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NITRATE CONTAMINATION OF GROUNDWATER FROM
AGRICULTURE IN CANTERBURY, NEW ZEALAND:
MEASUREMENT AND MANAGEMENT OF A HIDDEN
PROBLEM
KJW Taylor
Environment Canterbury, 58 Kilmore Street, PO Box 345, Christchurch, New Zealand
8001, E-mail: Ken.Taylor@ecan.govt.nz
SUMMARY
Nitrate contamination of groundwater from agriculture is an increasingly important
issue for resource management in Canterbury. Most people in the region are
dependent on untreated groundwater for drinking, and although communities
place a high value on groundwater quality, over much of the plains the resource is
unconfined and therefore at risk from nitrate contamination. While samples from
only a small proportion of wells in the monitoring network (2-6%) have nitrate-N
concentrations in excess of NZ Drinking Water Standards, the data show a trend
of increasing concentrations (up to 0.7 mgL -1 yr -1 ) across large parts of the alluvial
aquifer system. This is particularly marked in those areas where the primary source
of recharge is rainfall, as opposed to seepage from rivers. Agricultural development
on the Canterbury Plains has been ongoing for many years, but there has been a
shift in production systems over the last decade in particular, from mixed cropping
and dry-land sheep grazing to more intensive irrigated pastoral and arable farming,
driven in part by developments in irrigation technology. Dairying has emerged as
a major land use in formerly dry-land areas. This intensification has the potential
to contribute to further increases in nitrate concentrations in groundwater. The
management response to the nitrate trend has included: increased research effort
to quantify N contributions from multiple sources over time and at a range of spatial
scales, more stringent regulation of point-source discharges, and the promotion of
best management practices. The most important new initiative is a proposed rule
requiring landowners to estimate nitrate-leaching losses, and to undertake nutrient
budgeting and other measures if leaching thresholds are exceeded.
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