EDITOR'S NOTE: The federal funding that made this research possible is under extreme threat under both the Trump budget and the Republican Congress as they continue to mount an attack on science in general and environmental science in particular. - W. Collette
Increasing water temperatures are responsible for the accumulation
of a chemical called nitrite in marine environments throughout the world, a
symptom of broader changes in normal ocean biochemical pathways that could
ultimately disrupt ocean food webs, according to new research from the
University of Georgia.
Nitrite is produced when
microorganisms consume ammonium in waste products from fertilizers, treated
sewage and animal waste.
Too much nitrite can alter the kinds and amounts of single-celled
plants living in marine environments, potentially affecting the animals that
feed on them, said James Hollibaugh, co-author of the study published recently
in Environmental Science and Technology.
It also could lead to toxic algal blooms and create dead zones
where no fish or animals can live.
"Rising ocean temperatures are changing the way coastal ecosystems-and probably terrestrial ecosystems, too-process nitrogen," said Hollibaugh, Distinguished Research Professor of Marine Sciences in UGA's Franklin College of Arts and Sciences. "Much of the global nitrogen cycle takes place in the coastal zone."
Hollibaugh and researcher
Sylvia Schaefer found midsummer peaks in concentrations of nitrite alongside
massive increases in numbers of the microorganisms that produce it in the
coastal waters off Sapelo Island, Georgia, in data collected over the course of
eight years.
Although most researchers believe nitrite accumulation is a
consequence of oxygen deficiency in a marine environment, Hollibaugh and
Schaefer thought something else had to be driving the accumulation.
"The paradigm taught
when I was in school was that hypoxia, or lack of oxygen, results in nitrite
accumulation," Hollibaugh said. "But the Georgia coast does not go
hypoxic. It just didn't fit."
After performing lab
experiments that exposed the single-celled organisms known as Thaumarchaea to
varying water temperatures, the researchers discovered that higher temperatures
prompted the microorganisms to produce more nitrite.
"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."
To see if the pattern held
beyond the island, Schaefer and Hollibaugh analyzed environmental monitoring
data from 270 locations across the U.S., France and Bermuda, ultimately
affirming the relationship between higher temperatures and nitrite
accumulation.
This dependence on
temperature wasn't appreciated by the research community until now, and it can
have widespread consequences even beyond coastal water quality management,
Hollibaugh said.
"The same process, though
we didn't look at it specifically, takes place in regards to fertilizing soil
for agricultural purposes," he said. "It affects farmers and their
efficient use of fertilizer-when they should apply it and what form it should
be in-and ultimately much of that fertilizer will end up in the waterways,
which can lead to algal blooms that choke out other species."
Nitrite accumulation can
also result in more production of nitrous oxide, a powerful greenhouse gas that
has more of an effect on climate change per molecule than carbon dioxide,
Hollibaugh said. That nitrous oxide production then increases global
temperatures more, causing more nitrite accumulation and creating a positive
feedback loop.
"If you live on a marsh
and look out over the water, you're probably not going to notice it, but if you
like shellfish, like to fish, like recreational water sports, then these
findings do matter," Hollibaugh said.
"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. The data collected by these programs are important for wise management
of our resources."
The study was published in Environmental Science and Technology
and is available at http://pubs.acs.org/doi/abs/10.1021/acs.est.6b03483. The
research was supported the National Science Foundation's Division of Ocean
Sciences grants 13-35838 and 12-37130.