Dataset: Autonomously collected pH data from Narragansett Bay in 2022 and 2023

This dataset contains temperature, salinity, DOI, and pH data autonomously collected as part of the study. See the "Related Publications" section for discrete data (TA, DIC) also described in this methodology.

The Mount View (MV) and Quonset Point (QP) sensors are maintained by the Narragansett Bay Fixed Station Monitoring Network (NBFSMN). Each sensor measures pH, along with temperature, salinity, and DO in the surface, every 15 and were deployed only from spring to fall. Complete documentation provided by the Rhode Island Department of Environmental Management (RIDEM, 2020; https://dem.ri.gov/sites/g/files/xkgbur861/files/programs/benviron/water/quality/surfwq/pdfs/nbfsmn.pdf).

The Conanicut Hydrocat 620 and Potowomut Hydrocat 720 sensors are maintained by the Rhode Island Consortium for Coastal Ecology Assessment, Innovation, and Modeling (RI C-AIM; https://data-explorer.riddc.brown.edu/dataset/buoy-telemetry/summary) and Rhode Island Sea Grant. Each sensor measures pH, along with temperature, salinity, and DO, every 15 minutes approximately 1 meter below the surface (RI C-AIM, 2024). The hydrocat sensors were deployed year-round and were recovered every 2 to 4 weeks, weather permitting, for maintenance, at which point the flow path and the conductivity cell are flushed with 1% Triton detergent followed by vigorous flushing with DI water.

Discrete bottle samples were collected to verify the sensor data. Samples for the southern region of the bay (i.e. near QP and Conanicut buoy) were collected weekly as part of the Narragansett Bay Long Term Phytoplankton Time Series (PLT), which is located just off the Conanicut buoy. The time series typically collects samples on Monday mornings at approximately 7:30am, barring weeks when inclement weather conditions delayed or canceled sampling. Samples for the northern region of the bay (i.e. Greenwich Bay near MV and Potowomut buoy) were collected approximately once a month. After collection, samples were poisoned with 100 uM  of saturated mercuric chloride solution and stored in the refrigerator until analysis for DIC and TA. DIC and TA were measured according to Dickson et al. (2007) using the Apollo SciTech Model AS-C6L Dissolved Inorganic Carbon Analyzer and the Apollo SciTech Model AS-ALK3 Total Alkalinity Titrator. Instruments were calibrated to Certified Reference Material (CRM) from Scripps Institute of Oceanography at room temperature (21 - 22° C). For DIC analysis, a sample of CRM was run prior to and at the end of sample analysis for quality control. TA analysis was calibrated to CRM, and either a sample of CRM or aged open ocean water was run at beginning of daily analysis and end of daily analysis for quality control. Lab-based measurements carry a ±0.2% uncertainty for alkalinity and ±0.1% uncertainty for DIC.

Instruments:
(additional context to accompany the list in the "Instruments" section)

The Mount View (MV; EXO V2) and Quonset Point (QP; 6600EDS) sensors are YSI brand multi-parameter sondes maintained by the Narragansett Bay Fixed Station Monitoring Network (NBFSMN). Both sondes were equipped to measure temperature, salinity, dissolved oxygen, pH [NBS], depth, and chlorophyll. The surface equipment was housed in a tube on a monitoring buoy station with the instrument depth about 1 meter from surface. All NBFSMN data were subject to quality assurance measures including verification of calibrations and consistency among multiple instruments, corrections for sensor drift and biases due to biofouling, removal of outliers, and interpolation across selected intervals of missing data, in accordance with the NBFSMN’s EPA approved Quality Assurance Project Plan (RIDEM, 2020). To keep consistency among instruments, servicing protocols consist of swapping the deployed instruments with newly calibrated instruments on a 2-week interval to minimize biofouling. All data are verified through a three-point comparison: data from the retrieved sonde are compared to the newly calibrated sonde, as well as an independent profiling sonde, all at the deployment depth. Outliers and data errors are removed based on criteria set in the NBFSMN’s Quality Assurance Project Plan. Data correction and gaps in coverage on average affect up to 6% of the record at an individual station for an annual assessment. Corrections were filled using linear interpolation and/or sensor offsets following Quality Assurance and Quality Control (QA/QC) protocols detailed in the NBFSMN’s Quality Assurance Project Plan.

The Conanicut Hydrocat 620 and Potowomut Hydrocat 720 sensors were equipped with Seabird Hydrocat-EP CTD sensors (model number# HC-EP.1011S), equipped with a Seabird Hydrocat-EP pH Module (model#802532). Hydrocat-EPs collected multiple parameters including temperature, salinity, pH, dissolved oxygen. The hydrocat sensors were deployed year-round and were recovered every 2 to 4 weeks, weather permitting, for maintenance at which point the flow path and the conductivity cell are flushed with 1% Triton detergent followed by vigorous flushing with DI water. Following the cleaning, conductivity checks with conductivity standards (1413 μS,10,000 μS) ensures proper function, as well as a three point pH calibration of the pH Module (pH 4,7,10). pH calibrations were performed in Seabird's UCI software using their pH calibration wizard. Sensors were sent back to Seabird Scientific for yearly manufacturer calibrations. QA/QC was conducted in R using the R package OCE (Kelley & Richards, 2024), following QA/QC tests established by OOIO (NSF Ocean Observatories Initiative, 2012) including, a stuck value test, despiking, and a range test against global values for measured parameters provided by OOIO and local values in Narragansett Bay provided by the Narragansett Bay Long-Term Plankton Time Series (https://web.uri.edu/gso/research/plankton/).

DIC and TA in discrete samples were measured according to Dickson et al. (2007) using the Apollo SciTech Model AS-C6L Dissolved Inorganic Carbon Analyzer and the Apollo SciTech Model AS-ALK3 Total Alkalinity Titrator. Instruments were calibrated to Certified Reference Material (CRM) from Scripps Institute of Oceanography at room temperature (21 - 22° C). For DIC analysis, a sample of CRM was run prior to and at the end of sample analysis for quality control. TA analysis was calibrated to CRM, and either a sample of CRM or aged open ocean water was run at beginning of daily analysis and end of daily analysis for quality control. Lab-based measurements carry a ±0.2% uncertainty for alkalinity and ±0.1% uncertainty for DIC.