In the summer and fall of 2011, a green tide of blue-green algae enshrouded 230 square miles of Lake Erie's western basin. This algae "bloom" poisoned the water with toxins, suffocating the aquatic life of oxygen, burdening the city of Toledo, Ohio's water treatment plant and threatening a $11.5 billion tourism industry in Ohio.
This algal bloom broke the record for Lake Erie, in terms of both size and concentration. And with climate change, these blooms could become a regular occurrence in the next century, says a team of scientists in a paper published yesterday in the Proceedings of the National Academy of Sciences.
The bloom began on July 15, 2011. By September, it was clear it was the biggest one on record, said Anna Michalak, who headed the research team and now works as an environmental scientist in the Department of Global Ecology at the Carnegie Institution for Science.
"It was certainly clear that this was unlike anything we'd seen," said Michalak. Algal blooms are created when high levels of nutrients, like nitrogen and phosphorus, enter a waterway and stay put for an extended period. Cyanobacteria, commonly known as blue-green algae, feed off streams of phosphorus and nitrogen, usually from plant fertilizers, manure, sewage, commercial detergents and industrial waste.
Weak circulation of waters and warm temperatures encourage the cyanobacteria to thrive in nutrient-rich waters. In 2011, unusually heavy spring rains washed a lot of phosphorus fertilizer into Lake Erie's western basin. That summer, water that had arrived from the Maumee River tributary did not mix with Detroit River water as usual, said Michalak, causing a poor circulation of water. The nutrient-rich waters did not flow out of the western basin, and the algae were allowed to proliferate.
The scientists determined the record impact of the algal bloom by measuring the volume of cyanobacteria in the water and with NASA satellite images. Using 12 climate change models, the researchers concluded that the heavy precipitation, coupled with warming over the region and weaker wind speeds, will mean more algal blooms for the region.
During the 2011 bloom, the volume of microcytosis blue-green algae, which are toxic to the liver, peaked at 224 times the World Health Organization's guidelines. Increases in anabaena toxin, which affects the neurological system, are also expected as blooms become more common. Algae can also clog boat motors and hamper fishing.
Farming in the Great Swamp
The Native Indians of Ohio called the area that is now northwestern Ohio and southeastern Michigan the "Great Black Swamp" -- a land of marshy wetlands. The early pioneers were able to dredge the land and turn it into the rich, productive region it is today. Corn and soybeans dominate in the region, and high prices for both commodities in recent years have encouraged farmers to keep sowing more rows, said Joe Logan, director of agricultural programs for the Ohio Environmental Council.
"There is a compelling economic interest for farmers to maximize productivity," Logan said.
Below the surface of the fields lie networks of perforated tubing, which pull excess water from the soil and send it to the lake, rich in phosphorus, Logan said.
Before the 1970s, phosphorus runoff to Lake Erie's western basin was mostly due to municipal sewers and industry, said David Baker, who founded the National Center for Water Quality Research at Heidelberg University in Tiffin, Ohio, in 1969. By 1980, the phosphorus from agricultural runoff was almost twice the amount from municipal sources, he said.
The patterns also changed. While municipal sources of pollution tend to be consistent throughout the year, agricultural runoff increases tremendously in the spring with the swelling of rivers and streams from the rain.