During the panel discussions, the nature of the disagreement that we see in the media became clear. Scientists disagree about three things:
- The meaning of “maintain or improve” in the Government’s objectives for freshwater
- The adequacy of water quality standards (as captured in the Government’s proposed indicators)
- Whether New Zealand is being sufficiently cautious in management standards for freshwater given the uncertainties in the science
Maintain or Improve
The panel agrees that the current wording in the National Policy Statement (“overall quality of fresh water within a region is maintained or improved”) is confusing. The scientists were divided on how to remedy this situation.
Some were concerned that if all waterways had to be maintained or improved from here it would stop development. Others argued that without this clarity, many waterways would continue to decline until they hit the bottom lines.
We are seeing this in action in Canterbury. The most affected catchments now have limits, but development continues in other catchments, which will almost inevitably degrade. In any areas that have had community processes so far, no one wants water quality to deteriorate – so why are we continuing to let it happen in areas with good water quality?
Where we got to: Maintain or improve should be enforced for every waterway, effective immediately. This would be measured through the MCI (Macro Invertebrate Index). Any exceptions (for waterways to decline) need to be sanctioned by the local community.
Water Quality Indicators
The science panel agree that the indicators of water quality (proposed by the Government) need further development, but they can’t agree on exact changes. There is a lot more work to do here in coming years.
The main area of disagreement is whether the Government’s proposed bottom lines (the measures below which water quality must be improved) are sufficient to protect our waterways. Water quality is influenced by many different factors. Sometimes each of those factors might look reasonable, but when taken together they prove to be a toxic cocktail for a given waterway. This can be difficult to predict in advance and depends on the waterway.
Where we got to: There needs to be greater national guidance for regions on setting algae limits, and what that means for appropriate nitrogen levels. Combined effects are another reason to be cautious about further dairy conversions. This would be less of a risk if all farms (including sheep/beef) in a catchment have fenced and planted waterways and implemented soil conservation plans – as this would reduce phosphorous and temperature levels in the waterways.
Nitrogen is a good example of cumulative impacts.
On its own, nitrogen only causes problems in high quantities. This problem is known as nitrogen toxicity – when the nitrogen levels in water start to affect the animals living in it. The proposed bottom line (6.9mg/L) relates to the point where nitrogen toxicity stunts growth among the most sensitive 20% of species. Some scientists suggest this is too high a bar to define as toxicity, because nitrogen starts having an impact on animals at lower levels. The analogy used is that an alcoholic is sick long before their liver fails. The WHO guideline for human drinking water is 11.3mg/L.
However, nitrogen is also a problem when it combines with other nutrients and produces algal blooms, which rob waterways of oxygen. In certain conditions (if phosphorus and light/warmth are present) nitrogen will contribute to algal blooms at much lower levels than toxicity.
It can be very difficult to know whether adding nitrogen to a waterway (such as by increasing dairy farming in the catchment) will result in algal blooms or not. By the time the results are clear in practice, it would be impossible to stop.
There’s broad agreement over science in a laboratory. However, out in the field measurement can be difficult, ecosystems have natural variation, and there can be time lags and uncertainties. The panel agrees that more monitoring is needed to manage water quality well. But top quality measurement will not always be possible, and there are different attitudes on how to manage water in the absence of good quality data.
Some panel members felt that the bottom lines should be more precautionary to make up for uncertainties elsewhere – time lags, measurement problems and the difficulties of getting a community consensus. Others felt that it is up to communities to decide how precautionary they want to be.
Where we got to: From our 2011 review of fish resource management we found that NZ’s approach would have benefitted from being more precautionary from the outset. It seems a logical approach for water management.