Time-series of biogeochemical and flow data from a tidal salt-marsh creek, Sage Lot Pond, Waquoit Bay, Massachusetts, 2012-2016 (ver. 2.0, July 2023)

Drift and fouling of each sensor on the YSI EXO2 sonde were evaluated after each field deployment. Correction factors based on fouling and drift were calculated and applied according to Wagner and others, 2006. Fouling was determined as the difference between a sensor reading in solution prior to cleaning and after cleaning. Calibration drift was determined as the difference between the prepared value of a calibration solution and cleaned sensor reading in calibration solution. If the absolute value of the sum of the fouling and drift are beyond a predetermined acceptable amount of fouling (Table 1, Wagner and others, 2006), then a correction factor (calculated from these fouling and drift assessments) would be applied to the data. If the data required a correction factor beyond an acceptable threshold (Table 1), the data were removed from the dataset. Fouling was determined in three different ways during the 2012-2016 field seasons: field comparison of dirty deployed EXO and clean replacement EXO; laboratory comparison of sensor data in a bucket of field water prior to and after cleaning; laboratory comparison of sensor data in known standards prior to and after cleaning. Bucket tests were not ideal for all parameters; for some parameters the concentration in the bucket was near to the detection limit of the sensor (for example turbidity and total algae). Field comparison was not available for all deployments (due to battery failure of deployed sondes). Comparison in standards was most consistently assessed. Calibration drift was assessed on cleaned sensors post deployment. After the fouling evaluation was complete, sensors were cleaned and placed in clean standards. Readings were noted and sensors were recalibrated, if necessary, prior to next deployment. Data from optical sensors not included in Wagner and others, 2006 (fluorescent dissolved organic matter (fDOM) and chlorophyll) were corrected using the same criteria as turbidity.
Water flow and water depth data were measured by a SonTek IQ-Plus Acoustic Doppler current profiler (ADCP), using SonTek IQ Firmware version 1.10. The minimum operating depth of the IQ-plus is 0.08 meters, and maximum is 5.0 meters. Water level accuracy was 0.1% of measured depth or +-0.003 meters, whichever was greater. Pressure sensor accuracy was 0.1% of full scale, and sensor range was 10 meters. Velocity accuracy was +-1% of measured velocity, or +-0.5 centimeters per second. Data were evaluated between deployments, based on the signal to noise ratio. Data with a signal to noise ratio below 4 were omitted, as the velocity signal may become compromised. Depth values less than 0.01 meters were also removed because they were determined to be below detection.
Dissolved CO2 was measured by a Pro-Oceanus Mini CO2 sensor. Dissolved CO2 accuracy was ±2% of the max range, and resolution was 0.1% of the max range. Accuracy of Total Dissolved Gas Pressure was ±1%. The measurement range of CO2 was 0-10,000 ppm. Note: the temperature sensor of the Pro-Oceanus Mini CO2 sensor is housed inside of the sensor housing. Therefore, the temperature readings are higher than the surrounding water temperature. The CO2 in uatm is reliable to 3 decimal places.
Citation used: Wagner, R.J., Boulger, R.W., Jr., Oblinger, C.J., and Smith, B.A., 2006, Guidelines and standard procedures for continuous water-quality monitors—Station operation, record computation, and data reporting: U.S. Geological Survey Techniques and Methods 1-D3, 51 p.