COMPARING MICROBIAL PARAMETERS IN NATURAL AND CONSTRUCTED WETLANDS

Microbial biomass C, soil respiration, denitrification enzyme activity (DEA), and potential net N mineralization and nitrification were compared in two constructed and three natural wetlands in Massachusetts and Rhode Island. The constructed wetlands studied had marsh and wet meadow vegetation and received storm cater discharge directly from a large shopping mall and its associated parking lots. The natural sites encompassed three soil drainage classes (moderately well drained, poorly drained, and very poorly drained) across an upland to wetland transition zone with red maple (Acer rubrum L.) swamps and mixed oak (Quercus sp.) forests in the transition zone. Our objective was to determine if microbial biomass and activity were similar in the constructed wetlands and the most common type of natural wetland in our area. Microbial biomass C, DEA, and potential net N mineralization and nitrification were similar among the constructed and natural wetland sites. In all cases, levels of these parameters in the constructed wetlands fell within the range of variability observed in the natural wetlands. Denitrification enzyme activity was higher (p < 0.05) in the constructed wetlands than in the moderately wed drained soils at the natural sites. Soil respiration was generally lower (p < 0.05) in the constructed wetlands than in the natural wetlands. The results suggest that the constructed wetlands have a significant and active microbial community that facilitates nutrient cycling and water quality maintenance functions similar to natural wetlands. The successful development of the microbial community in these wetlands was likely due to the use of organic substrates and aggressive establishment of the plant community during wetland construction.