ENVIRONMENTAL
RESULTS
AREA: 9.45 km2
ABOUT THE ZONE
South Trees Inlet is a mangrove and salt pan-lined tidal inlet that flows into the Mid Harbour Zone. The zone contains one monitored seagrass meadow which sits just off the northern tip of South Trees Island. At 10.9ha it is the second smallest of the monitored meadows. The area contains a large number of industrial developments, including South Trees Wharf on South Trees Island at the inlet’s mouth, Queensland Alumina Ltd to the west of the inlet, and Boyne Smelters to the south-west of the inlet. The South Trees Industrial Estate is located next to Wapentake Creek which flows into the western side of the inlet just south of South Trees Island.
This zone has six water and sediment monitoring sites, three monitored seagrass meadows, three fish monitoring sites and one mangrove monitoring sub-zone.
WATER & SEDIMENT
South Trees Inlet received an overall water quality score of 0.85 (B).
Sediment quality of South Trees Inlet was very good with an overall score of 0.97 (A).
The following graphs compare the Water and Sediment scores reported for 2023 (top line) to those from the previous year.
WATER
SEDIMENT
Very good (0.85-1.00)
Poor (0.25-0.49)
Good (0.65-0.84)
Satisfactory (0.5-0.64)
Very Poor (0.00-0.24)
No data available
Overall, Water quality in South Trees Inlet scored 0.85 and received a very good grade (A), an improvement from the 2022 report card. This score was calculated by aggregating the three sub-indicator and associated measure scores (Physiochemical – pH and turbidity, Nutrients – total nitrogen, total phosphorus and dissolved metals, and dissolved metals – aluminum, copper, lead, manganese, nickel and zinc).
Within the Physiochemical sub-indicator, South Trees Inlet received a score of 1.00 and a very good grade (A) for pH indicating that the average pH was well below the guideline value. This zone received a score of 0.75 and a good grade (B) for turbidity indicating that average turbidity was below the guideline value.
Within the Nutrient sub-indicator group, total nitrogen (0.65) and total phosphorus (0.82) received good grades (B) indicating concentrations for this measure were below guideline values. In contrast, chlorophyll-a (0.56) received a satisfactory grade (C), indicating that average concentrations for these measures were within the guideline value.
All six Dissolved metals received high scores (1.00) and very good grades (A) indicating that average concentrations were well below the water quality guideline values.
For Sediment quality, South Trees Inlet received an overall score of 0.96 and a very good grade (A), also a similar result to the previous year. This score was calculated by aggregating one sub-indicator and associated measure scores (Metal and metalloids – arsenic, cadmium, copper, lead, mercury, nickel and zinc).
In 2023, six of the seven Metal and metalloid sub-indicator measures received very high scores (0.91–1.00) and very good grades (A), while one measure – arsenic – received a score of 0.81 and a good grade (B). These results reflect that all concentrations were below the guideline values.
HABITATS
SEAGRASS (MEADOW 60)
This zone has one monitored meadow which sits off the northern tip of South Trees Island. Meadow 60 is an intertidal meadow and the second smallest of the monitored meadows.
Compared to the previous year, the South Trees Inlet received a lower overall score (2022: 1.00, 2023: 0.81) and a downgrade to good grade (B) from the very good grade (A). This was due to a lower biomass score (2022: 1.00, 2023: 0.81). Area and species composition scores remained the same (1.00).
MANGROVE RESULTS
No mangrove assessment was conducted in 0223, results are from monitoring conducted in 2019. The overall score was 0.60 indicating a satisfactory condition for mangroves. Canopy condition (0.50) and shoreline condition (0.51) were satisfactory. Mangrove extent (0.79) received a good score, a result of a net gain in relative mangrove area. However, it is important to note that the health of mangroves is being measured from a 2013-14 baseline and considerable clearing and habitat modification has occurred in these areas in the past.
FISH & CRABS
FISH RECRUITMENT RESULTS
Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream Acanthopagrus pacificus. The overall score for 2023 was lower than the previous year (2022: 0.53, 2023: 0.31) and declined one grade to
poor (D). This decline in score is a result of a decrease in number of bream caught during the 2022–23 reporting period
(2022 report card: 90 fish, 2023 report card: 41 fish).
Fish health is assessed though two sub-indicators, Fish condition and Fish Health Assessment Index (HAI).
The overall score for Fish health in 2023 was 0.81 and received a good grade (B). The 2023 results were calculated by the average of the Fish HAI score (0.90; results carried over from 2021) and new assessment of Fish condition which scored similar to the previous year (2022: 0.74, 2023: 0.73).