Overall Summary

The 2009 Report Card shows very substantial declines in grades in South East Queensland estuaries and Moreton bay. In Moreton bay, declines were the steepest since monitoring began 10 years ago. Major rain events appear to have transported sediment and nutrients from catchments into coastal streams (which also showed declines in grades), and subsequently into estuaries and the bay. Such large-scale changes highlight the work needed in catchments to protect the bay.

The estuarine and marine component of the Ecosystem Health Monitoring Program (EHMP) has operated for 10 years, producing annual report cards. Grades are calculated by comparing the degree to which monitoring data comply with water quality objectives in the Queensland Water Quality guidelines (2006; minor updates 2007). Current guidelines can be obtained here.

Estuarine ecosystem health

In 2008-09 the ecosystem health of 10 of the 18 estuaries monitored declined, with Cabbage Tree, Oxley, Bremer, Logan and Albert estuaries receiving an F rating. Of the remaining eight estuaries, seven retained the same grades as in 2007-08, and only one estuary, the Caboolture Estuary, improved, increasing in grade from F to D-.

In the Northern sub-region, declines in grades for the Noosa (A- to B+) and Maroochy (C to D) estuaries were associated with the high rainfall over the monitoring period.. The Mooloolah estuary grade remained unchanged with a B rating. All Northern estuaries recorded lower salinities resulting from high freshwater inputs.

The Moreton Bay sub-region is comprised of the Caboolture, Pine, Cabbage Tree, Brisbane, Tingalpa, Eprapah and Oxley estuaries. The Caboolture estuary was the only estuary in SEQ that improved in grade (F to D-). This improvement was due to lower phytoplankton abundance coupled with increases in dissolved oxygen concentrations

The 2009 report card grades resulted in declines for the Pine (C to D+), Cabbage Tree (D to F), Brisbane (D+ to D) and Oxley (D to F) estuaries. These declines were due in most cases to increased phytoplankton blooms, turbidity and reduced dissolved oxygen concentrations, most likely as a result of the sediment and nutrient laden runoff entering waterways during heavy rainfall.

Both the Tingalpa and Eprapah estuary grades remained unchanged from the 2007-08 monitoring period, with both estuaries retaining C ratings. The Eprapah estuary is a very short estuary dominated by excess nutrient loads from large WWTPs. Although grades remained unchanged, the 2008-09 results for the Eprapah estuary revealed an increase in nitrogen and phosphorous concentrations, and decreases in dissolved oxygen concentrations, whilst increases in turbidity were detected in the Tingalpa estuary.

The Southern sub-region consists of the Logan, Albert, Pimpama, Coomera, Nerang, Tallebudgera and Currumbin estuaries. The report card grades for the Logan (D- to F), Coomera (B to B-), Pimpama (C+ to C) and Currumbin (B to B-) estuaries all decreased as a result of the high rainfall received in the southern catchments over the 2008-09 monitoring period.

Despite lower phytoplankton abundance and an increase in dissolved oxygen concentrations, the Albert estuary retained its F rating in 2008-09, with continued high turbidity and nutrient levels throughout the system.

The Nerang (B) and Tallebudgera (B) estuary grades remained unchanged from previous years, with good water quality recorded, despite slight increases in nitrogen concentrations and phytoplankton abundance.

The Bremer estuary is a component of the Western sub-region. In 2008-09, a significant decline in dissolved oxygen concentrations and increases in turbidity, particularly in the lower reaches, meant that it remained as an F rated estuary.

The ecosystem health of Moreton Bay

The overall ecosystem health of Moreton Bay received its lowest rating (D) since the beginning of the EHMP (1999), as a result of deteriorating water quality in the Western and Southern Bays. Seven of the nine bay zones received lower grades than in the previous year, with only the Pumicestone Passage (C to C+) and Eastern Banks (A- to A) improving in grade. Pumicestone Passage improved in all indicators, while excellent water quality continued in the Eastern Banks bay zone.

The report card grades for Southern Bay (C to F) and the Broadwater (B to C-) declined. An extensive sewage nitrogen signal was detected within Southern Bay emerging from the Logan and Albert estuaries, while the water quality of the Broadwater declined as a result of increases in nitrogen and sewage nitrogen concentrations.

The declines in grades for Deception Bay (D to D-), Bramble Bay (C to F) and Waterloo Bay (A to D+) were a result of the influence of high sediment and nutrient discharges from surrounding estuaries. The Deception Bay grade was also affected by a reduction in seagrass depth range at Godwin Beach, indicating deteriorating water clarity.

In the open coastal zone of Moreton Bay, Central Bay (C to D) and Eastern Bay (B to B-) water quality declined as a result of increased phytoplankton abundance, nitrogen concentrations and reduced water clarity.

Abbreviations glossary