Bramble Bay was graded “F” in the 2009 Report Card, indicating a considerable deterioration in ecosystem health from the previous reporting period (“C”).  Water quality was poor with nutrient increases and other indicators likely affected by episodic flushing of the Brisbane River after heavy rainfall events.  Compliance with all EHI (water quality) indicators decreased throughout the Bay with the major changes being enhanced nutrient (TN) and sewage nitrogen (δ¹⁵N) concentrations although phytoplankton abundance also increased considerably.

In the past, the sewage nitrogen signal (sewage plume mapping) in the Bramble Bay zone has decreased considerably since the upgrade to the Luggage Point WWTP in 2001.  For example, in 2003 there was only 53% compliance with QWQ objectives for δ¹⁵N; however, in 2007/2008 the bay was fully compliant.  The heavy rainfall events in 2008/2009 and subsequent discharges from the estuaries flowing into Bramble Bay have likely caused the drop in compliance for this reporting period (42%).

Abbreviations glossary | Indicators and methods

ECOSYSTEM HEALTH INDEX (EHI)

The EHI is a measure of the proportion of a reporting zone that complied with the water quality objectives for key indicators monitored as part of the Ecosystem Health Monitoring Program. The water quality objectives are defined in the South East Queensland Regional Water Quality Management Strategy (2001).

• EHI 1 = 100% of area complies with the environmental objectives.
• EHI 0 = 0% of the area complies with the environmental objectives.

BIOLOGICAL HEALTH RATING (BHR)

The BHR forms 20% of the the Report Card Grade. The values in this sheets are calculated using the original method used since 2002-03 and is presented for comparison.