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Lower than average rainfall has slowed the amount of mud flowing downstream to Moreton Bay, but has left upstream catchments in poor condition.
Moreton Bay conditions have improved and seagrass beds are now flourishing in several sections of the bay, as reported in November 2018 by Brisbane Times.
However the upper Brisbane catchment - from Brisbane's western suburbs towards Ipswich - has again declined and remains in a poor condition.
About 80 per cent of the sediment flowing into Moreton Bay originates in agricultural areas upstream in the Lockyer Valley.
Port of Brisbane environment manager Craig Wilson in November 2018 said between 300,000 and 350,000 cubic metres of sediment flowed downstream.
That increased to more than 1 million cubic metres per year in the flood years: 2011, 2012, 2013 and 2014.
The 2019 Healthy Land and Water report card – an annual check on the health of Greater Brisbane’s rivers and streams – shows mud has shifted to the deepest parts of the bay and declined overall throughout Moreton Bay.
The report rates the environmental conditions of south-east Queensland’s waterways from A (excellent) to F (very poor).
Australian Rivers Institute director Professor Stuart Bunn said the 2019 outcome was much-improved Moreton Bay water quality with good, healthy seagrass beds.
“This highlights the resilience of Moreton Bay to recover from land-based pollution, so long as the bay has respite from these pressures,” Professor Bunn said.
“We are excited to see that seagrass has returned to the most degraded parts of Moreton Bay.”
“There has been significant recovery of seagrass meadows in Southern Deception Bay, which were lost entirely in 1996.
“In addition, seagrass meadows in Bramble Bay, which have not been seen since the 1950s, are also recovering,” Professor Bunn said.
Brisbane’s rainfall has decreased from 1266mm in 2015 at Brisbane Airport to 847mm in 2018 and 456mm in 2019 until October 22.
Healthy Land and Water board chairman Stephen Robertson repeated the message that planners needed to invest to reduce sediment, not rely on reduced rainfall.
“Despite the improvement of mud in Moreton Bay, without further investment in reducing sediment pollution, our waterways will continue to deteriorate, along with the many environmental, social and economic benefits they provide.”
South-east Queensland’s 2019 waterway health
Eastern Moreton Bay is rated A, has improved and is in excellent condition. Seagrass has been found at Crab Island and Pelican Banks.
Western Moreton Bay is rated A-minus. It includes Bramble Bay, Deception Bay and Waterloo bays.
There is a big seagrass meadow in Southern Deception Bay and a new seagrass bed in northern Bramble Bay.
It has improved slightly from good to excellent condition for the first time since the new monitoring program began in 2015.
Southern Moreton Bay is rated B-plus. The water quality is still very good, but is still impacted by flushing of the Logan River from Cyclone Debbie in 2013.
Gold and Sunshine coasts
Gold Coast Broadwater is rated A and is in excellent condition.
Noosa River catchment has improved, is in excellent condition and rated A-minus. Nitrogen levels have dropped in this catchment.
Brisbane and Ipswich
Lower Brisbane – towards the Port of Brisbane – is rated C-minus. It has improved from poor to fair for the first time since 2016.
The Mid-Brisbane Catchment – around the Brisbane CBD - is in a fair condition and is rated C-plus.
However, fish health has declined and the extent of stream bank vegetation remains poor.
Ipswich’s Bremer River catchment is in poor condition and is rated D-minus.
The freshwater health continues to decline, however the overall estuary conditions improved slightly from poor to good.
The extent of phosphorus in the river waters increased and the water is saltier.
The upper Brisbane and Lockyer catchments lies in the driest part of the catchment, essentially west of the Brisbane CBD out towards Gatton and the Lockyer Valley.
They are both rated D and are in poor condition.
Both these catchments declined, despite reduced pollutant loads and reduced nutrients in the water.
Laidley Creek ran dry in 2018-19 for the first time since 2016, the report shows.
The amount of nutrients in the water declined significantly from 213 kilograms per hectare to 19 kilograms per hectare.
However, all indicators in the 2019 Healthy Land and Water report show the Upper Brisbane and Lockyer catchment reducing.
“Freshwater health has declined and remains in very poor condition due to a decrease across all indicators, particularly fish communities and bug health,” the report summary shows.