Blooming algae: a Canadian perspective on the rise of toxic cyanobacteria

Abstract

Algal bloom reports are on the rise across Canada. While eutrophication is the main driver, other stressors of aquatic ecosystems, specifically climate change and food web alterations from the spread of invasive species and overfishing, are compounding factors acting in concert or independently. Current models can predict the average algal and cyanobacterial biomass concentrations across temperate lakes as a function of nutrients, but models to specifically predict harmful algal composition and toxicity are lacking. At the within-lake scale, where management occurs, strong year to year variations in cyanobacterial blooms remain challenging to explain, let alone predict. The most common cyanotoxins, the hepatotoxic microcystins, are chemically diverse with some variants more toxic than others and with greater propensity for persistence and bioaccumulation. These differences have been largely overlooked, as current guidelines have been based on microcystin-LR, considered the most common variant. Microcystin-LA is also encountered in Canadian waters and appears to exhibit greater persistence and bioaccumulation. With cyanobacterial blooms most likely to increase across the country, including the north, guidelines and policies for cyanotoxins in drinking and recreational waters as well as fish will need to be developed for the protection of ecosystem and human health. Ultimately, control of eutrophication is the most important option for managing toxic cyanobacterial blooms; nitrogen and phosphorus need to be considered as environmental contaminants, as both play a role in controlling the dominance of toxigenic cyanobacteria.Résumé : Les signalements de fleurs d'eau sont en hausse au Canada. Si l'eutrophisation en est la principale cause, d'autres facteurs de stress pour les écosystèmes aquatiques, plus précisément les changements climatiques et les modifications des réseaux trophiques découlant de la propagation d'espèces envahissantes et de la surpêche, agissent de concert avec cette dernière ou de manière indépendante. Les modèles actuels peuvent prédire les concentrations moyennes de biomasse d'algues et de cyanobactéries dans les lacs tempérés en fonction des nutriments, mais des modèles permettant de prédire la composition et la toxicité des algues nuisibles en particulier manquent toujours. À l'échelle d'un lac faisant l'objet d'une gestion, il est difficile d'expliquer et encore plus difficile de prédire les fortes variations interannuelles des proliférations de cyanobactéries observées. Les cyanotoxines les plus répandues, les microcystines hépatotoxiques, sont variées sur le plan chimique, certaines variantes étant plus toxiques que d'autres et plus susceptibles de persister et de se bioaccumuler. Ces différences ont été largement négligées, les directives actuelles étant basées sur la microcystine-LR, considérée comme la variante la plus répandue. La microcystine-LA est également présente dans les eaux canadiennes et semble caractérisée par une persistance et une bioaccumulation plus grandes. Co...

Multi-year succession of cyanobacteria blooms in a highland reservoir with changing nutrient status, Guizhou Province, China

“…There was no significant relationship between TN:TP ratios and cyanobacterial blooms, although some importance in the combined effect of these nutrients could be seen for Microcystis spp. This has also been reported by other authors (Pick, 2016 and references within). With lower nutrient loads (TP <0.04 mg L -1 ; TN <1.8 mg L -1 ) after 2010, competitive species shifts to P. limnetica occurred along with other taxa from the diatom, chlorophyte, chrysophyte and cryptophyte communities.…”

“…Relationships of cyanobacteria growth with nitrogen and phosphorus are still a hotspot of uncertainty in the scientific literature (Anderson et al, 2002;Pick, 2016), because N and P are essential elements for phytoplankton growth (Conley et al, 2009). Some studies have shown TP concentration below 0.01 mg L -1 , will limit the size of phytoplankton to <35-50 µm, while TP concentrations >0.05 mg L -1 , will encourage the dominance of larger phytoplankton species (Watson et al, 1992) Under fish farming, the dominant phytoplankton were colonial Microcystis spp, A. flos-aquae and Anabaena spp.…”

“…These blooms are associated with poor water quality, accumulation of aquatic biomass and low saturated oxygen levels (Jonas et al, 2014;Wiegand and Pflugmacher, 2005). Cyanobacteria under certain conditions can also produce toxins which along with taste and odor compounds have negative biological and human health effects (Jonas et al, 2014;Pick, 2016;Wiegand and Pflumacher, 2005). Massive proliferations of harmful algae in freshwater and marine ecosystems have caused losses to natural resources, national economies, and resulted in human sickness and death worldwide (Bláha et al, 2009;Lewitus et al, 2012;Ma et al, 2014).…”

“…Two contributors to cHABS, Aphanizomenon flosaquae Ralfs ex Bornet & Flahault and Microcystis spp have been correlated to increased nutrient inputs, especially phosphorus and nitrogen (Liqiang et al, 2003;Conley et al, 2009;Ma et al, 2015;O'Neil et al, 2013). Paerl and Huisman (2009) and Pick (2016) also attributed climate change (warmer temperatures) to changes in hydrological cycles and blooms. Further, Knoll et al (2008) have associated cHABs to invasive species events.…”

Food crops irrigated with cyanobacteria-contaminated water: an emerging public health issue in Canada

“…(Pick, 2016). An increase in extreme weather events, such as droughts, introduces competition for scarce water resources and drives cyanobacterial growth in diminished water bodies.…”