Nutrient sensor continuously gathering data at Shell Point
The Sanibel-Captiva Conservation Foundation’s Marine Laboratory is gathering data from a next-generation sensor that measures nutrients in the estuary autonomously.
Along with seven other sites from Texas to the Florida Keys, the existence and operation of RECON — River, Estuary, and Coastal Observation Network — and the ability to reliably produce hourly data throughout the region was an attractive platform on which to test and deploy a new sensor to measure inorganic nitrogen.
The combination pump, spectrometer and IV bags are secured to a frame and bolted to the navigation pilings next to existing RECON sensors. The system has an independent source of power, controller and data logger, and communication.
The data are collected continuously every two hours and does not require a boat and person collecting a water sample and analyzing in the lab. Typical water quality sampling programs focus on monthly sample collection to establish long term status and trends within a water body.
Continuous real-time data can better track storm events, tidal fluctuations and day/night differences in nutrient concentrations, which provides new insights about the dynamics of nutrients and the role of inorganic nutrients in the ecosystem.
The WIZ, or Water In Situ AnalyZer, was purchased by collaborators at the Gulf of Mexico Coastal Ocean Observation System in 2019. The sensor excelled in reliability and accuracy in tests conducted by an independent review of sensor technologies, called the Alliance for Coastal Technologies. A workshop at the University of Louisiana-Lafayette was held to train technicians on the operation, calibration and maintenance of the sensors.
The system was originally deployed in February, during the dry season. The instrument performs internal calibration checks, so the SCCF was confident that the WIZ was working correctly. Since there was little rain then, the inorganic nutrients were very low.
After COVID-19 restrictions were eased, the instrument was again deployed in August. The deployment demonstrated changes in nutrient concentrations consistent with changes in tide stage. At low tide, concentrations were high and at high tide, nutrient concentrations were low.
The finding confirms that the sources of inorganic nutrients are from lower salinity waters, like runoff, and not from the Gulf of Mexico, which has higher salinities. A graph plotting salinity versus nitrate concentration shows the relationship at the Shell Point Retirement Community during the deployment.
The RECON build-out plan for 2021 includes installing more nutrient sensors upstream at Beautiful Island to better track freshwater flows from the W.P. Franklin Lock and Dam versus rain events in the tidal basin.