Project highlights

  • You will gain new insights into river ecosystem responses to climate extremes, including the major drought of 2022.
  • You will have the opportunity to conduct innovative new flow experiments in state-of-the-art mesocosm facilities.
  • Project co-created with CASE partner Wessex Water, and you will have the opportunity to take up a placement opportunity as well as benefit from end-user engagement.


Across the globe, droughts have increased dramatically in frequency and intensity over the past 30 years, with potentially profound consequences for freshwater ecosystems. In some regions, river flows are shifting from perennial to intermittent, modifying the ecological connectivity among habitats within the river network. Where low river flows persist, connections to riparian ecosystems are likely to be enhanced as terrestrial flora and fauna colonise the riverscape, altering biodiversity and the structure and function of food webs. Despite its growing prevalence, research on the ecology of drought in streams and rivers lags far behind that of other stressors (e.g. acid pulses or pesticides) and has focused on in-stream responses at the community level. Far less is known about impacts on functioning, how aquatic-terrestrial linkages may change in response to altered hydrological connectivity, or ecosystem recovery from drought.

The successful candidate will undertake research to address these research gaps and conduct flow manipulation experiments in a new state of the art mesocosm facility at the University of Birmingham.

These experiments will be combined with sampling and analysis of long-term records of flow and biodiversity in chalk streams monitored by our industry partner Wessex Water. Chalk streams are much valued biodiversity hotspots (Environment Agency, 2021) in which there is growing interest in managing abstraction to protect river life.

Specifically, the project will test the effect of modification of low flow regimes on ecosystem functioning and food webs, including aquatic-terrestrial links. The doctoral researcher will: (1) Use artificial streams in the Birmingham EcoLaboratory facility to replicate elements of natural flow regimes and simulate natural and modified flow regimes; (2) Determine the mechanistic basis of flow change effects, via factorial manipulation of habitat connectivity, habitat/sediment area, temperature and water quality; and (3) Monitor effects on water quality and ecosystem processes using state of the art sensor networks. The results of the research will reveal how key ecosystem processes are affected by flow modification, identify tipping points and non-linear responses along gradients of low flow stress as well as key environmental stressors that modify ecosystem processes when flows are modified, to form the basis of management to balance the increasing demand of water for human versus ecological needs.

Image of Artificial stream channels at the Environmental Change Outdoor Laboratory (EcoLaboratory) on the University of Birmingham campus.
Figure 1: You will have the opportunity to use artificial stream channels in the Ecolab facility on the University of Birmingham campus.

Case funding

This project is suitable for CASE funding


University of Birmingham


  • Climate and Environmental Sustainability
  • Organisms and Ecosystems


Project investigator

Dr. Mark Ledger, University of Birmingham ([email protected])


How to apply


You will undertake a research project to determine the effect of drought on community structure and functioning (studying aquatic and terrestrial biota) and offers the flexibility to combine new environmental flow experiments conducted by the student in replicate freshwater mesocosms in our new facility at the University of Birmingham in conjunction with analysis of long-term data collected by Wessex Water (the industry partner).

Training and skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.

The successful candidate will receive interdisciplinary training in hydroecology from staff and students within the School of Geography Earth an Environmental Sciences (GEES), University of Birmingham. More specifically they will be trained in the use of mesocosms for global change research. A good understanding of experimental design, data science and statistical analysis will also be achieved.  In addition, there will be scope to develop expertise in environmental sensing using the sensor network at the EcoLaboratory facility. The school supports a large, vibrant and well-resourced community of postgraduate researchers. As part of this community you will have access to a wide range of training opportunities tailored to early career researcher development, focussing on transferable project management skill, personal development, research practice and careers.

Partners and collaboration

The project will benefit from links with Wessex Water who will provide CASE support, a placement opportunity, as well as access to long-term data records of flow and biodiversity in lowland rivers in their region.

