Barron Estuary

The area of the Barron estuary reporting zone can be defined by the pre-cleared extent of mangrove and saltmarsh remnant vegetation which is characterised by species that require periodic inundation of sea water. This area extends approximately 10.5 km north and 4.5 km south of the river mouth along the coastline and extends approximately 5.5 km inland. The area includes several tributaries that drain into the Barron River and coastal streams that drain directly into the sea. The assessment area of riparian extent extends further up the river than the mangrove and salt marsh communities to the upper tidal limit and includes vegetation types that are more typical of freshwater environments. Land use within and adjacent to the Barron estuary area is dominated by urban development. The northern beach suburbs of Machans Beach, Yorkeys Knob and Holloways beach, and the Cairns suburbs of Aeroglen, Cairns North and Whitfield overlay the estuary area. Industries within the estuary area include the Cairns international and domestic airport, quarries, aquaculture and sugarcane.

Scroll down for further detailed results for each indicator group.

Grading

gradesa1

very good

gradesb1

good

gradesc1

moderate

gradesd1

poor

gradese1

very poor

insufficient data

Confidence surrounding the data used in the circle diagrams has been assessed using a multi-criteria framework.

confidence

Water quality

Hover over each segment for indicator scores and data confidence.

The overall water quality grade in 2015-16 for the Barron estuary is ‘moderate’.

Water quality grades are based on aquatic ecosystem guidelines for protection of estuarine waters, and are not based on load reduction targets for the marine environment. The results are derived from a transect of five monitoring sites in the channel of the Barron River.

The physical and chemical score of 90.0 (‘very good’) is comprised of dissolved oxygen (DO) and turbidity scores of 90.0 (‘very good’) meaning the annual medians and at least 80% of the monthly medians for DO concentrations and turbidity comply with guideline values.

Nutrients scored 54.2 (‘moderate’) in the Barron estuary, comprising of a DIN (dissolved inorganic nitrogen) score of 53.5 (‘moderate’) and FRP (filterable reactive phosphorus) score of 54.8 (‘moderate’).

The chlorophyll a score in the Barron estuary is 8.8 (‘very poor’).

Pesticides are not monitored in the Barron estuary therefore a score and grade cannot be provided

Compared to 2014-15 the water quality index for the Barron estuary declined from ‘good’ to ‘moderate.

The decline was primarily due to a substantial decrease of the chlorophyll a score from 49.33 to 8.75. The high concentrations of chlorophyll a in the Barron estuary during 2015-16, which exceeded guideline values may be related to the lower than average river flows, and availability of nutrients for primary production. Low river flows can contribute towards higher chlorophyll a concentrations especially during warm periods when nutrients are available for algal growth.

Habitat and hydrology

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The overall habitat and hydrology grade for the Barron estuary is ‘moderate’.

The mangrove and saltmarsh extent scored 39.9 (‘poor’) with 31.1% loss from pre-clear to 2013. Riparian extent is assessed to the upper tidal limit of the river which extends upstream of the estuary area that is characterised by mangroves and saltmarsh. The riparian extent scored 22.7 (‘poor’) with 48.3% loss from pre-clear to 2013.

These results reflect the high level of development within the estuary area. The low mangrove and saltmarsh extent and riparian extent scores for the Barron are mostly the result of historic extensive clearing activity. More recently mangrove communities in the Barron estuary have been effectively managed to ensure there has been no major new clearing and to allow for some revegetation.

For estuary fish barriers, the Barron estuary scored 61 (‘good’) and is graded ‘good’ for barrier density, ‘poor’ for percentage of stream length to the first barrier, and has an absence of low passability barriers (graded ‘very good’).

Estuary riparian extent, mangrove and saltmarsh extent and estuary fish barriers are updated every four years. The data for riparian extent, mangrove and saltmarsh extent is to be updated in 2018.

The method for the flow indicator is currently under development and will be available for future report cards.

Fish

Hover over each segment for indicator scores and data confidence.

The fish index is currently under development and will be available in future report cards.

Further information on the methods used to produce the scores and grades and detailed results can be found here.