Scientists have tested a breakthrough in sensing sediment risks to reefs that uses bundles of fibre optic sensors and hundreds of countersunk holes to mimic coral.

Sedimentation is considered one of the most widespread causes of stress on coral reefs, and researchers are working to understand the patterns of suspension and resuspension caused by wind, wave, catchment run-off and dredging related activity to better inform about the environmental risks.

The newly designed sediment sensor, has 15 separate fibre optic bundles that produce three separate measurements, each an average of five bundles, and the three-millimetre-thick plate is perforated with hundreds of countersunk apertures, the size and spacing designed to mimic coral. The shape allows sediment to be naturally resuspended by wave action in a similar way to that which would occur on a coral.

(Whinney J, Jones R, Duckworth A, Ridd P (Dec 2016) Continuous in situ monitoring of sediment deposition in shallow benthic environments Coral Reefs DOI 10.1007/s00338-016-1536-7)

The sensor was tested as part of a Western Australian Marine Science Institution Dredging Science Node project against different conditions in the Australian Institute of Marine Science (AIMS) National Sea Simulator (SeaSim) laboratory and in the highly turbid inshore reef community of the Great Barrier Reef (GBR).

Researchers from James Cook University and AIMS were able to show previously undescribed patterns of sediment deposits on reef in the turbid coastal central GBR over periods of a few hours rather than averages over days or weeks, giving a greater understanding of the behaviour of one of the key pollutants on coral reefs.

“The in-situ deployment covered a range of physical conditions with peaks in sedimentation occurring after peaks in turbidity and waves when material began to settle out of suspension,” lead researcher, Dr James Whinney said. “The daily average sediment deposition rate was 19 ± 15 mg cm-2 d-1 over the deployment.”

“However, while Sedpods offer a low cost alternative to measure rates of sedimentation, they do not self clean and need to be changed over each day which involves the logistical and financial costs of daily boating and diving to collect and redeploy.

“The next stage is to carry out testing further offshore as well as during dredging campaigns to define the range of sediments rates corals are likely to experience,” ” Dr Whinney said.

Earlier versions of the deposition sensor used in this study have been deployed in Japan, Papua New Guinea and the inshore central GBR (Thomas et al. 2003a; Thomas and Ridd 2005).

 

 

Whinney J, Jones R, Duckworth A, Ridd P (Dec 2016) Continuous in situ monitoring of sediment deposition in shallow benthic environments Coral Reefs DOI 10.1007/s00338-016-1536-7

 

The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside, Chevron and BHP as environmental offsets. A further $9.5 million has been co-invested by the WAMSI Joint Venture partners, adding significantly more value to this initial industry investment. The node is also supported through critical data provided by Chevron, Woodside and Rio Tinto Iron Ore.

Dredging Science