Field Measurements of Fluorescein Dye Dispersion to Inform Dispersed-Oil Plume Sampling and Provide Input for Oil-Transport Modeling1

Abstract

The California Department of Fish and Game Office of Spill Prevention and Response (CA OSPR) is utilizing oil-spill fate and transport modeling to develop the time and spatial scales, and equipment needs, for a formal Dispersed Oil Monitoring Plan (DOMP). When fully implemented, the DOMP will aid in documenting hydrocarbon concentrations in the water column, potentially exposed organisms (zooplankton), and the impacts of entrained oil and dissolved hydrocarbons with and without dispersant applications. Fluorescein dye studies off San Diego, California (USA) have been completed to test the operational framework for repeated sampling of dispersed oil plumes as outlined in the DOMP, to allow evaluation of high-frequency radar (HF-Radar) for providing surface current input data to oil spill models, and to provide verification of model-predicted movement of subsurface oil (dye) by comparison with drogue movement and measured dye concentrations over three dimensions and time. Aerial photodocumentation, subsurface drogues, dye transport, and HF-Radar were used to measure near-surface current fields at varying depths. High-resolution subsurface dye-plume structure was mapped using an in situ GPS-coupled towed fluorometer equipped with pressure sensors to provide dye concentration data as a function of time, position, and depth. In addition, data from the more traditional Special Monitoring of Applied Response Technology (SMART) protocols utilized by the U.S. Coast Guard (USCG) were compared with the in situ towed-fluorometer measurements, and conventional CTD data were collected to determine the mixed layer depth, an important variable in monitoring dispersion of oil in the water column. As a result of these efforts, significant progress has been made on developing and testing sampling protocols for the DOMP, and nearly continuous and synoptic data have been obtained from seven cruises conducted over a 12-month period. These data sets (available on-line through the Coastal Response Research Center (CRRC) website: http://www.crrc.unh.edu/) are being analyzed and integrated to support oil spill model development and verification with direct applicability to spill response decision making, net environmental benefit analysis, natural resource damage assessments, and educating the spill community and public.