Do Top-Down and Bottom-Up Controls Interact to Exclude N-Fixing Cyanobacteria From the Plankton of Estuaries?

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Author: rwh2@cornell.edu (Robert W. Howarth) at NOTE Date: 3/26/96 12:08 PM Priority: Normal TO: cdahm at nsf2 CC: rmm3@cornell.edu at NOTE CC: 73753.2331@compuserve.com at NOTE Subject: Abstract for DEB 9527405 ------------------------------- Message Contents ------------------------------- Hi Cliff -- Here is my stab at the abstract you requested. Mike Pace and I are still working on the budget. Bob DEB-95-27405: "Do top-down and bottom-up controls interact to exclude nitrogen-fixing cyanobacteria from the plankton of estuaries?" Eutrophication and phytoplankton production are frequently limited by nitrogen in estuaries and by phosphorus in lakes. One reason for this striking differences is a difference in nitrogen fixation. In lakes when nitrogen availability is low, nitrogen-fixing organisms bloom and help alleviate the nitrogen deficit by fixing molecular nitrogen into biologically available forms. In most estuaries, no such response occurs. This proposal tests the hypothesis that low availabilities of trace metals (Fe and Mo) in estuaries relative to lakes leads to slow growth rates of nitrogen-fixing organisms, leaving these organisms vulnerable to consumption by animals, and thereby preventing nitrogen fixation. In preliminary experiments with tanks full of seawater, the investigators successfully grew nitrogen fixing organisms by keeping animal populations low. This was the first time nitrogen-fixing organisms of the sort common to lakes were found in estuarine water anywhere in North America. The new research will build on these tank studies to more completely test the hypothesized difference between lakes and estuaries.