Detecting Oil/Gas Plumes

What is in a plume?

CIOERT’s partner, UNCW has created a web page describing expected forms of oil, gas and chemical dispersants that may travel over Florida reefs.

How to detect a plume?

Oil and gas in the water takes many forms, from dissolved gases to large blobs (mousse) at the surface. Most mapping is done via satellites and visual aerial imagery. It is more difficult to map subsurface plumes. An EPA directive prescribes a subsurface monitoring plan for BP, with parameters that need to be measured to detect and monitor subsurface oil/gas and dispersants, and related technologies for sampling from the sea surface down to 550 meters, including:

  • Fluorometers: EPA document appendix includes a good discussion of hydrocarbon fluorescence. Many companies make sensors to detect different organic compounds, including crude oil. During the CIOERT expedition, the submersible payloads will include a fluorometric sensor package for measuring organic matter, chlorophyll, and oil.
  • ADCP: Acoustic Doppler Current Profiler, similar to what NOAA is using to assess leak rate at the well site; latest generation of current meters gives a three dimensional instanteous view of current speed and direction.
  • LISST particle analysis: Laser In Situ Scattering and Transmissometry (LISST) measures volume concentrations and size spectra of particles using laser diffraction, measuring the intensity of scattered laser light at different angles.
  • Dissolved Oxygen: A DO sensor will be used during the CIOERT expedition, but the Spill Command Center has protocol for determining dissolved oxygen, which involves doing Winkler Titrations in the lab on water samples.
  • CTD (Conductivity, Temperature, and Depth): Standard information that supports all other data collections. Salinity, derived from conductivity data, and temperature provide important clues as to the water mass sampled.
  • Water sampling: The research submersible can collect water samples using various devices. A rosette of water bottles, a rack of bottles that can be tripped from the surface to collect samples at various depths, will also be deployed from the ship.
  • PAH analysis: One type of hydrocarbon found in oil, polycyclic aromatic hydrocarbons are known carcinogens and detected using gas chromatography on lab samples.
  • Rototox toxicity testing: A toxicity assay on sediments or water samples using rotifers. Rotifers are sensitive small invertebrates that occur in the Gulf of Mexico and are important to the food chain. They feed on bacteria and other small pieces of organic matter and, in turn, are fed upon by crustaceans and other organisms. Rototox® is a commercially-available procedure and is specified for the BP dispersant monitoring directive because it is a rapid test that can be performed remotely on a ship. The test exposes rotifers to water collected at different distances from the oil release location. Toxicity is determined by comparing the survival of the rotifers exposed to the offshore samples to survival in clean water.
  • Spectrometry: There are a variety of underwater sensors that use spectrometry to detect a variety of elements in seawater, including hydrocarbon gases and fluids. CIOERT partners FAU and SRI International both have mass spectrometers for this purpose. SRI’s unit will be deployed by the research submersible during the expedition.