Development of a Low-Cost Automated Nitrate Sensor for Agricultural Settings and Natural Waters

Tuesday, 16 December 2014
Douglas R Cobos, Noa Bruhis and Leonardo Daniel Rivera, Decagon Devices, Research and Development, Pullman, WA, United States
Nitrate is found in agricultural runoff and natural water sources, and is known to be harmful to humans who ingest it, as well as to aquatic ecosystems into which it is transported. In the interest of simplifying and reducing cost of nitrate detection, we are developing a dedicated nitrate absorption spectrophotometer that is portable, automated, low maintenance, and appropriate for tile drains and agricultural runoff settings, and for natural streams and water bodies. Spectrophotometric and other optical methods for detecting concentrations of given substances have been well studied and implemented for both lab and field applications, but are often expensive and are rarely designed or well suited for long-term in-situ continuous monitoring of settings with low flow or minimal water.

Nitrate’s absorption spectrum ranges from below 200 nm to approximately 240 nm. Dissolved organic carbon’s absorption spectrum overlaps that of nitrate, ranging from below 200 nm to above 300 nm. By taking one absorption reading at a low wavelength within nitrate’s peak and a second reading between 240 nm and 300 nm, we see contributions of each substance. With a rough knowledge of the composition of samples of interest, this instrument is able to step outside the absorption spectra of expected interfering species, while staying within nitrate’s peak, effectively measuring exclusively nitrate and dissolved organic carbon.