Water quality information for farmer decision making in the Nguturoa catchment, Manawatu

Abstract

In 2021 a group of farmers and landowners along the Nguturoa Stream in the Manawatū-Whanganui Region began a study into water quality. The farmers felt that they needed precise information to establish their farming priorities for improving the waterway, and for monitoring the effects of making management changes. Monthly sampling and laboratory testing were carried out across the catchment and field tests were
also undertaken at the time of sampling. The results were compared to those in the Manawatū River, the ultimate receiving environment for the catchment. The results highlighted that throughout the year the water in the Nguturoa Stream had lower dissolved inorganic nitrogen concentrations than the Manawatū River, but it had higher organic nitrogen concentrations in most months. Almost all the phosphorus results were above those measured in the Manawatū River as were the turbidity results. On seven occasions the Nguturoa Stream had E.coli results above the standard in the National Policy Statement for Freshwater Management 2020. Compared to the laboratory test results, the field
tests that were used were found to be inconsistent and unreliable for catchment and farm management decision making. The results highlighted for the farmers that overland flow was a more important source of instream contamination than they expected, for nitrogen,
phosphorus and E.coli as well as sediment.