"I looked at five years of satellite data," said Beman, lead author of the study. "There were roughly four irrigation events per year, and right after each one, you'd see a bloom appear within a matter of days."
Each bloom was enormous, he said, covering from 19 to 223 square miles (50 to 577 square kilometers) of the gulf and lasting several days. "Sometimes eddies actually pulled the plumes across the gulf, from the mainland side all the way to the Baja Peninsula," Beman added.
"Mike found that immediately following each one-week window in which much of the valley was irrigated, there was a response in the ocean off the coast of the Yaqui Valley," Matson explained.
"We were quite surprised," Arrigo added, noting that the Nature paper marks the first time that scientists have documented a "one-to-one correspondence between an irrigation event and a massive algal bloom."
Red tides and dead zones
According to the researchers, artificially induced algal blooms could have major impacts on recreational and commercial fishing, major industries in the gulf. Red tides, for example, can cause outbreaks of life-threatening diseases, such as paralytic shellfish poisoning, which can shut down mussel and clam harvesting for long periods of time.
Another concern is hypoxia, or oxygen depletion, caused by excessive algae growth. As the algal mass sinks, it is consumed by bacteria, which use up most of the oxygen in the water as they multiply. The result is an oxygen-depleted dead zone at the bottom of the sea where few creatures can survive. A massive dead zone appears every summer in the Gulf of Mexico off the coast of Louisiana and Texas. Scientists believe that agricultural runoff from the Mississippi River plays a pivotal role in creating this annual dead zone, which measured 8,500 square miles (22,000 square kilometers) in 2002-an area bigger