Project highlights

  • You will have the opportunity to conduct innovative experiments in a state of the art mesocosm facility.
  • With Wessex Water involved in the project, there will be a placement opportunity so you can experience research in an industry environment.
  • Research outputs with real-world application that can inform practice in the water industry and environmental policy


Combined Sewer Overflows (CSOs) are a legacy of Victorian sewerage and storm-drainage infrastructure. With ~17,000 CSOs distributed across the UK they represent a major point source of pollution and are the focus of new government policy to reduce discharges1. Their operation is highly variable in space and time with unique disturbance regimes that vary in timing, frequency, and duration of releases. Understanding of the impacts on river ecosystems across temporal scales remains limited, partly due to the episodic nature of releases and reliance on either structural bio-indicators or routine discrete water quality sampling to define impacts.

To date event duration monitors have been used to define when, and for how long a CSO discharges, but with no indication of the associated organic load. Hence, to better understand impacts of variable CSO releases (regimes) on river ecosystems new monitoring approaches are required. With the recent advance in optical sensors (e.g. dissolved oxygen, DO) and inverse modelling approaches there is now potential to calculate river metabolism (i.e. whole system – gross primary production and respiration) at more resolved spatiotemporal scales than previously possible. This new whole system metabolism data, at environmentally relevant time steps, has potential to unravel the impact of variable CSO releases on river ecosystem. However, we still need to rigorously assess the approach as a viable indicator of river health below overflows and understand: (1) the sensitivity of metabolism to varied CSO regimes across different river types; and, (2) the underlying mechanistic links between metabolism and microbial processes.

You will join a vibrant research team addressing an environmental issue of major public concern2.  There will be the opportunity to conduct field-based monitoring, field-experiments and controlled experiments in a new state of the art mesocosm facility at the University of Birmingham (EcoLaboratory; Fig. 1). Historical data from sites monitored by project partner Wessex Water and the Environment Agency will inform field site selection and flume experiments at the EcoLaboratory.  The experiments will also explore how river metabolism is likely to respond to various CSO regimes under current and future climate scenarios. The results of this research will provide a basis to inform monitoring practices and better target where discharge reductions need to be prioritised improving the current CSO assessment framework1.

Image of Artificial stream channels at the Environmental Change Outdoor Laboratory (EcoLaboratory) on the University of Birmingham campus.
Figure 1: Artificial stream channels you will use at the Environmental Change Outdoor Laboratory (EcoLaboratory) on the University of Birmingham campus.


CENTA Flagship

This is a CENTA Flagship Project

Case funding

This project is suitable for CASE funding


University of Birmingham


  • Climate and Environmental Sustainability
  • Organisms and Ecosystems


Project investigator

Dr Kieran Khamis, University of Birmingham ([email protected])


How to apply


This project will determine the effect of CSOs on river metabolism under current and future climate scenarios.  The successful candidate will:

(1) undertake analysis of secondary data collected by Wessex Water, and the Environment Agency,

(2) establish monitoring locations across a gradient of rivers impacted by CSO spills and assess metabolism responses alongside traditional indicators of river health; and,

(3) experimentally assess the impact of environmentally relevant CSO regimes (i.e. timing, frequency, and duration) on river metabolism and microbial functioning under current and future climate scenarios.

The experiments will be informed by environmental surveys and data collected by Wessex Water (the project partner). This project also benefits from being closely linked with ecologists at Wessex Water, who seek to better understand pollution impacts on river life in their catchments in southern England.

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 be trained in the use of mesocosms (artificial streams and ponds) for research in aquatic ecology. 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 various field deployable sensors and also the sensor network at the EcoLaboratory facility on the campus at Birmingham. The successful candidate will also gain a broad spectrum of soft skills from being part of a large, interdisciplinary, research team based at the University of Birmingham.

Partners and collaboration

The project will benefit from a collaboration with our partners Wessex Water and the UK Centre for Ecology & Hydrology. You will have access to extensive historical datasets enabling comparative analysis of CSO impacts on water quality and biota. There will be placement opportunities with the CASE partner (Wessex Water) to give the successful candidate industry experience. You will also have the opportunity to visit our research partner, UK CEH, to use their cutting-edge microbiology laboratory.

Further details

For more information or to arrange an informal chat please contact Dr Kieran Khamis ([email protected]) or Dr Mark Ledger ([email protected]).

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_B30 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

Review literature, analyse historical data, plan and undertake fieldwork to identify suitable monitoring locations. Plan experiments. Opportunity for first placement with project partners.

Year 2

Undertake field monitoring exploring impacts on populations. Establish experiments exploring impact of CSO release regime under a changing climate on river metabolism and microbial function. Opportunity for second placement with project partners.

Year 3

Complete experiments, all laboratory analysis and data analysis. Thesis write-up with view to publish findings in international peer-reviewed journals.

Further reading


  1. DEFRA. 2022. Storm Overflows Discharge Reduction Plan. Available at: (Accessed 23 September 2022).
  2. Laville S. 2022. “Conservationists seek judicial review of UK sewage discharge plan”, Guardian, 31 August. Available at: (Accessed 23 September 2022).

Further reading:

  • Bernhardt ES, Heffernan JB, Grimm NB, Stanley EH, Harvey JW, Arroita M, Appling AP, Cohen MJ, McDowell WH, Hall RO Jr, et al. 2018. The metabolic regimes of flowing waters. Limnology and Oceanography 63 (S1): S99–S118
  • Bertuzzo E, Hotchkiss ER, Argerich A, Kominoski JS, Oviedo-Vargas D, Savoy P, Scarlett R, von Schiller D, Heffernan JB. 2022. Respiration regimes in rivers: Partitioning source‐specific respiration from metabolism time series. Limnology and Oceanography DOI: 10.1002/lno.12207
  • Kay P, Hughes SR, Ault JR, Ashcroft AE, Brown LE. 2017. Widespread, routine occurrence of pharmaceuticals in sewage effluent, combined sewer overflows and receiving waters. Environmental pollution 220 (Pt B): 1447–1455 DOI: 10.1016/j.envpol.2016.10.087
  • Riechel, Matzinger, Pawlowsky-Reusing. 2016. Impacts of combined sewer overflows on a large urban river–understanding the effect of different management strategies. Water Research 105: 264–273 DOI: 10.1016/j.watres.2016.08.017
  • von Schiller D, Acuña V, Aristi I, Arroita M, Basaguren A, Bellin A, Boyero L, Butturini A, Ginebreda A, Kalogianni E, et al. 2017. River ecosystem processes: A synthesis of approaches, criteria of use and sensitivity to environmental stressors. The Science of the Total Environment 596-597: 465–480 DOI: 10.1016/j.scitotenv.2017.04.081


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.