NERC RESEARCH STUDENTSHIPS
NAME OF LEAD SUPERVISOR
Guenther Uher
NAME(S) OF CO-SUPERVISOR(S)
François L. L. Muller, Environmental Research Institute, UHI, Thurso, Caithness
TITLE OF PROJECT (250 CHARACTERS INCLUDING SPACES)
Do interactions between iron and organic colloids affect dissolved organic matter reactivity?
SUMMARY OF RESEARCH PROGRAMME: (UP TO 2 SIDES A4)
A brief description of the proposed research is required, including details of research training. Any associated research grants should be mentioned
with reference numbers.
Executive summary. Riverine fluxes contribute significantly to the marine pools of dissolved organic carbon (DOC) [1] and the
trace element iron (Fe) [2]. DOC and Fe fluxes are closely linked due to DOC-Fe binding (complexation) and biogeochemical
interactions particularly in the colloidal size fraction, which contains up to 40% and 80% of total DOC and Fe, respectively [3]. Colloidal
DOC-Fe interactions may therefore have significant implications for riverine fluxes of DOC and Fe, and consequently for global carbon
and iron cycles pivotal to Climate Change. Specifically, we hypothesise that DOC reactivity towards photochemical degradation (its
major sink) is significantly affected by DOC-Fe binding strength, molecular size and colloidal aggregation, which in turn are controlled
by DOC molecular composition as reflected in its optical properties. We will study this hypothesis using samples from two contrasting
river–sea systems (Thurso & Tyne) and selected DOC reference materials reconstituted in fresh- and seawater matrices.
Background. Riverine DOC and Fe inputs play important yet distinct roles in global biogeochemistry. Riverine DOC fluxes link
large reactive organic carbon reservoirs in soils and oceans, with northern peat lands alone accounting for ~500 Pg C, comparable to
global C pools in vegetation (~600 Pg C) and atmosphere (~750 Pg C) [4]. Importantly, DOC exports from UK peat lands, which
dominate riverine DOC fluxes from the UK, have doubled over the last 40 years due to Global Climate Change [5], raising the
dramatic prospect of peat organic carbon relocation into the atmospheric CO2 pool, via sequential photochemical-microbial DOC
degradation in sunlit surface waters [6]. Increasing DOC exports from rivers will also have implications for coastal ecosystems,
because dissolved organic matter (DOM) acts as a nutrient reservoir, and its coloured fraction (CDOM) affects levels of photosynthetic
and biologically harmful radiation and the photoreactivity of surface waters [7].
Iron plays important roles in phytoplankton nutrition and limitation of marine primary production [2]. However, uncertainties remain
with regard to its fluvial inputs, not least because of significant knowledge gaps with regard to salinity-induced flocculation and
adsorptive removal of colloidal material at the freshwater-seawater interface. Recent work showed that the effects of Fe-DOM binding
strength on salinity induced flocculation can cause a ~4-fold difference in the fraction of exported, bioavailable Fe [8]. Furthermore, our
own results indicate the complete absence of flocculative and adsorptive removal of DOC and Fe in the Thurso river-sea system ([9],
F.L.L. Muller, unpubl.), in sharp contrast to significant DOC removal in the Tyne estuary [10, 11]. This contrasting behaviour may
plausibly reflect differences in estuarine residence time, as both estuaries show similar levels of peat-derived DOC.
Besides salinity-induced flocculation and adsorptive removal in estuaries, DOC pools are significantly affected by sequential
photochemical-microbial degradation, as evidenced by the loss of total DOC, CDOM photobleaching (i.e. loss of absorbance &
fluorescence) and changes in its molecular size spectrum [7]. Conversely, photochemical DOM transformation have also been
implicated in Fe redox cycling and bioavailability [12]. However, the overall role of colloidal DOC-Fe interactions in photochemically
induced DOC degradation is less well documented, and previous reports are largely concerned with freshwaters, excluding marine
DOM. These reports indicate that Fe accelerates DOM photodegradation in lake water [13], and that photobleaching of riverine DOM
may be controlled by photochemically active intermolecular charge transfer complexes [14]. Given that intermolecular charge transfer
interactions are dependant on molecular conformation and aggregation, which in turn are affected by DOC-metal binding, colloidal
DOM-Fe interactions should affect DOM photoreactivity. Furthermore, we hypothesise that significant changes in surface water
properties along the river–sea continuum (such as salinity, pH, DOM size spectra and chemical composition) will affect colloid
aggregation and DOM-metal binding and therefore the reactivity of DOM itself.
