High-frequency water quality monitoring in an urban catchment: hydrochemical dynamics, primary production and implications for the Water Framework Directive

Sarah J. Halliday, Richard A. Skeffington, Andrew J. Wade, Michael J. Bowes, Emma Gozzard, Jonathan R. Newman, Matthew Loewenthal, Elizabeth J. Palmer-Felgate, Helen P. Jarvie

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Abstract

This paper describes the hydrochemistry of a lowland, urbanised river-system, The Cut in England, using in situ sub-daily sampling. The Cut receives effluent discharges from four major sewage treatment works serving around 190 000 people. These discharges consist largely of treated water, originally abstracted from the River Thames and returned via the water supply network, substantially increasing the natural flow. The hourly water quality data were supplemented by weekly manual sampling with laboratory analysis to check the hourly data and measure further determinands. Mean phosphorus and nitrate concentrations were very high, breaching standards set by EU legislation. Although 56% of the catchment area is agricultural, the hydrochemical dynamics were significantly impacted by effluent discharges which accounted for approximately 50% of the annual P catchment input loads and, on average, 59% of river flow at the monitoring point. Diurnal dissolved oxygen data demonstrated high in-stream productivity. From a comparison of high frequency and conventional monitoring data, it is inferred that much of the primary production was dominated by benthic algae, largely diatoms. Despite the high productivity and nutrient concentrations, the river water did not become anoxic, and major phytoplankton blooms were not observed. The strong diurnal and annual variation observed showed that assessments of water quality made under the Water Framework Directive (WFD) are sensitive to the time and season of sampling. It is recommended that specific sampling time windows be specified for each determinand, and that WFD targets should be applied in combination to help identify periods of greatest ecological risk.

Original languageEnglish
Pages (from-to)3388-3407
Number of pages20
JournalHydrological Processes
Volume29
Issue number15
Early online date24 Mar 2015
DOIs
Publication statusPublished - 2015

Keywords

  • diurnal dynamics
  • instream productivity
  • phosphorus
  • sewage treatment works
  • The Cut
  • Water Framework Directive

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    Halliday, S. J., Skeffington, R. A., Wade, A. J., Bowes, M. J., Gozzard, E., Newman, J. R., Loewenthal, M., Palmer-Felgate, E. J., & Jarvie, H. P. (2015). High-frequency water quality monitoring in an urban catchment: hydrochemical dynamics, primary production and implications for the Water Framework Directive. Hydrological Processes, 29(15), 3388-3407. https://doi.org/10.1002/hyp.10453