Unravelling the ecological mysteries of freshwater marl lakes: What is their blue carbon potential?

   School of Biological & Environmental Sciences

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  Dr Eileen Tisdall, Dr Heather Moorhouse, Dr I Jones  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Carbon captured and sequestered in marine and coastal environments, known as blue carbon, is recognised as a nature-based solution and a key part of the UK transition to net zero (Smeaton et al 2020, Shafiee 2021). However, the potential of freshwater Blue Carbon, with carbon stored in fluvial and lacustrine sediments, is less well defined. Freshwater marl lakes are unique freshwater habitats and home to diverse and rare aquatic communities(Wiik et al 2015a). They depend on a balance between the correct bedrock geology and aquatic productivity, actively accumulating calcium carbonate rich sediment (marl), which like coral reefs, have the potential to capture and store carbon. The pathways both biological and chemical in these marl lakes that actively draw down carbon out of the atmosphere are complex and poorly understood, with these lakes representing a potentially important contribution to freshwater Blue Carbon.

The accumulation of calcium carbonate as marl in these lake systems is through a combination of direct precipitation, driven by seasonal variations in a range of physicochemical parameters, and biochemical processes as the calcite forms as incrustations on specialist aquatic plants (Duston, 1986). The aquatic plant diversity of a healthy marl lake can lead to very rapid accumulation of marl sediment particularly during the summer months. However, relatively few marl lakes are still considered as true marl lakes with reduced accumulation of marl, due to human-driven eutrophication disturbing and altering marl lake biology (Wiik et al, 2014; 2015a; Pentacost, 2009).

Many modern lake systems are a product of environmental changes first initiated in prehistory, with human activity altering lake catchments over millennia and initiating nutrient inputs which makes defining the aquatic ecosystem changes in the recent past a challenge (Jones et al., 2022; Wiik et al., 2015b). This project will use palaeoecological and geochemical analysis of marl sediments accumulated during the Late Glacial and early Holocene to better understand how marl lakes have responded to environmental change. The main research questions are; (1) How have these marl lake ecosystems adapted to rapid and extreme changes in the lacustrine and terrestrial environment in the absence of human activity? (2) How can we use this long view of the response to changes in the ecology, lacustrine chemistry and climate to define the health and resilience to environmental change of present-day marl lake systems? In terms of nature-based solutions, by defining the potential contribution of marl lake ecosystems to carbon sequestration and storage we are better placed to actively conserve and restore them. 


Previously identified Late Glacial and early Holocene sediments and palaeoecological data sets from a marl lake in Orkney will be used to refine the methodological approach used in this project. Within this project, there is scope to design a novel approach to generate the palaeoecological and geochemical data sets needed to define the record of environmental change. These data sets will also indicate potential drivers, those that switched on and off marl accumulation in the past.  

The methodological approach will then be applied to present day marl lakes, with sediment cores sampled from both active and recently inactive lake systems. Palaeoecological and palaeolimnological analysis using aquatic fossils (University of Stirling/Centre for Ecology and Hydrology) will provide specific and detailed information on past ecosystems and provide a direct link to the assessment of the current ecology and biogeochemistry (Centre for Ecology and Hydrology) of these lakes.  SEM and SEM-EDX (University of Stirling) will be used to provide a fuller picture of changes in water quality, processes of marl formation and carbon sequestration.  Lithostratigraphic analyses (organic content and micro-XRF geochemistry, supported by Dr Sarah Davies, University of Aberystwyth) will provide fine-scale evidence for the environmental induced changes in the water column and wider catchment. There is an option to further investigate lacustrine geochemistry and in particular the use of stable isotope analysis (CEH/NERC Facility). The palaeoenvironmental records will be constrained using radiocarbon dating (supported by NERC-RCF) and Pb210 (University of Stirling) to understand change on ecological timescales.

The methodology proposed here will integrate palaeoecological, ecological and geochemical techniques. This project will develop techniques and methodological approaches to overcome traditionally perceived challenges, bringing these disciplines together and gain a perspective that will connect past and future ecosystem dynamics.

Biological Sciences (4) Environmental Sciences (13) Geography (17) Geology (18)

Funding Notes

The application deadline is Friday 5th January 2024 at 12:00 noon. By this time applicants must have submitted an application through the IAPETUS DTP online application system. Further details on how to do this are here: https://www.iapetus2.ac.uk/how-to-apply/. However, serious applicants should contact the Dr Eileen Tisdall ([Email Address Removed]) by email well before the deadline to discuss their application.


UKRI eligibility rules enable a small proportion of IAPETUS PhD studentships to be awarded to non-UK applicants from overseas and for successful international candidates we will apply to the University of Stirling to waive overseas fee costs. International applicants must contact the primary supervisor by the earlier deadline of Monday 11th December 2023 if they wish to be considered for this PhD.

Initial shortlisting will take place immediately after the 5th January deadline. Those candidates who are successful in shortlisting will be required to attend an IAPETUS interview on Tuesday 27th February or Wednesday 28th February 2024.

In order to address historical imbalances in the higher education sector, IAPETUS2 is committed to recruiting a diverse, representative community of researchers in Environmental Science. The DTP has developed an Equality, Diversity and Inclusion policy to further this. This includes the Widening Participation Scheme, which identifies Home applicants from underrepresented groups. The DTP aims to give up to 30% of interview places to those eligible for this scheme. Also we are pleased to introduce the IAPETUS2 Diversifying Talent Scholarship Scheme, a separate competition designed for those from underrepresented groups. For more, please see the IAPETUS2 website.
Duston, N.M., Owen, R.M., Wilkinson, B.H. 1986 Water chemistry and sedimentological observations in Littlefield Lake, Michigan Implications for marl deposition. Environmental Geology and Water Sciences, 8, 229-236.
Jones, S.E., López-Costas, O., Cortizas, A.M., Mighall, T.M., Stratigos, M.J. and Noble, G., 2022. Lake and crannog: A 2500-year palaeoenvironmental record of continuity and change in NE Scotland. Quaternary Science Reviews, 285, p.107532.
Pentacost, A. 2009 The marl lakes of the British Isles. Freshwater Reviews, 2, 167-197.
Wiik, E., Bennion, H., Sayer, C.D., Willby, N.J. 2014 Chemical and biological responses of marl lakes to eutrophication. Freshwater Reviews, 6. 35-62.
Wiik E., Bennion, H., Sayer, C.D., Davidson, T.A., McGowan, S., Patmore, I.R. and Clarke, S.J. 2015a Ecological sensitivity of marl lakes to nutrient enrichment: evidence from Hawes Water, UK. Freshwater Biology 60, 2226-2247.
Wiik E., Bennion, H., Sayer, C.D., Davidson, T., Clarke, S.J., McGowan, S., Prentice, S., Simpson, G.L. and Stone, L. 2015b The coming and going of a marl lake:multi-indicator palaeolimnology reveals abrupt ecological change and alternative views of reference conditions. Frontiers in Ecology and Evolution 3, 82.
Shafiee, R. 2021 Blue Carbon. SPICe Briefing paper, The Scottish Parliament. https://digitalpublications.parliament.scot/ResearchBriefings/Report/2021/3/23/e8e93b3e-08b5-4209-8160-0b146bafec9d
Smeaton, W, Austin, W., and Turrell, W.R. 2020 Re-Evaluating Scotland’s Sedimentary Carbon Stocks. Scottish Marine and Freshwater Science 11 (2), 20pp.

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