frequently asked questions
Rivers and estuaries play an important role in delivering freshwater and materials such as sediments and contaminants to the coastal ocean. The role of waves in mixing and transporting this material along the coastline is not yet well understood. The non-toxic dye released in this experiment acts as a tracer for these freshwater outflows (plumes), which will help scientists better understand the fate of freshwater and land-derived materials from small plumes as they enter the coastal ocean and the surfzone. The improved understanding of this mixing in the coastal ocean is crucial to quantifying the spreading of sediment, pollutants, larvae, harmful algal blooms, and other important material near the coast where many people live and recreate.
The experiment will use an environmentally safe passive tracer called Rhodamine WT. The WT stands for “water tracer” because it is a water-soluble dye. The bright pink fluorescent dye occupies a very different range of wavelengths on the visible light spectrum than the background ocean water, making it straightforward to detect both with our eyes, with underwater sensors, and from above with optical cameras. In the water, an instrument called a fluorometer shines a green light to detect the red light emitted from the dye. The amount of red light is directly proportional to the concentration of the dye in the water, which scientists have calibrated with lab samples.
This chemical is not considered hazardous by the 2012 OSHA Hazard Communication Standard (29 CFR 1910.1200). The product contains no substances which, at their given concentration, are considered to be hazardous to health. This product is approved for use by the U.S Environmental Protection Agency (EPA) and Food and Drug Administration (FDA) in water tracing studies.
Scientists will release 15 gallons of dye during each of these dye releases. It will be visible to the naked eye in the water for several hours after the deployment, with small traces detectable by instruments for approximately 24 hours.
The project site is the estuary and surrounding coastline at Los Peñasquitos Lagoon, located within Torrey Pines State Beach and Natural Reserve in San Diego, California. The dye will be released near the estuary mouth during an ebb tide, the tidal phase when the water level is falling, so that it is carried out of the estuary into the coastal ocean. This site was chosen as a prime example of a small river plume discharging into the surfzone along a relatively uniform stretch of shoreline.
Yes, permits have been secured and approved from all necessary agencies.
This site was chosen because Los Peñasquitos Lagoon/Torrey Pines State Beach provides a prime example of a small river plume discharging into the surfzone along a relatively uniform stretch of coastline. The geography, wave, tide, weather, and river flow conditions make this location ideal for an experiment and a great example of these types of systems, which are found worldwide. Moreover, the location has been the site of many studies by other scientists such that the estuary and beach dynamics are relatively well understood. This site also benefits from a suite of long-term monitoring stations collecting complementary data (from USGS, NOAA, CDIP, NERR). This location was chosen for these physical properties and proximity to other measurements only.
The dye dispersal will be tracked in a variety of ways. Since the dye is fluorescent, scientists are able to track it using fluorometers that can measure the fluorescence or light emitted from the dye. These fluorometers, along with Conductivity-Temperature-Depth (CTD) sensors, which measure salinity and temperature, will be affixed to poles in the sand in the river mouth and surfzone. A jet ski outfitted with fluorometers, GPS and CTDs will also perform transects, or specified survey routes, along the shoreline. Offshore, beyond the breaking waves, several moorings have been deployed on the seafloor with CTDs, fluorometers, and instruments to measure ocean currents. Additionally, unpiloted aircraft systems (drones) will capture the structure and spatial extent of the dye plume from above, using RGB, hyperspectral, and infrared cameras. Beyond tracking of the dye, oceanographic conditions (waves, currents, tides, salinity, temperature, dissolved oxygen, and pH) will be monitored using sensors affixed to moorings deployed for this project.
The dye is nontoxic, so there are no harmful effects from being in the water. There will, however, be a lot of activity from researchers on the day of the dye release. Given this it may be advisable to recreate in an area further south or north of the estuary.
Scripps Institution of Oceanography scientists have successfully conducted nearshore dye experiments (using this same dye) at Huntington State Beach, Calif. (2006), Imperial Beach, Calif., (2009, 2015) and New River, N.C. (2013), and numerous experiments with surfzone, estuary, and offshore instruments. The City of San Diego also did a similar experiment in Mission Bay in 2021, where the dye was released from Rose Creek.
This experiment is sponsored by the National Science Foundation (Award #1924005 ). Complementary data at the same site examining estuarine dynamics and estuary mouth sedimentation is funded by the California Department of Parks and Recreation Natural Resources Division, Oceanography Program.
This project is led by scientists at UC San Diego’s Scripps Institution of Oceanography and the University of Washington. Additional collaborators include scientists from Universidad Técnica Federico Santa María (Chile), UC Irvine, UC San Diego Mechanical Engineering, and the Naval Postgraduate School. The lead investigator is coastal physical oceanographer Sarah Giddings.