The Brisbane estuary received a “D+” in the 2008 Report Card but in 2009 this dropped to a “D”.  This small reduction in grade was due to a combination of factors with the major ones being a decrease in compliance for turbidity (7% in 2008/2009 compared to 14% in 2008/2007) and a reduction in BHR in relation to sewage nitrogen (δ¹⁵N).

The Brisbane River estuary continued to be non-compliant for TP and only 6% compliant for TN.  DO compliance also continued to be low (30% compared with 34% the previous year).  Relative to other indicators, Chl-a continued to be mostly within QWQ objectives (88% compared to 86% the previous year) but this is likely because the low water clarity associated with high turbidity often limited phytoplankton growth.

The poorest water quality in the Brisbane estuary was found in the middle to upstream reaches with the nutrient and turbidity concentrations peaking around 50 – 70km from the mouth near Goodna, Wacol and Moggill.  There are three WWTPs and numerous small creeks that deliver both nutrients and sediments to these reaches and water quality is further compounded by the long residence times (poor flushing) in the same reaches.  Additionally, this part of the middle-to-upper estuary is where the low salinity zone (< 10 psu) occurs and flocculation of suspended sediments further exacerbates turbidity.  However, median TP concentrations throughout all except the upper reaches of the Brisbane estuary were the lowest recorded since the inception of the EHMP, likely because of upgrades to WWTP including the recent operation of 3 Advanced Wastewater Treatment Plants (AWTP).

Overall, 32% of the total Brisbane estuary contains unmodified riparian habitat with most of that found in the intertidal zones upstream of the city reaches.

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 Partnership's Scientific Expert Panel has endorsed a change to the BHR in 2006-07 which increase the BHR from 20% to 30% of the Report Card Grade.

The reason for the change is the implementation of the Riparian Assessment Program (RAP) which will comprise 15% of the total grade (half of the BHR). The other BHR indicators will make up the last 15%

The data from the riparian assessment is available as PDF document.