The potential activity was reflected by the genetic potential for denitrification and rates correlated positively with the abundance of denitrifiers based on detection of the nirS and nirK gene (r ¼ 0.76, p < 0.001 and r ¼ 0.68, p < 0.01, respectively), but showed only a positive trend based on the nosZI gene (r ¼ 0.50, p ¼ 0.057).