My research is geared towards advancing knowledge on the characterisation and cycling of organic nitrogen in estuaries, including abundance, bioavailability and reactivity. Globally, nitrogen (N) loadings to rivers and estuaries are predicted to further increase as a result of changes in climate, transport, agriculture and urbanisation. The estuarine supply of N to coastal waters is a critical component of fisheries production and water quality, including eutrophication. Thus, predictions of the behaviour of N species, coupled with accurate estimates of their fluxes, are of vital strategic, scientific and social importance.
In natural waters, nitrogen is partitioned between the dissolved and particulate phases. More than 50% of the annual global riverine flux of N is likely to be in the form of particulate N, which is almost entirely organic, while dissolved organic N may also constitute a significant fraction of this total. The importance of land-derived particulate N to coastal zone productivity has been inferred from the effects of river damming, and from comparisons between concentrations of N on particles in rivers and their adjacent coastal sediments. However, the speciation and reactivity of organic N in rivers and estuaries are generally poorly quantified, which gives rise to major uncertainties regarding the factors controlling the flux of N from estuaries to coastal seas. The key to reducing these uncertainties lies in understanding the particle-water interactions of organic N and, in particular, the role of estuarine master variables (e.g. salinity, dissolved organic carbon, bacteria, particle morphology) in modifying N partitioning and reactivity.
Studies on the reactivity of the total organic N fraction are valuable, but provide little information on the most biogeochemically reactive components. Complementary research on the bioavailability of organic matter at the compound or molecular level has been undertaken, but has focussed largely on carbon (C). The few studies undertaken on DON have revealed that it is preferentially utilised relative to C. The organic N pool comprises the particulate and dissolved phases and is a complex, heterogeneous mixture of compounds, where the low molecular weight fraction is quantitatively important. This fraction (<1 kDa) includes free and combined amino acids, urea, glycine betaine, amines, amino sugars, nucleosides and nucleotides, all of which are important bacterial substrates. Some peptides, proteins and labile polymers, including amino acids bound in or to humic materials, also appear to be bioavailable. In contrast, some organic N compounds appear not to be bioavailable, perhaps because of earlier bacterial processing or sorptive preservation. The occurrence, speciation and bioavailability of individual DON compounds originating from anthropogenic sources (e.g. combustion, waste effluents) is barely understood. Their bioavailability may be primarily related to oxidation state, the C/N ratio of the organic matter, or the bacterial assemblage present.
The major obstacle to the study of organic nitrogen cycling, in both particulate and dissolved form, has been a paucity of methods for both bulk and molecular analyses. My PhD was a study of a group of low molecular organic nitrogen compounds, the methylamines, in freshwater and inter- and sub-tidal sediments from a variety of locations around the UK. The methylamines are chemical analogues of ammonia and exist mainly in protonated form (e.g. CH3NH3+) at natural water pH, which allows them to compete with other dissolved cations for particle exchange sites Early studies with co-workers led to development of a sensitive method for the analysis of these compounds (Abdul-Rashid et al., 1991), facilitating studies on their quantification in pristine and impacted estuarine sediments (Fitzsimons et al., 1997; 2001).
Sediments are now recognised as a significant source of nitrogen. Field and laboratory measurements of the effects of sediment resuspension in the Thames Estuary, UK, showed that the resulting benthic organic N flux can significantly augment water column dissolved organic N concentrations (Fitzsimons et al., 2006). The role of mariculture in N cycling was investigated through analyses of sediments populated by the clam Ruditapes decussatus L. in the Ria Formosa, Portugal, where a substantial flux of benthic dissolved organic N was measured (Fitzsimons et al., 2005), consistent with reports of increased concentrations of dissolved N within this lagoon system. I am co-investigator of a follow up study "Organic Nitrogen cycling pathways in intertidal sediments of contrasting permeability of the Ria Formosa coastal lagoon" led by Dr Carlos Rocha, University of the Algarve, funded by the Portuguese Ministry of Science and Technology.
I have received Leverhulme Trust funding to measure the reactivity of organic N with estuarine suspended particulate matter and results show that microbes play a critical role in the sorption behaviour of ON (Tappin et al., 2007; 2010). Molecular characterization of organic N is now possible using electrospray ionisation (ESI), and we have developed a method for the pre-concentration, separation and detection of low molecular weight peptides using LC-ESI-MS through a NERC studentship (Curtis-Jackson et al., 2009). The development of ESI for determination of macromolecules led to the awarding of the Nobel Prize in Chemistry in 2002 to J.B. Fenn and K. Tanaka "for their development of soft desorption ionisation methods for mass spectrometric analyses of biological macromolecules". ESI allows the transfer of intact molecules to the gas phase allowing structural information to be obtained from molecular or pseudomolecular ions by mass spectrometric detection. It is a relatively new technique for studying polar, non-volatile compounds and, as such, is ideal for molecular characterisation of organic N in dissolved form.
Other research on water quality includes analytical development for the determination of sewage indicator compounds in aqueous systems (e.g. purge and trap), the application of nuclear magnetic resonance spectroscopy to environmental studies, and the effects of water pollutants on the distribution of tropical coral ecosystems. I was President of the Association of Chemistry and the Environment and I am currently Secretary of the Estuarine and Coastal Sciences Association. I am an Associate Editor of the journal Environmental Chemistry Letters, and review for a number of journals, including Limnology & Oceanography, Marine Chemistry, Organic Geochemistry, Chemosphere and Marine Environmental Research. I am a member of the NERC Peer Review College (2009-2012).
