A recent item by New York Times blogger Emma Bryce on the Yangtze River in China changing color from brown to a reddish orange caused a reader to write in and describe what she saw as a spate of red tide events around the world and inquired about the cause.
While the Yangtze River color change was later found to probably be a result of heavy clay deposits or industrial dye, Ms. Bryce did further research and found that algal blooms had caused this reddening phenomenon in several places this year. She cited 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.
Dr. Juhl, a biological oceanographer at Columbia University and an algal expert, acknowledged “ there’s a whole spate of anecdotal reports that create the impression that something is going on,” 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. 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.” Tracking an increase in occurrences is difficult because no one has been sampling blooms globally for long enough.
The warming of the seas as a result of climate change and a trend of increased salinity could be shaping blooming episodes as well as fertilizer in agricultural runoff and sewage that create nutrient rich environments where algae can thrive. Even weather events can help it flourish said Dr. Juhl.