Development of a Low-Cost Automated Nitrate Sensor for Natural Waters.

Nitrate is found in natural water sources and is known to be harmful to both humans who ingest it, and aquatic ecosystems into which it is transported.  According to the United States Environmental Protection Agency, when infants and children are exposed to high levels of nitrate from drinking sources or otherwise, they experience adverse health effects, most notable of which is oxygen deficiency-induced suffocation, known as “blue baby syndrome” (methemoglobinemia).  When agricultural runoff and leaching reaches streams, nitrate can cause accelerated eutrophication, which harms fish habitats.

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 and runoff settings.  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 agricultural applications.

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 ions, while staying within nitrate’s peak, effectively measuring exclusively nitrate and dissolved organic carbon.