Challenges with collecting data for measured pH and dissolved inorganic carbon (DIC) in coastal waters

Three sensors, pH, dissolved CO
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, and a CTD with a dissolved oxygen sensor were co-located on a submerged platform connected to a buoy platform in the Saanich Inlet close to Patricia Bay near Sidney, British Columbia. The sensors were moored at a depth of 23 metres for one year continuous sampling deployment to assess the ability of these sensors to monitor the edge of a dynamic, dissolved inorganic CO
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zone. Weekly bottle sampling was performed to use as a reference to verify the sensor readings. Many challenges presented themselves before and during the yearlong deployment. Some of these challenges involved providing power and communications to the instrument package. Other challenges were mooring design limitations, interference with the platform from prawn traps, and steep DIC gradients due to tidal, seasonal effects and unique characteristics of Saanich Inlet. This multi-sensor deployment provided an opportunity to learn from these challenges by identifying key planning considerations for new deployments. Clearly identifying subsurface moorings, choosing sea depths less dynamic for instrument testing and verification would have kept more of the data valid. Bottle samples taken during fast transition events made these references unusable. All of these considerations are critical for data integrity. Making these crucial identifications in the design phase will also help to keep labour and maintenance costs as low as possible.