No impact from dredging

Latest water quality test results for Port Curtis show no evidence that dredging is having any impact on water quality, nor any link between water quality and fish health.

The Department of Environment and Resource Management today released a report on water quality sampling carried out in November and December 2011.

Director General Jim Reeves said dissolved metal concentrations were lower in October, November and December compared with the initial samples taken in September.

"The tests were unable to detect dissolved cadmium, chromium, silver and thallium," Mr Reeves said.

"The only metals to exceed water quality guideline trigger values in December samplings were dissolved copper at four of 19 sites and dissolved aluminium at two sites.

"The detection of copper in the Gladstone marina may be related to general marine activities, as copper is a component of antifouling paints.

"However, the number of sites where dissolved copper was detected was the lowest recorded in this investigation program since September 2011.

"The number of sites where dissolved aluminium was detected in December was substantially lower than the previous sampling in November but similar to September and October.

"Varying levels of dissolved aluminium have been found in a number of sites including reference sites over the four months of sampling.

"Natural variations in metals at the levels reported in Gladstone are quite common especially following flood events or when there is high natural mineralisation.

"The latest results also found turbidity has varied over the four months of sampling and also across Gladstone waterways.

"For example, we had very low turbidity at Boat Creek in December where we recorded very high turbidity in November.

"This indicates that turbidity naturally rises and falls in some areas within Port Curtis.

"As you would expect in summer, water temperatures continued to increase which meant that dissolved oxygen concentrations also fell slightly.

"However, dissolved oxygen levels were always more than 70 per cent saturation and these are unlikely to have caused distress to fish.

"The December water samples also found pH levels in all waterways continue to be slightly alkaline which is not unusual.

"We did find nutrient concentrations increased over much of Port Curtis, in particular an increase in total nitrogen. 

"The major component of this increase is organic nitrogen which could be the result of run-off from catchments following increased rain in December," Mr Reeves said. 

The full report is on the DERM website .

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