Denitrification Efficiency in Groundwater Adjacent to Ditches within Constructed Riparian Wetlands: Kankakee Watershed,Illinois-Indiana,U.S.A.

Dual isotope evaluations of NO₃ ^- in groundwater adjacentto ditches within constructed riparian wetlands across the Kankakee watershed may assist the determination of denitrificationefficiency. Groundwater sampling indicates that NO₃ ^--N exceeded 10 mg L^-1 in constructed riparian wetlands but not innative wetlands within the riparian zones of the Kankakee basin. Anapparent local empirical threshold for nitrification occurs in groundwater near ditches with less then 1:11 depth to width dimensions within similar hydrogeology. The ¹⁵N and ¹⁸Ocomposition of groundwater nitrate varies widely in these constructed riparian wetlands. Groundwater nitrate associated with broader ditches (e.g. 1:35) most closely matches the denitrification isotope signature of native riparian wetlands in the basin. The geometry of various cut and fill landforms may need evaluation in engineering designs for constructed riparian wetlands to ensure the establishment of local natural groundwaterflow conditions for efficient nitrate attenuation.