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Science Media Centre: Shifts in farming put pressure on water quality – report


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Changes in the way New Zealanders use land are negatively affecting the water quality of our lakes and rivers and we need to do something about it, according to the latest report from the Parliamentary Commissioner for the Environment.

The Commissioner Dr Jan Wright released the report titled Water quality in New Zealand: Land use and nutrient pollution this morning.

The document details how a shift from sheep and beef farming to dairying has lead to increased leaching of nitrogen and phosphorus into waterways which in turn causes excessive growth of weeds and algae, choking waterways. Drawing on modelling of land use and nutrient run-off, the report also paints a grim picture of the future, predicting that loss of nitrogen and phosphorus into waterways will continue to increase — even under “optimistic” assumptions.

“I applaud the effort that is being put into environmental mitigation on dairy farms,”Dr Wright said in a media release. “Unfortunately, it is particularly difficult to control nitrogen. Nitrogen – in the form of nitrate – is so soluble that I think of it as the ‘elusive’ pollutant.

“I am pleased that fresh water policy is very much on the Government’s agenda with the recent release of a discussion paper on setting ‘bottom lines’ for water quality. I hope that this report will better inform both the general public and those who make decisions on their behalf.”

A video of Dr Wright summarising the report is available here.

The SMC collected the following expert commentary.

Prof Jenny Webster-Brown, Director of the Waterways Centre for Freshwater Management, University of Canterbury & Lincoln University, comments:

“The PCE’s report sends a strong message – we cannot expect to achieve the water quality goals of the NPS for Freshwater Management in a regime of increased dairy production. Even if on-farm mitigation of nutrient leaching is as effective as we hope, the adverse effects of converting land to dairy, at the rate anticipated for the next seven years, are predicted to outstrip the benefits of this mitigation.  The modelling approach that has been used here is valid, in my opinion. The assumptions that have been made in the modelling scenarios are reasonable and defensible. This predicted environmental outcome of allowing immediate economic gain to continue to dictate our use of land should be taken seriously…it is a wake-up call.

“However, it would be wrong to treat this outcome as inevitable.  This national-scale modelling approach provides us with a very valuable tool, because (oddly) the greatest shortcoming of such modelling can also be its greatest strength.  All modelled outcomes are highly dependent on the assumptions made to create the modelled scenarios.  By changing these assumptions, and looking at how this affects the outcome, it is possible to identify the most important factors contributing to an outcome (the so-called “sensitivity analysis”).   We can use this combined land use-nutrient leaching model to see how the outcome changes for alternative economic and land use scenarios.  Identifying alternative agricultural and horticultural uses for our land, ones that can provide a similar economic benefit but have significantly less impact on water quality, would surely be a major step forward in future proofing NZ’s water quality.”

Assoc Prof Russell Death, Institute of Agriculture and Environment, Massey University, comments:

“As the son of a retired dairy farmer and a country lad at heart I would love to see the win-win for the economy and environment that Jan Wright alluded to in her report on the effects of land use on water quality in New Zealand. However, her report clearly illustrates what many scientists and economists already know, if we continue with increasing dairy intensification, without some drastic changes in how we farm, the most likely outcome is lose-lose. Many of our waterways are already badly degraded, agriculture creates pollutants (nitrogen, phosphorous and sediment) and thus increasing agriculture even with the best mitigation practices (none of which are even close to perfect) will still result in more pollutants entering our waterways. More pollutants, lower water quality, it’s not rocket science.

“The National Policy Statement for Freshwater Management was a good start, but without the appropriate bottom lines (or even the correct parameters) the National Objectives Framework in its current form will not help. Furthermore, focusing on just one pollutant (e.g., phosphorous) is also unlikely to work; ecosystems are too complex to manage in such a simplistic way. If we want the win-win we need to get serious about the discussion instead of hiding it with the current smoke screen promulgated by much of the industry and government supported “science”. This report goes some way towards some real science for that conversation.”

Dr Mike Scarsbrook, Environment Policy Manager for DairyNZ, comments:

“The latest water quality report from the Parliamentary Commissioner for the Environment presents one possible future for New Zealand. It looks ahead to 2020 and predicts changes in nutrient loads in rivers resulting from land use change. Market drivers (e.g. commodity prices) and land availability drive predictions of land use change. It assumes there are no regulated limits on nutrients in our waterways and no limits on the availability of water and other resources for our farms. It also assumes that farming systems will not change other than to meet current good practice targets, with gains offsetting intensification on existing farms. Is this realistic? Not really. The NPS for Freshwater Management, released in 2011, has fundamentally changed how we manage freshwater resources. The days of unconstrained growth in dairy farming are over.

“The value in the report from the PCE is in providing a very clear picture of the link between land use intensity and nitrogen loads. It is inescapable and undeniable that as more and more land shifts from low nitrogen loss activities to high nitrogen loss activities the load in rivers and other receiving waters will increase.

“The dilemma facing New Zealand is not a choice between economy and environment. To a large extent that decision was made generations ago when the land was cleared for agriculture. The challenge we face is in determining what levels of nitrogen and phosphorus are acceptable in our waterways.

