WET Labs Water Quality Monitor (WQM)

New Water Quality Monitor (WQM) provides the “Top 5” marine water quality parameters in one package (temperature, salinity, dissolved oxygen, chlorophyll fluorescence, and turbidity). The WQM’s sensors have the accuracy and precision to track subtle long-term changes in clean ocean environments. Multiple active and passive anti-fouling features effectively inhibit fouling, even in biologically rich coastal waters. The WQM has been extensively field-tested and demonstrated unprecedented long-term stability.

Anti-Fouling Features

The WQM employs multiple anti-fouling measures:

• Active pumping (short burst) delivers a completely new sample of water to the conductivity cell, independent of ambient circulation. This periodic sweeping also inhibits accumulation of debris within the cell, further preserving long term stability.

• Sea-Bird’s EPA-approved, broad spectrum, diffusive anti-foulant device is placed near the plumbing intake and exhaust. Between measurements, water is trapped in the cell and anti-foulant concentration slowly builds to effective levels by diffusion. The saturation point of TBTO in water is very low, and at saturation it stops diffusing, effectively self metering its dose. The TBTO is not flushed away until the next pump cycle at the beginning of a new sample. The self-metered application of anti-foulant allows season-long protection with a small, environmentally safe amount.

• A Bleach Injection System (BLIS) delivers a small volume of bleach into the dissolved oxygen sensor plenum after each measurement. Bleach is a fast-acting biocide that protects the plumbing from fouling immediately, while the TBTO concentration is building.

• The entire pumped volume is contained within black plastic and copper to block ambient light and further hinder algal growth.

• The C-T sensors are shrouded in a solid copper guard assembly, which prevents internal and external bio-fouling, keeping the plumbing intake and exhaust ports from being clogged by external fouling.

• The fluorescence and turbidity sensors sample through a common optical window protected by a copper faceplate and an effective and time-proven Bio-wiperÔ, which sweeps open on power-up and covers the window after each measurement.

Development Testing and Field Trial Data

Field Trial Procedure at Shilshole Marina

Sea-Bird ran extensive testing of the WQM in biologically rich waters at Shilshole Marina in Seattle, Washington. Multiple instruments were deployed side-by-side at 2 meters depth to test the efficacy of the anti-fouling features (all units incorporated the black plenum, black plumbing, and solid copper ring guard assembly):

The WQMs were all programmed to take a measurement every 10 minutes after flushing for 30 seconds, and (Units 2 and 3 only) to inject 8 uL of 6% commercial grade bleach into the dissolved oxygen sensor plenum after each measurement. The instruments were deployed on August 15, 2006 and recovered January 17, 2007. Weekly Winkler oxygen samples were collected in replicate (3) for comparison. Following recovery, conductivity, temperature, and dissolved oxygen calibrations were performed for all 3 units at Sea-Bird.

Field Trial Results from Shilshole Marina

Dissolved Oxygen ‑ Units 1 (AF only) and 3 (AF and BLIS) remained within 5% of the Winklers for the entire deployment (152 days). Unit 2 (BLIS only) suffered a bleach pump failure; the data diverged from Winklers after 120 days, due to fouling. In all cases, the Winkler samples typically read high of the sensor values. Pre- and post-deployment calibration data show dissolved oxygen sensor drift of -1.0% on unit 1 (AF only), -7.0% on unit 2 (BLIS only), and -0.3% on unit 3 (AF and BLIS). The large drift on the BLIS only unit is attributable to the bleach pump failure.

Note about differences between Winkler comparisons and post calibration: Looking at units 1 (AF only) and 3 (AF and BLIS) only, a drift of ~5% was observed toward the end of the deployment when compared to Winklers, but post calibration showed a drift of 1% or less. The difference is attributable to the treatment of the sensor after recovery. Before being placed in the calibration bath, the sensor is rinsed in DI water, which removes much of the fouling present and reduces the measured drift. Therefore, it is important to get a competent field comparison prior to recovery and factory calibration, to assess the condition of the sensor in its fouled state and allow for proper post-processing of the data.

Dissolved Oxygen

Temperature and Conductivity – The temperature and conductivity sensors for all three units were in agreement. Pre- and post-deployment data from laboratory calibrations show that all three units remained well within specifications, with drifts after 152 days of less than 0.00010° C and 0.006 [PSU], a smaller change than the width of data points in the following plots.

	Temperature
	Salinity

Additional Field Trials

WET Labs performed additional tests in Yaquina Bay, Oregon from September 13, 2006 to January 23, 2007, under similar growth conditions to those at Shilshole Marina. As a result of data from both testing programs, the current commercial design was developed, with all of the anti-fouling features described above.

Additional Information / Links:

The WQM is available only from WET Labs.

Published Papers -

• WQM: New Instrumentation for Coastal Monitoring
  Carol Janzen (Sea-Bird Electronics), Nordeen Larson (Sea-Bird Electronics), and Casey Moore (WET Labs),
  Sea Technology, Volume 49, Number 2, February 2008.
• WQM: A New Integrated Water Quality Monitoring Package for Long-Term In-Situ Observation of Physical and Biogeochemical Parameters
  Cristina M. Orrico ¹, Casey Moore ¹, Dave Romanko ¹, Alex Derr ¹, Andrew H. Barnard ¹, Carol Janzen ², Norge Larson ², David Murphy ², Rob Johnson ², Jesse Bauman ²
  (¹ WET Labs, Inc.          ² Sea-Bird Electronics, Inc.)
  Proceedings of Oceans 2007 MTS/IEEE Vancouver, B.C., Canada, October 1 - 4, 2007.

Field Data from Current WQM Deployments -

• Halifax, Canada
• Chesapeake Bay, USA
• Yaquina Bay, Oregon, USA

Last modified: 14-Apr-2008

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