9521254 Gilbert This project will study the composition, biological availability, and rates of uptake and release of dissolved organic nitrogen in two highly contrasting estuarine systems- the Chesapeake Bay and Georgia coastal rivers. These systems are vastly different with respect to the type, source and relative liability of dissolved organic nitrogen. Because the Principal Investigators will conduct their studies in conjunction with the two currently funded Land Margin Ecosystem Research studies at the these sites, the results will greatly enhance the understanding of these important coastal aquatic environments. The significance of the proposed research is several fold. First, in the broadcast, sense the eutrophication of nation's coastal waters and estuaries is a well recognized problem, yet we have little knowledge of the contribution and importance of organic nitrogen to this problem. Second, with the advent of new techniques, these studies will yield and appreciation of the mechanisms by which both bacteria and phytoplankton obtain their nitrogenous nitrogen will aid our ability to balance and control the flow of nitrogen through estuarine and coastal systems.