Nitrate discharge to groundwater from agricultural land use: An initial assessment for the Canterbury Plains
A report has been released assessing nitrate discharge into groundwater on the Canterbury Plains from rural land uses. The report, commissioned by the Canterbury Water Management Strategy Steering Group, arose from public concern about the effects of agricultural land use on groundwater quality.
The report looks at nitrate discharge from rural land use and its implications for water quality in two situations: shallow groundwater quality on the Canterbury Plains and deeper groundwater quality for Central Canterbury.
Continued access to clean drinking water always comes through in public consultation as one of the key issues for water management and the report provides the Steering Group with some predictions about the impact of nitrate discharge on groundwater quality.
The report, compiled over six years, provides evidence that nitrate discharge from agricultural land use on the Canterbury Plains has a negative impact on the quality of water at shallow groundwater levels, and in some situations, exceeds drinking water nitrate standards.
The report also shows groundwater quality generally improves with depths below the groundwater surface because of mixing with high quality groundwater from river recharge.
Most large drinking water supplies, including Christchurch, take water from deep groundwater. In Christchurch there are two other factors that help protect water quality from land use effects. The first is the confining layers above the aquifers where Christchurch city takes its water. The second is that we are in the process of implementing land use controls over the area of land where nitrate could get into the aquifer.
The report shows contamination in shallow ground water is directly related to land use and there are areas of compromised groundwater drinking supplies in rural Canterbury. Careful land use management is therefore a reality and further land use intensification in the Canterbury Plains will be dependent on reducing current levels of nitrate leaching.
The report compares the effects of improving practices on existing agricultural land to the effects of changing land use. Improving practices on existing agricultural land will have the greatest effect on the availability of quality drinking water from shallow groundwater.
The report will be used by the Canterbury Water Management Strategy, run by the Mayoral Forum, to help guide them and others when looking at the best way to sustainably manage Canterbury's future water resources.
Type: Technical Report