『Abstract
Two horizontal constructed wetlands with subsurface flow (CWs) of different age were monitored in a 2-year study. One of the CEs was new, while the second one had been in operation for 5 years in the first year of study. Transformations of C, P, and N were measured in each CW in the substrate of the vegetated bed under both aerobic and anaerobic conditions, and their rates were compared. C was mineralized in both CWs under both aerobic and anaerobic conditions, but mineralization rates differed between the CWs; they were cca ten times higher in the established CW compared to the new CW. Dissolved reactive phosphorus (DRP) was immobilized under aerobic conditions but was mobilized under anaerobic conditions. DRP transformation was cca five times faster in the established CW. Nitrification occurred under aerobic conditions at similar rates in both CWs. NH4⁺ concentration decreased under both aerobic and anaerobic conditions, but there was large variability. The age of the CW affected C mineralization rates and DRP immobilization rates under aerobic conditions and mobilization rates under anaerobic conditions; they increased as the CWs maturated, while no effect of CW age was observed on nitrogen removal rates.

Keywords: Constructed wetlands; Carbon; Nitrogen; Phosphorus; Mineralization; Microbial processes; Greenhouse gasses』

1. Introduction
2. Methods
　2.1. Site description
　2.2. Sampling
　2.3. Laboratory incubations
　2.4. Chemical analyses
　2.5. Data recalculation and statistical analyses
3. Results
　3.1. Nutrient and carbon transformations in substrate
　　3.1.1. Carbon mineralization
　　3.1.2. Phosphorus mineralization/immobilization
　　3.1.3. Nitrogen transformations
4. Discussion
　4.1. Carbon mineralization
　4.2. Phosphorus transformation
　4.3. Nitrogen transformations
5. Conclusions
Acknowledgements
References