Department of Chemistry
University of Otago
PO Box 56, Dunedin
New Zealand
Tel: +64-3-4797908
Fax: +64-3-4797906
email: chemistry@otago.ac.nz
Chris Kensington, MSc (2003)
Dr. Barrie Peake 
Chris Kensington, MSc (2003) - Thesis Title:
- Nitrogen species in the groundwater of the Taieri Plain aquifer system
- Supervisor:
- Dr. Barrie Peake
- Thesis Abstract:
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The increasing concentration of nitrogen species in the groundwater resources of New Zealand has become a very topical issue of late with the ever increasing intensification of agriculture overlying New Zealand aquifers. This study focuses on identifying and accounting for the distribution of nitrate, nitrite, and ammonium in the groundwater throughout the Taieri Plain aquifer system, Otago, in an attempt to strengthen the understanding of the physical structure of the system. Groundwater was sampled from 103 bores across the aquifer, over a period from March to November 2002. Samples were analysed for their nitrate, nitrite, and ammonium concentrations, while on-site measurements of conductivity and pH were also made. A smaller number of samples were also analysed for organic nitrogen, total iron, and total manganese to help interpret the results of the inorganic nitrogen analysis.
The concentrations of nitrate and ammonium showed a distinctive spatial distribution throughout the aquifer. Nitrate was present in elevated concentrations (up to 11.36 ppm NO3-N) in distinct regions in East Taieri, while it was present in universally low or undetectable concentrations in the confined region of West Taieri (i.e. <0.6 ppm NO3-N). Ammonium was present in elevated concentrations (up to 2.36 ppm NH4-N) along the Titri Fault side of West Taieri, while it was generally present in low or undetectable concentrations throughout the remainder of West Taieri and all of East Taieri (i.e. <0.2 ppm NH4-N). Both species showed no significant temporal variation. Nitrite concentrations were universally low throughout the system (<0.03 ppm NO2-N), with only a handful of bores yielding values above the detection limit of 0.002 ppm NO2-N. No distinct spatial distribution was identified, while too few bores had detectable nitrite for statistical analysis of temporal variation.
The results indicate the Waihola silt/sand unit is providing excellent confinement to the aquifer in West Taieri, thereby protecting it from any potential contamination that might be arising from the increasingly intensive dairying operations in this region. In contrast, nitrate is able to enter the alluvial fans along the northern and western margins of the basin, and the main aquifer in parts of East Taieri. Redox conditions are likely to be affecting the distribution of nitrate concentrations in the latter.
- Life since MSc
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