2024 Award Winner’s Spotlight: Postgraduate Student Project Award

Christopher Birks

Birkbeck, University of London

Changes in the nutrient flux of a wastewater-impacted reach of river when subjected to combined sewer overflow discharges

This award was sponsored by:



Combined sewer overflow discharges (CSODs) represent a known contributor of pollutants to UK rivers; however, their influence on fluvial nutrient concentrations is less well studied. Following a comprehensive  literature review, Christopher’s research identified a lack of studies on the impact of CSODs on fluvial nutrient concentrations.

The project drew on the established methodologies of peer-reviewed work in using the publicly-available data on UK river water chemistry. By combining this data with that obtained from Thames Water by environmental information requests, Christopher sought to identify study sites that would allow both CSOD nutrient inputs to be compared to those in treated effluent discharges (STWDs) and to measure the comparative downstream flux of these inputs. While the project was unable to identify such ideal sites, it set a clear methodology by which the research questions would be addressed.

The project was able to demonstrate (with limitations) that CSODs could be the driver behind significant reductions in fluvial nutrient concentrations (40.25% phosphorus; 38.65% nitrogen). When projected onto an identified STWD-impacted fluvial nutrient flux at an additional study site, these findings produced nutrient fluxes of -5.16 mg-N/L (46.78%) and 0.011 mg-P/L (14.29%). These represented 243% increases in fluvial nitrogen flux and 86% decreases in fluvial phosphorus flux when compared to STWD-impacted conditions. Critically, these outputs shifted the phosphate concentrations at the additional study site to within those determined ‘good’ by the Water Framework Directive, and to within 0.17 mg-N/L of nitrate limits for avoiding freshwater eutrophication.

Given the importance of nutrient availability in determining the stable states riverine environments, this project was able to make a strong case for developing a greater understanding of CSOD-derived nutrient inputs.