A detailed ecosystem model of phosphorus dynamics in created riparian wetlands

A generalized yet detailed wetland ecosystem model was calibrated and valid ated with 3 years's data from four similarly constructed wetlands in northe astern Illinois, USA. The model was used to explore the role of different w etland structure and function in relation to phosphorus retention, to integ rate collected data and provide a better understanding at the ecosystem lev el about constructed wetlands, and to predict the sediment and phosphorus r etentions under different hydrologic conditions. Four submodels - hydrology , primary productivity, sediments, and phosphorus - were included in the mo del. Phosphorus cycling was reasonably simulated with one set of parameters for a total of 10 wetland-years. The model showed that autochthonous organ ic matter production varies from 300 to 1036 g dw m(-2) year(-1) with 12 to 103 g dw m(-2) year(-1) accumulating as bottom detritus. This compares to inflows year (allochthonous) of 192-934 g dw m(-2) year(-1). Simulated sedi ment accumulation ranged of sediments from the nver from 6 to 29 mm year(-1 ) with high inflow wetlands having higher sediment accumulation rates than low flow wetlands. Model estimates are well below the 50-100 mm year(-1) ra tes predicted by sedimentation trap data in previous studies. Total phospho rus retained with sedimentation is simulated at a rate of 1.08-2.47 g P m(- 2) year(-1) in the range of values reported for other wetlands. Simulations showed that macrophytes pumped about 0.31-1.66 g P m(-2) year(-1) out of d eep sediments, and increased total phosphorus in the water column mostly du ring the non-growing season. Simulated phosphorus retention increased by 5. 1% when macrophytes were removed from the wetland. Simulated phosphorus ret ention decreased from 90 to 50% when inflow increases from 8 cm week(-1) to 200 cm week(-1). Manipulating the hydrologic regime to increase phosphorus removal efficiency may be a desirable strategy for constructed wetlands. C onstructed wetlands are dynamic ecosystems for which we generally have poor predictive capabilities; ecological modelling provides us with a useful to ol for understanding wetland function and structure, testing hypothesis, an d making predictions. (C) 2000 Elsevier Science B.V. All rights reserved.