Characterisation of the nature, origins and ecological significance of dissolved organic matter in freshwater ecosystems

Lead Research Organisation: University of Bristol
Department Name: Chemistry

Abstract

Evidence indicating that nutrient flux to inland and coastal waters is increasing worldwide is clear. Despite significant management effort to reduce theses fluxes, while N & P concentrations have recently levelled off or decreased in some European catchments, in others an increase is reported, particularly in rivers draining through rapidly developing economic regions. A rising trend in Dissolved Organic Carbon (DOC) flux to freshwaters & coastal areas such as the Baltic Sea is also widely reported, particularly in the N Temperate & Boreal regions. Impacts on ecosystem health are extensive & undesirable in both freshwaters & coastal waters, & there are implications for human health where DOC & DON are also known to support carcinogen formation in water supplies.

In Europe the control of nutrient flux to all freshwaters & the coastal zone is required in order to meet the target of restoring waters to Good Ecological Status under the EU Water Framework Directive, while the UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP) is currently revising Annex IX of the Gothenburg Protocol (to Abate Acidification, Eutrophication & Ground-level Ozone) to further reduce the emission of ammonia from land-based activities.

Simultaneously, the UN has listed coastal nutrient pollution and hypoxia as the one of the greatest current threats to the global environment. Impacts include eutrophication of coastal waters and oxygen depletion, and the associated damage to ecosystems, biodiversity & coastal water quality. The UNEP Manila Declaration (Jan 2012) identifies nutrient enrichment of the marine environment as one of 3 foci for its Global Programme of Action for the Protection of the Marine Environment from Land-based Activities, and this was one of the key foci at the Rio+20 UN Conference on Sustainable Development, June 2012.

A detailed understanding of the nature, origins & rates of nutrient delivery to waters is essential if we are to control these impacts through management intervention, yet much of the necessary evidence base is lacking. Routine water quality monitoring is largely based on inorganic nutrient fractions, and substantially underestimates the total nutrient flux to waters, while research confirms that dissolved organic matter (DOM) plays an important role in ecosystem function including supporting microbial metabolism, primary production and pollutant transport, suggesting that its oversight in routine monitoring may undermine international efforts to bring nutrient enrichment impacts under control.

Here, we address this knowledge gap, building on the specific expertise of project members, undertaking a suite of interlinked experimental & observational research from molecular to catchment scale. We will use a combination of well-established approaches widely used in catchment research, with a range of cutting-edge approaches which are novel in their application to nutrient cycling research, or employ novel technologies, bringing new insights into the process controls on nutrient cycling at a molecular to river reach scale.

The programme will deliver improved understanding of:

1. the role of DOM in the transport of N & P from source to sea & the ways in which this might alter nutrient delivery to freshwaters & the coastal zone under a changing climate;
2. the ecological significance of DOM as a source of nutrient uptake & utilisation by algal, plant and microbial communities in waters of contrasting nutrient status & DOM character; and
3. the impacts of DOM flux from soils, livestock & human waste fluxes on the ecological status, goods & services provided by freshwaters.

It will also deliver knowledge exchange between the 5 groups & the wider science community, and have an impact beyond the lifetime of this project, building capacity through staff & PhD appointments in a field where current understanding is uncertain, undermining business planning and international policy development.

Planned Impact

Impact in the user community will be realised through the development of KE partnerships with those involved in policy and operational management of the environment. To this end, we have held a suite of meetings and discussion sessions with a wide range of stakeholders prior to finalising our proposal, in order to ensure that their interests and concerns are properly represented in the programme, and that the science we propose is transferable and useful beyond the immediate academic beneficiaries.

Nine stakeholder organisations have agreed to join us as Project Partners, providing access to data and infrastructure assets, staff expertise, project placements and training. These include Government organisations (Defra, Environment Agency, Natural England, Countryside Council for Wales), charities (The Rivers Trust), and the water utilities including Wessex Water (Hampshire Avon), Welsh Water (Conwy) and Scottish Water who have significant problems with DBP formation in a number of their water supply catchments.

We will also develop a number of novel technologies, including the testing of novel sensor technologies to capture high resolution information on CDOM flux at catchment scale, and the development of a novel proteomic/metabolomics approaches to allow holistic study of the metabolic processes controlling nutrient utilisation by microbial communities, and characterisation of the enzymatic functions involved. The group at Bangor is world-leading in this field, and we have secured a letter of support from Dr Ferrer, Institute of Catalysis, Madrid confirming his support for and involvement in the application of this technology to this project as a Project Partner.

We will deliver KE through a 5 step process:

1. all Project Partners have participated in the final formulation of this bid, providing valuable suggestions to hone the programme to ensure that anticipated outcomes meet their interests and operational needs; they will join the Project Board, establish a programme of placements and working partnerships with staff and PhD students, and participate in a start-up workshop to refine the proposed sampling programme, to ensure that this capitalises on their existing data, infrastructure assets and focus areas;
2. we will produce a series of briefing notes on specific policy implications of our research findings for our Project Partner organisations throughout the programme making these publicly available through our project website and the publicity activities of our Project Partner organisations;
3. we will develop links with the wider stakeholder community through the project website and existing KT networks in which we are already involved in our Hampshire Avon and Conwy research, and will ensure wider public engagement through University Science Days and local and national media;
4. we will engage with the wider academic community through: (i) free weekly access for external researchers to our high frequency quantitative data; (ii) publication of 10 core papers in international peer reviewed journals, a suite of integrative papers in a special issue of Global Biogeochemical Cycles, and an overarching paper in Nature on the 'Environmental Role and Significance of DOM Flux in Freshwaters'; (iii) feedback on our findings to the international policy arena through our participation as expert members of the IPCC, UNECE Task Force for Reactive N and UNEP Foresight programmes, (iv) presentation of our findings at international conferences, and (iv) a contribution to Planet Earth;
5. we will to host an end-of-programme interactive workshop on 'The Role and Management of DOM in Freshwater Systems' for our Project Partners and the wider stakeholder community, and will host an international research meeting at The Royal Society on 'The Global Significance of DOM in Potable, Inland and Coastal Waters' with invited international speakers, focusing on KE with the wider international research community.

