IAP-24-111
Do organic-mineral interactions increase or decrease greenhouse gas release from rivers?
Greenhouse gases (GHG) are released to the atmosphere via human activities but also via i) weathering of organic matter in exposed rock; ii) degradation (~ breakdown) of organic matter in soils; and iii) degradation of organic matter in aquatic systems. In soils and aquatic systems (e.g., a river), a portion of organic matter is attached to mineral surfaces (e.g., to clays and iron oxides) and complexed with mineral elements (e.g., iron (Fe) and aluminium (Al)). This project asks: what role do these minerals/mineral elements play in promoting or decreasing organic matter degradation and GHG release? The answer to this question is important for understanding what mediates atmospheric GHG concentrations and climate over short timescales (tens to hundreds of years) and for understanding the supply of terrestrial organic matter to marine sediments, in which organic matter burial over long timescales (thousands to millions of years) regulates long term climate.
This PhD project will use in-lab experiments to investigate the degradation of mineral associated-organic matter as a function of the redox condition (how oxidised or reduced the soil is), metabolism (oxidation of OM by microbes in aquatic systems) and light (breakdown of OM by absorption of photons in aquatic systems). The project will use these in-lab experiments to answer the following sub-questions:
1. How does the chemical composition and age of the mineral/mineral element (e.g., aluminium (oxy)hydroxide, iron (oxy)hydroxide) impact organic matter degradation?
2. How does the type of organic matter (composition – e.g., amount of carboxyl groups) associated with a certain mineral/mineral element impact organic matter degradation?
This PhD student will have the opportunity to compare the results from in-lab experiments with organic-mineral associations in a selection of soil pore waters and river waters spanning a range of redox conditions (e.g., high and low water table depth), metabolism (e.g., river water temperature) and light (e.g., day versus night) in rivers impacted by enhanced weathering experiments and amplified high latitude climate change the UK and Scandinavia.
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Image Captions
Transmission electron microscope images showing the association between iron and organic carbon in river particles (preliminary data from C.Hirst, S.Shaw, R.Harrison),Iron is associated with organic carbon in high latitude streams. These streams are key emitters of greenhouse gases to Earth’s atmosphere. Does the iron-organic carbon association amplify or dampen this GHG release?
Methodology
• Synthetic iron (oxy)hydroxide (fresh and aged) and aluminium (oxy)hydroxide – organic matter co-precipitates will be made in the lab. Co-precipitates will be made for a range of organic matter composition (in collaboration with Caroline Peacock, Leeds University).
• A sub-sample of synthesised material will be taken for Day 0 data analysis of mineralogy, mineral element concentrations and organic matter characterisation (see steps 1 and 2 below).
• Synthesised samples will be incubated i) under redox oscillating conditions (‘redox’ factor), ii) under oxic conditions with a microbial inoculum addition (‘metabolism’ factor), iii) in day-light without microbe addition (‘light’ factor). Samples will be sacrificed for analysis (see below) at regular intervals over a 28-day period. The incubation set-up and greenhouse gas analysis will be established by collaboration with Kirsi Keskitalo, Jorien Vonk and Paul Mann. Incubation set-up and knowledge exchange will require a 1-month secondment to Northumbria University and Leeds University.
• Experimental data will be compared with field incubation data of mineral-organic carbon associations and inorganic carbon concentrations from river waters in the UK and Scandinavia (lead by the PI) and in collaboration with Tom Reershemius (Newcastle University).
• The project sub-questions will be answered with the following data obtained on the particles (operationally defined at > 0.45 μm) and colloids+truly dissolved (operationally defined at < 0.45 μm) in samples collected at day 0, 1, 3, 7, 14 and 28 of each incubation:
1. The composition and redox state of minerals associated with organic matter will be determined using Mössbauer spectroscopy (in collaboration with Christian Schroeder), the degree of crystallinity and redox state of minerals associated with organic matter will be determined using transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) (in collaboration with Sam Shaw). The concentration of mineral elements (Fe, Al, Mn) will be measured in particulate, colloidal + truly dissolved fractions (using size separation techniques developed with Sophie Opfergelt).
2. The composition of organic matter associated with minerals will be determined using scanning transmission x-ray microscopy (combining x-ray microscopy and near edge x-ray absorption fine structure spectroscopy (NEXAFS)) and Fourier Transform Infrared Spectroscopy (in collaboration with Caroline Peacock). The composition of organic matter in the different size fractions will be determined using carbon/nitrogen (C/N) ratios and an index of organic matter degradation called SUVA254 (in collaboration with Paul Mann). The concentration of organic matter will be measured in the particulate (POM) and colloidal+truly dissolved fractions (using size separation techniques developed with Sophie Opfergelt).
3. The dissolved inorganic carbon (DIC) in the 0.45 μm filtered sample and carbon dioxide gas (CO2) released from the vessel will be measured, alongside water temperature and pH – to monitor the change in the inorganic carbon because of organic matter degradation overtime (in collaboration with Jorien Vonk, Kirsi Keskitalo, Paul Mann).
