (Nanny & Minear 1997). For
solution
31
P-NMR, the sediment samples are usually
concentrated by extraction with a NaOH-EDTA
solution followed by lyophilization (Cade-Menun
et al.
2005) or by rotatory evaporation (Ahlgren
et al.
2006a) or just concentrating and fractionating
13
C) and lignin phenol analysis, to study
the mechanisms controlling the preservation of
organic carbon in ocean sediments. Sediment samples
were demineralized in preparation for NMR analysis
to remove paramagnetic cations that would interfere
with NMR analysis, and to concentrate organic
carbon. They studied two marine sediments, one
containing a mixture of terrestrial and marine inputs,
the other containing entirely marine organic carbon
(from an anoxic region). Using solid-state CPMAS
13
C NMR spectroscopy, these authors identifi ed and
quantifi ed functional groups such as alkyl C, unsatu-
rated C, O-alkyl C, carbonyl and amide C, or ketone
C for different size and density fractions for the two
sediments. This information allowed inferences to be
made about the molecular structure of the organic
matter and investigated the mechanisms allowing
preservation of organic carbon. Therefore,
13
C-NMR
spectroscopy is a useful tool for determining how
organic carbon is preserved in sediment.
In environmental samples, NMR can also be
applied to the study of phosphorus, an essential
nutrient used by all living organisms. Phosphorus (P)
is easily detected by NMR spectroscopy, owing to
the large magnetogyric ratio of
31
P and its natural
abundance (Paytan
et al.
2003).
31
P-NMR spectros-
copy is a suitable method for identifying and quan-
tifying phosphorus species in environmental samples.
Phosphorus is present in aquatic systems in dissolved
and particulate forms. In contrast to nitrogen, phos-
phorus has no gaseous phase; thus, its supply for
living organisms in aquatic environments depends on
external sources as well as internal recycling (Ahlgren
et al.
2006b). Orthophosphate is the most important
bioavailable form of phosphorus, although other
inorganic and organic forms can also be used by
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