Size isn’t everything: The role of small water bodies in aquatic-atmosphere methane exchange.

Overview

Methane (CH4) is 34 times more potent than carbon dioxide (CO2) as a greenhouse gas (GHG) and is a key component of the global C-cycle. Emissions from inland water bodies are a key pathway for methane flux and while significant, estimates of CH4 fluxes from surface waters are still highly uncertain with error bars up to ± 90 % (Saunois et al. 2016). This uncertainty stems from multiple avenues, including the variable balance between diffusive and ebullitive (bubble) fluxes, as well as the spatiotemporal variability within and between water bodies. A critical unknown is the role small water bodies (ponds, ditches, drains, etc) play in these dynamics, though initial evidence suggests they are disproportionately important (Quinn et al. 2019). This project will quantify CH4 fluxes from a range of small water bodies, determine spatial-temporal dynamics and elucidate controlling factors. Combined with a remote sensing approach to surface water mapping it will fill a critical gap in our current understanding, better equipping scientists and policy makers to manage these systems for maximum carbon benefit.

Small inland water bodies have a disproportionate impact in terms of CH4 emissions per unit surface area. For example, small water bodies (1 year) in-situ measurements of CH4 flux.
ii) Investigate biogeochemical controls on CH4 across a water body size continuum.
iii) Utilise remote sensing techniques to upscale findings to regional scale.

Methodology

This project will adopt a range of multidisciplinary techniques to establish rates, characteristics and drivers of CH4 efflux. Utilising a range of sensors and analytical methods the findings will allow a full carbon cycle accounting and enable a detailed understanding of the biogeochemical drivers to be established. Specifically, this project will hinge on the following key research approaches:

i) Long-term high- and medium-resolution gas flux measurements:
Utilising automated high-resolution sensors, alongside lower-resolution manual sampling, monitoring of gas fluxes will be performed across a range of different water body types and sizes.

ii) Characterising water chemistry & whole system carbon accounting:
Utilising in-situ sensors (for water chemistry) and the Glasgow carbon labs analytical suite, all facets of the aquatic carbon pool will be quantified allowing for biogeochemical controls to be elucidated both between and within sites. Discovered biogeochemical controls will be used for flux upscaling.

iii) Regional water body mapping & flux upscaling:
Accurate upscaling requires information on waterbody surface area, waterbody type and the distribution of productivity-related predictor variables (e.g. DOC and chlorophyll a.) (Deemer et al., 2021). High spatial resolution multispectral satellite imagery will be used to characterise waterbody type and surface area and predictive models developed for retrieving chlorophyll a from satellite observations. A time series analysis will characterise the inter-annual and intra-annual surface water dynamics.

Project Timeline

Year 1

1. Literature review
2. Site selection for undertaking of long-term sampling. Initial data used to inform selection of ‘sentinel’ sites for detailed spatial-temporal monitoring.
3. Construction of new, and deployment of existing CH4 and CO2 sensors
4. Initial sample collection to test and optimise field and laboratory protocols

Year 2

1. Physicochemical measurements and sample collection from all field sites
2. Characterisation of the overall carbon pools across selected ‘sentinel’ sites.
3. Stable isotope & other water chemistry characterisation to elucidate carbon cycle controls.
4. Image analysis and model development
5. Research dissemination

Year 3

1. Flux upscaling
2. Statistical data interpretation
3. Thesis and paper writing
4. Research dissemination

Year 3.5

1. Completion of thesis and paper writing
2. Viva preparation
3. Research dissemination

Training
& Skills

This project provides an excellent opportunity to gain multidisciplinary training in an exciting and critical field. It will cut across carbon cycle biogeochemistry, sensor development and statistical validation, and remote sensing / spatial analysis techniques equipping the candidate excellently for multiple career opportunities.

The candidate will work closely with all three supervisors to benefit from their individual expertise. Dr Bass will oversee the direction, development and overall progress of the candidate & project as well as providing training in all techniques provided by the UoG carbon analytical suite. This includes techniques such as carbon stock and flux quantification, as well as water quality / chemistry determination and advanced techniques such as stable isotope measurement and interpretation. Prof. Subke will advise on flux techniques, including use of chamber methods and gas chromatograohy to complement ebullition sensors. Dr. Barrett will provide guidance and training in remote sensing and machine learning approaches. The candidate will additionally have access to post-graduate training courses at the UoG as well as an extensive IAPETUS2-cohort and NERC training workshops, allowing for a wealth of broader, transferable research skills and knowledge to be gained.

The candidate will join vibrant research communities at the University of Glasgow and at Stirling University, 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 national and two international research conferences. Furthermore, they will be encouraged to disseminate their result to the general public at school and community events, and to share their findings with other research institutes, national networks.

References & further reading

Deemer, B. R., & Holgerson, M. A. (2021). Drivers of methane flux differ between lakes and reservoirs, complicating global upscaling efforts. Journal of Geophysical Research: Biogeosciences, 126, e2019JG005600. https://doi.org/10.1029/2019JG005600

Holgerson & Raymond (2016) Large contributions to inland water CO2 and CH4 emissions from very small ponds. Nat. Geosci. 9: 222-226.

Quinn et al. (2019) Punching above their weight: Large releases of greenhouse gases from small agricultural dams. Glob. Chang. Biol. 25: 721-732.

Saunois et al. (2016) The Global Methane Budget 2000-2012. Earth. Syst. Sci. Data. 8: 697-751.

Schilder et al. (2016) Spatiotemporal patterns in methane flux and gas transfer velocity at low wind speeds: Implications for upscaling studies on small lakes. J. Geophys. Res. Biogeosci. 121: 1456-1467.

Walter et al (2008) Methane production and bubble emissions from arctic lakes: Isotopic implications for source pathways and ages. 113: doi.org/10.1029/2007JG000569

Further Information

Dr Adrian M. Bass
email: adrian.bass@glasgow.ac.uk
phone: 01413306654 / 07470172550

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