ARTICLE Development of Soil Properties and Nitrogen Cycling in Created Wetlands Kristin L. Wolf & Changwoo Ahn & Gregory B. Noe Received: 16 November 2010 /Accepted: 13 May 2011 /Published online: 10 June 2011 # Society of Wetland Scientists 2011 Abstract Mitigation wetlands are expected to compensate for the loss of structure and function of natural wetlands within 5–10 years of creation; however, the age-based trajectory of development in wetlands is unclear. This study investigates the development of coupled structural (soil properties) and functional (nitrogen cycling) attributes of created non-tidal freshwater wetlands of varying ages and natural reference wetlands to determine if created wetlands attain the water quality ecosystem service of nitrogen (N) cycling over time. Soil condition component and its constituents, gravimetric soil moisture, total organic carbon, and total N, generally increased and bulk density decreased with age of the created wetland. Nitrogen flux rates demonstrated age-related patterns, with younger created wetlands having lower rates of ammonification, nitrifica- tion, nitrogen mineralization, and denitrification potential than older created wetlands and natural reference wetlands. Results show a clear age-related trajectory in coupled soil condition and N cycle development, which is essential for water quality improvement. These findings can be used to enhance N processing in created wetlands and inform the regulatory evaluation of mitigation wetlands by identifying structural indicators of N processing performance. Keywords Age-trajectory . Denitrification potential . Freshwater created wetlands . Nitrogen cycling . Nitrogen mineralization . Organic carbon Introduction Under Section 404 of the Clean Water Act and the 1990 Memorandum of Agreement between the Environmental Protection Agency and the Army Corps of Engineers, wetlands that are structurally or functionally impacted by development in the United States must be compensated for by the creation of additional wetlands or the restoration, enhancement, or preservation of existing ones. The practice of compensatory mitigation assumes that created and restored wetlands will replace losses in wetland structure and function within the 5–10 year monitoring period required by mitigation regulations (U.S. Army Corps of Engineers 2010). The developmental trajec- tory of mitigation wetlands, however, is highly variable (Simenstad and Thom 1996; Zedler and Callaway 1999; Morgan and Short 2002) and some wetlands never develop the structural or functional attributes of their natural counter- parts (Erwin 1991; Kentula et al. 1992; Hoeltje and Cole 2007). Created and restored wetlands have been shown to differ from comparable natural wetlands in their hydrology (Confer and Niering 1992; Shaffer et al. 1999; Cole and Brooks 2002), vegetation (Confer and Niering 1992; Galatowitsch and van der Valk 1996; Campbell et al. 2002), and soil characteristics (Bishel-Machung et al. 1996; Stolt et al. 2000; Verhoeven et al. 2001; Campbell et al. 2002; Bruland and Richardson 2005), and have been generally unsuccessful in meeting the performance criteria that have been legally mandated (National Research Council 2001). Among the primary wetland components that are evaluated in mitigation projects, soils are often the least considered K. L. Wolf : C. Ahn Department of Environmental Science and Policy, George Mason University, 4400 University Drive, Fairfax, VA 22030, USA K. L. Wolf(*) : G. B. Noe U.S. Geological Survey, 430 National Center, Reston, VA 20192, USA e-mail: kwolf2@gmu.edu Wetlands (2011) 31:699–712 DOI 10.1007/s13157-011-0185-4