We therefore propose a detailed study of colloidal material along the river sea continuum in two river-sea systems, the Thurso and
Tyne, and adjacent coastal waters. Both model systems receive DOC-rich water exported from blanket peat, show contrasting
estuarine removal and therefore discharge DOM of contrasting properties to the coastal sea. Field measurements will be
complemented by controlled irradiations to determine the effects of Fe, metal binding strength, molecular size, colloidal aggregation,
DOM source and environmental factors (e.g. salinity, pH). These experiments will be complemented by irradiations of Nordic
Reservoir NOM reference material (International Humic Substances Society) for which detailed molecular characterisation data are
available [15].
Specifically we will
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Determine DOC concentrations, spectral absorbance and fluorescence characteristics before and after size fractionation
by cross flow ultrafiltration (CFUF),
Elucidate DOM source and composition using a variety of spectral indices (e.g. spectral slope, SUVA, McKnight
fluorescence index) [16-18] and PARAFAC modelling of DOM fluorescence excitation emission matrices (EEMs) [19],
Measure Fe concentrations and Fe-DOC binding strengths using cathodic stripping voltammetry,
Carry out controlled irradiation experiments (solar simulator & monochromatic) to quantify the DOC photoreactivity and
to study the effects of Fe, DOM source and sample matrix on DOC photodegradation,
Characterise particle aggregation using scanning electron microscopy (SEM), dynamic light scattering (DLS) [20] and
atomic force microscopy (AFM) [21],
Relate Fe, DOC-Fe binding strength, DOM composition, aggregation state and sample matrix properties to DOM
reactivity using multivariate statistics.
Methods and student training. The student will join two active research laboratories with complementary expertise in DOM and
trace metal biogeochemistry. Newcastle will provide access to a state-of-the-art photochemical laboratory and to spectroscopic CDOM
characterisation. Fluorescence excitation emission matrices (EEMs) will be recorded on a Varian Eclipse spectrofluorometer which
was calibrated by us during a recent laboratory intercomparison under NERC FLUORONET funding (NE/D000939/1) within an
existing NERC studentship (Paul Mann, NER/S/A/2004/14351). PARAFAC decomposition of fluorescence EEMs into independent
spectral components will facilitate identification of terrestrial and marine humic-like and protein-like DOM [19]. Similarly, fluorescence
index, SUVA and spectral slope will trace DOM source (microbial vs terrestrial), DOM aromaticity and photobleaching history [16-18].
Cathodic stripping voltammetry (ERI) is the technique of choice because it allows determination of Fe abundance and binding strength
without the application of preconcentration techniques that could alter DOM aggregation. The student would also be able to explore
trace metal analysis by ICP-OES (ERI) for the determination of a wide range of elements. Particle aggregation in the colloidal phase
will be assessed by scanning electron microscopy (SEM). Coupled with x-ray detection, this technique allows identification of Fe oxy
hydroxides in the sample, and thus allows distinguishing between DOM and mineral colloids. DLS and AFM techniques will be made
available through application to the NERC Facility for Environmental Environmental Nanoparticle Analysis and Characterisation
(FENAC), Birmingham. AFM in particular complements SEM as it allows colloid sampling with minimal disturbance and delivers high
resolution down to ~1 nm. Please note that we have established collaborations between the head of FENAC (JR Lead) and FLL Muller
[9]. We intend to apply for additional student training in nanoparticle analysis through the NERC nomination route, specifically for the
FENAC summer school 2010. Additional training will be available through ERI via the UHI postgraduate school.
References
1. Sarmiento, J.L. and E.T. Sundquist, Revised budget for the oceanic uptake of anthropogenic carbon dioxide. Nature, 1992. 356: p.
589-593. 2. Achterberg, E.P., et al., Determination of iron in seawater. Analytica Chimica Acta, 2001. 442(1): p. 1-14.
3. SanudoWilhelmy, S.A., I. RiveraDuarte, and A.R. Flegal, Distribution of colloidal trace metals in the San Francisco Bay estuary.
Geochimica Et Cosmochimica Acta, 1996. 60(24): p. 4933-4944. 4. IPCC, ed. Climate Change 2001. The scientific basis. ed. J.T.
