Week in Review

Weight of the past poisoning lakes of the present

We have been on a collision course with freshwater in this country for over a century, writes Victoria University of Wellington's Dr Jonathan West. We are going to have to make some difficult and uncomfortable choices. 

Writing shortly before his death in 1940, Hawke’s Bay farmer Herbert Guthrie-Smith asked himself whether for the previous 60 years he had “desecrated God’s earth and dubbed it improvement”.

This was a markedly changed view from when – in 1884 as a young man fresh from England – Guthrie-Smith first took up his hill station around Lake Tūtira north of Napier and embarked on “murdering the sheep and making the country”.

By the end of his life he was painfully aware of the damage he had done to the land – his “substitution of one flora and fauna for another”, his “more quickly melting New Zealand through erosion”.

Guthrie-Smith understood his station was just a microcosm of the whole Pākehā settlement of New Zealand, especially in the North Island, where man and sheep together forced so much marginal hill country into pasture. The immense effort to do this speaks to a settler culture in which the idea any land might lie idle was anathema. As Guthrie-Smith showed, it has had severe environmental consequences – nowhere more so than for Lake Tūtira, which has had severe water quality problems since the 1950s.

Water quality problems in lakes are caused by what we do to the land around them and to understand lakes’ present problems we need to understand their history.

The main problem is something scientists call eutrophication, which means to make nutrient-rich, to make fertile.

It refers to the enrichment of water with nutrients, above all nitrogen and phosphorous. We do not like fertility in freshwater. It fuels plant growth, all too often algal blooms, some toxic to human health, all a problem for ecosystem health.

Lakes accumulate. They compress in the layers laid down in their beds traces of everything that has occurred in their catchments. Lake beds, then, are nature’s archives, geological whakapapa. Lakes are mirrors on the land. More, lakes are the land’s focal points.

The causes of eutrophication in New Zealand are well-known. While urban run-off is responsible for some of our most polluted waterways, overall, agriculture is the primary driver. And this is not new information. As long ago as 1977, New Zealand’s leading lake scientist Eddy White prophetically warned, “The intensity of land use in much of New Zealand is sufficient to make most lakes prone to eutrophication. Only upland lakes of the South Island are substantially free of the problem. There seems to be little prospect of improving water quality ... without major reductions in the intensity of land use.”

Since the removal of agricultural subsidies in the mid-1980s, there has been a more or less continuous thrust to intensify farming further. A key driver has been cheap synthetic nitrogen fertiliser. In using it we belatedly joined the rest of the world – for this is the defining feature of agricultural modernity. Synthetic nitrogen now feeds half the world. And we are now world leaders in the intensity of our fertiliser use.

Increased nitrogen fertiliser use, alongside irrigation and imported feed, has accompanied the shift from sheep and beef farming to dairy. And dairy stock density is the crux of our nitrogen problem. It is the sheer number and size of dairy cows – and hence the intensity of their pee and poo – that has propelled our skyrocketing rates of nitrogen leaching.

So how bad have our lakes become?

Somewhat mysteriously, studies done for the Ministry for the Environment’s national reporting no longer correlate catchment use and lake water quality. The last time they did was in 2010. Of 50 monitored lakes with pastoral catchments, 43 were polluted. The seven that weren’t were largely Canterbury high country lakes whose catchments have carried only a thin skein of sheep. Even they seem to have been sliding since - possibly because of climate change - so now of those seven, only one can confidently be said to have good water quality. Eddy White’s prophecy has come to pass.

Perhaps in the future things will be different. Perhaps we can turn things around. Alison Dewes, now Head of Environment at Landcorp, has shown dairy farmers can cut nitrogen losses 30 percent or more, and in only five years, without necessarily affecting profits. Perhaps we do not yet know if intensive farming and good water quality can coexist. Do we dare hope so?

One reason for doubt is that climate change is already exacerbating eutrophication. Another is that lakes suffering eutrophication can cross ecological tipping points and ‘flip’ from being in a stable state dominated by plants, to choked with algae – sometimes permanently, sometimes oscillating back and forth, but in either case we have had little success restabilising the situation.

Lakes are freighted with the weight of their past: they carry the legacies of their history in their water and beds. In Tūtira, it is the effects of decades past, recycling again and again out of the lake bed, that cause the blooms poisoning the present.

Having suffered at our hands, lakes will stay polluted unless we help them. Restoring even moderately polluted lakes means significant, sustained, expensive interventions. Our worst lakes require drastic emergency surgery. Measures such as spraying chemicals into the water or introducing alien fish might make us deeply uncomfortable. But we need to do these things to buy time while we change what we are doing to lake catchments.

The scale of this challenge should not be underestimated. We have been on a collision course with freshwater in this country for over a century. We can’t turn this around overnight. Or in five years. We face starker and more difficult choices. Professor David Hamilton, until recently Chair in Lake Restoration at the University of Waikato, told me his great fear is that, as the scale of the problem emerges ever more clearly, we retreat to decide, “Which few lakes in each region will we seriously try to save?” I think this is all too likely.

This article is an abridged adaptation of Dr Jonathan West’s 2019 JD Stout Annual Lecture at Victoria University of Wellington.

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