Eutrophication hotspots resulting from biogeochemical transformations and bioavailability of organic phosphorus in the fluvial suspended sediment of geologically contrasting agricultural catchments

Project Website

Laurence Gill 

Prof. Laurence Gill (Trinity College Dublin)

Projects  Partner and Institution:
Dr. Yongfeng Hu (Canadian Light Soure & University of Saskatchewan)

Prof. Kevin Bishop (Swedish University of Agriculture)

Key words: Fluvial sediments, eutrophication, phosphorus, Catchment science, nutrient biogeochemisty


This research project evaluated the impact of particulate phosphorus associated with fluvial suspended sediments as an eco-hydrological hazard in geologically contrasting agricultural catchments in terms of bioavailability for algal growth and as a source of water pollution to surface water in small catchments. The release of phosphorus (P) from river sediments has been identified as a contributing factor to waters failing the criteria for ‘good ecological status’ under the EU Water Framework Directive (WFD). To identify the contribution of suspended sediment bound and streambed P in agricultural catchments, an understanding of the controlling factors for its sequestration, mobilization and mobility is required. Fluvial sediment bound P can play a role in in-stream productivity (i.e. macrophyte growth) and degradation of water quality but little is known in relation to the actual bioavailability of suspended and streambed sediment bound organic P in agricultural catchments. Thus, this project aims to examine the relative importance of suspended and streambed sediment bound P for cycling in geologically contrasting agricultural catchments in Ireland and Sweden using state of the art analysis and monitoring techniques. 

The project has been structured to answer four main research questions: (i) from where does the sediment originate, (ii) what different forms is the sediment bound P in, (iii) how bioavailable is the P being carried by the sediment and (iv) can models be developed which are able to predict the fate and transport of such P through agricultural catchments.  In terms of determining where the sediment has originated on the agricultural catchments, sediment source maps have been developed based on high resolution digital elevation models (DEMs) using methodology developed by the Swedish University of Agriculture. These source areas have been validated by radionuclide (CS137& Pb210) and trace metal sediment analysis. Fluvial sediment has then been collected at different parts of the Irish and Swedish catchments over a two-year period in special traps designed to capture suspended sediment. This sediment has then been tested using a variety of state-of the-art analytical technotes to separate out the inorganic from the organic fraction and then assess the nature of binding mechanism of P to the sediment. A combined approach has been followed using advanced synchrotron and NMR spectroscopy at the Canadian Light Source and the University of Saskatchewan (i.e. XANES and 31P NMR). In addition, crystallography (i.e. XRD) has been used to examine inorganic and organic P speciation and binding mechanisms to show seasonal mineralogical and P speciation dynamics. XANES has shown that Fe is mostly in oxide or hydroxyl oxide form and microanalysis detected Fe-P with seasonal variations due to dilution effects. Phosphorus fractionation through chemical extractions has also shown seasonal and temporal dynamics in fluvial sediment P speciation with a general decrease in organic and increase in Al bound P fractions from autumn to winter. Loosely sorbed P, Ca bound P and residual P all remain relatively stable across the different seasons. Phosphorus bioavailability of the sediments has then been assessed by running algal bioassay experiments on the sediments recovered from the stream. Sequential chemical P fractionations as well as XANES analysis were carried out on the sediment before and after the bioassay experiments to reveal where the P that has been taken up by the algae has come from. Finally, hydrological models of the catchments have been developed in order to simulate and then make predictions about the total sediment loads passing down through the small river catchments. In Ireland, these models are predicting ~ 10 to 90 tonnes of suspended sediment per km2 of catchment area per year, for example. The final stage is to then incorporate these findings about the sediment sources, and P fractions in the suspended sediment into predictive water quality model. These models of P transport and transformation can yield valuable insights for catchment management, particularly with respect identifying the likely sources and quantifying the amount of bioavailability P carried in fluvial suspended sediment. This knowledge can then be used to develop catchment specific mitigation strategies in accordance with the objectives of the Water Framework Directive.

