Nutrient release from riverine particulates in estuaries

Biogeochemical Cycles

IAP2-21-349

Overview

Continental weathering and erosion are integral processes responsible for the evolution of the landscape and exert a major control on the transport of material from the continents to the oceans, and on the cycles of many elements at the Earth’s surface. On geological timescales the chemical weathering of Ca–Mg silicates is amongst the primary feedbacks regulating atmospheric levels of the greenhouse gas carbon dioxide (CO2), thereby moderating the Earth’s climate (e.g. Walker et al., 1981). Continental weathering is also a major source of nutrients to the ocean, thereby playing a crucial role in ocean productivity and the carbon cycle (e.g. Sigman & Boyle, 2000).

Rivers are the dominant means of transport of many elements to the ocean (e.g. Geibert, 2018), but the dissolved input from rivers cannot account for the oceanic budget, taken by some to indicate that the oceans are not in steady-state. However, elemental transport by rivers occurs not only via dissolved species, but also as particulate material, and estimates suggest that rivers transport 16-20 Gt/yr of suspended material to the ocean (e.g. Syvitski et al., 2003; Oelkers et al., 2011), more than an order of magnitude larger than the dissolved riverine and aeolian fluxes combined.

Riverine particulates incorporate elements through (i) adsorption to the surface exchange complex (ii) carbonate (iii) organic material (iv) clays (v) Fe-Mn oxides and (vi) residual silicate material. Solubilisation of just a small fraction (<0.1%) of this particulate material has the potential to dominate the nutrient flux to the oceans (e.g. Oelkers et al., 2011; Jones et al., 2014; Rousseau et al., 2015).

This project aims to trace the release of nutrients from river particulates in estuaries, with a particular focus on the transition metals Fe, Cu, Zn and Ni and their stable isotopes (amongst a number of key micronutrients). Fieldwork will involve sampling rivers, estuary waters, suspended particulate material and bedload, from a range of settings. Including the UK, and rivers in Iceland and France.

Analytical work will involve (i) Quantification of chemical and mineralogical variations in riverine particulate chemistry with weathering intensity and grain size in terrains showing contrasting rock types, temperature, runoff and degrees of weathering (ii) Characterisation of the mineralogical, elemental and isotope behaviour of particulates in estuarine environments. (iii) Complementary experimental work to determine dissolution rates, elemental release/uptake, and the net isotope release and fractionation accompanying dissolution of riverine particulates in seawater. With a particular focus on the behaviour of Fe-Mn oxides and organic material in the estuarine environment.

Methodology

The project will involve fieldwork, sampling of estuarine waters, particulates and bedload, in the UK, Iceland and France. Measurement of transition metal stable isotopes by MC-IC-MS, in addition to other trace elements and macronutrients. Interpretation of elemental and isotope data to achieve the project aims outlined above.

Project Timeline

Year 1

Fieldwork in Iceland and UK. Training in the measurement of metal stable isotopes and elemental abundances. Year 1 Research Proposal and review. Attendance of a national conference.

Year 2

Further fieldwork, in France, and isotope and elemental analysis of river and estuary samples. River and estuary sampling. Prepare research for presentation/publication. Attend national conference.

Year 3

Completion of isotope work and interpretation and modelling of data. Presentation at national and international conferences. Work on publication and thesis writing.

Year 3.5

Complete and submit thesis, finalise manuscripts for publication.

Training
& Skills

Fieldwork in the UK, Iceland and France involving the collection of river and estuary samples

Training in the measurement of metal stable isotopes using high precision MC-ICP-MS and TIMs techniques at Durham, as well as elemental analysis and sample characterisation.

Interpretation and modeling of river and estuary data, to quantify the sources and nature of elemental release from riverine particulates in estuaries

Presentation of research at both national and international geochemistry conferences.

References & further reading

Walker J.C.G., Hays P.B., Kasting J.R. , A negative feedback mechanism for the long-term stabilization of Earth’s surface temperature. J. Geophys. Res., 86 9776-9782 (1981)

Sigman D.M. & Boyle E.A., Antarctic stratification and glacial CO2.Nature 407, 859-869 (2000).

Geibert W., Processes that regulate trace element distribution in the oceans. Elements, 14, 391–396 (2018).

Syvitski J., Peckham S., Hilberman R., Mulder T., Predicting the terrestrial flux of sediment to the global ocean: a planetary perspective. Sediment. Geol., 162 (2003), pp. 5-24

E.H. Oelkers, S.R. Gislason, E.S. Eiriksdottir, M.T. Jones, C.R. Pearce, C. Jeandel
The role of riverine particulate material on the global cycles of the elements
Appl. Geochem., 26 (2011), pp. S365-S369

Jones M.T., Gislason S.R., Burton K.W., Pearce C.R., Mavromatis V., von Strandmann P., Oelker E.H. . Quantifying the impact of riverine particulate dissolution in seawater and ocean chemistry, Earth Planet. Sci. Lett., 395, 91-111 (2014)

Rousseau T T.C., Sonke J.E., Chmeleff J., Van Beek P., Souhaut T., Boaventura G., Seyler P., Jeandel C. Rapid neodymium release to marine waters from lithogenic sediments in the Amazon estuary. Nat. Commun. 6, 7592 (2015)

Further Information

For further information please contact Kevin Burton (kevin.burton@durham.ac.uk)

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