The barramundi are excited by the amount of feed washed out.
The barramundi are excited by the amount of feed washed out.

Excessive sediment from floods hit region's oceans hard

THE rain just keeps coming and it's not only the commercial and recreational fishers counting the costs.

Fishing charters have been doing it tough too as the rain has kept most clients off the water, or the seas have been too extreme to go anywhere except the rivers, creeks, estuaries or inland waterways.

The fresh flush does clean out the rivers, creeks and estuaries but the nutrient surge can cause further long-term problems.

Scientist and aquatic animal expert Ben Diggles, of DigsFish Services, said there were some short-term benefits but it was the long-term problems associated with the floods that were of concern.

Asked whether the extra nutrients washed into the ocean were a good thing, Dr Diggles said: "No, there is already an excess of background nutrients in most estuarine and inshore locations nowadays due to dumping of sewage and run-off from farmland.

"Excessive nutrients promotes algal blooms (such as lyngbya), algal overgrowth of seagrasses and corals, and the sediments that come with floodwaters these days.

"That represents a 10 to 20 fold increase over historical background levels of natural sediment input that occurred during rainfall events prior to European settlement," he said.

"Today's excessive sediment load is due to widespread clearing of river catchments for crops and cattle and destruction of riparian vegetation.

"The extra sediments also damage oyster reefs and coral reefs, so damaging the very structure of inshore ecosystems that evolved over a very long time to be adapted to relatively low sediment/nutrient loads.

"This also does not even consider the pollutants that are now bought down - mine waste being one example."

Dr Diggles said the only species to benefit from modern floods were prawns, which could feed on microbes suspended in sediments, and species such as barra which could access nursery areas or parts of rivers that they were usually excluded from by barriers to migrations such as weirs.



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