Terrestrial contaminants 2011

Reef Plan is a decadal commitment (2003-2013) by Australian and Queensland Governments to halt and reverse the decline of water quality entering the receiving waters of the Great Barrier Reef.

While the investment in Reef Plan confirms concern about the loads of land-derived pollutants (sediments, nutrients, pesticides) that can be measured at the ends of major rivers draining catchments affected by human activity, there is insufficient knowledge about what happens to the organic (non-sediment) materials after they are discharged to the GBR Lagoon.

The possible routes are wide and complex. The most useful elements will be assimilated quickly into marine food chains and may be (1) recycled, (2) buried in seabed sediments, or (3) released to the atmosphere. The spatial footprints of these processes will depend on physical processes like temperature and those (winds, waves, currents) affecting transport.

The GBR is a complex domain covering 210,000 km2 where almost every bio-physical variable is confounded. To cover this variability, AIMS has been conducting systematic surveys of regional patterns and processes during different seasonal conditions using its research vessels.

In 2010-11, the WQEH team concluded its study of the southern-central section of the GBR. This is an area where the broadening of the continental shelf produces a wide coastal lagoon but with strong tidal mixing. By following the degradation of organic biomarkers, the study concluded that terrestrial exports were moved offshore quickly with little storage of organic materials in the lagoon or reef sediments.

The importance of flushing in this rapid cross-shelf transport was confirmed by tracking persistent contaminants such as coal dust from a coastal loading facility, which was traced from the coast to the edge of the continental shelf.