After studying 71 lakes in 33 countries, researchers found that phytoplankton and algae blooms are generally increasing around the world.
Through episodic and regional studies, scientists have observed that phytoplankton blooms have been occurring more often in lakes around the world in recent decades. But until recently, no one had assembled a global, wholistic view of the phenomenon. Scientists from Stanford University and NASA recently decided to measure the blooming trends globally. What they found was discouraging.
Working with the long satellite record from Landsat, Stanford environmental scientist Jeff Ho and colleagues examined 71 lakes in 33 countries on six continents. They focused on summertime conditions in large lakes (greater than 100 square kilometers/40 square miles) with different physical settings, latitudes, and levels of human impact.
They used computers to analyze nearly 32,000 images spread across 28 years, training the computer to detect strong near-infrared signals. Phytoplankton blooms have high concentrations of chlorophyll, the same pigment that helps land-based plants absorb sunlight to make energy. Chlorophyll tends to reflect near-infrared light and absorb blue and green light, so intense blooms produce strong near-infrared signals in infrared imagery.
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Image via NASA Earth Observatory
