IAP-25-007

The role of ditches in the global carbon cycle: A critical & unrecognised player.

The world’s carbon cycle is significantly unbalanced in modern times, leading to accumulation of greenhouse gases in the atmosphere and destabilisation of the climate system. A key component in global carbon cycle processes is aquatic environments, including lakes, rivers and the oceans, and their subsequent linkages with terrestrial ecosystems (Regnier et al. 2022). However, whilst we have a comprehensive understanding of the significance of many aquatic ecosystems’ biogeochemistry, others remain poorly elucidated, yet likely of critical importance in closing our carbon cycle models. In this PhD, you will help shed light on the dynamics of one such environment, ditches!

Ditches are ubiquitous environmental features, indicative of humanities history with managing and controlling surface water resources (Clifford et al. 2025). We may take them for granted, but the widescale adoption of artificial water channelisation has been critical in the development of modern civilisation. As a by-product, we have created a host of new, dynamic, and variable aquatic ecosystems that contribute to the global aquatic carbon cycle. The dynamics and extent of this contribution is unclear, and the successful candidate will play a pivotal role in pushing forward our understanding.

Whilst all aquatic ecosystems act as biogeochemical reactors (to varying magnitudes) as well as transport pipes of organic and inorganic material (Cole et al. 2007), ditches occupy a unique biogeochemical niche, being embedded in the terrestrial landscape, and thus subject to potentially substantial (and rapid) additions of nutrients, sediments, and pollutants. Ditches are subject to variable and often extreme changes in hydrology and water residence time – key biogeochemical drivers that have been shown to impact GHG producing processes (Looman et al. 2017). Ditches can act as nutrient and water sources and sinks, meaning elucidating robust models of their biogeochemical dynamics is complex.

To further refine our models of terrestrial-aquatic carbon cycle linkages, a detailed mechanistic understanding of ditches’ role in biogeochemical cycles is required. In this PhD we will quantify the magnitude of biogeochemical pathways and the key environmental, hydrological, and management drivers. This work will inform the future management of such systems to optimise their roll in achieving a net-zero future. To achieve this, this project will address the following key objectives:

i) Characterise the key carbon cycle fluxes & stocks in a suite of ditch ecosystems over short- and medium-terms, elucidating controls of key greenhouse gas fluxes (carbon dioxide, methane, nitrous oxide).
ii) Determine sediment water interactions and their impacts on ditch biogeochemistry through a series of drought-flood cycles.
iii) Model the environmental / climatic / hydrological and management impacts of ditch biogeochemical processes.

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Image Captions

Ditches are ubiquitous, yet overlooked landscape features with a significant biogeochemical footprint witing to be elucidated. Image taken from Clifford et al. (2025),The Carbon Analytical Suite at the UofG, alongside a suite of field sensors and analytical equipment at partenr institutes will allow for detailed exploration of biogeochemical processes. Image credit: Adrian Bass

Methodology

This project will adopt a range of techniques to establish the key spatial and temporal controls on biogeochemical cycles in a range of ditch environments. Critical will be the quantification and characterisation of key biogeochemical stocks and fluxes, including organic and inorganic carbon, nitrogen, micro-nutrients, and the measurements of greenhouse gas fluxes between the water and atmosphere. The successful candidate will have access to analytical facilities and field portable sensors from the supervisory institutions.

Project Timeline

Year 1

Their will be some degree of flexibility of the research plan based upon discussions and preliminary work in the first few months of the PhD, but roughly we anticipate a potential timeline as follows:

1. Literature review, research gap exploration.
2. Site selection and initial sampling for characterisation.
3. Spatial and temporal sampling initiated.

Year 2

1. Continuation of sampling campaign established in year one.
2. Undertaking of seasonal diurnal experiments to explore short-term variations in biogeochemical processes
3. First manuscript production based on short-term diurnal experiments.

Year 3

1. Mesocosm experiments examining sediment drivers of ditch BGC at UKCEH
2. Manuscript production, global data synthesis and experimental results

Year 3.5

1. Complete sampling campaigns
2. Preparation of manuscript reporting large scale temporal and spatial drivers of ditch BGC
3. Thesis submission and viva preparation

Training
& Skills

This project provides an excellent opportunity for training is state-of-the-art water monitoring, sediment sampling and biogeochemistry techniques, equipping the successful candidate with a suite of techniques for multiple career opportunities.

The candidate will work closely with all four supervisors and collaborators. In Glasgow, Dr Bass will oversee the project direction, development and overall progress of the candidate as well as providing training in all techniques and instrumentation available in the UofG carbon analytical suite. At the Centre for Ecology & Hydrology, Dr Pickard will lead the sediment mesocosm experiments and contribute her knowledge and expertise in aquatic biogeochemical cycles. At the University of Stirling, Prof Subke will provide additional supervision of C cycle and greenhouse gas measurements and facilitate access to analytical facilities and established research platforms (Forth-ERA). Project collaborator Dr Mike Peacock at Liverpool University will provide his knowledge and experience of ditch GHG dynamics, including different sampling and methods techniques, and ways to partition fluxes into diffusive and ebullitive pathways. Through him, the student will have access to the advanced sediment analytical equipment at UoL.

The candidate will additionally have access to post-graduate training courses at the UoG as well as extensive IAPETUS DLA-cohort and NERC training workshops, allowing for a wealth of both specific and broader, transferable research skills and knowledge to be gained.

References & further reading

Clifford C, Bieroza M, Clarke SJ, et al. (2025) Lines in the Landscape. Commun. Earth. Environ. 6: 693-709. https://doi.org/10.1038/s43247-025-02699-y

Cole JJ, Prairie YT, Caraco NF, et al. (2007) Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget. Ecosystems. 10: 172-185. https://doi.org/10.1007/s10021-006-9013-8

Looman A, Maher DT, Pendall E, Bass AM, Santos IR (2017) The carbon dioxide evasion cycle of an intermittent first-order stream: contrasting water–air and soil–air exchange. Biogeochemistry. http://dx.doi.org/10.1007/s10533-016-0289-2

Regnier P, Resplandy L, Najjer RG, et al. (2022) The land-to-ocean loops of the global carbon cycle. Nature. 603: 401-410. https://doi.org/10.1038/s41586-021-04339-9

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