How much light should reach the sea floor? Using benthic light as a water quality indicator

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Benthic photosynthetically active radiation (bPAR¸ light that reaches the sea floor), is critical to the health of coastal marine environments including coral reefs and seagrasses, and may serve as an effective indicator for water quality. A new remote sensing model for benthic light has now been specifically developed for the Great Barrier Reef by researchers working under a Tropical Water Quality Hub project, through PhD student Marites Canto at JCU, Dr Barbara Robson and Dr Katharina Fabricius at the Australian Institute of Marine Science, and Dr Lachlan McKinna from NASA. The model, described in a journal article recently published in Optics Express, combines sea surface sunlight levels obtained from satellite, high resolution seafloor bathymetry data, optical properties of the seafloor, and the optical properties specific to each 1 km x 1 km pixel and each day of the water in the Great Barrier Reef. The model has been tested at four sites with contrasting water quality, and was found to have strong agreement, small bias and low mean absolute error.  This provides researchers with precise information about benthic light levels for each location and each cloudless day for the whole Great Barrier Reef since January 2002. Early field demonstrations of the model in a small test region in the central Great Barrier Reef reveal major changes in bPAR over the 16-years observation period in this region. The model may also be useful for other coastal areas, provided the necessary spectral IOP and bathymetry data are available.

 

Photo: © Aims / Sam Noonan