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Aims

Cyanobacteria, has become a significant water quality issue in New Zealand over the past decade. Cyanobacteria can produce toxins fatal to humans and dogs under certain conditions with obvious public concern. Reduced river flows from drought and increased water abstraction, combined with increasing nutrient levels have been linked with the increased growth of cyanobacteria. However, the relationship between hydrological regimes and cyanobacteria growth is unclear. Does substrate movement, or lack of it, contribute to biomass accrual. Understanding the relationship between substrate stability and cyanobacteria growth may allow river managers to limit growth by managing for greater bed turn-over. However, there is currently no effective method to assess substrate stability. This paper examines a new index for the rapid assessment of substrate stability, and the link with cyanobacterial biomass in a range of Canterbury rivers.