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This country faces urgent and difficult choices on dairying expansion and the health of its waterways, writes Sir David Skegg, the president of the Royal Society of New Zealand.... before it's too late, let's stop pretending that we can have our cake and eat it too.
Every New Zealander knows that one of the worst threats to our natural environment is the degradation of rivers and lakes.
Some fresh waterways that were previously clean and inviting have become choked with weeds, slime and algal blooms - with adverse effects on insects, fish, and birds as well.
Two other facts are widely known. First, a major reason for the pollution of waterways is the expansion of the dairy industry.
Second, dairy products are New Zealand's biggest source of export dollars.
Every one of us benefits from the success of the dairy industry. Without its recent expansion, our economic situation might be gloomy today.
Driving through the South Island, I have seen small towns that were dying rejuvenated by local dairy conversions. And I am conscious the sectors in which I work - health, education and research - are crucially dependent on a vibrant economy.
In November, the Parliamentary Commissioner for the Environment issued a report in which she concludes that New Zealand faces ''a classic economy versus environment dilemma''. Jan Wright's advice is worded diplomatically, but her message is blunt.
Unless New Zealand takes urgent steps to slow the expansion of dairying, many more rivers and lakes will be degraded. None of the steps being taken to lessen environmental impacts can reverse this trend in the near future.
This sobering conclusion emerges ineluctably from analyses linking two models - one predicting changes in land use between now and 2020, and the other predicting the amounts of unwanted nutrients (especially nitrogen) running off farms into streams and rivers.
Dairy farming has become more intensive, leading to a remarkable 60% increase in productivity per hectare over the past 20 years. This has been achieved by applying more water, more supplementary feed and more nitrogen fertiliser to the land.
While good news in terms of revenue, such intensification leads to increased run-off of pollutants into rivers. But the modelling in Dr Wright's report shows that although intensification is an important factor in the degradation of rivers, the conversion of more and more land to dairy farms is having the greater impact nationwide.
Despite rhetoric from critics about ''dirty dairying'', many farmers have made sterling efforts to reduce the run-off of nutrients from their land. Measures taken include fencing streams and planting ''riparian strips'' along river banks.
Unfortunately, such precautions have a limited effect on the seepage of nitrogen (mainly from animal urine patches) into waterways. Other measures - such as employing nitrogen fertiliser more efficiently or breeding animals that excrete less nitrogen - may eventually yield benefits.
Yet a group of experts convened by the commissioner concluded that even taking an optimistic view, plausible improvements by 2020 could at best balance the effects of likely further intensification.
They could not counteract the much greater threat from expanding the number of hectares used for dairying.
Forecasts based on modelling can never be exact, and sometimes they can be wrong. In the four months since Dr Wright's report was released, however, I have seen no expert rebuttal of her main conclusion.
I have tried to read all the statements issued by agencies involved. That has been a depressing task, because so many have ducked the key point. Consider a couple of examples.
DairyNZ assured citizens that it is ''working with farmers, regional councils and other stakeholders to contribute to desired water outcomes''. IrrigationNZ rubbished the report and thought ''a far more useful question to be tackled is how we grow farming whilst at the same time improve water quality''.
Two of the most cautious and realistic responses were from Fonterra and Federated Farmers.
The Minister for the Environment was less troubled. While acknowledging the need for more work, she was ''confident that with the combined will of our council, communities, iwi, and water users - and with the support of our science community - we will see significant water quality gains within a generation''.
Scientific research certainly has a role to play, but unfortunately investment in this area has been ramped up only recently and is still modest in comparison with the size of the industry.
There is an urgent need to build scientific capability, and I hope the proposed National Science Challenge (''Our Land and Water'') will help to achieve this. We need to be realistic about what can be delivered in a short period: Dr Wright's experts did not envisage any breakthroughs that could improve things materially by 2020.
The Government has targets that appear mutually contradictory. One target is to double the value of agricultural exports by 2025. As part of this effort, irrigation schemes are being funded to expand the areas suitable for dairying.
On the other hand, the National Policy Statement for Freshwater Management requires that the overall quality of fresh water within each region must be maintained or improved. In the light of Dr Wright's report, can anyone explain how these aims could be reconciled?
We face urgent and difficult choices. If we want to restrict the expansion of dairying in vulnerable river catchments, are we prepared to contemplate a less buoyant economy - at least in the short term?
If we do not limit the expansion, what will be the impact on our second major export earner (tourism) as well as on our quality of life?
How could restrictions be implemented in a way that is equitable for farmers and regions? But before it's too late, let's stop pretending that we can have our cake and eat it too.
- Sir David Skegg, from Dunedin, is a former vice-chancellor of the University of Otago.