IAP2-23-007

Black & Blue: The dynamics of black carbon in fluvial networks.

This project will develop and refine state of the art methods to quantify and characterise the role of black carbon in river networks.

Rivers are the primary conduits and biogeochemical reactors of carbon in the terrestrial environment. Included in the transport is so-called ‘Black’ carbon (BC), the resulting product of the incomplete combustion of organic material. This BC flux is substantial, with over 27 Tg exported to the oceans each year, yet the specific properties, transport dynamics, and lifespans of fluvial BC are still poorly constrained. Filling this knowledge gap fills a critical hole in our understanding of global carbon fluxes in a changing world.

To date, the vast majority of our work on fluvial carbon has focussed on dissolved and particulate organic carbon (D/POC). We have known for some time that the dissolved black carbon (DBC) flux is a significant and major loss pathway of terrestrial C (Jaffé et al. 2013). Initial work has in some cases shown a correlation between DOC and DBC fluxes at regional scales (e.g., Ding et al. 2013). This has led to the conclusion that DOC and DBC mobilisation pathways are shared and/or there is a physio-chemical affinity between them. However, while often observed, this relationship is not ubiquitous with preliminary data in the River Kelvin catchment, Glasgow showing both spatial and seasonal decoupling in the DOC:DBC ratio, challenging the accepted narrative (Image 1).

Building on this initial data, in this project you will elucidate the spatial and temporal drivers of dissolved and particulate BC in a temperate catchment with a history of industry and extraction, quantifying and characterising its biogeochemical significance and signature. Specifically, you will use this framework with the aim of answering the following questions:

1. To what extent do DBC mobilisation dynamics correspond to wider organic matter and how is this driven by spatial (land-use / land-cover) and temporal (seasonal / hydrological) controls?
2. How do environmental and landscape controls drive the physio-chemical characteristics of the fluvial BC pool and how do these impact the participation of BC in the global C-cycle more broadly?

The project will focus on the River Almond in Scotland (Image 2), nested in the wider Forth catchment. The Almond represents a typical anthropogenic river system, comprising a range of land-use and land-histories. Shifts in economic development (shale mining to electronics and chemical industries; agricultural intensification; urbanisation) coupled to regions of lesser development make it an ideal case study to examine DBC dynamics.

Click on an image to expand

Image Captions

Image 1: Initial quantification of DBC in the River Kelvin network in Scotland suggests a decoupling of DOC and DBC (B) when compared to previous work that has found consistent mobilisation drivers between them (A). This suggests potentially different sources of BC in these heavily anthropomorphic catchments over time and space. Different symbols represent different sampling locations in the catchment. Previous data taken from Ding et al. (2013).,Image 2: The River Almond catchment, Scotland. Images show four of the potential 20 sites we will investigate.

Methodology

This project will utilise the state of the art Ramped Oxidation (RO: Garnett et al. 2023) technique to isolate and characterise black carbon in a heavily anthropogenic catchment in central Scotland. Combining this data with wider water quality and carbon stocks and fluxes, alongside fluvial solute modelling approaches.

1) Alongside established methods such as hydrogen pyrolysis, the student will develop and use Ramped Oxidation to extract and partition the refractory component of the fluvial dissolved and particulate carbon matrix. This process will allow for the separation of black- and non-black constituents of fluvial carbon and provide information of spatial and temporal (de)coupling between fractions.
2) Catchment scale hydrological and physio-chemical characterisation will be undertaken using a suite of state-of-the-art sensors and laboratory analytical techniques based at the University of Glasgow, including Cavity Ring-down Spectrometry, Spectrophotometry, Infrared Gas Analysis, UV-Vis light Spectrometry, and others.
3) Local – catchment scale carbon flux quantification including lateral flows of dissolved and particulate carbon, coupled to evasive fluxes through river / lake atmospheric degassing will allow the role of black carbon in wider carbon cycle dynamics to be elucidated.
4) Analysis of the composition of DBC using state of the art mass spectrometry techniques including GC-MS and LC-MS QQQ which will give insights into the feedstock types and pyrolysis temperatures. This will help to disentangle the compositional complexity of DBC and improve our understanding of its sorption behaviours in the environment and mobilisation capacity.
5) Radiocarbon dating (alongside other tracer methods such as stable isotope ratios) will allow us to untangle the sources of BC to the river network and elucidate variable flow paths across different land-uses and types.

