Simplistic water rules that cannot be used



NOTICE: What is simple is always wrong. What is not is unusable.

The French philosopher and poet Paul Valery wrote these sentences in 1942. We must remember the words in our struggles to find a way forward for agriculture.

Around New Zealand, regional and local authorities deal with national policy statements, especially those related to freshwater. The objective is to find an indicator of the quality of the water and to apply a regulation.

It is not an easy task.

Soil scientist Emeritus Professor Ian Cornforth of the University of Lincoln worked on indicators in the 1990s. He concluded that they must be sensitive, respond predictably to a change in management and influence the area of ​​concern. ‘in a predictable way (either through a functional relationship or through threshold values).

The indicators must also be well correlated with ecosystem processes and be scientifically valid.

The correlations are excellent. The relationship indicates that when one factor changes, another changes too. Statistics help establish validity. The closer the correlation is to 1, the better the cause and effect and the predictability. Below 1, predictability decreases. At 0.5 only 50% of the variability is explained by the factor examined.

The New Zealand Local Government (LGNZ) has attempted to explain these difficulties. In ‘Initial Economic Advisory Report on the Essential Freshwater Package’, published in July 2019, its authors stated:). Other factors may be more important in determining the quality of the environment. “

Australian and New Zealand researchers have quantified the problem this year. Their article “Nutritional Criteria for Achieving New Zealand River Macroinvertebrate Targets” derives from the criteria “to support the national aspiration to improve water quality”. However, the relationships explain very little (0.11 for dissolved inorganic nitrogen (DIN) and 0.10 for dissolved reactive phosphate (DRP)) for the variation in MCI.

Another example is periphyton mass (algae). Various reports have failed to establish a convincing relationship between DIN and algal growth. Some have shown that the nature of the river bottom (stony or loose) and the magnitude of the flow (fast or slow) have a greater effect than the nutrient concentration.

The problem with sorting out cause and effect is that many of these factors are intertwined – rivers near the source tend to be fast, have stony bottoms, and low nutrient concentrations. They pick up sediment and nutrients as they flow. Closer to the sea on flatter lands, they slow down and sediment falls, coating the bottom. In between, different life forms are supported and the MCI has been modeled as excellent or good for 78% of the total length of the New Zealand river (

Less than 1% of the total length of the river had a poor MCI score in the 2020 report. About 70% of the length of the river crossing the native land cover class had an excellent MCI score. Less than 1% crossing the urban land cover class (land with an urban cover exceeding 15% of the watershed) obtained an “excellent” rating.

Human activities, including urban development and agriculture, have affected water quality globally. Trying to find a simple solution will not achieve what is needed and a complex solution will be unusable. Worse, the implications of the implementation will have a negative effect on the economy without any guarantee of improving water quality.

LGNZ said this: “Since profitability is a necessary condition for effectiveness, the choice of DIN and Dissolved Reactive Phosphate as policy targets would be expected to fail the policy effectiveness test if the actions in reducing nutrients are not cost effective. “

The Treasury estimated that the reduction in nitrogen load induced by the nitrogen attributes of the lake and periphyton in the existing national policy statement for freshwater management would cost $ 394 million per year by now. 2050.

This is a lot of money to waste without any certainty that doing what is suggested will have any effect on the quality of the water.

Obviously, more research is needed.

Dr Jacqueline Rowarth, Assistant Professor at Lincoln University, is a farmer-elected director of DairyNZ and Ravensdown. The above analysis and conclusions are his. This e-mail address is protected from spam. You need JavaScript enabled to view it.


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