URI researchers find surprise change <br> in biochemistry of Narragansett Bay

NARRAGANSETT – University of Rhode Island scientists studying the sediments and plankton of Narragansett Bay have found an unexpected increase in the amount of nitrogen, they report in the July 12 issue of the journal Nature.
Chlorophyll concentrations in the mid-Bay appear to have been falling since the 1970s, URI Graduate School of Oceanography researchers Robinson Fulweiler and Scott Nixon wrote, indicating that fewer plankton are sinking to the bottom.
Instead of removing nitrogen from the water, they found, the Bay’s sediments have begun adding nitrogen through the bacterial process called nitrogen fixation.
“We know that organic matter affects the rate of denitrification, but no one else has observed a switch from denitrification to nitrogen fixation (production), and no one predicted that the absence of organic matter would lead to nitrogen fixation,” Fulweiler said.
“Instead of removing some of the nitrogen we put into it,” Nixon added, “in the summer of 2006 the Bay sediments brought nitrogen into the system. In fact, last summer, the Bay’s sediments added 1.5 times more nitrogen than the direct discharge of sewage.”
The duo were assisted by colleagues Steve Granger and Betty Buckley.
Their research was supported by grants from the National Science Foundation, through the R.I. EPSCoR Program; R.I. Sea Grant; the Switzer Foundation; and the R.I. Coastal Resources Management Council.
Nixon and Fulweiler said their results raise many questions, such as why chlorophyll concentrations are declining and whether other estuaries – long known for nitrogen removal – have also become sources of nitrogen production. They speculate that the decline in chlorophyll and the reversal of the nitrogen cycle may be linked to climate change, specifically, the warming of the Bay.
“Benthic-pelagic coupling – the relationship between the water column and the bottom – has changed dramatically in the Bay in the last 30 years,” Nixon said. “It’s a story that hasn’t been appreciated yet.”
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