Decomposition and Nutrient Stability in Constructed Wetland Soils of Submergent and Emergent Vegetation.

Decomposition influences nutrient stability through stable soil accretion and breakdown of organic forms, serving as an indicator of nutrient limitation in the system. Vegetation regulates these processes through retention of phosphorus (P) and relative microbial efficiency. Everglades constructed wetlands have two dominant vegetation types: emergent aquatic vegetation (EAV) and submergent aquatic vegetation (SAV). However, little is known of differences in vegetation type effects on decomposition and nutrient stability. This study determined enzyme activities for carbon (C, ß-glucosidase), nitrogen (N, Leucine aminopeptidase/N-acetyl-ß- D-glucosaminidase), and phosphorus (P, phosphomonoesterase/ phosphodiesterase) in surface floc and recently accreted soil (RAS) materials which were collected along transect sites in Cell 1 (EAV) and Cell 3 (SAV) of STA 2 (Stormwater Treatment Area). Microbial parameters regarding C, N, and P (i.e., microbial biomass and enzyme activity) were also measured. Overall, EAV showed higher enzyme activity and microbial biomass, indicating a greater microbial influence in this vegetation type. Enzyme N: P ratio increased at the inflow supporting higher bioavailable forms at the inflow and higher P limitation at the outflow. Microbial N:P indicated that combined EAV and SAV vegetation showed different limitation patterns (N limitation at the inflow to P limitation at the outflow) compared to predominantly EAV and SAV (P limitation at the inflow to N limitation at the outflow). Furthermore, ratios proved fungal dominant microbial communities for all litter samples. Understanding the impact of enzymes in the constructed wetlands of the Everglades has implications for decomposition, nutrient uptake by plants, and overall nutrient retention in the systems. When coupled with soil fractionation data, results of this study could lead to a better understanding of enzyme inhibitory mechanisms and microbial decomposition processes involved in nutrient removal.