Baltimore Ecosystem Study Institute of Ecosystem Studies

2010 BES Annual Meeting Presentation and Poster Abstracts

Preliminary evaluation of SUNA nitrate sensors in the laboratory
Grese, Melissa
Co-Authors: Melissa Grese, Sujay Kaushal, Claire Welty

Abstract: Continuous measurements transmitted from sensors deployed in the field allow observation of high-frequency chemical fluxes in natural waters. However, analytical challenges may exist in effectiveness of sensors across ranges in water quality conditions (e.g. temperature, turbidity, dissolved organic carbon (DOC) concentrations). As part of an NSF project, we are in the process of deploying six Satlantic SUNAs (Submersible Ultraviolet Nitrate Analyzers) to provide continuous nitrate measurements in BES streams. Before deploying the first SUNA in-stream, we evaluated its accuracy across simulated ranges in water quality conditions using nitrate standards ranging from 0 to 10 mg-N/L. We tested: (1) sensor temperature sensitivity at -20 Deg C, 0 Deg C, 20 Deg C, and 40 Deg C (2) effects of water color on SUNA accuracy using IHSS fulvic and humic acid standards ranging from 0.1 to 15 mg-DOC/L and (3) effects of turbidity using titanium oxide standards ranging from 0 to 1500 NTU. To quantify the accuracy of the SUNA in each simulated water quality condition, we collected all standards directly from the SUNA flow cell and analyzed them using ion chromatography. Results indicate that temperature and color had little effect on sensor nitrate measurements compared to data obtained by ion chromatography. Initial analysis indicated that turbidity values up to 1500 NTU had little effect on the SUNA nitrate measurements. However, there appeared to be considerable percent error in certain turbidity ranges. Ongoing work includes expanded analysis of sensor sensitivity to turbidity.