Did spatial and temporal variations in water quality influence cyanobacterial abundance, community composition and cell size in the Murray River, Australia during a drought-affected low-flow summer?

Abstract

Severe drought in south-eastern Australia during the 2008–2009 spring, summer and autumn period resulted in low flows in the Murray and Edward Rivers, a major river system of the region. We investigated whether such conditions produced marked spatial and temporal variations in water quality and in the abundance, community composition and cell size of six commonly occurring cyanobacterial species in the river. Water quality data and cyanobacterial samples were collected at 22 sites spanning almost 1900 km of river. Significant spatial and temporal variation in water quality was found in the rivers. Four cyanobacterial species had significantly higher abundances in the upper and middle sections of the Murray and Edward Rivers, and significant temporal variations occurred in three species. Community composition also varied significantly both spatially and temporally. There were significant spatial differences in the cell size of three species, and significant temporal variation occurred in five species. However, water quality was found to provide a poor explanation of the variance observed in the cyanobacteria, possibly due to their continual replacement by river flow at the sampling sites. Increased cyanobacterial occurrence in rivers is likely to be more common under future climate change scenarios.