Pollution by Mud of Great Barrier Reef Coastal Waters

Abstract

Oceanographic data from the coastal waters of the Great Barrier Reef near Cairns were obtained for two months in the 1997 dry season when river runoff was negligible. A muddy coastal zone was found with suspended sediment concentration reaching 1000 mg/L during trade winds. These high turbidity events are very stressful conditions for coral reefs and were caused by resuspension of sediment by wind waves. In calm weather a nepheloid layer prevailed, extending about 30 km offshore and carrying coastal mud toward offshore coral reefs. In this layer, muddy marine snow with flocs exceeding 1000 µm in diameter was found inshore, while only small flocs < 100 µm were found offshore. Near-surface visibility may have decreased by 50% in the last 70 years. High turbidity appears to be due to man and ultimately threatens the main body of the Great Barrier Reef.