The Power of the Current Monitoring Network to Detect Nitrate Reductions in the Selwyn-Waihora Zone

Plan Change 1 (PC1) of the Canterbury Land andWater Regional Plan included requirements for farmers in the Selwyn-Waihora catchment to reduce nitrate discharges to groundwater to support water quality improvements. PC1 became operational in 2016 with a requirement for NO3-N (nitrate nitrogen) reductions to be fully implemented by 2022. Very few monitoring sites in the Selwyn-Waihora catchment and assessed by this report show decreasing NO3-N concentrations to date. This study evaluates the change detection power analysis of 56 sites (46 groundwater wells and 10 surface water features) to identify when and if PC1 reductions might become detectable in the current monitoring programme.