Didymo Experimental Site, Otiake. 
Graeme Hughes.

A portable six channel, flume system has been set up near the confluence of a spring fed stream and a side stream of the Waitaki River near the Otiake River.  Planned experiments by New Zealand’s National Institute of Water and Atmospheric Research, Environment Canada with assistance from Fish and Game New Zealand, have just begun with the artificial substrates growing didymo supplied by  pumped didymo affected Waitaki River water.

Didymosphenia geminata has now been recorded in over 60 rivers in the South Island. In some spring fed tributaries, which should have been affected by the algae due to their close proximity to didymo affected water, or animal or human contamination, didymo refuses to grow. This led to earlier experiments which indicated that when actively growing didymo was introduced to water sourced from these springs the growth of didymo declined.  Despite the obvious affect on algal growth, due to the differing water chemistry of the individual springs, no consistent causative factor could be identified.

The research just begun is designed to demonstrate that there is a factor in spring water that inhibits the growth of didymo, and that the effect of this factor is concentration dependent. When didymo has been established in the 6 flumes a range of concentrations of spring fed water will be introduced to the flumes. After a period samples of didymo will be checked for cell viability, cell counts, biomass and algal composition. The expectation is that there is something in or something missing from spring water that inhibits the growth of didymo.  Depending on the results of the first experiments a second trial will test a hypothesis that a lack of dissolved organic material in ground waters is unfavourable for didymo.

The experiments are expected to continue for approximately 8 to 12 weeks and the results of the experiments will be presented in a report to Fish and Game New Zealand by 30th June 2009.

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