delta N-15 studies of nitrogen use by the red mangrove, Rhizophora mangle L. in South Florida

To help define nitrogen (N) sources and patterns of N processing in mangrov e ecosystems, mangrove leaf nitrogen contents and delta(15)N values were as sayed in three marshes along the south Florida coast. In each marsh, leaf s amples were collected from dwarf mangroves at interior locations and taller mangroves at the ocean fringe. Leaf % N and delta(15)N values did not diff er consistently between dwarf and tall mangroves, even though there were la rge variations in delta(15)N (18 parts per thousand range, -5 to +13 parts per thousand) and % N (1.2% range, 0.9-2.1%). Highest % N and delta(15)N va lues occurred along the western margin of Biscayne Bay where canals drainin g agricultural lands deliver high-nitrate waters to fringing mangrove marsh es. High mangrove delta(15)N values may be good biomonitors of anthropogeni c N loading to south Florida estuaries. Lower values likely reflect less an thropogenic N entering the mangrove marshes, as well as differences in plan t physiology that occur along the fringe-dwarf gradient. (C) 2000 Academic Press.