Further details

Dr Mark Ledger:

Dr Kieran Khamis:

Dr Tom Aspin:

Read about our EcoLaboratory:

If you wish to apply to the project, applications should include:

  • A CV with the names of at least two referees (preferably three and who can comment on your academic abilities)
  • Submit your application and complete the host institution application process via:: and go to Apply Now in the PhD Geography and Environmental Science (CENTA) section. Please quote CENTA23_B32 when completing the application form.

Applications to be received by the end of the day on Wednesday 11th January 2023. 

Additional information for international applicants

  • All international applicants must ensure they can fulfil the University of Birmingham’s international student entry requirements, which includes English language requirements.  For further information please visit
  • Please be aware that CENTA funding will only cover University fees at the level of support for Home-fee eligible students.  The University is only able to waive the difference on the international fee level for a maximum of two successful international applicants.

Possible timeline

Year 1

You will establish experimental mesocosms and communities; refine methodologies and design of experiments; implementation of experiments. Undertake a literature review of the research field and begin analysis of historical data from Wessex Water.

Year 2

Run experiments; sampling and data processing. Placement with Wessex Water (Bath, UK) to analyse long-term data.

Year 3

Data analysis, reporting and write-up.

Further reading

  • Aspin, T.W.H., Matthews, T.J., Khamis, K., Milner, A.M., Wang, Z., O’Callaghan, M. & Ledger, M.E.  (2018) Drought intensification drives turnover of structure and function in stream invertebrate communities. Ecography. DOI: 10.1111/ecog.03711.
  • Environment Agency (2018). New chalk streams strategy launched to protect ‘England’s rain forests’. Accessed on 26/09/2022.
  • Lu, X., Gray, C., Brown, L.E., Ledger, M.E., Milner, A.M., Mondragon, R., Woodward, G., Ma, A. (2016) Drought rewires the cores of food webs. Nature Climate Change, 6, 875–878.
  • Woodward, G., Bonada, N., Brown, L.E., Death, R.G., Durance, I., Hladyz, S., Ledger, M.E., Milner, A.M., Ormerod, S.J., Thompson, R.M. (2016) Extreme climatic events and their consequences for biodiversity, food webs and ecosystem properties in running waters. Philosophical Transactions of the Royal Society B: Biological Sciences, 371, doi: 10.1098/rstb.2015.0274.
  • Ledger, M.E. & Milner, A.M. (2015) Extreme events in running waters. Freshwater Biology, 60, 2455-2460.Ledger, M.E. & Milner, A.M. (2015) Extreme events in running waters. Freshwater Biology. doi:10.1111/fwb.12673.
  • Ledger, M.E., Brown, L.E., Edwards, F.K., Hudson, L.N., Milner, A.M., Woodward, G. (2013). Extreme climatic events alter complex food webs: evidence from a mesocosm drought experiment. Advances in Ecological Research, 48, 343-395.
  • Ledger M.E., Brown L.E., Edwards F., Woodward G., Milner A.M. (2013) Drought impacts on the structure and functioning of complex food webs. Nature Climate Change, 3, 223-227.
  • Ledger M.E., Harris R.M.L., Armitage P.D. & Milner, A.M. (2012). Climate change impacts on community resilience: experimental evidence from a drought disturbance experiment. Advances in Ecological Research, 46, 211-258.
  • Woodward, G., Brown, L., Edwards, F.K., Hudson, L.N., Milner, A.M., Reuman, D.C. & Ledger, M.E.(2012). Climate change impacts in multispecies systems: drought alters food web size-structure in a field experiment. Philosophical Transactions of the Royal Society B, 367 (1605), 2990-2997.
  • Ledger, M.E., Edwards, F., Brown, L.E., Woodward, G. & Milner, A.M. (2011) Impact of simulated drought on ecosystem biomass production: an experimental test in stream mesocosms. Global Change Biology, 17, 2288-2297.


The project is resilient to the impacts of any respiratory or contact pandemic; experiments are conducted in an open air mesocosm facility which operated without interruption during 2020-21. Data driven aspects of the project are manageable and unlikely to be problematic.