Wetland restoration and hydrologic reconnection result in enhanced watershed nitrogen retention and removal

摘要

Restoration of freshwater wetlands presents a potential water quality benefit via removal of nutrients, but complex and unresolved changes in nutrient cycling can occur following restoration. In this study, we evaluated N removal and release in a deltaic wetland under scenarios of hydrologic reconnection and sediment dredging, and we modeled potential downstream impacts of these restoration activities in a Bayesian framework. Denitrification, N2O production, and anammox were measured via the isotope pairing technique in intact sediment cores. Anammox was not detected. Denitrification rates in the control scenario (78.2-87.2 mu mol N m(-2) h(-1)) were significantly higher than those under hydrologic reconnection and dredging scenarios (14.7-56.0 mu mol N m(-2) h(-1)). N2O production rates were typical of wetland environments. Denitrification and N2O production were stimulated shortly following simulated dredging, indicating a short-term response to sediment disturbance. Under hydrologic reconnection, NH4 (+) availability was decreased, inhibiting coupled nitrification-denitrification. Despite a decrease in denitrification activity, the wetland has the capacity to remove up to 10% of stream NO3 (-) following hydrologic reconnection. Restoration is predicted to fully mitigate NH4 (+) delivery to a downstream eutrophic lake, yet permanent N removal may be reduced due to the decoupling of nitrification and denitrification.