Houghton, et al. 2001, Cambridge University Press: Cambridge. 881. 5. Freeman, C., et al., Export of organic carbon from peat
soils. Nature, 2001. 412: p. 785. 6. Mopper, K. and D.J. Kieber, Photochemistry of Carbon, Sulfur, Nitrogen and Phosphorus, in
Biogeochemistry of dissolved organic matter, D.A. Hansell and C.A. Carlson, Editors. 2002, Academic Press: Amsterdam, The
Netherlands. p. 455-507. 7.Zepp, R.G., et al., Interactive effects of solar UV radiation and climate change on biogeochemical cycling,
in Photochemical and Photobiological Sciences. 2007. p. 286-300. 8. Krachler, R., F. Jirsa, and S. Ayromlou, Factors influencing the
dissolved iron input by river water to the open ocean. Biogeosciences, 2005. 2(4): p. 311-315. 9. Batchellia, S., et al., Size
fractionation and optical properties of colloids in an organic-rich estuary (Thurso, UK). Marine Chemistry, 2009. 113(3-4): p. 227-237.
10. Spencer, R.G.M., et al., The estuarine mixing behaviour of peatland derived dissolved organic carbon and its relationship to
chromophoric dissolved organic matter in two North Sea estuaries (UK). Estuarine Coastal and Shelf Science, 2007. 74(1-2): p. 131144. 11. Uher, G., et al., Non-conservative mixing behavior of colored dissolved organic matter in a humic-rich, turbid estuary.
Geophys. Res. Lett., 2001. 28(17): p. 3309-3312. 12. Miller, W.L., et al., Photochemical redox cycling of iron in coastal seawater.
Marine Chemistry, 1995. 50(1-4): p. 63-77. 13. Brinkmann, T., D. Sartorius, and F.H. Frimmel, Photobleaching of humic rich dissolved
organic matter. Aquatic Sciences, 2003. 65(4): p. 415-424. 14. Hefner, K.H., J.M. Fisher, and J.L. Ferry, A multifactor exploration of
the photobleaching of Suwannee River dissolved organic matter across the freshwater/saltwater interface. Environmental Science and
Technology, 2006. 40(12): p. 3717-3722. 15. Thorn, K.A., D.W. Folan, and P. MacCarthy, Characterization of the International
Humic Substances Society Standard and Reference Fulvic and Humic Acids by Solution State Carbon-13 (13C) and Hydrogen-1 (1H)
Nuclear Magnetic Resonance Spectrometry. 1989, U.S. Geological Survey: Denver, CO. p. 93 pp. 16. Helms, J.R., et al., Absorption
spectral slopes and slope ratios as indicators of molecular weight, source, and photobleaching of chromophoric dissolved organic
matter. Limnol. Oceanogr., 2008. 53(3): p. 955–969. 17. McKnight, D.M., et al., Spectrofluorometric characterization of dissolved
organic matter for indication of precursor organic material and aromaticity. Limnol. Oceanogr., 2001. 46(1): p. 38-48. 18. Weishaar,
J.L., et al., Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic
carbon. Environmental Science & Technology, 2003. 37(20): p. 4702-4708. 19. Stedmon, C.A., S. Markager, and R. Bro, Tracing
dissolved organic matter in aquatic environments using a new approach to fluorescence spectroscopy. Marine Chemistry, 2003. 82(34): p. 239-254. 20. Muller, F.L.L., Measurement of electrokinetic and size characteristics of estuarine colloids by dynamic light
scattering spectroscopy. Analytica Chimica Acta, 1996. 331(1-2): p. 1-15. 21. Lead, J.R., D. Muirhead, and C.T. Gibson,
Characterization of freshwater natural aquatic colloids by atomic force microscopy (AFM). Environmental Science and Technology,
2005. 39(18): p. 6930-6936.
Name of all supervisors
(including CASE)
Present post
Length of
research
experience
Number of students currently being supervised who are in
the:
1st year
Guenther Uher
F.L.L.Muller
Teaching and
Research
Fellow
Principal
Investigator,
ERI
2nd year
3rd year
3rd year+
TOTAL
15
-
-
1
2
3
21
-
-
2
-
2
Recent publications by supervisor(s) relevant to research area:
Ahad, J.M.E, Barth, J.A.C, Ganeshram, R.S, Spencer, R.G.M, Uher, G. Controls on carbon cycling in two
contrasting temperate zone estuaries: The Tyne and Tweed, UK. Estuarine, Coastal and Shelf Science
2008, 78(4), 685-693.
