Oct. 14 (UPI) -- In lakes all over the world, algal blooms are getting more severe. In a new global survey of large, freshwater lakes -- the first of its kind -- scientists found algal blooms have become more frequent and intense over the last 30 years.
Algal blooms can negatively affect humans and ecosystems by robbing freshwater of sufficient oxygen supplies and producing dangerous toxins.
"Toxic algal blooms affect drinking water supplies, agriculture, fishing, recreation, and tourism," Jeff Ho, researcher at the Carnegie Institution for Science, said in a news release. "Studies indicate that just in the United States, freshwater blooms result in the loss of $4 billion each year."
Most studies of algal growth have focused on specific bodies or water or regions, like the Great Lakes. For the new study, published this week in the journal Nature, researchers used images captured by the NASA's Landsat 5 near-Earth satellite to analyze the size and growth patterns of algal blooms in 71 large lakes across 33 countries and six continents.
With the help of Google Earth Engine's algorithms, scientists analyzed more than 72 million data points.
"We found that the peak intensity of summertime algal blooms increased in more than two-thirds of lakes but decreased in a statistically significant way in only six of the lakes," said Carnegie scientist Anna Michalak. "This means that algal blooms really are getting more widespread and more intense, and it's not just that we are paying more attention to them now than we were decades ago."
Though the survey revealed a global trend in the intensification of algal blooms, the reasons for bigger, denser and faster growing blooms were different in each lake. Different combinations of factors -- including fertilizer use, rainfall and temperature -- accounted for the increased summertime algae growth.
Despite the differences in the causes of more intense algal blooms, the latest analysis showed the lakes that experienced the lowest amount of warming over the last three decades were more likely to avoid intense algae growth and maintain their water quality.
Lago de Cahora Bassa in Mozambique was one of the few lakes that showed improvements in water conditions over the last 30 years. Meanwhile, the water quality in Florida's Lake Okeechobee has dramatically deteriorated in recent years as algae blooms have grown larger and more intense.
"This finding illustrates how important it is to identify the factors that make some lakes more susceptible to climate change," Michalak said. "We need to develop water management strategies that better reflect the ways that local hydrological conditions are affected by a changing climate."