Comparing ecosystem structure and function of constructed and naturally occuring wetlands: empirical field indicators and theoreticl indices

The question of the validity of constructed wetlands as analogs for naturally occurring systems continues to be the subject of considerable controversy. The objective of this study is to quantify the degree of similarity in ecosystem structure and function between two eight-year-old experimental wetlands located at the Des Plaines River Wetland Demonstration Project northeastern Illinois and five naturally occurring wetlands in Lake County, Illinois. Emergy analysis and theoretical informational assessment procedures are presented and applied in the assessment of the experimental wetlands. Greater amplitudes were noted in the hydroperiods of the naturally occurring wetland systems. Peak biomass measurements from the reference wetlands were significantly greater (p<0.05) than those from the experimental wetlands. Bulk densities of soils were significantly higher in the experimental wetlands (p<0.05). One experimental wetland soil showed significant differences in organic matter content from 3 of 5 reference wetland soils. The second experimental wetland soil consistently contained less organic matter than the reference wetland soils.Emergy analysis suggests human emergy inputs exceed emergy production in the experimental wetlands while in the reference wetlands emergy production exceeds emergy inputs. This suggests the experimental wetlands provide no net benefit to their surrounding environment while the naturally occurring reference wetlands do provide a net benefit. Information theoretical analysis of several key indicators of ecosystem function suggests the experimental wetlands are more distinguishable from the reference wetlands than the reference wetlands are from each other. With further development the use of informational indices and key indicators of ecosystem function may provide a relatively simple, quantitative tool for the functional assessment of wetlands. The use of functional indicators to assess the success or failure constructed wetlands encourages greater consideration of functional characteristics in wetland design and management. This study suggest that after eight years of development the constructed wetlands are still substantially different from naturally occurring riverine wetlands in northeastern Illinois.