Ammonium Transport Simulation in Horizontal Soil Columns from a Natural Inland Alkaline Wetland

Ammonium transport was simulated in horizontal soil columns from an inland alkaline wetland (Fulaowenpao wetland) of Northeast China. The primary objectives of this work are to investigate the changes in ammonium transport rate with increasing distances along horizontal soil column and to determine the effects of water diffusion rate and volumetric water content on ammonium transport rate. Our results showed that water diffusion coefficient was the lowest at the soil layer of 10–20 cm, followed by the 0–10 cm soil layer, and the highest value occured at the soil layer of 20–60 cm. The highest ammonium transport rate also appeared at the soil layer of 20–60 cm, while the lowest value was observed at the soil layer of 10–20 cm. Ammonium transport rates decreased with increasing distances along horizontal soil columns. The ammonium transport rates showed higher values at the distance from 0 to 6 cm and then decreased rapidly from 6 to 18 cm. However, they nearly kept constant and approached to zero after exceeding the distance of 18 cm. Ammonium transport rates increased exponentially with increasing volumetric water contents and water diffusion rates. The alkaline wetland soils prevented ammonium from horizontal diffusion at all soil layers under drying conditions.