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Flood damage to Great Barrier Reef minimal, water quality report finds

By Tom Major, Wednesday July 29, 2020 - 08:42 EST
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While inshore coral suffered from poor water quality, recovering offshore reefs were better placed and continue to improve their coverage, the report found. - Audience submitted

North Queensland's coastal and offshore ecosystems fared better than expected during last year's devastating Townsville floods, a study has found.

The 2018-19 report card released by the Dry Tropics Partnership for Healthy Waters rated water quality in moderate (C) to very good (A) categories.

Independent chair of the partnership Diane Tarte said water on the offshore Great Barrier Reef scored an A for very good, with low concentrations of suspended sediment.

"Interestingly the flood didn't seem to hang around for a long time, as has been experienced in other floods on the Great Barrier Reef," she said.

"Data we've got for coral cover in the mid-shelf, outer-shelf areas off Townsville is showing good juvenile coral growing."

Many North Queensland region reefs were impacted by severe coral bleaching in 2016 and 2017, followed by infestations.

Inshore areas suffer

The report found high levels of nutrients in waterways including the Bohle and Black rivers, resulting in low to moderate water quality scores for Halifax and Cleveland bays.

"We do have real concern about the level of nutrients, nitrogen and particular, in those waterways," Ms Tarte said.

Seagrass meadows in Cleveland Bay, a major food source for the endangered dugong, experienced a decline in biomass.

But the report found that seagrass coverage remained above the long-term average.

"In fact, monitoring shows the bulk of the immediate impact seemed to flush out of the system in five days," Ms Tarte said.

"Within about a month to two months that immediate impact had settled back to normal background conditions.

"All the seagrass meadows survived the flood — however, they have been knocked about, and overall condition is less than what we expected."

Changes noticed

Adrenalin Dive owner Paul Crocombe said inshore reefs and wrecks could be affected by freshwater runoff.

"Certainly close to the coast, near Magnetic Island and at the wreck of the Yongala, visibility did drop," he said.

"That impacts the corals by reducing the light the corals get."

After decades of diving and snorkelling the reef, Mr Crocombe said he found the impact of cyclones was most devastating to coral.

"I think the main damage to the reefs was from cyclones, not freshwater runoff from the coast," he said.

"On the outside of the Great Barrier Reef there's a lot of rejuvenation — new corals, small coral clusters there.

"Those reefs seem to be recovering pretty well."

More data needed

The Dry Tropics Partnership, made up of stakeholders from industry, scientific research groups, and government, is in its second year of reporting.

Ms Tarte said another two years of funding was locked in, but five continuous years of reporting was required to reveal water quality trends.

"It depends whether it's a wet year or a dry year, you've got to filter out the natural variability in the system when you're looking for trends," she said.

"We're looking to improve our inclusion of some citizen science data and extend our knowledge to do some more monitoring.

"Already Townsville City Council and the Port of Townsville are looking at putting in more gross pollutant traps in to capture litter from our catchments."


© ABC 2020

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