GNS Science researchers have been able to use hydrogen isotopes to show how intensifying agriculture since World War 2 has increasingly put nitrates, sulphates, pesticides, chromium, and CFC refrigerant chemicals into underground reservoirs.

Previously the isotopes were ignored as a way of radio-dating water because nuclear testing in the 1960s released massive amounts of isotopes into the global atmosphere, masking the trace amounts that could be used to determine the age of groundwater aquifers.

Now the effects of nuclear testing have faded enough for the  hydrogen isotopes to be used in the Southern Hemisphere.

The research by scientists Uwe Morgenstern and Chris Daughney has been accepted for publication in the Journal of Hydrology.

"Groundwater resources are under threat by pollution from land use activities in the recharge area," their article said.

Worldwide concerns were growing about nutrients in groundwater from fertilisers and high intensity animal farming. Poisonous algal blooms and lake eutrophication were occurring when groundwater discharged into streams and lakes, while nitrates were exceeding recommended concentrations for drinking water supplies.

The article reported that a sharp rise in nitrate and other agrochemicals due to high intensity agriculture was seen in groundwater recharged since 1955, coinciding with the start of industrialised agriculture.

An earlier transition to  a slightly elevated nitrate concentration, due to low intensity land use,  was found in groundwater recharged since about 1880. That coincided with the start of the meat export industry.

The authors noted no elevated levels of phosphate had been found in young groundwater.

That implied that fertiliser phosphate from non-point sources was still retained in the soil and had not yet reached saturated groundwater  systems, they said.

Phosphate is a main compound in agriculture fertilisers and, together with nitrogen, a trigger of algae blooms in lakes.

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