More precipitation due to climate change = greater runoff and worsening water quality

Satellite imagery of a toxic algal bloom on Lake Erie in 2011. The image is gorgeous, but microcystis aeruginosa, the green algae pictured here, is toxic to mammals.
NASA Earth Observatory via Popular Science.

From Popular Science (Kendra Pierre-Louis):

When we think about how climate change will impact water, we “tend to think about droughts or flooding or extreme rainfall,” says Anna Michalak. “But the linkages between climate and water quality are potentially just as strong as climate and water quantity.”

Michalak, who heads up a lab in Department of Global Ecology at the Carnegie Institution for Science on the campus of Stanford University, published a study today in Science suggesting that because climate change will lead to more rain in some places, water quality around the world will decline.

To explain how rain can kill water quality, let’s start with a refresher on the Gulf of Mexico: an aquatic dead zone has developed there every summer for the past 32 years. In 2016, the dead zone spanned 6,000 square miles (roughly the size of the state of Connecticut). This year the National Oceanic Atmospheric Administration (NOAA) predicts it will reach the size of New Jersey, or around 8,700 square miles. The source of the Gulf’s woes is the Midwestern Corn Belt, where nitrogen from fertilizers runs off of the farms into streams and rivulets, causing what’s known as eutrophication. Eutrophication, in short, happens when there are too many nutrients in the water.

From the corn belt, the nutrients make their way to the Mississippi River and down to the Gulf. The combination of nitrogen and warm summer temperatures feeds the region’s algae, who for one brief moment become rock stars. They bloom brilliantly—then die all at once. When they die, bacteria feast upon their remains, sucking oxygen from the water in the process. Fish might not breathe air, but they do need oxygen to survive. So the speediest species leave in search of better aerated waters. Slower critters, like the Gulf Coast’s famed oyster, simply die. Their decaying remains feed the dead zone and help it grow, perpetuating the region’s loss of life. The process only slows when fall’s cooler temperatures help close that terrible feedback loop.

Along with lead study author Eve Sinha, a research student in Michalak’s lab, Michalak found is that increased rains caused by climate change will make this whole process worse. Why? Because more rain means more nutrients—the feedstock of this whole process—get washed into waterways. In the United States, this pattern will be especially strong in the corn belt and in the Northeast. Globally, this is likely to worsen eutrophication in India, China, and Southeast Asia.

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