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Southern Cross GeoScience

July news items

Impact of acid sulfate soil runoff on mangrove sediment geochemistry

Researchers from Southern Cross GeoScience are investigating the long term effects of acid sulfate soil runoff on the geochemistry of downstream mangrove sediments.

Dr Bree Morgan and Assoc.Prof. Scott Johnston sampling porewaters and mangrove sediments.

Dr Bree Morgan and Assoc.Prof. Scott Johnston sampling porewaters and mangrove sediments.

The site under investigation is a small estuarine tributary in the Hastings River, on the mid-North Coast of NSW. Between 1987 and 2004, the tributary received regular episodes of acute acid sulfate soil run-off from a large upstream wetland, which had been extensively drained.

During this period, downstream intertidal mangrove sediments were periodically subject to acid and trace element-rich runoff and were visibly stained in iron(III) precipitates.

The study is comparing the site to an adjacent estuarine tributary that has not received any acid sulfate soil runoff.

Big differences are emerging in iron and sulfur geochemistry and in the abundance and partitioning of both trace elements and rare earth elements. In particular, the site receiving acid sulfate soil runoff is very rich in reactive iron-phases (see photo below).

Visually contrasting sediments (a) mangrove site affected by acid sulfate soil run-off and (b) unaffected mangrove site.

Visually contrasting sediments (a) mangrove site affected by acid sulfate soil run-off and (b) unaffected mangrove site.

There are plans to investigate trace element accumulation in mangrove tissues at the same sites, using the new LA-ICPMS facility. Researchers will use the new analytical device to look for a possible geochemical signature that may have been recorded in the tree tissues during the period of acid runoff.

Collecting intact cores from mangrove trees for trace element analysis.

Collecting intact cores from mangrove trees for trace element analysis.

The project involves Assoc. Prof. Scott Johnston, Assoc. Prof Ed Burton, former SCGS student Dr Bree Morgan, Research Technician Roz Hagan and Dr Renaud Joannes-Boyau.

For further information contact Assoc. Prof. Scott Johnston scott.johnston@scu.edu.au

Updated: 03 February 2014