Development of a constructed subsurface-flow wetland simulation model

This paper presents a mechanistic, compartmental simulation model of subsur face-flow constructed wetlands. The model consists of six submodels, includ ing the nitrogen and carbon cycles, both autotrophic and heterotrophic bact eria growth and metabolism, and water and oxygen balances. Data from an exi sting constructed wetland in Maryland were used to calibrate the model. Mod el results reproduced seasonal trends well. Interactions between the carbon , nitrogen, and oxygen cycles were evident in model output. In general, eff luent biochemical oxygen demand, organic nitrogen, ammonium and nitrate con centrations were predicted well. Because little is known about rootzone aer ation by wetland plants, oxygen predictions were fair. The model is general ly insensitive to changes in individual parameters. This is due to the comp lexity of the ecosystem and the model, as well as the numerous feedback mec hanisms. The model is most sensitive to changes in parameters that affect m icrobial growth and substrate use directly. This dynamic, compartmental, si mulation model is an effective tool for evaluating the performance of subsu rface-flow constructed wetlands. The model provided insights into treatment problems at an existing constructed wetland. With further evaluation and r efinement, the model will be a useful design tool for subsurface-flow const ructed wetlands. (C) 2001 Elsevier Science B.V. All rights reserved.