Continuous nitrate monitoring in estuarine and river waters – Aquamonitrix® versus UV Probe Nitrate Analyser

Continuous nitrate monitoring in estuarine and river waters – Aquamonitrix® versus UV Probe Nitrate Analyser

by | Mar 1, 2024 | Case Study, Environmental Case Study, NOx-monitrix mobile Case Study | 0 comments

Photograph of Aquamonitrix nitrite and nitrate WEXFORD
Aquamonitrix® nitrate analysers were deployed at sites in Wexford, Ireland to monitor surface waters. Existing commercial UV probes were in-situ at these sites for nitrate monitoring and multiparameter sondes were also in-situ to deliver additional parameter information. Analysers were deployed within kiosks for continuous nitrate monitoring of surface river waters. The installation and deployment site located in Wexford Bay is depicted in figure 1 below. The nitrate concentration data generated over the course of the deployment for both the Aquamonitrix® analyser and the UV probe are shown in figure 2. Due to tidal influences, the salinity of the surface water changes over time resulting in overestimations for the UV probe.
Figure 1: Photograph of Aquamonitrix nitrite and nitrate analyser (Left) and photograph of UV probe (Right) deployed to monitor brackish waters of Wexford Bay, Ireland.
Continuous nitrate concentration data generated by Aquamonitrix® deployed within surface water of Wexford Bay, Ireland. The salinity of the water fluctuated overtime due to tidal influence.
Continuous nitrate concentration data generated by UV nitrate probe deployed within surface water of Wexford Bay, Ireland. Due to fluctuating salinity, overestimations were observed using UV probe.
The installation and deployment site located at Wellingtonbridge, Wexford, Ireland is depicted in figure 3 below. Here, fresh river water with fluctuating high turbidity levels was monitored. The nitrate concentration data generated over the course of the deployment for the Aquamonitrix® analyser and the UV nitrate probe are shown in figure 4. High levels of turbidity were experienced from 02/October onwards.

Figure 4: Continuous nitrate concentration data generated by Aquamonitrix®, and the UV probe nitrate analyser deployed for surface water monitoring at Wellingtonbridge, Wexford, Ireland.

Summary

For optical ultra-violet (UV) absorbance-based NO3- probes, challenges arise with flucuating salinity and turbidity. Turbidity causes a scattering effect which affects the absorption spectrum and, without sufficient compensation procedures, can introduce large detection errors [1]. UV probes are also impacted by interferences and matrix effects, since a range of dissolved constituents (including bromide, nitrite, and hydrogen sulphide) present in natural waters also absorb across the UV wavelengths [1,2]. Aquamonitrix® nitrate and nitrite analysers employ rapid ion chromatography and patented UV-LED detection which enables high selectivity and ensures accuracy is maintained despite high levels of turbidity or varying salinity [3].

[1]. Y. Guo, L. Chunhong, Y. Rongke, D. Qingling, Advances on water quality detection by UV-vis spectroscopy, Appl. Sci. 10 (19) (2020) 6874.
[2]. J. Luna, M. Jason, T. Skinner, E. Bertone, R.A. Stewart, Development of a real-time, mobile nitrate monitoring station for high-frequency data collection, Sustainability 12 (14) (2020) 5780.
[3]. M.G. Butinyac, V.A. Montaño, J. Downes, N.M. Ruane, E. Ryder, F. Egan, T. Staessen, B. Paull, E. Murray, Continuous nitrite and nitrate monitoring of recirculating aquaculture systems using a deployable ion chromatography-based analyser, Aquaculture International (2023).