As part of this project, the student will be able to collaborate with researchers on the NERC funded Monitoring, Modelling and Mitigating Pollution Impacts In A Changing World: Science And Tools For Tomorrow’s Rivers (MOT4Rivers), of which principal supervisor Bass is a project lead. The research proposed in this studentship would add a significant block of additional information into this wider project and also allow the student to access wide ranging expertise from a range of hydrological, biogeochemical, biological, ecological, and environmental / fluvial modelling.

Project Timeline

Year 1

• Literature review
• RO method development and training
• Catchment land-use / land-history analysis to inform site selection.
• Field monitoring of water quality and carbon parameters
• Training in other key field and analytical techniques

Year 2

• Ongoing field monitoring and data collection
• High temporal resolution hydrological event monitoring
• Hydrological / solute modelling of key carbon parameters
• Isotopic modelling of carbon source dynamics
• Manuscript preparation

Year 3

• Ongoing field monitoring and data collection
• Statistical analysis of results and integration into wider fluvial modelling approaches
• Radiocarbon analysis of select samples (subject to funding to NERC Environmental Isotope Facility – Yr 2)
• Manuscript preparation
• Research dissemination

Year 3.5

• Completion of manuscripts and thesis
• Viva preparation.
• Research dissemination

Training
& Skills

This project provides an excellent platform to gain multidisciplinary training in an exciting, important, and timely research area. It will cross the fields of hydrology, biogeochemistry, organic chemistry, landscape management and modelling, equipping the successful candidate with a wealth of skills, experience and collaborators to take forward into their career.

The candidate will work closely with all four supervisors to gain directly from their expertise. Dr Bass will oversee the direction, development and progress of the candidate and the project, and will provide expertise in experimental design, execution and dissemination, field techniques for water physio-chemical monitoring, carbon flux measurements and modelling, hydrological / time series modelling, and career development. Dr Ascough will provide expertise in black carbon analytical techniques and interpretation along with Dr Garnett who will guide the development and utilisation of the RO methodology. Dr Cavazzin will advise on mass spectrometry analysis of BC and statistical methods with Prof. Subke providing insights into project design, data interpretation and its wider incorporation into the terrestrial BC understanding. The candidate will additionally have access to extensive IAPETUS2-cohort and NERC training workshops, allowing for a wealth of broader, transferable research skills and knowledge to be gained.

With the potential incorporation of the student into the wider NERC MOT4Rivers programme, they will have access to a multitude of additional experts and analytical techniques to further their training as the project develops.

The successful candidate will join vibrant research communities at the University of Glasgow and the University of Stirling, where they will be welcomed and encouraged to network with colleagues and their collaborators. The candidate will have the opportunity to present their results to at least one international and one national conference. Furthermore, they will be encouraged and facilitated to disseminate their results to the general public at School events and community events, and to share findings with other research institutes and national networks.

References & further reading

Ding, Y., Yamashita, Y. Dodds, W.K. and Jaffe, R. (2013) Dissolved black carbon in grassland streams: Is there an effect of recent fire history? Chemosphere. 90: 2557-2562.

Garnett MH, Pereira R, Taylor C, Murray C, Ascough PL. (In press). A new ramped oxidation-14C analysis facility at the NEIF Radiocarbon Laboratory, East Kilbride, UK. Radiocarbon:

Jaffé, R., Ding, J. Niggeman, A.V. Vähätalo, A. Stubbins, R.G.M. Campbell, J. and Dittmar, T. (2013). Global charcoal mobilisation via dissolution and riverine transport to the oceans. Science. 340: 345-347.

Butman, D.E. Wilson, H.F. Barnes, R.T. Xenopoulos, M.A. and Raymond, P.A. (2015) Increased mobilisation of aged carbon to rivers by human disturbance. Nat. Geosci. 8: 112-116.

Gu, C., Waldron, S. Bass, A.M. (2022) Anthropogenic land use and urbanization alter the dynamics and increase the export of dissolved carbon in an urbanized river system. Sci. Tot. Environ. http://dx.doi.org/10.1016/j.scitotenv.2022.157436.

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