Nitrate levels in New Zealand groundwater

You can check the nitrate levels of your local river by visiting this interactive map from Statistics NZ

You’ll notice that the Forks Stream near Tekapo has a nitrate concentration of 3mg/L.

If you drive approximately 120 km west you’ll get to Hinds, where the Rhodes Stream has a nitrate concentration of 10.9mg/L. A little further north, the Boundary Drain reading is 10.3mg/L. 

To put this into perspective the highest nitrate reading in NZ is 13.5mg/L in the market gardening capital of NZ, Pukekohe. 

I often think of that when someone tells me plant-based agriculture will save the planet, but I digress.

One of the differences between the Forks Stream in Tekapo & the waterways near Hinds, is there are 250,000 dairy cows on the flats of South Canterbury compared with 0 dairy cows in Tekapo.

However, that is about to change. Despite many objections, Environment Canterbury has granted consent for a 15,000 cow dairy farm just outside of Tekapo.

Now, I’m no ecologist but I think I can see where the Forks Stream is heading.

This is a continuation of a trend of adding cows to places where dairy cows haven’t been before. 

But we’re also adding cows to places where we already have lots of cows.

Ngai Tahu is still planning on adding 14,000 dairy cows onto the banks of the Waimakariri River.

So, the intensification of the Canterbury plains is clearly continuing. Apparently, ECan’s new directives will require agriculture to reduce nitrate leaching by just 15% by 2030 & 30% by 2040.

With these developments in mind, It doesn’t appear ECan is serious about water quality, but the government certainly is.

They made it clear how serious they are in their discussion document titled Action for Healthy Waterways. 

They’ve said, from this point onwards our waterways are not going to get any worse.

Any further intensification can not have an adverse effect on waterways from now on. Over the next generation, the plan is to restore our waterways back to health.

Central government has set new freshwater standards and its giving regional councils 5 years to draw up plans to manage their catchments in line with the new requirements.

Of course, farmer reaction was not so enthusiastic.

The headline in The Farmers Weekly read “Farmers despair” & judging by rural social media, farmers are indeed despairing. 

The always forward-thinking optimists at Federated Farmers said: “The long term targets for nitrogen reduction, are effectively unachievable in some parts of the country, and will end pastoral farming in these areas.”.

One of the reasons The Feds are claiming the targets are “unachievable” is the reduction in the nitrate concentration target from 6.9mg/L to 1mg/L. 

That’s an 85% reduction, but that does not mean an 85% reduction in per farm nitrate leaching.

When a waterway has a nitrate concentration of 6.9mg/L, the fish will die from actual nitrate poisoning. 

Farmers seem to be under the impression that fish can live in anything less than 6.9mg/L & that it is an appropriate target.

But in nature, a fish would have likely died from a lack of oxygen long before the waterway got anywhere near 6.9mg/L.

Slime forms in waterways when nitrate concentrations reach about 0.5mg/L. The slime absorbs the oxygen from the water, leaving none for the fish to breathe.

The more nutrients in the waterway the more slime there is and the less oxygen is available for the fish and other critters.

The limit of 1mg/L is a measure of a waterway that is under nutrient pressure but still has some life left in it.

If we allowed our rivers to get to 6.9 mg/L we’d have no fish in any of them.

Most NZ waterways are well below the 1mg/L mark. In fact, the top quartile (25%) of rivers ranked by nitrate concentration has a mean of .866 mg/L. 

There are actually a very small number of rivers that actually exceed the 1mg/L criteria.

So the waterways around Hinds are in the small minority that exceeds the 1mg/L limit. 

The freshwater proposals are designed to ensure that those small number of rivers don’t get worse and then actually get better over the next generation.

In 2019, that’s hardly an unachievable goal.

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