Under higher pressure, though, below 100 meters, the vesicle ruptures and the organism dies. In the past, normal mixing annually rotated these phytoplankton (a larger category of micro-organisms that includes cyanobacteria) below 100 meters, killing them off. Now, they're not always mixed below their survival threshold.
As Posch put it: "Lake surface warming creates a fertilizing effect." The results do not bode well, neither for Lake Zurich nor for many other lakes around the world.
Lake Garda in the southern Alps, part of a chain of deepwater lakes in northern Italy, also has a thriving population of P. rubescens. Nico Salmaso, a researcher at the Limnology and Fresh Water Ecology research group at Fondazione Edmund Mach, an agrarian institution, has studied this lake for many years. He says P. rubescens constitutes 85 percent of the cyanobacterial biomass found in the lake.
The health of Lake Garda and its neighbors in Italy's northern Lake District, including lakes Como, Orta and Maggiore, is the foundation of the area's economy.
"Lake Garda alone brings in over 25 million tourists a year," Salmaso said. And then there is the much larger Lake Como, which also has a seasonal cyanobacterial bloom. Its presence, and the presence of other phytoplankton, makes lake water appear muddy and unappealing.
"All of these lakes were once oligotrophic," Salmaso said, meaning low nutrient concentrations, little plant growth, not supporting life. "The only way to control the cyanobacteria is by controlling the external nutrient load."
A successful remediation effort at Lake Maggiore has restored that lake to near-oligotrophic status. With the help of a huge inflow of money from the European and Italian governments, residents and visitors hope to see the same in Lake Garda.
A toxic legacy
P. rubescens and its close cousins in the algae and phytoplankton world, including several other kinds of cyanobacteria, threaten people in ways that are far more serious than soupy-appearing waters.
"Cyanobacteria produce hepatotoxins as well as neurotoxins," Salmaso said. "There is huge concern at the European level in different [subalpine] lake typologies. In Europe, animals are already dying in certain badly affected lakes. A little cyanotoxin can go a long way, and you don't want that."
Cyanobacteria are also now suspected to be at the root of major neurological diseases, long thought to be caused by inherited genetic mutation.
In a landmark scientific paper, researcher Paul Cox and his colleagues, now at the Institute for EthnoMedicine in Jackson, Wyo., found that cyanobacteria produce a neurotoxic amino acid known as BMAA. It has been found in the brains of patients with amyotrophic lateral sclerosis (ALS), Alzheimer's disease and Parkinson's disease. Epidemiologically speaking, this correlation is hardly far-fetched.
In areas surrounding Lake Mascoma in New Hampshire, researchers mapping new ALS cases found the prevalence of the disease to be 10 to 25 times the normal rate among patients who lived in areas with known cyanobacterial blooms. In southern France, where a substantial cluster of ALS cases has occurred, researchers found high BMAA levels in oysters, a favorite local delicacy, which concentrate the toxin.
Although scientists shy away from ascribing direct causality between particular micro-organisms and a specific cluster of disease outbreaks, it is clear to many observers that climate change is making the world a friendlier place to some organisms that can cause harm. The evidence for a causal effect between cyanobacteria and the incidence of ALS, Parkinson's disease and Alzheimer's disease is slowly but surely mounting.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500