Wetland-water column exchanges of carbon, nitrogen, and phosphorus in a southern Everglades dwarf mangrove

We used enclosures to quantify wetland-water column nutrient exchanges in a dwarf red mangrove (Rhizophora mangle L.) system near Taylor River, an imp ortant hydraulic linkage between the southern Everglades and eastern Florid a Bay, Florida, USA. Circular enclosures were constructed around small (2.5 -4 m diam) mangrove islands (n=3) and sampled quarterly from August 1996 to May 1998 to quantify net exchanges of carbon, nitrogen, and phosphorus. Th e dwarf mangrove wetland was a net nitrifying environment, with consistent uptake of ammonium (6.6-31.4 mu mol m(2) h(-1)) and release of nitrite + ni trate (7.1-139.5 mu mol m(-2) h(-1)) to the water column. Significant flux of soluble reactive phosphorus was rarely detected in this nutrient-poor, P -limited environment. We did observe recurrent uptake of total phosphorus a nd nitrogen (2.1-8.3 and 98-502 mu mol m(-2) h(-1), respectively), as well as dissolved organic carbon (1.8-6.9 mu mol m(-2) h(-1)) from the water col umn. Total organic carbon flux shifted unexplainably from uptake, during Ye ar 1, to export, during Year 2. The use of unvegetated (control) enclosures during the second year allowed us to distinguish the influence of mangrove vegetation from soil-water column processes on these fluxes. Nutrient flux es in control chambers typically paralleled the direction (uptake or releas e) of mangrove enclosure fluxes, but not the magnitude. In several instance s, nutrient fluxes were more than twofold greater in the absence of mangrov es, suggesting an influence of the vegetation on wetland-water column proce sses. Our findings characterize wetland nutrient exchanges in a mangrove fo rest type that has received such little attention in the past, and serve as baseline data for a system undergoing hydrologic restoration.