I grew up by the Irish Sea and greatly enjoyed Chemistry at school, which led me to search for a university degree programme that could combine my love of both. I graduated in BSc (Hons) in Chemistry with Oceanography from the University of Liverpool, U.K., and remained there to continue my PhD research under the supervision of Professor George Wolff (thesis title: "The Geochemistry of the Methylamines in Recent Marine and Lacustrine Sediments") in the Environmental Organic Chemistry and Geochemistry Group, Department of Earth and Ocean Sciences. I moved on to the
I joined the University of Plymouth in 2001. As a member of the Centre for Chemical Sciences (CCS), I teach organic chemistry, analytical chemistry and scientific and professional skills, on the BSc Analytical Chemistry and BSc Applied Chemistry programmes. I also contribute to chemistry teaching on the well-established BSc Environmental Science. I manage the CCS webpages.
I have continued to pursue my research interests in the marine organic nitrogen cycle, with projects funded by the NERC and the Leverhulme Trust (see research interests).
I teach on the BSc Analytical Chemistry and BSc Chemistry Programmes in the following areas: organic chemistry (molecular rearrangements; carbonyl chemistry), analytical chemistry (gas chromatography; high performance liquid chromatography), marine chemistry and professional and scientific skills (scientific writing; research project preparation and management).
My refereed publications are listed below (reverse chronological) and my 'My Citations' page from Google Scholar provides additional bibliographic metrics:
Studentships since 1996:
|2014-2017||M. Raccagni||MARES PhD Student||In progress|
|Organic nitrogen uptake by marine algae: consequences for marine ecosystem functioning and biodiversity
Dr Mark Fitzsimons (Director of Studies) and Dr Ian Probert (Roscoff Culture Collection, Station Biologique de Roscoff)
|2011-2014||H.K. Schofield||EU Studentship||In progress|
|The perfect soil: an investigation of the chemical characteristics needed for healthy, artificial soils at the Eden Project, Cornwall
Dr Mark Fitzsimons (Director of Studies), Dr Alan Tappin, Dr Tim Pettitt (Eden Project) and Dr Gavyn Rollinson (University of Exeter)
|2010-2014||C.H.L. Cree||NERC Studentship||In progress|
|Climate regulators? An investigation of amine cycling in marine systems
Dr Mark Fitzsimons (Director of Studies), Dr C. Anthony Lewis, Dr Steve Archer (Plymouth Marine Laboratory) and Dr Ruth Airs (Plymouth Marine Laboratory)
|2009-2012||E. Pidduck||NERC Studentship||In progress|
|Do suspended sedimentary processes influence fluxes of nitrogen and phosphorus in estuaries?
Dr Andrew Manning (Director of Studies), Professor Paul Worsfold and Dr Alex Souza (Proudman Oceanogrphic Laboratory)
|2008-2012||J. Pino||Government of Portugal||In progress|
|Nitrogen reduction in marine systems: in-situ study of alternative metabolic pathways linked to coastal groundwater discharge
With Dr Carlos Rocha, Trinity College Dublin (Director of Studies)
|2004-2007||C. Leakey||NERC Studentship||Ph.D.
|Scottish Natural Heritage, U.K.|
|Quantifying estuarine carbon subsidies to coastal ecosystems and fisheries
With Dr Martin Attrill (Director of Studies)
|2003-2006||C.H. Redshaw||BBSRC CASE Studentship/Astrazeneca Brixham Environmental Laboratory||Ph.D.
|Queen's University, Belfast, Northern Ireland, U.K.|
|The transport and fate of fluoxetine hydrochloride, diazepam and their human metabolites in sewage sludge-amended soil [abstract]
With Professor S.J. Rowland (Director of Studies) and Dr G.P Matthews
|2002-2005||P. Curtis-Jackson||NERC Studentship||Ph.D.
|AstraZeneca, Brixham Environmental Laboratories, Brixham, U.K.|
|Characterisation of algal derived organic nitrogen [abstract]
With Dr Guillaume Massé
|M. Dawitt||Middlesex University Studentship||Ph.D.
|Bespak Europe Ltd., U.K.|
|Organic nitrogen cycling in European inter-tidal sediments
With Professor Mike Revitt, Middlesex University
|A.L.B. Abdullah||Middlesex University Studentship||Ph.D.
|University Sains Malaysia, Malaysia|
|Modelling of suspended sediment in coastal waters using remote sensing and GIS techniques
With Professor Brian Shutes, Middlesex University and Dr Wan Ruslan, University Sains Malaysia
Income since 1996:
|Dates||Funding Body and Project||Amount|
|2014-2017||EU Marine Ecosystem Health and Conservation programme (MARES)
Organic nitrogen uptake by marine algae: consequences for marine ecosystem functioning and biodiversity
with Roscoff Marine Station
|2008-2012||Government of Portugal
Nitrogen reduction in marine systems: in-situ study of alternative metabolic pathways linked to coastal groundwater discharge
with Dr Carlos Rocha, Trinity College Dublin, Ireland
|2007-2008||Royal Society of Chemistry
Cohesive sediment flocculation dynamics and their effect on nitrogen concentrations in estuaries
(with Dr Andrew Manning, SEOES)
Bacterial assimilation of riverine organic nitrogen
(with Professor Alan McCarthy [Co-Investigator], School of Biological Sciences, University of Liverpool and Dr Alan Tappin [Researcher Co-Investigator])
|2003-2006||The Leverhulme Trust
Natural estuarine particles and their uptake of nitrogen in estuaries
Identification of Aromatic UCM Components of Petroleum Using Semi-Preparative HPLC
Nitrogen geocycling in the Thames Estuary
|2000||Commonwealth Science Council
Organic nitrogen cycling in European inter-tidal systems
|1998||Royal Society of Chemistry
1-Aminopropanone as a biochemical sewage indicator compound
|Total Since 1996 =||>£650,000|
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