Publications: Research reports and publications

Benthic cyanobacteria and toxin production in the Manawatu - Wanganui region

1 January, 2011
Cawthron Report 1959. Prepared for Horizons Regional Council.


Benthic, mat-forming cyanobacteria are common throughout New Zealand rivers. The most widespread mat-forming genus is Phormidium. In New Zealand Phormidium is known to produce two neurotoxic compounds; anatoxin-a (ATX) and homoanatoxin-a (HTX). These toxins are a health threat to humans and animals when consumed or when there is contact with contaminated water. There have been numerous dog deaths and health warnings resulting from proliferations of toxic Phormidium in New Zealand's rivers.

Marked differences in the presence of Phormidium mats, and the presence and concentrations of toxins within mats, have been observed both within and between rivers. Until recently there has been limited knowledge on mechanisms leading to Phormidium proliferations and on why some mats contain toxins and others do not.

Phormidium prevalence in the Manawatu-Wanganui region has been notable over the past few years. This is of particular concern in rivers that are used as drinking water sources or at sites used for recreational activities. Prior to this study there was limited information on possible reasons for variability in Phormidium abundance among Manawatu-Wanganui Rivers and no toxins had been detected in Phormidium from this region, although only a limited number of samples had been analysed.

Phormidium abundance was surveyed (weekly or monthly) at fourteen sites from ten rivers. When mats were present, samples comprised of sub-samples pooled from ten Phormidium mats, were collected. The pooled samples were analysed for ATX, HTX and their degradation products using liquid chromatography-mass spectrometry. Water temperature was recorded and samples were collected monthly for analysis of nitrite (NO2-N), nitrate (NO3-N), ammonia (NH4-N), total nitrogen (TN), dissolved reactive phosphorus (DRP) and total phosphorus (TP)...