Invasion of Great Lakes coastal marshes by the aggressive exotic cattail Typha x glauca can significantly decrease biodiversity and modify biogeochemical cycling.  We studied changes in ecosystem structure and function along transects extending from the remnant native plant community through the T. x glauca-dominated vegetation zone in a recently invaded Lake Huron coastal wetland in northern Michigan.  We measured multiple physical and chemical parameters, and biogeochemical processes including denitrification potential and N-fixation rates in these sediments to determine differences related to T. x glauca.  Inorganic N levels and soil organic carbon in sediments associated with T. x glauca were 7 and 4 times higher, respectively, than N and OC in sediments associated with the native plant community.  As T. x glauca densities increased across the vegetational gradient, concurrent increases in denitrification and N-fixation rates were demonstrated.  Parallel studies in wetland mesocosms where soil organic C and water levels could be controlled demonstrated patterns with T. x glauca invasions similar to those found in the wetland.  Redox, water level, soil OC and soil N appear to be most closely related to T. x glauca densities, and are the drivers of denitrification potential and N-fixation rates in this wetland.