Mitigating E. coli in Taranaki and Manawatū-Whanganui

Water that is contaminated with animal faecal matter – which E. coli is an indicator for – poses a significant health risk and limits how we can use water for drinking, mahinga kai, or recreational activities.

Both TRC and HRC wanted advice around existing and new mitigation strategies to model E. coli reduction in their respective regions. In the long term, this will inform approaches for reducing E. coli levels in rivers and streams and enable both councils to implement Essential Freshwater polices under the National Policy Statement for Freshwater Management (NPS-FM).

Richard Muirhead, Sandy Elliot and other experts provided their support by reviewing existing industry scientific information and literature. They also identified mitigation strategies that could be modelled to determine their effectiveness for reducing E. coli loads in the Taranaki and Manawatū-Whanganui regions. Mitigation strategies were evaluated and prioritised in a joint memorandum summarising their findings.

A range of mitigation strategies were recommended for further modelling based on current evidence of their effectiveness. These included:

• Additional retirement of marginal land through sustainable land management programmes.
• Additional stream fencing for stock exclusion.
• Additional improvements to municipal and domestic wastewater treatment processes.
• Detainment bunds for intercepting contaminated overland flow.
• Additional vegetated riparian buffers, including grass buffer strips adjacent to waterways.

Richard and Sandy also recommended the implementation of several other mitigation strategies, despite difficulties associated with modelling their benefits at the regional level. These mitigations were recommended as they are considered ‘common-sense’ measures, or because they have been included in recent regulations. These include:

• Deferred or low-rate dairy effluent irrigation in locations with risky soils.
• Bridged stream crossing regulations.
• Stock exclusion from wetlands and critical source areas.
• Provision of alternative deer wallows.
• Strategic grazing of forage crops.

This was critical advice for both TRC and HRC to assist them with considering the tools and strategies available for reducing E. coli in freshwater. The strategies identified can be progressed to the modelling stage, which will help determine overall costs and benefits for regional implementation.

It has also been encouraged that TRC and HRC share these findings with other regional councils and unitary authorities, to help increase knowledge around the country and assist other councils to respond to the NPS-FM.