ENVIRONMENTAL
RESULTS
AREA: 3.62 km2
ABOUT THE ZONE
The Boyne River is dammed at Lake Awoonga to provide potable water for the Gladstone area. Large numbers of barramundi are stocked in Lake Awoonga and may be introduced into the Boyne Estuary when the dam overtops. The Boyne Estuary was the site of large-scale mortality of many of these introduced barramundi and other fish in 2011. The lower reach of the Boyne River flows from the dam through predominately agricultural land that has pockets of remnant vegetation. Before entering the south-eastern section of the Mid Harbour Zone the Boyne River flows through the residential communities of Boyne Island and Tannum Sands.
This zone has one water and sediment monitoring site, two fish monitoring sites and one mangrove monitoring sub-zone.
WATER & SEDIMENT
Boyne Estuary received an overall water quality score of 0.70 (B).
Sediment quality of Boyne Estuary was very good with an overall score of 0.99 (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 the Boyne Estuary scored 0.70 and received a good grade (B), a decline 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, Boyne Estuary 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 range. In contrast, a significant decline in the turbidity score between report cards (2022: 0.83, 2023: 0.19) and resulting very poor grade (E), indicate that average turbidity was well above the guideline value for this zone this year.
Within the Nutrient sub-indicator group, total nitrogen (0.45) received a poor grade (D) indicating concentrations for this measure were above guideline values. In contrast, total phosphorus (0.60) and chlorophyll-a (0.52) received satisfactory grades (C), indicating that average concentrations for these measures were within the guideline values.
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, Boyne Estuary received an overall score of 0.99 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, all seven Metal and metalloid sub-indicator measures received very high scores (0.93–1.00) and very good grades (A), indicating that average concentrations were well below the guideline values for this zone.
HABITATS
MANGROVE RESULTS
The overall condition of mangroves in Boyne Estuary was 0.26 (D), indicating a poor condition. While mangrove extent (0.39) was poor both canopy condition (0.19) and shoreline condition (0.19) were very poor.
The score for Boyne Estuary fell from 0.41 in 2018 to 0.26 in 2019. This was largely a result of changes in canopy condition where the score declined from 0.49 in 2018 to 0.19. This may reflect the impacts off decreased rainfall over the reporting year.
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: 0.63, 2023: 0.37) 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: 73 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).