Project Timeline
Year 1
– Project meeting with all collaborators to introduce student and discuss timeline.
– Secondment to Leeds University to learn about synthesising mineral-organic matter associations and incubation experiments.
– Secondment to Northumbria University to learn about incubation experiments and inorganic carbon measurements.
– Incubation set-up practice and equipment preparation in Durham
Year 2
– Synthesise mineral-organic matter associations in Durham
– Incubation of synthesised samples in Durham
– Incubation of soil and river waters from sites in UK and Scandinavia – in collaboration with Tom Reershemius.
– TEM and EELS analysis on mineral particles and colloids at the University of Manchester
– Spectrophotometry analysis on water fractions to obtain carbon composition data in Durham
– Mineral element and organic matter concentration analysis in Durham
– National conference (e.g., The UK Geochemistry Group research in progress meeting)
Year 3
– STXM analysis of organic matter composition at Beamline I08, Diamond Light Source Synchrotron, UK
– FTIR analysis of organic matter composition at Leeds University.
– DIC and CO2 concentration measurements in Durham
– Data compiling and data analysis
– Project meeting with all collaborators to present data and discuss data interpretation.
– International conference (e.g., Goldschmidt)
Year 3.5
– Manuscript writing
– Thesis submission
– Thesis defence
Training
& Skills
The student will learn a wide range of skills from an assembled group of experts in environmental geochemistry.
The student will obtain the following training:
– Training in synthesising mineral-organic associations in the laboratory
– Training in GHG and dissolved inorganic carbon concentration measurements
– Training in incubation methods
– Training in mineralogical analysis (TEM, EELS, Mössbauer)
– Training in organic matter analysis (spectrophotometry, synchrotron techniques and mass spectrometry techniques)
– Training in soil pore water and river water sampling and sample filtration
– Training in scientific communication (oral and poster presentations at conferences)
– Training in manuscript writing
References & further reading
Fritzsche, A., J. Bosch, M. Sander, C. Schröder, J. M. Byrne, T. Ritschel, P. Joshi, M. Maisch, R. U. Meckenstock, A. Kappler, and K. U. Totsche (2021), Organic matter from redoximorphic soils accelerates and sustains microbial Fe(III) reduction, Environmental Science & Technology 55, 10821-10831,
Fritzsche, A., C. Schröder, A.K. Wieczorek, M. Händel, T. Ritschel, and K.U. Totsche (2015), Structure and composition of Fe-OM co-precipitates that form in soil-derived solutions, Geochimica et Cosmochimica Acta 169, 167–183,
Keskitalo, K.H., Bröder, L., Jong, D., Zimov, N., Davydova, A., Davydov, S., Tesi, T., Mann, P.J., Haghipour, N., Eglinton, T.I. and Vonk, J.E., 2022. Seasonal variability in particulate organic carbon degradation in the Kolyma River, Siberia. Environmental Research Letters, 17(3), p.034007.
Moore, O.W., Curti, L., Woulds, C., Bradley, J.A., Babakhani, P., Mills, B.J., Homoky, W.B., Xiao, K.Q., Bray, A.W., Fisher, B.J. and Kazemian, M., 2023. Long-term organic carbon preservation enhanced by iron and manganese. Nature, pp.1-6.
Curti, L., Moore, O.W., Babakhani, P., Xiao, K.Q., Woulds, C., Bray, A.W., Fisher, B.J., Kazemian, M., Kaulich, B. and Peacock, C.L., 2021. Carboxyl-richness controls organic carbon preservation during coprecipitation with iron (oxyhydr) oxides in the natural environment. Communications Earth & Environment, 2(1), p.229.
Opfergelt, S., 2020. The next generation of climate model should account for the evolution of mineral-organic interactions with permafrost thaw. Environmental Research Letters, 15(9), p.091003.
Mann, P.J., Davydova, A., Zimov, N., Spencer, R.G.M., Davydov, S., Bulygina, E., Zimov, S. and Holmes, R.M., 2012. Controls on the composition and lability of dissolved organic matter in Siberia’s Kolyma River basin. Journal of Geophysical Research: Biogeosciences, 117(G1).
Hirst, C., Andersson, P.S., Shaw, S., Burke, I.T., Kutscher, L., Murphy, M.J., Maximov, T., Pokrovsky, O.S., Mörth, C.M. and Porcelli, D., 2017. Characterisation of Fe-bearing particles and colloids in the Lena River basin, NE Russia. Geochimica et Cosmochimica Acta, 213, pp.553-573.
Hirst, C., Mauclet, E., Monhonval, A., Tihon, E., Ledman, J., Schuur, E.A. and Opfergelt, S., 2022. Seasonal changes in hydrology and permafrost degradation control mineral element‐bound DOC transport from permafrost soils to streams. Global Biogeochemical Cycles, 36(2), p.e2021GB007105.
Chen, C., Hall, S.J., Coward, E. and Thompson, A., 2020. Iron-mediated organic matter decomposition in humid soils can counteract protection. Nature communications, 11(1), p.2255.