Publications

10 25 50

 
Description Several wholly novel methods for untargeted molecular characterisation of DON and DOP using high resolution mass spectrometry have now been developed, allowing wider exploration of the molecular composition of DOM from the range of samples and environmental conditions collected in the WP1 Tier 1 programme. The range of analytical methods have been explored to investigate the composition of dissolved organic matter (DOM)in river water includes ESP-Orbitrap MS, Py-GC/MS, ion exchange chromatography, etc. The preliminary findings indicate that the DOM has extremely compositions which vary with location, between catchments and within catchments. This subset of samples from contrasting sources, seasons and sites, to which we are adding samples from storm events currently being sampled, have been freeze dried ready for analysis in WP2. With the methods now developed, we are making steady progress in working our way through the archive, while the novel protocols are currently being written up for publication in a high impact factor journal.

Elsewhere in WP2 we have developed a workflow for analysing direct infusion mass spectrometry data using statistical approaches to identify the analytes of interest, and discriminate between sites and sources based on their molecular scale organic chemistry signatures. Our novel method developed for organic phosphorus characterisation using ion chromatography to separate a key compound, phytic acid, from complex environmental matrices followed by analysis using high resolution mass spectrometry has been published.

Finally, we are investigating the specificity of the well-used, but poorly understood automated urea detection method in place on our Skalar instrument. A range of nitrogenous compounds have been tested using this method, with reactivity with heterocyclic compounds and both purine and pyrimidine derivatives noted in our early work. This suggests that interpretation of analytical data generated from this method need to proceed with care: the method is not only detecting the concentration of urea, but of a range of compounds that react colourimetrically in the same manner, using this method. A new LC-MS based method has been developed to validate the calourimetric method. This work has been written up for publication, with the clarified method used to support a range of soil and manure-based incubation experiments in one of our programme PhD studentships. Early findings from WP1 and WP2 to date and from linked work undertaken by members of WP3 suggest the importance of higher molecular weight (HMW) compounds in the flux from peaty catchments, the degradation and/or dissolution of peatland DOC along the length of the Conwy and the appearance of a discrete set of DOM compounds which appear only in waters draining from the peat. A second set of low molecular weight DOM compounds present in the Hampshire Avon appear at this stage to be linked to the delivery of animal waste from livestock production and effluent discharges to the river. Further analysis currently underway is allowing us to determine the nature of this material in WP2. A wide range of anthropogenic compounds, including pharmaceutical products and cosmetic/food additives have been identified from a range of sewage outfalls using a new high resolution mass spectrometric approach based on ESI-Orbitrap technology with and without uhplc. A particularly novel aspect of this work is the development of an untargeted approach to the deconvolution of the exceptionally complex mixtures present in water.

For full details please see the report of Professor Penny Johnes the lead PI on the grant.
Exploitation Route For full details please see the report of Professor Penny Johnes the lead PI on the grant.
Sectors Agriculture, Food and Drink,Chemicals,Environment,Healthcare,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology

 
Description For full details please see the report of Professor Penny Johnes the lead PI on the grant.
Sector Agriculture, Food and Drink,Chemicals,Communities and Social Services/Policy,Environment
 
Title Comprehensive assessment of dissolved organic matter in river water using untargeted high resolution MS 
Description RATIONALE: Anthropogenic organic inputs to freshwaters can exert detrimental effects on aquatic ecosystems, raising growing concern for both environmental conservation and water security. Current regulation by the EU water framework directive (European Union, 2000/60/EC) relates to organic pollution by monitoring selected micropollutants, however, aquatic ecosystem responses requires a comprehensive understanding of dissolved organic matter (DOM) composition. The introduction of high-resolution mass spectrometry (HRMS) is set to greatly increase our understanding of thecomposition of DOM of both natural and anthropogenic origin derived from diffuse and point sources. METHODS: DOM was extracted from riverine and treated sewage effluent using solid phase extraction (SPE) and analysed using dissolved organic carbon (DOC) analysis, direct infusion-high resolution Orbitrap™ mass spectrometry (DI-HRMS) and high-performance liquid chromatography (HPLC/HRMS). The data obtained were analysed using univariate and multivariate statistics to demonstrate differences in background DOM, anthropogenic inputs and in-river mixing. Compound identifications were achieved based on MS2 spectra searched against on-line databases. RESULTS: DI-HRMS spectra showed the highly complex nature of all DOM SPE extracts. Classification and visualisation of extracts containing many thousands of individual compounds were achieved using PCA and hierarchical cluster analysis. Kruskal-Wallis analyses highlighted significant discriminating ions originating from the sewage treatment works for more in-depth investigation by HPLC/HRMS. The generation of MS2 spectra in HPLC/HRMS provided the basis for identification of anthropogenic compounds including; pharmaceuticals, illicit drugs, metabolites and polymers, although many thousands of compounds remain unidentified. CONCLUSIONS: This new approach enables comprehensive analysis of DOM in extracts without any preconceived ideas of the compounds which may be present. This approach has the potential to be used as a high throughput, qualitative, screening method to determine if the composition of point sources differs from that of the receiving water bodies, providing a new approach to the identification of hitherto unrecognised organic contribution to water bodies. 
Type Of Material Technology assay or reagent 
Year Produced 2020 
Provided To Others? Yes  
Impact Method being applied in a newly submitted funding application in relation to Highlight Topic Call from NERC.