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Wyoming-Montana Water Science Center
Photo of Tongue River
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Tongue River Surface-Water-Quality Monitoring Network
Project Chief: Jill Frankforter
Update on Field Sodium Adsorption Ratio (SAR) Analyzer
The field SAR analyzer is a instrument designed for long-term deployment in streams or other water bodies. The instrument periodically performs sequential analyses to determine sodium, magnesium, and calcium concentrations. These concentrations are used to calculate the SAR. The concentration and SAR data can be transmitted in real time by satellite for display on the USGS Tongue River Surface-Water-Quality Monitoring Network website. The frequency of measurements is adjustable, with hourly measurements being a good compromise between very frequent measurements that could quickly exhaust analytical reagents in the analyzer and infrequent measurements that may not adequately characterize SAR fluctuations in the river.
Several analytical methods were considered during development of the instrument, and two methods were finally chosen. An ion selective micro-electrode is used to determine sodium, and spectrophotometric methods are used to determine magnesium and calcium. Photographs of the instrument are shown below.
The SAR analyzer was field tested for the first time during September 2004 at Tongue River at State Line (06036300). This initial deployment was generally successful. Mechanically, the instrument performed well, but further refinement of the analytical methods and resolution of data logging and transmission issues will be necessary to ensure reliable results. We will continue to refine the analytical techniques and resolve the data logging and transmission issues during the winter. We expect to have a fully functional field SAR analyzer installed at the State Line site by the end of spring 2005.
Figure 1. Photograph of the pumping, control, and analytical equipment installed in the field SAR analyzer.
Figure 2. Photograph of the micro sodium electrode and the micro reference electrode used in the field SAR analyzer to measure sodium concentration.
Figure 3. Photograph of the field SAR analyzer.
Figure. 4. Photograph showing watertight housing of field SAR analyzer. The electronics, pump, and valves are inside the housing.
Figure 5. Photograph of USGS gaging station at Tongue River at State Line, where the field SAR analyzer will be installed in 2005. The analyzer will be deployed in the 8-inch-diameter PVC pipe.
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