DETERMINING ACCURACY OF FIELD WATER QUALITY TESTS FOR CITIZEN SCIENCE USE

Citizen science may enable more public engagement with stormwater issues, including water quality of ponds or streams in their communities, but management based on citizen science requires data accuracy. The purpose of this study was to assess the reliability of simple water quality test kits using known concentrations of nitrate (NO3-N) for on-site water quality monitoring of stormwater ponds. Nitrate is an important parameter for establishing the nutrient availability of a system. The study was conducted with a large participant number (N=16) by creating a laboratory exercise for an undergraduate Analytical Chemistry course. The test kits involve the cadmium reduction method, a colorimetric reaction with a premixed powder pillow reagent which reacts with nitrate to form an amber-colored compound. Students created a calibration curve using a nitrate standard stock, used powder pillows for the reaction, and measured the resulting solution at two different absorption wavelengths (400 nm and 520 nm). They then evaluated an unknown sample (7.8 ppm) using i) pre-programmed calibration (Hach Model DR900), ii) absorption at 520 nm (Hach Model DR900) and iii) absorption at 400 nm and 520 nm using a spectrophotometer device (either Vernier SpectroVis Plus or Oceans Optics USB-650 Red Tide) with calculation of concentration using their standard curves at both wavelengths. Analysis of the data showed that when students used the pre-programmed Hach Model DR900 (at 520 nm), 25% of results were within 10% of the known concentration, 44% within 15%, and 50% within 20%. When the concentration was calculated using the created standard curve for the Hach Model DR900 at 520 nm these results improved to 31% within 10%, 62% within 15%, and 75% within 20%; however, some students had difficulty applying the calibration curve calculation so data needed quality control. Differences between equipment was also observed. The hand-held colorimeter may be a reliable and affordable tool for monitoring nitrate, and accuracy in the lab improves when a proper calibration curve is applied, however further testing is required for assessing in-field accuracy if it is to be employed for citizen science. Additional analyses will establish the accuracy compared to ion chromatography, and issues of interferences in natural water samples.