Can improving biodiversity help reduce greenhouse gas emissions from small waterbodies?

Overview

Climate change and the intensification of land use practices are causing widespread changes in ecosystems globally. This is particularly evident in freshwater ecosystems, a critical resource for society, where high connectivity within and between ecosystems allows multiple stressors to degrade these habitats. Small waterbodies, such as ponds, are some of the most numerous freshwaters globally with numbers estimated in the order of three hundred million. In addition, ponds are disproportionately biodiverse and, consequently, numerous schemes exist to create, restore or improve them. However, a growing body of research has also pin-pointed small waterbodies as significant sources of greenhouse gases (GHG) such as carbon dioxide, methane and nitrous oxide (Holgerson & Raymond, 2016). Despite this, little is known about the processes and mechanisms driving GHG release from small waterbodies and therefore the contribution of small waterbodies to the global carbon cycle and GHG emissions remains highly uncertain.

One of the primary aims of pond restoration is the recovery of biodiversity, in particular aquatic plants. Aquatic plants are a fundamental component of aquatic food webs, influencing nutrient flux, physico-chemical quality, biodiversity and hydrodynamics (Andersen, Sand-Jensen, Iestyn Woolway, & Jones, 2017; Law et al., 2019). By influencing the physical habitat of a waterbody (e.g. by mediating temperature variation or mixing from wind action) it is possible that aquatic plants may also regulate GHG emissions, as increased temperatures and mixing of the water column are speculated as drivers of GHG release (Ortega et al., 2019).

Studies on standing waterbodies have indicated high levels of dissolved carbon dioxide (CO2) and methane (CH4) particularly in smaller waterbodies, such as ponds (Figure 1). Further investigation is now required to; (i) identify the underlying drivers, (ii) determine whether high dissolved concentrations translate into emissions and (iii) assess if increased aquatic plant coverage influences GHG release via alterations of the local physical or biochemical environment.

The overall aim of this PhD project is therefore to identify and understand the drivers of greenhouse gas emissions from small waterbodies whilst assessing the potential role that improved biodiversity plays in regulating emissions. This PhD will expand on existing knowledge in restoration ecology to determine if there are additional benefits to the carbon cycle as well as to biodiversity. Fieldwork will be focussed in an agricultural catchment (North Norfolk) studying a suite of ponds across a restoration gradient in a before-after-control-impact (BACI) designed project covering unrestored, newly restored (1-3 years) and long-term restored (> 5 yrs) ponds.

Click on an image to expand

Image Captions

Fig. 1. CO2 and CH4 concentrations in relation to waterbody surface and area (from Holgerson & Raymond (2016)).

Fig 2. An overgrown, unrestored pond (upper panel) and a newly restored pond (lower panel) in North Norfolk.

Methodology

Replicates from each restoration treatment will be established, with measurements of dissolved GHG, nutrients, and water physico-chemistry carried out within ponds located in an agricultural landscape. Seasonal field campaigns will collect gas and water samples from numerous ponds to observe diel differences, the effect of shading and the longer-term influence of aquatic vegetation. Water and nutrients will be analysed at Stirling and CEH using a suite of laboratory instruments (gas chromatograph, TOC analyser, spectrophotometer and ion chromatograph). In-situ data from each site will also be collected from a variety of GHG sensors. Multivariate analysis will be conducted to determine variables that influence and drive GHG emissions.
This project shall also benefit from co-supervision by freshwater science and restoration expert Dr Carl Sayer (University College London).

Project Timeline

Year 1

Literature review, learning gas and water sampling methods, skills training, and conducting pilot/test studies with the aim of creating a robust experimental design for future fieldwork.

Year 2

Sampling campaign, data analysis, skills training, writing, conference.

Year 3

Data analysis, skills training, thesis/manuscript write-up.

Year 3.5

Data analysis, manuscript submission, thesis write-up, conference.

Training
& Skills

This project will benefit from a mix of field, lab and computer skills to quantify GHG gas emissions and their drivers, thereby building a platform for an interdisciplinary research or research-related career in environmental science. The supervisory team are highly experienced in freshwater ecology, biogeochemistry, physics and restoration, with access to a breadth of facilities at University of Stirling, Centre for Ecology and Hydrology (Edinburgh) and University College London, and also an inclusive and productive lab group and PhD cohort at Stirling and CEH. A comprehensive training programme will be provided on specialist scientific skills, but also generic and professional skills, including high quality internal training on sampling and monitoring techniques, statistical analysis using R and GIS. The student will also have the opportunity to engage with large research projects at Stirling and CEH involving their supervisors e.g. Hydroscape, Pond Restoration Research Group and
Professional Transferable Skills: Development here will be supported through IAPETUS specific provision. Example courses include: Media Training; Insights to industry; Leadership skills; Conference skills (e.g., networking, poster and oral presentation skills); and Grant writing.

References & further reading

Andersen, M. R., Sand-Jensen, K., Iestyn Woolway, R., & Jones, I. D. (2017). Profound daily vertical stratification and mixing in a small, shallow, wind-exposed lake with submerged macrophytes. Aquatic Sciences, 79(2), 395-406. https://doi.org/10.1007/s00027-016-0505-0

Holgerson, M. A., & Raymond, P. A. (2016). Large contribution to inland water CO2 and CH4 emissions from very small ponds. Nature Geoscience, 9(3), 222-226. https://doi.org/10.1038/ngeo2654

Law, A., Baker, A. G., Sayer, C. D., Foster, G. N., Gunn, I. D. M., Taylor, P., … Willby, N. J. (2019). The effectiveness of aquatic plants as surrogates for wider biodiversity in standing fresh waters. Freshwater Biology, 64(9), 1664-1675. Retrieved from https://onlinelibrary.wiley.com/doi/10.1111/fwb.13369

Ortega, S. H., Romero, C., Quijano, G., Casper, P., Singer, G. A., & Gessner, M. O. (2019). Methane emissions from contrasting urban freshwaters: Rates, drivers, and a wholeâ€city footprint. Global Change Biology, (February), In press. https://doi.org/10.1111/gcb.14799

Further Information

Dr Alan Law, email: alan.law1@stir.ac.uk, telephone: 01786 467869.

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