Andrew Yuill’s Feedback to Takaka FLAG’s Interim Decisions Report

Andrew Yuill of Takaka is Co-Applicant with Ngati Tama ki Te Tau Ihu for a Water Conservation Order to protect Te Waikoropupu Springs and the Arthur Marble Aquifer that supplies the Springs.

Lisa McGlinchey
Tasman District Council

31 January 2017

To Takaka Freshwater and Land Advisory Group

Thank you for the opportunity to comment on the Summary of Interim Decisions.

I record first, that I support and concur with the comments submitted by Friends of Golden Bay this month. I particularly emphasise the following 6 points.

1. For Te Waikoropupū, action triggers should be set at present water quality levels so that any deterioration of water quality leads promptly to corrective action.

2. FLAG should reach agreement with local Iwi about their values for the waters of Te Waikoropupū and the Takaka River and its tributaries, before advancing its interim decisions further.

3. There should be no increase in the amount of irrigation allowed in the AMA recharge zone.

4. Water takes from rivers should cease when flow downstream of the takes is at MALF or less.

5. Application and sale of nitrogen and phosphorus fertiliser should be a controlled activity, requiring consent and public record of the date, place, fertiliser type and amount sold or applied.

6. Holders of water consents should pay a levy sufficient to fund proper monitoring of environmental effects, in return for the privilege of water use.

I will present some further observations and analysis.

It appears that the one major issue FLAG has to deal with, is the proposed increases in water allocation from the recharge zone of the Arthur marble aquifer, and the consequences of those proposals. Further, the main management issues arise in the flats of the Takaka Valley, upstream of the Coal Measures. It is clearly evident from the September 2016 ‘Zone by Zone Allocation Summaries’ presented to the Environment and Planning Committee, that there is no impetus for allocation changes in any of the other zones. Yet in the AMA recharge zone an increase of 356 litres per second is proposed, which is between a 70% and an 87% increase on present practice, depending on what amount between 500 and 410 litres one takes the present allocation to be.

The proposals are clearly driven by a list of queued applications; downstream of the recharge zone is of course Te Waikoropupū. I have already observed in an email to FLAG how Dr Young’s recommendations for allocation and protected flow for the major rivers and AMA recharge, could have been derived exactly from the queued applications, so I will not repeat that here. There are further coincidences though.

We have still not seen the report of the Science Panel which met in March 2016, however in July 2016 Dr Young presented provisional recommendations, including trigger levels for nitrate-N and dissolved oxygen in Te Waikoropupū. The recommended trigger level he gave for Nitrate-N was 0.5 mg/l, which is coincidentally the level expected by Andrew Fenemor’s group (Nov 2015) to result from allocation of 766 l/s in the AMA recharge zone.

For dissolved oxygen the report noted DO Saturation early 1970’s (Michaelis) as 58-64%, and DO Saturation April May 2016 as 50-53%. The average of the 1970 values is 61%, and the average of the 2016 values is 51.5%, indicating a reduction of 9.5 percentage points. Suppose this were suspected of being due to irrigation and its associated intensification, and suppose one were proposing to increase the irrigation by 70%, then one might expect to lose another 70% of 9.5, i.e. another 6.65 percentage points. That comes out to 44.85% saturation, which is coincidentally remarkably close to the proposed 45% trigger level. We have still been given no other explanation for the proposed 45% trigger level.

In the absence of the final Science Panel report, the only reliable advice we have for the nitrate and dissolved oxygen in Te Waikoropupū is NIWA’s values of 0.4 mg/l maximum for nitrate-N and 60% saturation for dissolved oxygen. I strongly recommend that FLAG keeps to those recommendations.

