Rangitīkei farmers take lead in water quality monitoring

RRCC now supports 24 sub-catchment groups and more than 110 water-quality monitoring sites across the Rangitīkei, Turakina and Whangaehu river catchments – a network that continues to grow.  

Established in 2017, the farmer led RRCC is focussed on understanding and improving  water quality and ecology in local waterways.

Landowners have consistently sampled river and stream sites, on a monthly basis, for between one and seven years, with newer sites continuing to be added, creating one of the most robust and comprehensive long-term freshwater datasets in the Horizons Region.

Sampling tracks key water quality indicators of suspended fine sediment (turbidity), nutrients (ammoniacal nitrogen, nitrate nitrogen and dissolved reactive phosphorous), and pathogens (E. coli). This data provides a valuable picture of stream health in catchments that were previously largely unmonitored.

“Parts of the Rangitīkei River and its tributaries are popular with anglers for their clear waters and abundant rainbow trout population, and our monitoring helps us understand what’s supporting that,” Dalrymple says.

Supported by Ministry for Primary Industries Catchment Extension Services Funding, all monthly samples are analysed by Central Environment Laboratories in Palmerston North, with independent assessment of the results by Traverse Environmental. Results are compared between sites and against National Policy Statement for Freshwater Management attributes and Horizons One Plan targets.  

This provides landowners with a clear picture of how their local streams are tracking.

Overall, plant-available nitrogen and phosphorus concentrations suggest a generally low risk of nuisance periphyton growth across many mainstem and tributary sites.

However, the monitoring results also revealed some unexpected finding . Several “reference sites” – with predominantly natural land cover – did not meet One Plan targets for suspended fine sediment and plant available phosphorus.

This has also been found in some other New Zealand waterways and indicates that elevated dissolved reactive phosphorous (DRP) is not always solely related to land use. Urban run-off, road run-off, wastewater, natural geology, legacy soil disturbance, forestry and land conversion all play important roles depending on the area. In the Rangitīkei catchment, elevated DRP is likely influenced in part by the naturally phosphate-enriched soft sedimentary and volcanic geology, soils, and natural erosion processes of the Rangitīkei. 

Monitoring results for E. coli, an indicator of the potential presence of nasty pathogens such as Campylobacter, show that many sites are suitable for swimming during dry weather conditions when this is likely to occur. However, there are also some sites that are sometimes impacted, highlighting that, while progress is being made, there is still work to do to improve water quality in parts of the catchment.

Dalrymple says none of this work would be possible without support from the Ministry for Primary Industries, Horizons Regional Council, and – most importantly – the commitment of local landowners. 

“Dedication from our landowners is helping us all better understand the true condition of our waterways and where we can make meaningful improvements.”