Nutrients
Sources for nutrients into the Great Barrier Reef system include river discharges, urban run-off, atmospheric input, nitrogen fixation by marine organisms, deeps ocean supply from upwellings, deposition of dust from storms and wind, and resuspension of nearshore sediments.
Nutrients from land-based run-off are considered one of the greatest threats to the Reef ecosystem. Once dissolved inorganic nutrients enter the marine system, they are taken up by phytoplankton, bacteria and seafloor plants such as macroalgae and seagrasses.