3
year PhD scholarship available
CRC for Water Quality and
Treatment, Curtin Water Quality Research Centre and Stable Isotope and
Biogeochemistry Research Group, Centre for Applied Organic Geochemistry, Department
of Applied Chemistry,
The use
of stable isotopes for the characterisation of NOM and investigation of the
different organic precursors of aquatic systems.
Background:
There are many different biological
(e.g., algae, bacteria and macrophytes) and anthropogenic (storm water,
industrial waste) sources of aquatic organics and the exact identity of the main
precursors of dissolved organic carbon (DOC) often remains ambiguous. Different
organic species can also impact water system to different degrees at different
times. Identification of the major organic inputs to source water is crucial
for catchment and reservoir strategies aimed at minimising organic loads. Such
knowledge may also optimise holistic treatment protocols with respect to efficient
DOC removal.
Stable isotope analysis
is a useful method for distinguishing the different organic inputs of natural
environments. The stable isotopes of carbon, nitrogen, sulfur, oxygen, and
hydrogen are commonly used in ecological and environmental research and are
measured by isotope ratio-mass spectrometry (Grice, 2001, and references
therein). It is quantitative and non-intrusive, without the environmental
hazards of radioisotope investigations. It can provide valuable data on
chemical, biological, and physical transformations of organic compounds in the
environment (Grice et al., 2001). Several examples of environmental
applications of stable isotopic analysis which should also be applicable to the
analysis of NOM include: 1. distinguish the contributions of different organic
precursors (Schouten et al., 1996; Klein Breteler et al., 2002); 2. monitor
temporal and spatial variations of bioproductivity (Kuypers, 2001; Hinrichs et
al., 2003) - the seasonal and spatial molecular variance of NOM in surface
waters was recently monitored to assess source, transport and fate of humic and
non-humic DOM (Lu et al., 2003); 3. Understand degradation and humification
processes (Lu et al., 2003); 4. to chemically monitor the effect of natural
bioremediation or other treatment processes on molecular composition (Steinbach
et al., 2002).
Traditionally
conducted on bulk samples, stable isotopic analysis of individual compounds is
now also possible following the advent of GCirMS (Hayes, 1983). Compound specific isotope analysis (CSIA) of individual compounds
can facilitate the high resolution distinction of different organic sources. Isotopic
data can compliment the measurement of molecular distributions with respect to
biomarker identification. Just like the occurrence of certain biomarkers, the
stable isotopic value of certain products can be diagnostic of particular
organic precursors. Many naturally occurring organic compounds can derive from
one or more precursors and the different source possibilities may be
distinguished by their stable isotopic characteristics. Stable isotopic data
may also allow the seasonal productivity of DOC precursors to be monitored, as
well as provide information about the aquifer residence time of particular
organic compounds (Lu et al., 2003).
The load of organic precursors
can vary considerably over time. Bioproductivity, for example, can vary with
environmental or seasonal changes, but again little is known about the triggers
or mechanism of this phenomena. The continuum of organic species may simply
change with the changing rate of some source inputs, whilst specific compounds
may be linked to a particular source, season or other environmental factor. The
catchment environment can also impact on the composition of DOM as organic
compounds will degrade at different rates. Stable isotopic analysis offers some
potential for monitoring the occurrence, cause and effect of these dynamics.
Description
of Project:
This PhD project aims to
develop and test the utility of stable isotopic analysis for characterising and
establishing the main precursors of DOC.
Stable isotopic data of
NOM will be obtained on both a whole sample and a compound specific basis to investigate
the utility of stable isotope analysis for studying the source input, temporal
and spatial dynamics (e.g., bioproductivity), transportation and fate of
organic material in source water systems. A range of NOM samples will be
studied since the chemical and physical nature of NOM is dependent on the
source materials and surrounding environmental conditions, hence NOM from
different locations can vary considerably in structure and behaviour. NOM fractions will be separately
studied to establish the relationship between the structural moieties of NOM
and specific organic precursors. A correlation of the source inputs of organics
in the source waters with the subsequent occurrence of certain DBPs following
treatment may also help identify which precursors are most significant with
respect to DBP formation.
Accurate CSIA measurements
require baseline GC resolution since values are calculated from the
ratio of the m/z 45 (13CO2)
and m/z 44 (12CO2)
peaks. That means that complex organics such as NOM often need to be separated
into simplistic fractions prior to analysis. This can be achieved by chemical
degradation (e.g. CuO) or off-line pyrolysis followed by column chromatography
to produce less complex fractions on the basis of solubility in solvents of
different polarity. New chemical and enzymatic degradation techniques, which
selectively target specific structural bonds (e.g., C-N, C-O, C-S bonds), will
be developed to produce relatively clean fractions suitable for compound
specific isotope analysis (CSIA).
The utility of stable
isotope analysis for following seasonal and geographical variations of organic
species will be examined. The organic composition of source waters is likely
influenced by a number of variables including the catchment environment,
climate, seasons, etc. NOM will be periodically collected and isolated from selected
source waters to cover seasonal and climatic variations.
Skills/Interests
Required:
First class Honours or equivalent science degree- preferably in
Chemistry. Interest in analytical organic chemistry; laboratory skills in trace
analysis; familiarity with and skills in pyrolysis,
wet chemical methods, GC, or GCMS instrumentation; awareness of stable isotopic
concepts. Overseas applicants are also welcome to apply.
Contact Details for Further
Information:
Forward CV and 2 referees to:
Assoc. Prof Kliti Grice, Stable Isotope and Biogeochemistry group, Centre for Applied Organic
Geochemistry, Curtin University of Technology,
Ph: +61 (08) 9266 2474; 0401 103 353
Fax: +61 (08)
9266 2300
www.caog.chemistry.curtin.edu.au
Regards,
Kliti Grice
Dr
Kliti Grice
Associate
Professor of Organic and Isotope Geochemistry
ARC (QEII) Fellow
Stable Isotope and
Biogeochemistry Group Leader
Centre for Applied
Organic Geochemistry
Department of Applied
Chemistry
WA
Australia
tel +61 8 9266
2474
fax + 61 8 9266
2300