Water level and barometric pressure measurements in two salt marshes, Humboldt Bay, CA, 2016-2019

Water levels are an important driver of salt marsh processes. In Humboldt Bay, CA, water-level data loggers were deployed in the tidal channels of two USGS study marshes (Mad River marsh and Hookton marsh). From 03/16/2016 to 12/08/2016, Onset-Hobo loggers (Model U-20-001-01-Ti, Onset Computer Corp., Bourne, MA, USA; +/-0.5cm or 0.005 meters accuracy), with a combined barometric pressure sensor, were deployed. The Hobo loggers were replaced by higher accuracy Solinst-Edge LT water-level and Barologgers (Model 3001, Solinst Canada Ltd., Georgetown, Ontario, Canada; +/- 0.3 cm or 0.003 meters accuracy) which were deployed from 12/08/2016 to 09/05/2019. The water-level sensors were placed as low in the tide frame as possible, while still maintaining access to the sensors at low tide. The sensors captured water levels during high tides; but sensor elevations were too high to capture water levels during low tides. The Solinst water-level loggers, deployed in the two study marshes, were programmed to record continuous measurements of absolute pressure, air temperature, and water temperature on a 6-minute timestep. A single barometric pressure logger can be used to correct water-level data within a 30km radius and/or 300 m change in elevation. A single Solinst barometric logger, deployed at the USFWS Humboldt Bay Wildlife Refuge Complex Headquarters Office (https://www.fws.gov/refuge/humboldt-bay), and recorded barometric pressure on a 6 -minute timestep. Following deployment, sensor elevations were surveyed using Real-Time Kinematic GPS (Leica GS-15, Leica Geosystems, Norcross, GA, USA) relative to the North American Vertical Datum of 1988 (NAVD88). The water-level height data collected at Hookton and Mad River marshes was atmospherically corrected using the barometric data. The corrected water-level height data were converted to water-level elevations relative to NAVD88.