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The district council’s chemical testing results show nitrate levels have increased in more than half of the tested water schemes over the last two years.
Dunsandel, Rolleston, Kirwee, Lincoln, Darfield, Southbridge, Sheffield, Glentunnel, West Melton, Springston and Springfield water sources all have increased concentrations, some of which are more than twice the 2017 levels.
An Environment Canterbury spokesperson said the increases have come from the intensification of farming.
“The 1990s is the latest phase of intensification, but concentrations were already increasing earlier than that, as fertiliser application and stocking rates increased. By the 1970s, nitrate concentrations were well above natural levels.
“The increases have been greatest in areas where the groundwater comes predominantly from rainfall that percolates through soil. This includes the Selwyn-Waihora zone. The rainwater leaches nitrate from the soil and carries it from the land surface into groundwater,” said the ECan spokesperson
Federated Farmers was approached for comment but was unable to respond.
Selwyn-Waihora zone committee chairwoman Megan Hands said the nitrate levels in the district are not a direct result of farming practice now.
“We talk about nitrate being in the post which is from land use that’s occurred over a number of years, and we are only starting to see it come through in those concentrations now,” she said.
ECan chief scientist Tim Davie said the district will continue to see increases for potentially up to 20 years until they start to taper off.
He said there is a nitrate issue in the district compared to the rest of Canterbury.
“Are there high nitrate concentrations in Selwyn? Definitely. What we are concerned about is two things, biodiversity and public health,” Dr Davie said.
“There is a health risk associated with high nitrate concentration. The main one is when you get above a certain amount, you are at risk of blue baby syndrome, which affects newborn babies that are bottle-fed and it can cause health problems for them.”
Dr Davie said there is a lot of contention around what concentration of nitrate we should be concerned about.
“A recent Danish study says when you get above 0.88mg/L there is an increased risk of colorectal cancer. It hasn’t been proven so it hasn’t changed our drinking standards but it does suggest that high nitrate levels in drinking water are not a good thing.”
The current maximum acceptable level of nitrate in drinking water is 11.3mg/L
As of February, the water source on Illinois Drive in Rolleston has a concentration of 6.98. In Dunsandel it is 6.54 and in Darfield it is 5.02.
Waterways Centre for Freshwater Management director Jenny Webster-Brown said those numbers are relatively high.
“Any time something is getting up to half of the recommended drinking water standard, it’s time to pay attention, especially if it’s increasing,” she said.
It is likely things will get a lot worse before they get better, Ms Webster-Brown said.
“We won’t know whether the systems we have put in place are working for many years to come because of this lag time.”
In 2016 ECan set nitrate limits for farmers across the region as part of the Canterbury Land and Water Regional Plan
In Selwyn, the limits were set specifically at a point where nitrate concentrations would be reduced.
Farmers now need to monitor the amount of nitrogen being lost in the soil and ensure they don’t exceed their baseline nitrogen loss rates from 2009-2013.
By 2022, high emitters need to significantly reduce nitrogen loss rates – dairy farms, for example, will need to make a 30 per cent reduction.