Green Blog: A Red Tide Epidemic?

As we mentioned here in an On Our Radar item this week, the Yangtze River in China changed from a warm brown to a deep, rusty orange a few days ago. Striking photographs showed a ??crimson current advancing alongside a stretch of untainted water. One Green reader wrote in to describe what she saw as ?a spate of ?red tide? events around the world and inquired about the cause.

At first some scientists suspected that an algal bloom might have caused the Yangtze River to change color, but researchers now suggest that a heavy clay deposit or industrial dye was responsible. Yet ?algal blooms do seem to have caused this reddening phenomenon in several other places this year. Here?s a brief sampling.

Patches of orange and pink spread across Lake Maharlou in Iran in April; salt collectors had to wade through waters resembling a strawberry milkshake at Lake Retba in Senegal in June. The Azov Sea on the southern coast of Russia and Ukraine assumed a ?ruby-like hue in July. An intensely salty lake in Camargue, France turned red in August, as did Lake Tuz in Turkey, which is usually chalky.

The Senegalese are so accustomed to Lake Retba?s change in color that they refer to it as Lac Rose, or the Pink Lake. Which is part of the point here: these gaudy displays are fairly common. The question is whether ?they?re on the rise.

We consulted Andrew Juhl, a biological oceanographer ?at ?Lamont-Doherty Earth Observatory at Columbia University who is an expert in all things algal.

?There?s a whole spate of anecdotal reports that create the impression that something is going on,? Dr. Juhl acknowledged. But he cautioned against assuming that algae is spreading in any extraordinary way this year.

?It?s really hard to say, because in order to say whether there is a change in the frequency of blooms you have to be out sampling,? Dr. Juhl said. ?There is a reasonably good reason to believe that these blooms are more frequent and more widespread and occurring in places that they didn?t before, but it?s very hard to talk about a particular year.?

Researchers know that algal blooms have been sprouting for millenniums. Yet tracking an uptick in occurrences is difficult because no one has been sampling blooms globally for long enough, he said.

The warming of the seas as a result of climate change ?and a trend of increased salinity could be shaping blooming episodes, but for the time being the phenomenon can easily be attributed to more direct factors, Dr. Juhl said.

Fertilizer in agricultural runoff and sewage create nutrient-rich environments where algae can thrive, for example, he said, and ballast water from traveling ships takes algae on far-flung voyages, helping it to spread.

Weather events ?like the 1989 big freeze in Texas?s Laguna Madre, which killed off protozoans that prey on algae, can also help it flourish unchecked, Dr. Juhl added.

There?s even a species that craves the special circumstances created by salinity and restricted lake environments: Dunaliella salina, he said. This elliptical algae produces the pigment beta carotene, which helps the algae tolerate ?intense sun. The spread of this pigment in turn gives lakes their various hues of crimson, ?sienna and strawberry. ?It looks weird and people stay away from it,? Dr. Juhl said, but D. salina is mostly harmless to humans.

While it?s hard to judge the extent to which climate change played into this year?s events, Dr. Juhl said it was important to remember that global warming is not the only environmental negative resulting from human activity.

?The fertilization of terrestrial environments by massive application of nitrogen compounds to the earth ? that is also causing massive global change,? Dr. Juhl said. ?When you mess with those things, there will be a response.?

Source: http://green.blogs.nytimes.com/2012/09/13/a-red-tide-epidemic/?partner=rss&emc=rss

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