Biogeochemical consequences of North Carolina’s largest wetland mitigation project

Natural wetlands have a high and long-term capacity to retain nitrogen and phosphorus from surface and subsurface runoff. Wetlands have the ability to transform reactive nitrogen into inert gaseous forms (N₂) through microbial uptake and immobilization.  Sedimentation, soil adsorption and plant uptake are important mechanisms for phosphorus uptake in wetland ecosystems.  Wetland mitigation attempts to compensate for these lost functions through creation or restoration of new or improved wetland ecosystems.  Typically, meeting mitigation success criteria involves effectively restoring wetland hydrology, and although functional benefits are often the goal, functional responses to restoration are rarely measured.  We are investigating the effects of NC's largest wetland mitigation project to date in a) altering nutrient export patterns; b) sequestering carbon in plant biomass; and c) altering the forms and quantity of trace gas emissions.  In this talk we will discuss the immediate (1 month) impacts of hydrologically reconnecting a 400 ha coastal plain agricultural field that was ditched and drained in 1981, maintained for corn and soybean production until 2004, and planted with 750,000 wetland trees in 2005.  Hydrologic reconnection in winter 2007 inundated ~ 80 ha of the field, mobilized soil P and altered denitrification potential and emission of N₂O.  We report these initial findings and discuss how integrating a mass balance approach with patch scale empirical measurements of trace gas emissions and soil and soil solution chemistry can help us predict the short and long-term consequences of wetlands restoration in coastal plain watersheds.