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In 2016, the National Groundwater Monitoring Programme (NGMP) sampling kit was modified by adding a 100 mL sulfuric-acidified sampling bottle for the analysis of ammonia-nitrogen (NH3-N). This change was prompted by a review applying the most recent version of Standard Methods (Rice et al. 2012), which is the basis for the sampling protocol adopted by the programme since 2006. Acidification was recommended to inhibit bacterial activity and prevent salt formation with organic bases. This report aims to inform on (i) the impact of this operational change on measured NH3-N concentrations at NGMP sites and (ii) the implication of this change on the long-term NGMP dataset. NGMP samples, including the new bottle, were collected by regional council staff as part of quarterly monitoring. Collected samples were then analysed at the New Zealand Geothermal Analytical laboratory for NH3-N, one of the monitored parameters using acid-preserved bottles, and for other parameters, including major ions and trace metals. Duplicate analysis of NH3-N (flow-injection analysis APHA 4500-NH3-H method) was performed on a subset of the unpreserved bottles for cost-effectiveness. The subset was selected to encompass a range of concentrations ( |
