The area of the Trinity Inlet 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 14 km inland south of the inlet’s mouth and is approximately 8 km in width. It includes numerous tributaries that drain into Trinity Inlet.

Land use within and adjacent to the Trinity estuary area includes residential, industrial and commercial developments associated with the central business district of Cairns.

Trinity inlet includes the Port of Cairns which is a multi-purpose port that caters for bulk cargo cruise shipping, fishing vessels and reef passenger vessels. Land use adjacent to the smaller upstream tributaries is dominated by cropping (sugarcane) with some residential development.

The Trinity Inlet estuary grade remained ‘good’ in 2021-22 and the score remained 64.

The diagram below shows the detailed results for each indicator by year. Click on the timeslider to see data from previous years.

 

WATER QUALITY

Trinity Inlet estuary water quality remained ‘good’ and the score of 73 was unchanged since the previous year.

Dissolved oxygen (low) improved from ‘poor’ to ‘moderate’ and the score increased from 31 to 42, with monthly median values sometimes meeting guideline values. Chlorophyll a remained ‘good’ with monthly median values often meeting guideline values.

Nutrients (dissolved inorganic nitrogen (DIN) and filterable reactive phosphorus (FRP)) and turbidity all remained ‘very good’, with monthly median values mostly meeting guideline values.

More information on the water quality results, including the very poor grade for dissolved oxygen are provided in the results technical report.

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 eight monitoring sites in the channel of Trinity Inlet.

Pesticides are not monitored in the Trinity Inlet estuary therefore a score and grade cannot be provided.

HABITAT AND HYDROLOGY

The habitat and hydrology index is comprised of seagrass, which is assessed annually, and three longer-term indicator categories that are updated every four years: mangrove and saltmarsh (extent and shoreline habitat updated in 2021-22), riparian extent (updated in 2021-22) and fish barriers (date of next update to be confirmed). The habitat and hydrology score declined from 57 in 2020-21 to 54, and the grade remained ‘moderate’.

Mangrove and saltmarsh scored 60 (‘moderate’). Shoreline mangrove habitat scored 67 (‘good’), whilst mangrove and saltmarsh extent scored 53 (‘moderate’) with 21 per cent loss from pre-clear to 2019. Riparian extent scored 58 (‘moderate’) with 16 per cent loss from pre-clear to 2019. There was no change to mangrove and saltmarsh extent and riparian extent between the previous assessment for 2017 and the updated assessment for 2019.

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

Estuary fish barriers for Trinity Inlet scored 61 (‘good’) and were graded ‘moderate’ for barrier density, ‘moderate’ for percentage of stream length to the first barrier, with an absence of low passability barriers (graded ‘very good’).

The seagrass at Trinity Inlet declined from ‘moderate’ to ‘poor’ and the score decreased from 42 to 38 since 2020-21. The small meadows within Trinity Inlet consist of pioneering, ephemeral species and have been highly variable during the life of the monitoring program. Positive and negative change in condition scores between years is not unexpected.

The flow indicator could not be assessed for the Trinity Inlet estuary due to the lack of pre-development modelled flow, which is required for the analysis.

FISH

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

See detailed reports for further information on the methods used to produce the scores and grades and detailed results