“For some waterways in the country, communities have already determined that the acceptable loads of nutrients have been exceeded (e.g. Manawatu River). For others there may be potential for further load increases, so long as the water quality objectives set by the community are achieved (e.g Tukituki River). A long process of setting water quality limits around the country is only just beginning.”

“We discriminate between good practice and mitigation. Continual improvement in feed and fertiliser use, protection of soils and good effluent management are basic industry expectations as set out in the Sustainable Dairying: Water Accord. Mitigation actions go beyond this good practice and will need to be employed in all catchments where reductions in nutrient loads are required to meet community-determined limits or targets. In our most over-allocated catchments, radical shifts in farm systems are likely to be required along with some changes in catchment land use. Existing farmers will do their bit to achieve these targets, but the targets will be impossible if there is uncontrolled intensification in over-allocated catchments.

David Hamilton, President, New Zealand Freshwater Sciences Society, comments:

“The PCE has again provided a report that enables the public to gain knowledge of water quality issues in New Zealand and to be engaged in debate around this topic.  This report follows on from an excellent report on ‘Water Quality in New Zealand: Understanding the Science’ published earlier in 2013, which provides a valuable introduction to the subject matter of the present report.

“The new report clearly highlights the enormous challenge that we face as a nation: how to meet the government’s goals of doubling the value of agricultural exports by 2025 whilst meeting the 2011 National Policy Statement for Freshwater Management (the NPS) which requires that the “overall quality of fresh water” in all regions of the country be maintained or improved.  It is clear from the report that ‘business as usual’ will not get us over the line and that a step change and solution-focused approach are required, mostly in environmental management in the agricultural industry, to meet the NPS objectives.

“The PCE report shows how major gains in productivity from large-scale land conversions to more intensive agricultural land use (e.g. dairy farming) and fertiliser applications have not been matched by capacity to mitigate these effects over the past decade.  It hints at the need to both regulate land conversions as well as adopting best management practices to address nutrient runoff from farming.”

Detailed comments

“Whilst this report is not focused on agricultural mitigation techniques to reduce nutrient runoff from farms, it is noted that only a basic and conservative consideration of the techniques available has been adopted in the 2020 scenarios of land use change and nutrient runoff.  A far more comprehensive evaluation of mitigation techniques is available in McDowell et al. (2013) and these techniques are being rapidly adopted in the agricultural industry.  The PCE convened only a small expert group to advise on the extent of adoption of mitigation techniques.  It would have been valuable for these experts to have also run a scenario of 2020 best practice to have potentially incentivised adoption of mitigation techniques by showing what is potentially possible, whether NPS objectives could be met, and to re-emphasise the importance of best practice.

“The PCE makes the assertion that nitrogen limitation of freshwater algae is less common in NZ than phosphorus limitation; “this is almost certain the case for lakes” and cites our work (Abell et al. 2010).  This statement is incorrect and it raises an important point that assumptions about nutrient limitation should not be based solely on concentrations of nitrogen and phosphorus.  From bioassay work involving artificially adding nutrients to lake water, it has been found that nitrogen is far more likely to stimulate growth of algae than phosphorus (Abell et al. 2010).  It is important to emphasise that concentrations of total nitrogen and total phosphorus only provide a proxy for nutrient limitation – and not a particularly accurate one for NZ lakes.”

 Dr Rich McDowell, Senior Scientist, AgResearch, comments: 

“I would make two points on this report, the first being on mitigation.

“1)      The view the PCE has taken is that mitigation has not kept up with expansion and intensification of farming (viz. dairy) systems. This is rather simplistic as we can also provide cases where there is much potential to mitigate N and P losses. There are many more mitigations that have been presented in the report. However, the main point is that N and P losses vary in space and time and so too does the suitability of different strategies to mitigate N and P loss. If optimised, i.e. the right strategy used in the right place and at the right time then we can cause losses to decrease significantly at little (or perhaps no) cost.

“2)      However, implementation is another matter and the PCE report does not give due consideration to current policy (which tend to focus on obvious bad practice) and the  recently announced freshwater reforms which could require a step change in N and P management on-farm. Within the reforms, the national objectives framework provides a bottom line which should act as a backstop against severe water quality deterioration. Another part of the freshwater reforms is a collaborative process whereby values (e.g. for water quality) are set on a catchment by catchment basis. This recognises the fact that communities may accept a state of water quality for a catchment if, for example, it is naturally poor or if there is an additional 10% profit to be made without degrading water quality. The PCE report makes a blanket assumption regarding N and P losses.

“ In addition, there is also a technical mis-representation for P inputs. The PCE report makes the assumption in several places that it is total P that affects streams and rivers, but also recognises in a couple that it is dissolved P that influences, for example, periphyton growth. It is the ability of eroded sediment to desorb P into the water column not how much P the sediment contains that is the controlling factor for in-stream P concentrations. In other words, you could argue that the input of sediment that is P-rich but where P is very tightly bound is probably better than a less P-enriched sediment that desorbs P readily.”

 


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