New Zealand’s alluvial aquifers in Canterbury, Hawkes Bay, Wairarapa, Southland, Waimea and Marlborough supply irrigation water to large, highly productive farming areas. However, the enhanced production also increases the use of fertiliser and the amount of animal waste that is generated. The nitrogen from these products washes straight through the alluvial soils, into the aquifers, which have little capacity to reduce the nitrates. These aquifers feed lakes and rivers, putting ever increasing quantities of nitrates into the environments loved by New Zealanders.
This tension between farming needs and the environment is increasing, making it likely that production will be constrained in many areas such as Canterbury and the Hawkes Bay.
Finding an innovative solution
Alluvial aquifers are characterised by fast and heterogeneous groundwater flow patterns, which makes it very challenging to develop, design and implement remediation options. Our research is instead looking at creating conditions in fast-flowing alluvial aquifiers that will bring about denitrification.
ESR is developing innovative approaches such as denitrifying Permeable Reactive Barriers (PRB). We use advanced shallow depth geophysics, DNA tracers and groundwater microbial community analysis to characterise the aquifer and effectively design and implement mitigation tools like this.
Another technology being trialed is the use of denitrifying bioreactors to treat nitrate from artificial drains. An instream bioreactor using woodchips is being installed near the end of a drainage system that collects shallow groundwater in the Barkers Creek catchment, South Canterbury. The bioreactor stimulates denitrification and reduces the nitrate before it enters Barkers Creek. Denitrification walls are a tried and tested concept in slow moving sandy aquifer systems where they have proven effective at treating nitrate from point pollution sources. There are no examples, however, of these remediation systems having been installed in gravel aquifers such as those found in Canterbury. In this regard, ESR's pilot study represents a world-first.
These new methods for on-farm denitrification will enable more sustainable farming systems. It is estimated that our technology can reduce nitrogen by around 13 kgN/ha/yr, which is a significant proportion of required reductions (typically 10 – 30 kgN/ha/yr.
The research team
Our current research team includes people from ESR and Southern Geophysical, and the previous related project also included collaboration with Lincoln Agritech(external link), Aqualinc Reseach(external link), and University of Canterbury(external link).
Ngāi Tahu Farming and Environment Canterbury have been involved in proposal development and field site selection and actively monitor progress and results.
Murray Close, ESR Christchurch, email@example.com, DDI: 03 351 0014
Theo Sarris, ESR Christchurch, firstname.lastname@example.org, DDI: 03 351 0079