Phosphorus water quality model evaluation and comparison for natural and constructed wetlands

Abstract

Constructed and natural wetlands have been used to treat wastewater from both point and nonpoint sources. Phosphorus concentrations in receiving waters are a prime concern due to the role phosphorus plays in freshwater lake eutrophication. Various numerical models have been developed to predict total phosphorus outflow concentrations and annual phosphorus retention within treatment wetlands. Three phosphorus models, the mass balance model with first order areal uptake, the Vollenweider-based wetland model, and the detailed ecosystem model, were evaluated at three wetland sites across the U.S. The three sites included: Boney Marsh Experimental Area, Florida; Jackson Bottom Experimental Wetlands, Oregon; and the Des Plaines River Wetland Demonstration Project, Illinois. The mass balance model with first order areal uptake provided the smallest average percent error for outflow concentration, with percent error ranging from-6.8 % to 6.0 %. Although the Vollenweider-based wetland model consistently over-predicted annual phosphorus retention, the model provided the smallest average percent error for annual retention, with percent error ranging from 0. I % to 6.9 %. The detailed ecosystem model yielded the highest average percent error in both outflow concentration and annual phosphorus retention. However, the detailed model most accurately predicted total phosphorus outflow concentration trends at all three of the wetland sites.