Legislative requirements such as the National Policy Statement for Freshwater Management 2014 and other central government policies have put pressure on farmers to farm within water quality limits, while still increasing productivity and yield. This has furthered the need for research investigating contamination in water sources resulting from increasing effluent discharge and use of fertilisers, to find potential cost-effective mitigation measures that can be adopted across the farming sector.

The ESR groundwater team are working on developing passive remediation technologies based on enhancing natural attenuation processes to target removal of nitrate contamination in groundwater. In collaboration with NIWA, the team recently launched a 3-year long research project that aims to pilot an in-stream woodchip denitrifying bioreactor as a method for removing nitrogen in drainage water on agricultural land.

The work is being led by ESR senior groundwater scientist Lee Burbery and groundwater technician Phil Abraham. The field pilot study is being conducted on a dairy farm in Woodbury, South Canterbury with support from farmer John Saywell who is keen to see the betterment of dairying, and is happy to be working alongside ESR scientists to find sustainable solutions that will boost the profile of the dairying sector.

A bioreactor is a buried trench packed with woodchips, through which nitrate-laden drainage water is diverted before it discharges to a natural water course that might be sensitive to nitrogen pollution. The woodchips act as a host for bacteria which remove nitrate from water by converting it to harmless atmospheric nitrogen gas.

Denitrifying bioreactors are proving a popular edge-of-field nitrate mitigation measure in US farming states like Ohio, Iowa and Dakota. The goal of the project at Woodbury is to examine the effectiveness of these engineered systems in a Canterbury setting to assess whether they offer a practicable solution for Canterbury farmers.  

The project is in its first phase, collecting baseline data to characterise the hydrodynamics of the drainage system on John Saywell’s farm and evaluate nitrate fluxes that will inform design of the bioreactor. Automated measurements are being made of flow and nitrate concentrations in the drains on John’s farm every 15 minutes. A telemetry system operated by NIWA channels the results to the internet so that the in-stream water quality farm can be monitored remotely. The second phase will see design and installation of a denitrifying bioreactor, planned for 2017.


Read more in this article(external link) published in the Geraldine News.


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