Abstract
Cyanobacterial blooms are becoming more common in freshwater systems, causing ecological degradation and human health risks through exposure to cyanotoxins. The role of phosphorus and nitrogen in cyanobacterial bloom formation is well documented and these are regularly the focus of management plans. There is also strong evidence that trace metals are required for a wide range of cellular processes, however their importance as a limiting factor of cyanobacterial growth in ecological systems is unclear. Furthermore, some studies have suggested a direct link between cyanotoxin production and some trace metals. This review synthesises current knowledge on the following: (1) the biochemical role of trace metals (particularly iron, cobalt, copper, manganese, molybdenum and zinc), (2) the growth limitation of cyanobacteria by trace metals, (3) the trace metal regulation of the phytoplankton community structure and (4) the role of trace metals in cyanotoxin production. Iron dominated the literature and regularly influenced bloom formation, with 15 of 18 studies indicating limitation or colimitation of cyanobacterial growth. A range of other trace metals were found to have a demonstrated capacity to limit cyanobacterial growth, and these metals require further study. The effect of trace metals on cyanotoxin production is equivocal and highly variable. Better understanding the role of trace metals in cyanobacterial growth and bloom formation is an essential component of freshwater management and a direction for future research.
Highlights
Introduction to Cyanobacteria in Freshwater SystemsThroughout the world, there is an increasing demand for freshwater utilised for irrigation, industry, recreation and direct consumption [1]
Better understanding the role of trace metals in cyanobacterial growth and bloom formation is an essential component of freshwater management and a direction for future research
Identifying sources of trace metals and how they impact phytoplankton communities may be important in understanding toxic cyanobacterial bloom dynamics
Summary
Throughout the world, there is an increasing demand for freshwater utilised for irrigation, industry, recreation and direct consumption [1] Satisfying both ecological and anthropogenic water requirements is challenging and may prove more difficult in the context of climate change and a growing human population [2]. Nutrient pollution and low-velocity flow regimes promote the development of dense, toxic, cyanobacteria blooms [18,19,20,21] This trend is likely to continue as cyanobacteria are expected to flourish under the environmental conditions predicted for global climate change [22,23,24] and toxic cyanobacterial taxa are comprising an increasing proportion of the phytoplankton community under bloom conditions [19,22]
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