Near real-time, water quality event monitoring in small rivers, in the context of increasing frequency and intensity of hydrodynamic events due to climate change.

Freshwater quality continues to decline despite the adoption of the Water Framework Directive (WFD) almost twenty five years ago with the recovery of water quality in Europe plateauing since the 2010s (Haase et al., 2010).  Pollution from diffuse sources, particularly from agriculture remains a key challenge to restoring water quality to at least ‘good status’ under the WFD (EEA, 2018) compounded by water quality declines due to increased frequency and intensity of hydrodynamic events (van Vliet et al., 2023). 

Assigning accurate WFD classes and detecting changing trends in water quality have been challenging where traditional low frequency monitoring approaches have been implemented (Skeffington et al., 2015).  Higher monitoring frequency and spatial coverage is required to effectively identify improvements in water quality (Westerhoff et al., 2022) particularly when detecting changes over shorter time periods (Mcdowell et al., 2012).  High frequency monitoring is required to identify temporal water quality changes linked to rainfall driven pollutant transfer from land to waters (Métadier and Bertrand-Krajewski, 2012) with monitoring over multiple events required to capture the variability in pollutant concentrations and pollutant loads across events (Kozak et al., 2019).  Furthermore, 50% of surface waterbodies in the EU are impacted by multiple pressures (EEA, 2018), with increased urbanisation requiring a more complex, multi-pollutant approach to assessing impacts on river quality (Strokal et al., 2021).

The aim of this research was to identify if rainfall driven transient pollution events were occurring at two monitoring stations in a river catchment, and if continuous instream monitoring of turbidity and other water quality parameters could be used to capture changes in water quality and potential instances of such events.  One of the objectives was to identify if continuous monitoring could create a site-specific water quality profile that could be used to identify early warning indicators of rainfall driven or other transient pollution events. 

Results from this study indicate that changes in water quality are happening during rainfall events and that turbidity alongside other parameters can be used to track such events, trigger alarms when a probable event is occurring and automatically activate more intense monitoring during these events.  The integrated monitoring approach adopted allows for the tracking of water quality changes across temporal and spatial scales for multiple pollutants and allows for temporal fluctuations, and variation in pollutant loads during hydrodynamic events to be determined. 

The significant advantages of this approach are it’s suitability for remote deployments with no requirement for permanent infrastructure, the use of site specific water quality profiles to identify potential water quality events at individual sites and to activate further monitoring if required, the ability to tailor the monitoring for pollutant screening or more specific pollutants of concern, and the cost effectiveness of moving the integrated monitoring station between different water bodies.