Denitrification enzyme activity is limited by soil aeration in a wastewater irrigated forest soil

In land-based wastewater treatment systems (LTS), denitrification is an imp ortant nitrogen removal process. We investigated the factors limiting the d enitrifying population in a forested LTS, by studying the individual and co mbined effects of soil aeration, water content, nitrate and carbon on denit rification enzyme activity (DEA), The size of the soil denitrifying populat ion in the LTS appeared to be limited by soil aeration, and limiting oxygen availability increased the denitrifying population above that observed in the field. Furthermore, we found that wastewater irrigation altered the sho rt-term response of denitrifiers to anaerobic soil conditions. Under low ox ygen conditions, denitrifiers in the wastewater-irrigated soils produced en zymes sooner and at a greater rate than soils without a history of wastewat er irrigation. We propose that the size of the denitrifying population cann ot be expected to be large in free-draining, coarsely textured soils even w hen provided with additional nitrogen and water inputs.