Project structure: The proposed OrgP-Sed project will be divided into three main work packages discussed belwo, each building upon the success of the other. Contingency plans will be inbuilt into each work packages to provide a safety net in case of anything going off course. . The administrative management of Eutro-Sed will be coordinated by the lead partner at TCD, with backup from Prof. Kevin Bishop and Prof. Yongfeng Hu, consortium partners at SLU and Canada. The person-months allocated to each task is appropriate in order for completion of the goals and objectives. Field sampling and analysis will be carried initially while concurrently isotope and predictive model development will overlap. This is necessary for amalgamation of field data to feed predictive model development and the time allowed is the minimum in developing ground-breaking predictive models.

Implementation: Work package 1. will focus on the biogeochemical processes and properties of fluvial sediment bound organic phosphorus. Specifically, the effects of redox oscillations on P exchanges and speciation will be examined in the field and in laboratory incubations.
Work package 2. will test the hypothesis that the strong biogeochemical gradients and fluctuations within suspended and streambed sediments of geologically contrasting agricultural catchment streams result in phosphorus bio-availability dynamics.
Work package 3. will address the regional scale impacts of biogeochemical transformations within suspended and streambed sediment bound phosphorus in geologically contrasting agricultural catchments.

Outcome/deliverables: Several academic papers will be generated from this project under the following subject areas and submitted to the following target high impact international journals (1) Hydrology & Biogeochemistry (2) Suspended sediment and advanced spectroscopy (3) Hydro-sedimentary biogeochemical modelling. A workshop will be organised to to discuss and raise awareness of the importance of suspended/stream bed sediment on surface water quality. The workshop will also stimulate brainstorming on the frontiers of this important area of research. Results from the project will be presented at international conferences such as Goldschmidt (Boston 2018), AGU (San Francisco, 2019), EGU (Vienna, 2019).

References coordinator and  leaders of  each WP:
Dr.David O'Connell,
Prof. Laurence Gill,
Dr. Yongfeng Hu,
Dr. Faruk Djodjic,
Prof. Kevin Bishop (WP-1)
Dr.David O'Connell,
Prof. Laurence Gill,
Dr. Yongfeng Hu,
Dr. Faruk Djodjic,
Prof. Kevin Bishop (WP-2)
Dr.David O'Connell,
Prof. Laurence Gill,
Dr. Yongfeng Hu,
Dr. Faruk Djodjic,
Prof. Kevin Bishop (WP-3)

Main outputs:

  • Sandström, S., M.N. Futter, K. Kyllmar, K. Bishop, D.W. O'Connell and F. Djodjic. 2020. Particulate phosphorus and suspended solids losses from small agricultural catchments: Links to stream and catchment characteristics. Science of The Total Environment: 134616.
  • Zhang Q., Wieler M., O'Connell D., Gill L., Xiao X., Hu Y. (2020). Speciation of phosphorus from suspended sediment studied by bulk and micro-XANES. Soil Systems 4(3), 51
  • Sandström S., Futter M.N., O’Connell D.W., Lannergård E.E., Rakovic J., Kyllmar K., Gill L.W., Djodjic F. (2021). Variation in fluvial suspended sediment phosphorus fractions in small agricultural streams – relations to water quality and streambed sediment. Journal of Environmental Quality

More results on the project: Data and resources

Contact Point for  Communication/Dissemination activities: Dr. David O'Connell & Prof. Laurence Gill (Project manager and co-ordinator)

Contact Point for Open Data/Open Access activities: Dr. David O'Connell & Professor Laurence Gill (Project manager and co-ordinator)

Photo of the Research Team:

David OConnell

Dr David O'connel

Faruk Djodjic

Dr. Faruk Djodjic

Laurence Gill

Prof. Laurence Gill

Yonfeng Hu

Dr. Yofen Hu

Kevin Bishop

Prof. Kevin Bishop

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published on 2017/07/11 08:00:00 GMT+1 last modified 2022-05-10T14:32:16+01:00