Batchellia, S., Muller, F.L.L., Baaloushab, M. and Lead, J.R., 2009. Size fractionation and optical properties
of colloids in an organic-rich estuary (Thurso, UK). Marine Chemistry, 113(3-4): 227-237.
G. Uher; Claire Hughes; Gordon Henry; R. C. Upstill-Goddard. Non-conservative mixing behavior of
colored dissolved organic matter in a humic-rich, turbid estuary. Geophysical Research Letters 2001,
28(17), 3309-3312.
Kitidis,V, Uher, G, Woodward, E.M.S, Owens, N.J.P. and Upstill-Goddard, R.C. Photochemical production
and consumption of ammonium in a temperate river-sea system. Marine Chemistry 2008, 112, 118-127.
Muller, F.L.L., 1996. Measurement of electrokinetic and size characteristics of estuarine colloids by
dynamic light scattering spectroscopy. Analytica Chimica Acta, 331(1-2): 1-15.
Muller, F.L.L., 1998. Colloid/solution partitioning of metal-selective organic ligands, and its relevance to
Cu, Pb and Cd cycling in the Firth of Clyde. Estuarine Coastal and Shelf Science, 46(3): 419-437.
Muller, F.L.L., Larsen, A., Stedmon, C.A. and Sondergaard, M., 2005. Interactions between algal-bacterial
populations and trace metals in fjord surface waters during a nutrient-stimulated summer bloom.
Limnology and Oceanography, 50(6): 1855-1871.
Spencer, R.G.M, Ahad, J.M, Baker, A, Cowie, G.L, Ganeshram, R, Upstill-Goddard, R.C, and Uher, G. The
estuarine mixing behaviour of peatland derived dissolved organic carbon and its relationship to
chromophoric dissolved organic matter in two North Sea estuaries (U.K.). Estuarine, Coastal and Shelf
Science 2007, 74, 131-144.
Stubbins, A, Hubbard, V, Uher, G, Law, C. S, Upstill-Goddard, R.C, Aiken, G.R, and Mopper, K. Relating
carbon monoxide photoproduction to dissolved organic matter functionality. Environmental Science and
Technology 2008, 42, 3271-3276.
PART 3 – TO BE COMPLETED BY THE CASE PARTNER (S)
(FOR OPEN CASE STUDENTSHIPS ONLY COMPLETE IF THERE ARE ANY CHANGES FROM YOUR
ORIGINAL APPLICATION)
10. CO-OPERATING BODY (CASE) DETAILS - to be completed by the CASE partner(s) where applicable
Name and Address of Co-operating (CASE) body:
1. Environmental Research Institute,
2.
Castle Street, Thurso, Caithness, KW14 7JD
Co-operating (CASE) Body Supervisor (s)
Title:
1.Dr
Initials:
1.F.L.L.
Surname:
1.Muller
2.
2.
2.
Department
1. Environmental
Current Position
1.Principal Investigator
Research
Institute
Tel:
1. +44
2.
(0)1847 889585
2.
Fax:
1. +44
2.
(0)1847 890014
2.
E-mail:
1. Francois.Muller@thurso.uhi.ac.uk
2.
Description of work to be undertaken by the student at the premises of the CASE body and its role within the project:
Nature and frequency of contacts between the CASE body, student and supervisor (must be maintained throughout the duration of the award as
appropriate to the demands of the project):
Financial and other contributions from the CASE body (NOTE: CASE bodies must make a minimum contribution of £1000pa towards the student’s
maintenance, and it is expected that any additional support that is required for the student’s travel and subsistence whilst working at the CASE body’s
premises will be provided by the CASE partner).
Total value of funds to student for the whole award
£
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section. Details of the nominated student will not be publicised.
By signing this you are confirming that you accept the terms and conditions laid out in the NERC studentship
handbook.
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Signature:
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11.
AUTHORISATION FOR CASE COLLABORATION AND FINANCIAL CONTRIBUTION BY THE
APPROPRIATE AUTHORITY:
Signed:
Title:
Initials:
Date:
Position held:
Surname:
Has this company/organisation co-operated on a previous CASE studentship?
Y
N