Marine biologists James Hollibaugh and Sylvia Schaefer from the University of Georgia have determined a correlation between high water temperatures and the presence of nitrite in coastal ecosystems. Their results were published recently in Environmental Science and Technology.
Nitrite is a gas that microorganisms produce after they consume the ammonium found in animal waste, treated sewage or fertilizers. Too much nitrite acts as a fertilizer and can cause algal blooms, which create hypoxic zones in marine environments, resulting in the death of most marine life. Until now, it was thought that the lack of oxygen in these zones were the reason for accumulation of nitrite, which resulted in fish and other marine wildlife’s deaths. Nitrite is known to kill fish in aquariums, a phenomenon that provides a microcosm of how it affects marine life.
However, Hollibaugh and Schaefer decided to rethink the cause of nitrite accumulation. By analyzing environmental monitoring data from 270 locations across the U.S., France and Bermuda, they determined that in fact it is the rising temperature of waters that drives the accumulation of nitrite.
They also performed experiments that exposed the single-celled organisms called Thaumarchaea to varying water temperatures. "The microorganisms involved in this process are very tolerant to low oxygen levels," Schaefer said. "Typically, two groups of microorganisms work in really close concert with one another to convert ammonium to nitrate so that you don't see nitrite really accumulate at all, but we found that the activity of those two groups was decoupled as a result of the increased water temperatures." These experimented showed that higher water temperatures resulted in the microorganisms producing more nitrite.
The authors are hopeful for the significance of their study. "The information gained from monitoring programs, like the ones we used to analyze temperature and nitrite data across the country and in other countries, can be used not only to forecast what is going to happen down the road and the longer-term consequences of management decisions, but also to come up with potential solutions for the problem,” said Hollibaugh. “The data collected by these programs are important for wise management of our resources."
Management of resources, and pollution policies, specifically those for agricultural fertilizers will be key because nitrite accumulation can also produce nitrous oxide, which is a potent greenhouse gas that has more of an effect on climate change per molecule than carbon dioxide, Hollibaugh reports. Unfortunately, that sets off a positive feedback loop, because nitrous oxide production then increases global temperatures, raising sea temperatures, and resulting in more nitrite accumulation.