On Methods for In‐Well Nitrate Monitoring Using Optical Sensors

Abstract

Optical sensors are promising for collecting high resolution in-well groundwater nitrate monitoring data. Traditional well purging methods are labor intensive, can disturb ambient conditions and yield an unknown blend of groundwater in the samples collected, and obtain samples at a limited temporal resolution (i.e., monthly or seasonally). This study evaluated the Submersible Ultraviolet Nitrate Analyzer (SUNA) for in-well nitrate monitoring through new applications in shallow overburden and fractured bedrock environments. Results indicated that SUNA nitrate-N concentration measurements during flow cell testing were strongly correlated ( R 2 = 0.99) to purged sample concentrations. Vertical profiling of the water column identified distinct zones having different nitrate-N concentrations in conventional long-screened overburden wells and open bedrock boreholes. Real-time remote monitoring revealed dynamic responses in nitrate-N concentrations following recharge events. The monitoring platform significantly reduced labor requirements for the large amount of data produced. Practitioners should consider using optical sensors for real-time monitoring if nitrate concentrations are expected to change rapidly, or if a site's physical constraints make traditional sampling programs challenging. This study demonstrates the feasibility of applying the SUNA in shallow overburden and fractured bedrock environments to obtain reliable data, identifies operational challenges encountered, and discusses the range of insights available to groundwater professionals so they will seek to gather high resolution in-well monitoring data wherever possible.

Influence of nitrate supplementation on in-vitro methane emission, milk production, ruminal fermentation, and microbial methanotrophs in dairy cows fed at two forage levels

“…After 15 min, samples were centrifuged at 2500g for 10 min at 4°C. Supernatant, free from any solid particles, was recovered and analysed for nitrate and nitrite content using the cadmium-reduction procedure of MacDonald et al (2017).…”

Emerging technologies and radical collaboration to advance predictive understanding of watershed hydrobiogeochemistry

“…For example, fiber‐optic distributed sensors can now autonomously measure temperature and strain with very high spatiotemporal resolution in terrestrial and aquatic systems (Ajo‐Franklin et al, 2017; Joe, Yun, Jo, Jun, & Min, 2018; Slater et al, 2010), and fiber‐based approaches for sensing chemical and biological properties are in development (Ding et al, 2015; Lu, Thomas, & Hellevang, 2019). New sensing strategies are being tested to noninvasively monitor active plant‐root functions in situ (Benjamin et al, 2020; Peruzzo et al, 2020) and to monitor nutrient fluxes (MacDonald, Levison, & Parker, 2017). Autonomous unmanned aerial vehicles (UAVs) equipped with various instruments can now sense previously difficult‐to‐reach environments in high‐resolution.…”

An Improved Algorithm for Measuring Nitrate Concentrations in Seawater Based on Deep-Ultraviolet Spectrophotometry: A Case Study of the Aoshan Bay Seawater and Western Pacific Seawater

“…In 2002, Johnson and his colleagues developed an ISUS (in situ ultraviolet spectrophotometer) system that was commercialized by Sea-Bird Scientific [ 33 ]. Some research institutions have also improved the nitrate in-situ sensor and conducted sea trial, which contributed to the improvement of measurement accuracy [ 34 , 35 , 36 ]. Currently, more and more in-situ nitrate monitoring instruments based on ultraviolet spectroscopy have been used in rivers and seawater, such as TriOS OPUS multi-parameter analyzer and SUNA sensor [ 37 , 38 ].…”