Gerry Eckhoff: Realities of the Toxic Willow

When the political fog descends and obfuscates an issue such as water quality, the truth and clarity can remain hard to find. It is as though the authorities have decided that no further available evidence or action is required - so the fog remains.

Rural NZ has been found guilty of being the main cause of water pollution. The debate has been closed and laid at the feet of fertilizer and livestock. Yes, nitrates are a real issue especially where tile drains exist. Nitrates have also been carbon dated at around 100 years of age – well before irrigation and intensive dairying.

The public also needs to be aware that a crop of potatoes uses twice as much nitrogen fertilizer as a dairy farmer.

The reasons for poor water quality have been widely known within the science community, yet one particular reason has been ignored by local and central government.

It is inconceivable that authorities from Ministries to Regional councils do not know of the destructive capacities of rotting leaf litter from the willow trees, deeply lining the riparian margins of too many of our rivers and lakes.

What then is the truth of the causes of poor water quality where it occurs.

The noise from anti-farming lobby groups now overwhelms reasoned debate. The productive sector is met with continuous disdain. Add in the separation between local authorities and the actual authorities of land management and the problems multiply. And even worse - they are magnified.

Separation between management and governance is another major national problem. Staff are told not to speak to governance except in formal settings, and only when asked to explain issues to decision-makers who often lack a basic understanding of the need for a holistic approach to this long-unresolved problem in Otago.

Further, nobody seems to be able to explain why those responsible for the raw sewage spills in coastal waters and fresh water, in Queenstown, Wellington, and Auckland - as happens on a regular basis - offer mere expressions of regret, yet a burst pipe on a dairy farm means the perpetrator is strung up by his or her thumbs!

Willow trees can line both banks of a river for which everybody and nobody is responsible. These trees continue to be ignored, as the blame for water quality and quantity has been preset. Few would complain about a managed single line of willows on one side of a river to protect from riverbank erosion, but all too often the willows are anything from a couple of meters to 20 or so meters deep and on both banks. It has been well established in environmental literature that a mature willow tree can consume 400 litres of water a day during summer, which is of course when water demand is at an absolute premium with competing interests all stating their use is of the highest calibre possible.

The problems really start when autumn arrives and willow leaves turn to beautiful calming shades of golden hues. All the while - the poets’ collective souls wax lyrically about the shaded colors to gladden the hearts of all who gaze upon their occasional beauty. Little thought is given to the next biological stage and state of water quality as a result.

Enter the science guys. In moderate leaf litter falls, the willow can supply and support what they call detrital food webs and microbial food webs. However, where excessive inputs from where wall to wall willows exist far beyond the riparian zone (Lindis and Manuherikia rivers) then water quality falls and algae blooms can occur - and not a dairy or beef cow in sight.

Nobody has ever asked for a wide public discussion so as to ask the pertinent questions around environmental health of a water body. Questions as to whether the correct indexes are used for the opposing interests to debate along with the need to fully understand factual data so the problems can become workable solutions all can live with.

To suggest the only outcome possible is the environmental bottom line is simplistic. Willow leaf litter breaks down and releases nitrogen and phosphorus into the water body leading to localized oxygen depletion which in turn impacts on fish and invertebrates. This process has long been blamed on use of artificial fertilizer such as super phosphate and nitrogen fertilizer run-off entering the water body, which is rare. Only highly specialized isotope techniques can determine the true source of the enrichment.

A NZ Geographic article entitled “Our Deeply Toxic Relationship with Willows” has highlighted willows have fundamentally altered our river systems by creating slow, shaded and organic rich environments. Algal blooms can occur through a feedback loop where low oxygen promotes nutrient release from sediments. So much negative comment is also sheeted home to the rural farming practice regarding the loss of wetlands.

Again, no public discussion has ever taken place regarding the role of methylmercury in wetlands and slow-moving water bodies due to infestation of willows. Microbial activity can convert Inorganic mercury into methylmercury which can in turn enter the food chain and bio magnify in fish. Mercury is a highly toxic substance, yet no mention is ever made of this substance which is clearly associated with wetlands and is well supported in fresh water scientific journals. Such vital information is never mentioned by environmental advocates. Evidence appears to be deliberately suppressed.

Good outcomes really do depend on informed questions and indexes being used to promote solutions. It will start with the truth being told about the toxic role of willows. Removal on an industrial scale and financed by us all - local and central government - is vital. Ngai Tahu should also contribute due to their alleged interest and claims of ownership in and of fresh water. This interest must include responsibility for the riparian margins.

If nature and the environment need a true champion, then its first lieutenant is clearly the people who can make the difference and not those who wrongly appoint blame and demand compliance from afar. Perhaps the divide is now far too wide along with opinions from all sides being too entrenched. Curiously, Environment Canterbury (E Can) has apparently sprayed willows on the main stem of the Ahuriri River to great effect along with genuine environmental resilience. They also sprayed the willows along the Rangitata, Rakia, Ashburton and the Waimakariri rivers so why not Otago? As a world famous headline in 1898 screamed at authorities - then - as now - j’accuse.

Gerry Eckhoff is a former councillor on the Otago Regional Council and MP.