Fig. 4. Denitrification enzyme activity in constructed wetlands as affected by total soil nitrogen. (A) Nonamended control, (B) 200 mg L^-1 NO₃–N, (C) 2 g L^-1 glucose C, (D) 200 mg L^-1 NO₃–N and 2 g L^-1 glucose C, or (E) the previous treatment without acetylene added.