Nitrate discharge to groundwater from agricultural land use: an initial assessment for the Canterbury Plains

Abstract

This Technical Report arises from public concern about the effects of agricultural land use on groundwater quality. It applies existing tools and information to provide a strategic view of the issue of nitrate discharges to groundwater on the Canterbury Plains. The tools are being continually improved by scientists in consultation with Environment Canterbury and primary sector industries. Nitrate is one of the contaminants for which a threshold is set in the New Zealand Drinking-Water Standards of 11.3 mg/L nitrate-nitrogen. Nitrate-nitrogen is referred to as nitrate in this report. Existing monitoring of nitrate in groundwater is not an accurate indicator of the effects of existing land-use because of time lags. It can take up to several decades for the effect of a land-use change to be seen in groundwater. Nitrate concentrations also vary over a year, from year to year and are very influenced by day-to-day land use practices.