Special Sessions

Monitoring of water quality is traditionally based on laboratory measurements of water samples taken in the field. Emerging technologies are now enhancing possibilities of water quality monitoring. This is due to upcoming availability of high-resolution monitoring information received from sensors, drones and satellites, to be widely available in real time in near future. The large amount of high-resolution monitoring information requires automatic checking, processing and visualising of the required information by means of big-data artificial intelligence algorithms.

Innovation of the water quality monitoring can make monitoring cheaper, although field experience with sensor technology shows that this may not always be the case. The main advantage of using new technology is that, due to the larger resolution in time and space, monitoring data can be more accurate, can be available in real time, and will give more information on pollution sources and hydro-chemical processes.

The anthropogenic impact on surface water quality is often concealed due to natural variability in water temperature, sunlight radiation, and precipitation. Continuous monitoring of water quality with sensors will give a far better average concentration than sampling discontinuously since peak events will be monitored as well. Groundwater quality does not usually change that rapidly in time, but the spatial variability is often high. Soil is a heterogenous medium and groundwater quality (for example nitrate concentrations) can be totally different within several metres. Sensors that can cover a large surface area (like soil scanners from precision agriculture or geophysics) may increase the accuracy in comparison to only taking groundwater samples from boreholes or monitoring wells.

Real-time water quality monitoring using in situ and/or remote sensors is the subject of numerous scientific research programs. However, in the current practice of regional water quality monitoring and everyday water quality management, the application of real-time sensor data is far from common. In this session we want to examine what the consequences and opportunities are when real-time water quality monitoring data are made available for decision makers. What next steps are needed to bring sensor technology from the scientific arena into the real-life world of water management?

The following topics will be discussed:

• Incorporation of real-time monitoring in networks:
  What should be done to incorporate real-time water quality monitoring with sensors and remote sensing into regional monitoring networks and everyday water quality management?
• Opportunities of real-time monitoring:
  What opportunities appear for water managers when reliable high resolution, real-time water quality data are made available for them
• Barriers for the uptake of real-time monitoring:
  What are current barriers for the uptake of real-time water quality technology by water authorities and how can scientist help to overcome these barriers?
• Current practices & experiences with real-time monitoring
  Is this practice of sensor data fusion already used and will the power of persuasion be just as high as lab analyses? Most nutrients cannot be measured by a small and affordable sensor and are subject to field laboratories or auto-analysers. The sensors that can be easily applied and are affordable measure the generic parameters like EC, oxygen, pH and turbidity. Sensor data fusion is estimating or modelling the difficult/expensive parameters (like phosphate) using the easy/cheap ones (like conductivity, oxygen, temperature and acidity).
• Reliability of sensor data and proxies:
  Can policy makers rely on estimates of sensor data fusion or proxies or will lab analyses still be equally important?
• Sensors and spatial variability in groundwater:
  Sensor technology is often used in dynamic environments, like surface water. For monitoring in groundwater, the main challenge is not the variation in time but in space. How can we benefit from the combination of spatial sensors, remote sensing, and precision agriculture technology?
• Combining sensor data, lab analyses and models:
  What is, given a certain monitoring objective, the most efficient combination of lab analyses, modelling, and high frequency monitoring? Can a smart combination of real-time monitoring, conventional monitoring, and modelling make monitoring networks more efficient
• Increasing sensor data accuracy and precision:
  What agreements should be made to increase the accuracy of sensors and exchangeability of sensor data? Measurements with sensors are often less accurate than laboratory results. Laboratory protocols, work instructions and proficiency testing ensure a high standard in accuracy. Here and there initiatives exist to develop protocols for the use of water-quality sensors. However, these protocols are not yet fully developed and formalised and, therefore, not used in daily practice like they are used in laboratories.

This session will comprise solicited talks, ask for new innovating contributions, and provide particular room for in depth discussion. It is planned to summarize the outcome of this session in a review paper.

This Special Session S1 will be convened by

• Arno Hooijboer, RIVM National Institute for Public Health and the Environment, the Netherlands (arno.hooijboer@rivm.nl)
• Joachim Rozemeijer, Deltares, the Netherlands (Joachim.Rozemeijer@deltares.nl)
• Michael Rode, Helmhoz Centre for Environmental Research (UFZ), Germany (michael.rode@ufz.de)