Divers retrieve oxide deposits for study

Project involving Lough Derg Science Group

Divers with Lough Derg Sub Aqua Club retrieved several iron oxide deposits from the Shannon last Wednesday as part of a scientific study.

The thunder had passed earlier in the afternoon; it was still, warm and humid. Eight divers arrived and got kitted up alongside their RIB at the quayside in Portumna.

All were looking forward to the dive in the much cooler river. Tom Shaw, chairman of the Lough Derg SAC, addressed the group after the checking of equipment and personnel.

This dive was to be different. It was a project with the Lough Derg Science Group, who have been studying the Shannon environment over some decades.

The plan was to collect samples of an iron oxide deposit that looks like a miniature cow-pat in an area where the Asian clam had become abundant. The deposits are formed by bacteria oxidising mainly iron and manganese from of the passing water, most often forming a firm rind about a pebble. Only a few of the larger specimens were needed to study their formation and composition. The rest will be returned.

This is a scientific study on how these impact the riverbed habitat and the presence of invasive clams and mussels.

Soon the tanks were slung onto the shoulders of the eight divers. All alighted the RIB facing each other sitting on the pontoons. The powerful outboard started up and the expedition was on its way. Arriving on site, pairs of divers rolled back off the inflated pontoons to enter the water, then to descend to begin the search over the stony river bed at a depth of 4 to 9m.

On surfacing, evidence of such deposits was handed over. Some stones up to the size of a sliotar had an encircling dark brown to black crust of just a few centimetres.

One piece was a flat disc over ten centimetres that is now planned for sectioning and will be sent to North America in a collaboration with a geologist specialising in such deposits. He plans to undertake, with CT-scanning equipment, the elements in the sample and hopefully the possibility that the disc could be aged.

At the dive end there was a brief run of the outboard back to the quayside. With the dive ending, the suits were stripped off and the gear checked and gathered. It was a dive that successfully obtained a few nice pieces. There was a smile on each face.

Lough Derg SAC would like to thank Madden's Marina, Portland, Lorrha, for facilitating our boat launch.