Estimation of the water quality of a large urbanized river as defined by the European WFD: what is the optimal sampling frequency?

Lauriane Vilmin*, Nicolas Flipo, Nicolas Escoffier, Alexis Groleau

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Assessment of the quality of freshwater bodies is essential to determine the impact of human activities on water resources. The water quality status is estimated by comparing indicators with standard thresholds. Indicators are usually statistical criteria that are calculated on discrete measurements of water quality variables. If the time step of the measured time series is not sufficient to fully capture the variable’s variability, the deduced indicator may not reflect the system’s functioning. The goal of the present work is to assess, through a hydro-biogeochemical modeling approach, the optimal sampling frequency for an accurate estimation of 6 water quality indicators defined by the European Water Framework Directive (WFD) in a large human-impacted river, which receives large urban effluents (the Seine River across the Paris urban area). The optimal frequency depends on the sampling location and on the monitored variable. For fast varying compounds that originate from urban effluents, such as PO43−, NH4+ and NO2−, a sampling time step of one week or less is necessary. To be able to reflect the highly transient character of bloom events, chl a concentrations also require a short monitoring time step. On the contrary, for variables that exert high seasonal variability, as NO3− and O 2, monthly sampling can be sufficient for an accurate estimation of WFD indicators in locations far enough from major effluents. Integrative water quality variables, such as O 2, can be highly sensitive to hydrological conditions. It would therefore be relevant to assess the quality of water bodies at a seasonal scale rather than at annual or pluri-annual scales. This study points out the possibility to develop smarter monitoring systems by coupling both time adaptative automated monitoring networks and modeling tools used as spatio-temporal interpolators.

Original languageEnglish
Pages (from-to)23485-23501
Number of pages17
JournalEnvironmental Science and Pollution Research
Volume25
Issue number24
DOIs
Publication statusPublished - 1 Aug 2018
Externally publishedYes

Keywords

  • Chlorophyll a
  • European water framework directive
  • Hydro-biogeochemical modeling
  • Inorganic nitrogen
  • Optimal sampling frequency
  • Orthophosphate
  • Oxygen
  • River water quality assessment

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