Status of eutrophication in the Great Barrier Reef lagoon

Abstract

Historical data on the levels of nutrients and phytoplankton in the GBR lagoon are reviewed. The results indicate that background levels of P-PO 4 and phytoplankton have increased significantly over the past 50–60 years and that the levels appear be at or above the eutrophication threshold level for coral reef waters. Other data indicate that river discharge probably has a major impact on the nutrient status of the GBR lagoon, but other factors such the nitrogen-fixing blue-green alga, Trichodesmium, could also be important. Trichodesmium has the ability to introduce large amounts of new nitrogen and it appears that the increased phosphorus levels could be driving its growth. To-date little effort has been made to assess the impact of eutrophication on the coral reef communities. Because the background nutrient levels are relatively high both run-off and sewage discharges could have serious impacts on nearby coral reef communities. Tertiary treatment (i.e. nutrient removal) of sewage should be required for all discharges in the vicinity of coral reefs and special precautions need to be exercised when designing run-off drainage systems.