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Case study

Monitoring agricultural nutrient run-off to protect Ebro River Estuary (Ballobar, Spain)

A 3-month nitrate monitoring pilot project with Ebro River Authority confirmed significant agricultural fertiliser run-off, providing an indication of local river health to help guide remedial action. 


The Ebro is the longest river in Spain culminating in the protected Ebro River Delta wetlands. Agricultural run-offs along the way, particularly nitrates during irrigation season, are threatening river health and can lead to eutrophication. Ebro River Authority is monitoring the problem to drive remedial action. As a pilot site, a pumped measurement kiosk near Ballobar was selected.

The challenge

Ebro River Authority knows that extensive irrigation used by farmers during autumn irrigation has the adverse effect of fertiliser run-off into the Ebro, and that online sensor systems can help to understand and monitor the problem.

ADASA, a leading water sensor solutions provider, was commissioned by Ebro River Authority to manage the water quality monitoring network proposed to independently assess the suitability, usability and readiness of the SWS sensors.

As a pilot, SWS nitrate measuring device was deployed to a pumped measurement kiosk in Ballobar. The performance targets for the monitoring solution were as follows:

  • Accuracy & precision: >90% 
  • Unattended use valid measurements: >90%
  • Service interval: 1 month

The solution

A SWS DropletSens™ NO3 sensor probe with 20 μm mesh size inlet filter, alongside other physical sensors, was deployed in a measurement kiosk overflow reservoir, to which Ebro River water was pumped. The SWS sensor was installed & calibrated at Day 1 and reagent cartridge & inlet filter changes performed at Day 30 and Day 60. 

Throughout the 3-month deployment, the sensor was set to autonomously measure nitrate levels in the river water every 10 sec, with at least weekly switches to an onboard nitrate standard for quality control. Spot samples were also measured in the lab for performance bench- marking. 

The results

The deployment was successfully completed with the following validated monitoring performance:

  • All client targets on accuracy & precision, valid measurements and service interval achieved
  • Compatibility with high turbidities up to 250 NTU demonstrated  

The high-density, lab-quality data showed significant daily and short-term fluctuations of nitrate levels in the Ebro, but also a clear increase throughout the irrigation season.

  • > 750,000 sensor measurements points
  • Nitrate levels started at 30 mg/L in August, rising to >50mg/L end October

"This was an excellent opportunity to test SouthWestSensor’s nitrate sensors in a relevant scenario for our client Ebro River Authority. We found the sensors to measure nitrate levels accurately, whilst being compatible with standard servicing by our field operators. We are now advancing discussions with Ebro River Authority for further deployment and wider roll-out, to help them to monitor the health of this vital ecosystem and drive protection and remedial action against excess fertiliser run-off."

- Jordi Cros, Innovation Manager, Adasa

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