Interaction and spatial distribution of wetland nitrogen processes

A spatially-explicit, two-dimensional model was developed to evaluate the processes which determine the fate and transport of nitrogen (N) in wetland systems. The wetland soil profile was partitioned into floodwater, and aerobic, and anaerobic soil layers, with diffusion and settling accounting for the transport of N between layers. Nitrogen transformations considered in the model were; enzyme hydrolysis, mineralization, nitrification, NH4-N adsorption/desorption, NH3-N volatilization, denitrification, and vegetative assimilation and decay. Most processes were represented with first-order kinetics, except vegetative uptake, which was represented with Michaelis–Menten kinetics. STELLA® iconographic software was used to simulate processes regulating N removal from wetlands. Denitrification, ammonia volatilization, and accretion of organic N were identified as major pathways accounting for N removal. Downward flux of NO3− from floodwater to soil limited N removal through denitrification. Denitrification rates increased from 13 to 88 g N year−1 in response to augmented vertical flux of soluble N, caused by increasing diffusion coefficients two orders of magnitude. Edaphic organic N storage, through the production of inorganic N, negatively impacted N removal. Spatial simulation illustrated the phenomena of diminishing returns in the mass removal rates of N, which were in agreement with documented values.