Future marine Total Maximum Daily Load (TMDL; water cleanup) studies and water quality modeling projects in Puget Sound will need accurate and highly resolved time series of nitrate discharge from fluvial sources.
For this study, a Submersible Ultraviolet Nitrate Analyzer (SUNA; Satlantic Inc.) was deployed in the Deschutes River at the E. Street Bridge in Tumwater from November 1, 2009 through October 31, 2010. The Deschutes River is high in nitrate and discharges to the sensitive South Puget Sound basin.
Data collected was statistically analyzed to determine how nitrate concentrations (and other measured water quality parameters) behaved throughout the year, with special attention being paid to patterns observed during winter storm events. This knowledge was synthesized in the form of new or refined methods for predicting continuous daily loads of nitrate from a limited number of discrete observations.
Higher frequency sampling is required to:
After the stormwater fluctuation pattern of the Deschutes River is characterized, it is anticipated that the sensor will be deployed in both larger and smaller streams to provide a sense of daily nitrate variation by stream size.Ecology Publications
Sensor-derived water quality parameters were sampled continuously every 15 minutes (on the quarter-hour) in the Deschutes River at the E. Street Bridge in Tumwater, from November 1, 2009 to October 31, 2010. Real-time data from the station was transmitted to Ecology Headquarters in Olympia every hour where it was automatically imported into the streamflow database and published to Ecology's website.
Fig. 1 South Puget Sound, Washington.
Fig. 2 Deschutes River at E. Street Bridge, Tumwater, Washington.
Satlantic’s SUNA is a real-time, chemical-free sensor designed to overcome the traditional challenges associated with reagent-based nitrate analysis in aquatic environments. The SUNA uses advanced ultraviolet (UV) absorption technology to provide accurate nitrate concentration measurements in the sometimes highly turbid, high colored dissolved organic matter (CDOM) waters of rivers, lakes, and estuaries.
Many dissolved inorganic compounds, including, nitrate, nitrite, bi-sulfide, and bromide, absorb light at UV wavelengths. The SUNA uses the UV (200-400 nm) absorption spectra to provide in situ measurements of dissolved nitrate. The sensor contains three key components:
The components are housed within two pressure cases, connected with a rigid coupler containing the sample volume. By illuminating a sample of water with UV light onto a spectrometer, the absorption spectra can be measured.
The factory calibration of the SUNA uses standard solutions of dissolved potassium nitrate (KNO3) over a range of salinity conditions and temperatures to compute instrument-specific extinction coefficients for nitrate and bromide.
|15 October 2009||Pre-deployment Calibration|
|19 January 2010||Calibration #1|
|15 April 2010||Calibration #2|
|19 July 2010||Calibration #3|
|22 November 2010||Calibration #4|
Karol Erickson Environmental Assessment Program Washington State Department of Ecology P.O. Box 47600 Olympia, WA 98504-7600 Phone: (360) 407-6694 E-mail: email@example.com
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