Toxic algae and the dam

Wed, Mar 27 2013

Sandra Finnie, a reporter for farmer-oriented Straight Furrow (hardly an ultra-green propaganda sheet!), tried to go fishing on her favourite South Canterbury river recently.

As she reports in the 26 March issue of her newspaper, she couldn’t. The river was full of massive amounts of algae, which she was experienced enough to recognise as cyanobacteria — the toxic blue green algae that kills dogs from time to time along the Tukituki. Of course, she couldn’t fish.

She came back two days later and took samples. These she described to scientists at the Cawthron Institute, NZ’s premium water research outfit.

Cawthron’s senior scientist in the Freshwater Group, John Hayes, said: “Science has found that contrary to what people thought in the past, cyanobacteria is stimulated by nitrogen and deteriorating water quality is central to the cyanobacteria build-up.” He said that cyanobacteria was exacerbated by low flows and farming. He added that if dams didn’t provide ample flushing flows, cyanbacteria would build up even more.

[Note, when do you need the flushing most? At the same time demand is greatest for irrigation takes. Let's ponder who will get the water ... the river or the irrigators?]

Finnie next went to Dr Susie Wood, also at Cawthron, and considered a world authority on cyanobacteria. Pointing to high nitrate levels as the big driver of toxic algae blooms, she said: “Our approach is at the moment we are being reactive but we need to be proactive and look at land use practices. Potentially, this is having big impacts on our fresh water ecosystems.”

[I must note that the HB Regional Council in its wisdom insists that -- even with a many-fold increase in nitrates in the Tukituki projected from intensified farming due to the proposed dam -- the algae problem in the Tuki is attributable only to phosphorus run-off, and hence acceptable nitrate limits can actually be raised and left essentially unregulated. Uh huh!]

Back to Dr Wood, who says: “We now know these toxins can accumulate in aquatic organisms. The next step is look at higher up the food chain because no one else has done this.” She adds that in Canterbury it is only good luck that people have not been seriously harmed, and that many who get sick after swimming in a river probably don’t realise that algae is the cause of their sickness. In that region, 60 dogs have died in the past five years from ingesting toxic algae.

Reporter Finnie then moved on to Dr Dave Kelly, a fresh water quality specialist at Environment Canterbury, who keeps in regular contact with Dr Wood. He agreed with her comments about nitrates and said: “Susie’s research shows that high nitrates are potentially the big driver and it is cause for concern. There is no doubt about it if nitrogen continues to be used. It affects recreational use of rivers and it disflavours fish.”

But, as noted, our Regional Council stubbornly dismisses the need to regulate nitrates.

Why?

Because if they had to impose nitrate mitigation measures (and associated costs) on irrigators who are farming more intensively as a result of the dam, they would render the dam even more economically unattractive, farm by farm, than it already is. Did I say “unattractive’? I meant not financially viable.

So the HB Regional Council says, “Nitrates … no worries … not a problem here.”

Good luck on that one, HBRC. Issues like these need to be examined right here under the watchful and informed eyes of the people of Hawke’s Bay, who, as the ones directly affected, can then decide whether or not to give this project a mandate.

Just one of many reasons why this dam proposal is not ready for prime time. Not ready for a hasty, imprudent call-in by the Environment Minister.

Tom Belford

P.S. Hopefully our District Health Board will speak up on this one! They’re following the nitrate issue … too quietly for our health.
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