Every year around the Fourth of July, populations of a single-celled organism called Thaumarchaeota explode in the coastal waters throughout the southeastern U.S., increasing more than 1,000 times higher than normal. It’s a puzzling event that affects nitrogen availability and the fertility of coastal waters and may contribute to excess production of nitrous oxide, a greenhouse gas.
Now, UGA researchers have received a $727,000 grant from the National Science Foundation to determine why this happens, if it is limited to the Southeast and what impact these mid-summer blooms have on the environment.
“This is one of the most abundant organisms in the world, but we know very little about it,” said James Hollibaugh, principal investigator for the project and Distinguished Research Professor of Marine Sciences. “We do know that it plays an important role in the Earth’s nitrogen cycle, and that’s one of the reasons we’re so interested in it.”
Nitrogen is an important “fertilizer” element, essential for the growth of all living things. Nitrogen normally cycles between living biomass and dissolved nutrients. When plant and animal wastes decompose, the nitrogen they contain is released to the environment, where it can be recycled by plants to support additional growth. People and animals eventually eat the plants, and their waste re-enters the environment, beginning the cycle again.
However, excess nitrogen can leak into rivers, lakes and oceans as runoff from lawns or farmland, as sewage or as a byproduct of automobile use and certain industrial processes.
“Fertilizer in the water works just like fertilizer on land,” Hollibaugh said. “It accelerates the growth of plants.”
This surplus nitrogen can lead to over-fertilization of receiving waters and excessive growth of plants that eventually sink and rot, consuming the oxygen in the water around them. They also may produce toxins that harm other marine life. The Thaumarchaeota bloom helps rid the environment of this excess nitrogen by breaking the cycle and initiating the process of converting fertilizer to nitrogen gas.
As a byproduct of this activity, Thaumarchaeota also may cause excessive production of nitrous oxide, a powerful greenhouse gas that traps heat in the atmosphere and is thought to play a role in the destruction of the protective portion of the stratosphere commonly called the ozone layer.
“The well-defined blooms we see on the Georgia coast offer a great opportunity to examine Thaumarchaeota and nitrous oxide production,” Hollibaugh said.
Researchers will take numerous measurements along Georgia’s coast near Sapelo Island to track Thaumarchaeota populations and their influence on the nitrogen cycle, including nitrous oxide production, and they will conduct genetic analyses and experiments to determine processes within the organism that may contribute to these population explosions.