NASAのインスタグラム(nasa) - 4月14日 03時11分

For phytoplankton in Louisiana’s Lake Pontchartrain, ideal conditions to flourish recently included a combination of ample sunlight and nutrients, a long stretch of warm weather, and calm winds. Colorful blooms of phytoplankton appeared on the north side of Lake Pontchartrain several times in March 2018, seen here on March 3, 2018 by the Landsat 8 satellite.

Lake Pontchartrain and other nearby lakes and inlets compose a huge estuary east of the Mississippi Delta. Unusually warm temperatures in February and March helped spur the early spring bloom, even before nutrients from the Upper Mississippi River could pour into the region. Blooms become more likely when excess river nutrients reach the lake through the Bonnet Carré Spillway. During flood season, the spillway is occasionally opened to divert excess water from the Mississippi River and relieve pressure on levees near New Orleans.

On March 8, the U.S. Army Corps of Engineers started to open the spillway in response flooding along the Ohio and Mississippi Rivers. Such inputs of nutrients—often fertilizer from the Mississippi watershed—can set the stage for large blooms of algae and cyanobacteria—single-celled organisms that can contaminate drinking water and pose a risk to human and animal health. Satellite imagery can help identify the occurrence of a phytoplankton bloom, but direct sampling is required to discern the species.

Image credit: NASA/@USGS
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