The Ministry for the Environment released a report yesterday on New Zealand’s groundwater quality, prepared by Geological and Nuclear Sciences Ltd. Today, I read in the Christchurch Press that the report concludes that “groundwater quality has no significant relationship with land use”. What’s more, Green Party co-leader Russel Norman called it “propaganda”.
Bold claims indeed. Fortunately we can check some facts.
First, some more from the Press:
Quality was rapidly changing at a third of the sites, with “patterns that suggest human influence”. But the report said there was “no systematic or significant relationships” between groundwater quality and land use or land cover.
Green Party co-leader Russel Norman said the claim was absurd and “propaganda”.
He said the uncertainty in the report suited the Government’s political agenda “to downplay the environmental impacts of agricultural intensification”.
Early last year, the ministry pulled a controversial chapter from its state of the environment report that pointed to industrial dairying as the largest cause of environmental decline.
Norman suggested the latest report followed political pressure, but Smith said he was disappointed such accusations were being made of officials at independent Crown research institutes.
However, he was “a little surprised” at the conclusion because the popular notion was that land-use intensification led to water-quality problems.
Smith said he would defer to the specialists who prepared the report rather than favour popular opinion.
Ministry adviser Mike Thompson, who reviewed the report, said it was not the report’s intention to dismiss the link between groundwater and more intensive land use.
Now I’m not in a position to conjecture about any hidden politics, but I can tackle the science. So faced with the interesting conclusion I of course go to the source. From the executive summary (emphasis added):
… this report has not revealed any systematic or significant relationships between groundwater quality (state or trends) and land use or land cover around the monitoring sites.
This clearly differs from the journalist’s remarks, but does it really matter? Actually, yes. As the report explains:
… relationships between groundwater quality and land use are difficult to elucidate because:
â€¢ land use observations are usually made by eye and may not accurately describe land use or land use intensity;
â€¢ the groundwater at the monitoring site might not have entered the aquifer in the area where the land use observation was made;
â€¢ impacted groundwater might not have had time to travel all the way from its source area to the monitoring site; and/or
â€¢ substances indicative of land use impact (e.g. NO3-N) might have been transformed or degraded before reaching the monitoring site.
Groundwater quality is a result of local and regional effects, including effects tracing back to yesterday or decades ago. There is no expectation whatsoever that local groundwater quality should intimately reflect local land use at the time it was observed. What’s more, the land uses observed (if observed at all) make no mention of fertiliser or manure management practices (see spreadsheet #1 on the MfE site).
In any case, as the journalist writes, a third of the sites show trends indicative of humans – that is, of land use.
But the human fingerprint can actually be detected further afield. The report tells us that a nitrate-nitrogen concentration > 1.6 mg/L is “probably” indicative of human influence; > 3.5 mg/L is “almost certainly”. Analysis of spreadsheet #1 shows that 34% of the sites are “almost certainly” influenced by humans; a further 16% are “probably” influenced. That is, 50% of the sites probably show some human effect, over and above the third inferred from the trends.
Bottom line: Groundwater quality at at least half of the NZ sites analysed by GNS are probably affected by land use practices. Which practices, where and when is not clear.