Effects of sulphur cycle processes on ammonia removal in a laboratory-scale constructed wetland planted with Juncus effusus

The knowledge of detoxification by sulphide reoxidation in the rhizosphere of treatment wetlands and responses of microorganisms and plants is insufficient. In a laboratory-scale wetland Juncus effusus) with long-term, highly efficient sulphate reduction inside the rhizosphere, a short-term interruption of C/S-supply was carried out to study S-dynamics and responses of microorganisms and plants. Interruption of C/S-supply immediately caused reoxidation of the reduced S-compounds in the pore water. S2- decreased from 31.6mg1(-1) to 5.6mg1(-1), S-0 totally, and sulphate increased from 2.3 mgl(-1) to 16.8 mgl(-1). Continuous high values of total sulphur during the period without C/S-supply can be explained only by remobilization of deposited reduced sulphur. Continuous decrease of ammonia removal and plant transpiration and increase of the wilted state of the plants stopped immediately and started again when C/S-supply was reactivated. Thus, ammonia removal can be regulated by sulphur balance. The results indicate importance of oxygen release by plants and reoxidation of dissolved and immobilized reduced sulphur related to detoxification inside the rhizosphere. (C) 2008 Elsevier B.V. All rights reserved.