Using LiDAR and geographic information system data to identify optimal sites in southern Minnesota for constructed wetlands to intercept nonpoint source nitrogen

N itrate (NO3) carried in drainage from midwestern crop lands impairs local waters and makes a significant contribution to hypoxia in the Gulf of Mexico (Brezonik et al. 1999; Nangia et al. 2008). Conservation practices are being promoted in the Midwest to remedy water quality. Among them, improved farming practices such as reduced fertilizer use, constructed (either created or restored) wetlands, and riparian buffers are the three principal approaches for remedying Gulf of Mexico hypoxia (Mitsch et al. 2001; Randall and Mulla 2001; Mitsch and Gosselink 2007a). A constructed wetland was defined by Hammer and Bastian (1989) as “a designed and man-made complex of saturated substrate, emergent and submergent vegetation, animal life, and water that simulates natural wetlands for human use and benefits.” The microbial populations at the plant roots can transform nutrients and metallic ions and compounds; this makes wetlands effective at treating runoff from municipal, mining, and agricultural sources (Haan et al. 1994). Wetlands were once widely distributed in the Midwest, and many of them were drained for crop production. Therefore, the midwestern geomorphology and soils are favorable for wetland restoration. Wetland construction can control the growing problem of reactive nitrogen (N), primarily NO3, in the aquatic environment (Hey…