Nitrogen - the devil is in the detail

Last month the Government released its draft Essential Freshwater Package, which has a strong sense of urgency to improve water quality this generation. Charlotte Irving is taking a closer look at how the new bottom line for nitrogen levels came about and calls for more scientific research across the country’s local waterways.

Photo credit: Charlotte Irving

A lot of policy changes are currently proposed for the the New Zealand economy as a whole, and specifically for the agricultural industry: emission reduction targets, biodiversity protection, protecting highly productive land, carbon sequestration and reforming the Resource Management Act.

Last month the Government released its draft Essential Freshwater Package, which has a strong sense of urgency to improve water quality this generation. The profound response from the primary industry has struck me. I attended the Ashburton meeting, and the farmer turnout (400+) was overwhelming, given this is their busiest time of year. These policies have generated uncertainty and apprehension among farmers. We want to see improvement in waterways, and we support policies that protect ecosystem health and swimmability. I agree with most proposals made in the water policy strategy. Canterbury farmers are already meeting several of these through the provisions in the Land and Water Regional Plan. We acknowledge changes need to be made, and that nitrates need to be reduced in some waterways.

However, I do have some fundamental concerns. I’m talking about the new national policy statement bottom line for nitrogen in rivers at an annual median of 1.0 mg/L of dissolved inorganic nitrogen (DIN). This is a significant shift from the current bottom line for nitrate toxicity, which is set at 6.91 mg/l. Regional councils are required to develop or amend regional plans by 2025 to meet this new bottom line.

How will 1 mg/L DIN impact New Zealand agriculture regions?

The map below illustrates where DIN exceeds 1 mg/L; these areas are concentrated in the Waikato, Taranaki, Manawatu-Whanganui, Canterbury and Southland regions. It also indicates how much further nitrogen loads would have to be reduced under the proposed new bottom line, beyond the current National Policy Statement for Freshwater Management (NPSFM). The target requires a 27% reduction in DIN on average across all New Zealand. It shows that in some agricultural catchments significant reductions will need to be made. In the Selwyn Te Waihora catchment, it is estimated that a 76% reduction in nitrogen loads is required to meet the proposed NPSFM bottom lines for Te Waihora.

Figure 1: Indication of impact of proposed new DIN bottom line beyond current NPSFM. Source: Action for Health Waterways, MFE (2019, p.47)

How realistic is this threshold and how will current land use practices have to change to meet the new target? Economic modelling has found that achieving this goal across the Waikato catchment would require large-scale afforestation (160% increase) and a reduction in pastoral land use of 68% for drystock and 13% for dairy (LGNZ: Initial Economic Advisory Report on the Essential Freshwater Package 2019).

While aspirational goals are admirable, this low threshold is quite frankly unrealistic under existing land use in several catchments. Although the change from the status quo is both necessary and inevitable, it’s very confronting to imagine some of the highly productive lands of the Canterbury plains converted to pine forestry. Afterall, Canterbury is renowned for its efficient pastoral farming systems. Recently, the shift to forestry plantation from local sheep and beef properties (as a result of the One Billion Trees initiative) was met with immense resistance from the Wairarapa community. There are claims that this transformation will lead to depopulation and losses of farm service economy: forestry blocks offer little work or money flow over their 30-year life cycle (apart from initial planting and occasional pruning). While the impacts of this industry transformation have yet to be fully understood, current trends signal that we need to be careful of the triggers we pull and the unidentified consequences.

How did the Science and Technical Advisory Group decide on the standard of 1.0 mg/L DIN?

Finding supporting evidence for this figure proved difficult. The recommended freshwater nitrate toxicity guidelines classify 1.0 mg/L DIN as the highest species protection guideline for ecosystem health, a guideline for “effectively unmodified…ecosystems, typically occurring in national parks, conservation reserves or in remote, inaccessible locations”. Unmodified, remote, inaccessible – this sounds like a far cry from the rivers that flow through our developed agriculture catchments.

The current toxicity guidelines are based on thresholds for 22 species. Only seven resident species in New Zealand and two native species (mayfly and whitebait) are currently included in the assessment. The report acknowledges that there are significant information gaps for native species, including common bully and eels, which are widespread, major inhabitants of lowland streams where nitrate concentrations tend to be the highest. Further, factors such as water mineral content are significant modifiers of chronic nitrate toxicity. A robust evidence base is required to support any new bottom lines for nutrient pollution: this calls for further, objective scientific research in our local waterways.

There are significant issues with the ‘one-size fits all’ approach of the proposal

The use of national averages, without recognising the inherent complexity of local natural systems, will likely impose unnecessary, and potentially very large financial costs in locations where water quality is already high. For instance, national river water quality monitoring shows that over the last ten years, total nitrate concentrations been improving in 33% of waterways and worsening in 50%. Logic would suggest targeting catchments with negative trends through a risk-based approach, rather than exerting a blanket national approach. Imposing the cost of resource consents and waterway setbacks on farmers in catchments with good water quality is both ineffective and inefficient.

Figure 2: LAWA National River Water Quality 10-year trends (2009-13) for total nitrogen concentrations. Source: (LAWA, 2019)

We need to acknowledge the valuable contribution the pastoral sector makes to the New Zealand economy, while recognising the changes that need to be made. At the same time, we also need to acknowledge the activity that is already happening on a vast scale to protect waterways from further deterioration. But most of all, I am compelled to ask the New Zealand public to think about what we are asking of farmers. They truly do want to fix this, but they need realistic, achievable, scientifically robust targets.

Author: Charlotte Irving