Optical Nitrate is measured at several SATURN station with Satlantic SUNA and ISUS sensors.
|Click sensor name for link to manufacturer website||Satlantic SUNA or ISUS|
|Deployments||Saturn01, Saturn02, Saturn03, Saturn04
|Limit of Detection||0.5µM (fresh water or seawater with T/S correction)
2.0 µM (seawater 0-40 psu)
|Accuracy||± 2 μM (± 0.028 mg/I-N) or ± 10% of reading|
1 As part of a LOBO mooring
The sensors are factory calibrated to measure nitrate concentration (µM) in fresh or salt water mediums. When setting up the instrument, one of these mediums is selected and that calibration is used to determine nitrate concentration. There are several factors that can introduce bias or errors in these measuremtents including temperature/salinity, CDOM, and turbidity. See the white paper by Johnson et .al. for a revew of the SUNA and ISUS technology and measurement biases.
There will be drift due to aging of the lamp in the SUNA/ISUS. When the instrument drifts, the calibration can be updated, by re-zeroing the calibration against DI water. Calibrations are monitored with regular DI readings at SATURN-03 and SATURN-04 and with pre-deployment and post-deployment DI readings for all deployments. Recently the measurement of a nitrate standard has been added to the pre- & post-deployment checks. In addition, routine water samples are collected from the pumped systems at SATURN-03 and -04 and occasional near-station samples from some of the other SATURN stations. Nitrate concentration in these water samples is measured using standard wet chemistry methods. Results from the various monitoring data and sample measurements are used to evaluate and correct for calibration offset.
Currently no corrections are made for the T/S bias inherent to these measurements (the by white paper by Johnson et .al.) although applying this type of correcection to certain SATURN data is being investigated.
Nitrate QA/QC Archive
|s1nitrate_qc01.pdf||5/1/14 – 12/1/14||Data evaluation; correction for sensor offset/drift|
|s1nitrate_qc03.pdf||5/1/15 – 12/1/15||Data evaluation; correction for sensor offset/drift|
|s2nitrate_qc2014||6/26/14 – 9/28/14||Data evaluation|
|s2nitrate_qc2015||5/24/15 – 10/9/15||Data evaluation; correction for sensor offset/drift|
|s3nitrate_qc02.pdf||1/25/14 – 1/1/15||Data evaluation; correction for sensor offset/drift|
|s3nitrate_mar2015-may2016||3/4/15 – 5/18/16||Data evaluation; correction for sensor offset/drift|
|s3nitrate_may2016-oct2018||5/18/16 – 10/22/18||Data evaluation; correction for sensor offset/drift|
|s4nitrate_qc01.pdf||1/1/14 – 3/1/15||Data evaluation; correction for sensor offset/drift|
|s4nitrate_qc02_may2015-aug2016.pdf||5/18/15 – 8/1/16||Data evaluation; correction for sensor offset/drift|