Tracking the toxic consequences of hotter summers

Freshwater pollution already represents a widespread threat to the health of both humans and ecosystems. New findings reported in the journal Inland Water Biology reveal how rising temperatures can exacerbate this problem by fuelling the growth of toxic microbial species in polluted waters.

Historically, the surface waters of the Cheboksary Reservoir in western Russia reach a peak summer temperature of roughly 20 °C. But warmer weather has increasingly become the norm over the past several decades, and in July of 2010, the water temperature hit an unprecedented peak that exceeded normal conditions by an average of 8.7 °C.

“This was unexpected for meteorologists, hydrologists and hydrobiologists,” says Aleksandr Kopylov from the Russian Academy of Sciences. “And for the first time we had an opportunity to assess the features of ecosystem function in conditions of anomalously high water temperature that lasted almost two months.”

In order to characterize the effects of this climatic shift, Kopylov and his colleagues collected numerous water samples from various sites at the reservoir and profiled their algal and microbial content.

“We noted considerable negative changes in the structural and functional organization of the plankton community,” says Kopylov.

Perhaps the most striking of these shifts was a sharp increase in the population of cyanobacteria, a category of photosynthetic microbes that can produce an array of toxic compounds that are harmful to humans as well as other life. Importantly, the researchers noted that the levels of these ‘cyanotoxins’ in July 2010 were well above the safe threshold designated by the World Health Organization.

Warmer weather was not the sole factor influencing the growth of these harmful microbes, however. The Cheboksary Reservoir experiences significant pollution as a consequence of being downstream from a power station and the city of Nizhny Novgorod, and these elevated levels of pollutants included high concentrations of nutrients that helped promote these cyanobacterial blooms.

Kopylov notes that this reservoir is commonly used for drinking water, fishing and recreation, and such surges in cyanotoxin levels could put human health at risk. As global temperatures continue to rise, other bodies of water in high population density areas could also succumb to a similar phenomenon. Indeed, other reservoirs along the Volga river—the primary source of the Cheboksary Reservoir—have reported a steady climb in summer water temperatures. Kopylov’s team plan to continue to closely monitor these sites for similar microbial shifts as well as other negative consequences of climate change.