A Previously Unknown Source of Nitrogen in Estuaries, But What Does It All Mean?
I don’t have access to Nature but I’m going to quote from a press release that URI put out, since the scientists presumably approved it and therefore it presumably explains things in a way they consider adequate:
Estuaries have long been considered nitrogen “sinks” or filters, whereby bacteria in the sediments remove substantial quantities of nitrogen through a process called denitrification.
But a new study in Narragansett Bay by researchers at the University of Rhode Island and published this week in the journal Nature has revealed a surprising reversal in the nitrogen cycle. Instead of removing nitrogen, the sediments have become a source of nitrogen through a bacterial process called nitrogen fixation.
According to URI researchers Robinson Fulweiler and Scott Nixon, chlorophyll concentrations in mid-Narragansett Bay appear to have been declining since the 1970s. This has resulted in a decrease in plankton sinking to the bottom. This is an important change because the plankton are an important food source for the benthic community and are essential for the denitrification process.
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.
Added Nixon, “Instead of removing some of the nitrogen we put into it, 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.”
You can read the rest yourself, here.
Now here’s my problem. We know that nitrogen from sewage plants is the trigger that starts the hypoxia process in Long Island Sound and presumably in Narragansett Bay too. Or at least that’s what the entire cleanup of Long Island Sound and Narragansett Bay is based on. Here on the Sound, we have a 58.5 percent nitrogen reduction target; Rhode Island’s is 50 percent (more here).
So my question is, if nitrogen is being added through the sediments, and if New York, Connecticut and Rhode Island are spending more than a billion dollars combined to improve sewage treatment plants to remove nitrogen, is it possible we’re wasting our money?
That’s a fairly important public policy question and while it’s nice that Professor Nixon talks about global climate change in the press release, I would have liked to hear his opinion on whether his findings might be applicable to estuaries other than the Bay, and if so what are the implications for our clean-up plans.
I should add, by the way, that while Nixon is a top scientist, I’m not inclined to cut him any slack on non-science issues, solely because he wrote a tepid (to say the least) review of my book back in 2002 or 2003. My recollection is that he thought Bobby Kennedy’s name was too big on the cover and that my writing was melodramatic and that I didn’t provide some of the environmental history that he thought was important. You can read it here (and for balance you can read a review by another scientist, John Waldman, here.)