Regarding pre-European levels of nitrate in the Takaka catchment, the Jan 2017 report by Young and Hay concludes “Natural background levels of N were perhaps similar to or higher than that observed currently in Spittal Springs (0.22 mg/L)”. Inexplicably the report does not consider the two obvious examples of forest clad sub-catchments in the Takaka catchment; namely the Takaka above Harwoods and the Waingaro above Hanging Rock. Nitrate-N levels in both these are typically 0.01 mg/l. In November 2016, nitrate-N levels in Gorge Creek and Ironstone Creek were 0.06 mg/l and 0.03 mg/l respectively and this may reflect the small amounts of agriculture around Canaan. Cave divers who entered Spittal Spring speak of a complex system of water sources with some coming from Takaka River or groundwater in the valley flats. This would explain the elevated nitrate levels in Spittal Spring. I see no reason to suppose the pre-European nitrate levels would be at all different from the levels observed today at Harwoods and Hanging Rock.

One result of the Friends of Golden Bay measurement programme at Te Waikoropupū is confirmation that the deep aquifer has discharged 120 tonnes of nitrate-N in the last year. Owing to the weekly sampling we have high confidence in this figure. From the work of the Nitrate sub-group it became plain nobody had an explanation for the source of this nitrate so I investigated various possibilities.

I have established it is possible that modest but significant amounts of Takaka River water and valley rainfall could be contributing to recharge of the deep aquifer. This could occur within all the constraints imposed by mass balance, δ-18-O balance and residence time of the deep and shallow systems. I present here one possible table in a similar style to ‘Table 4’ in Stewart and Thomas’s 2008 conceptual model. This one shows 566 l/s of Takaka river water and 200 l/s of Valley rainfall recharging the deep aquifer.

If this amount of water were entering the deep aquifer with the nitrate levels expected under land leaching 100kg of nitrate-N per year, it would account for the whole of the observed 120 tonnes per year. Such land exists in the AMA recharge zone of the Takaka Valley flats. Although this analysis is speculative it is the first account we have of where the nitrate in the deep aquifer could be coming from, and it is consistent with all the observed data.

This carries important implications for nitrate management in the Takaka Valley. Firstly, it implies that essentially all the nitrate observed in the Main Springs and Fish Springs of Te Waikoropupū is coming from agricultural activity on the Valley flats. Secondly, that nitrate from this agricultural source will arrive at Te Waikoropupū after a ten year delay.

Put another way, it means the deep aquifer contains a potted history of the last ten years of farming. What has happened since 2006? There are two, possibly countervailing trends. During that time, farmers have improved their effluent control and fenced stock out of many waterways. At the same time there has been a dairy boom and farming has intensified considerably. Which of these influences has predominated? There is no way of finding out apart from waiting to see what comes out. In face of such uncertainty it would be rash indeed to approve a 70% increase in irrigation allocation.

There is an unavoidable link between irrigation and farm intensification. The argument is a financial one. Irrigation is expensive to install and run so it only makes business sense if it increases milk solids output, and another word for more milk solids is intensification.

Unfortunately FLAG didn’t make the opportunity to discuss this with the irrigators, so I will have to make do with some approximate figures to illustrate the argument. Irrigation may cost $6000 per ha to install. The interest rate might be 6% and the installation may be depreciated over 25 years i.e. 4% per year. The annual irrigation power bill could easily be $100 per ha. So it may cost $700 per ha annually to have and run irrigation. A well fed dairy cow may make 300 kg of milk solids per year and there may be two cows per ha. At a payout of $4 per kilo, the annual revenue would be $2400 per ha.

One could probably do the sums in several ways and get slightly different answers but it’s unavoidable that to pay for the irrigation there will have to be a significant increase in the farm’s intensity. Perhaps, for example in increase to 2.5 cows per ha or a much extended milking season. This basic arithmetic reinforces the conclusion of Andrew Fenemor’s modelling group that increasing the irrigated area in the AMA recharge zone will lead to greater nitrate concentrations at Te Waikoropupū. Nitrate in the aquifers is not the only issue. Intensification will also have impacts on dissolved oxygen, E.coli in the rivers and so on.

For reasons I gave at FLAG it’s unfair to give water consents then take them away again. We are already hovering at the nitrate limit NIWA gave, and below NIWA’s recommended dissolved oxygen level, so the only safe approach is for farms in the AMA to show they can reduce their impacts on the aquifers, and only after that talk about more irrigation.

Andrew Yuill
Paynes Ford, Takaka