Horizontal diffusion of ammonium nitrogen in marsh soils from a floodplain wetland on the lower reach of Huolin River of China.

Few studies have been carried out regarding horizontal movements of ammonium nitrogen in marsh soils of the floodplain wetlands,despite they play the very important role in protecting water quality of rivers or lakes.Horizontal movement of ammonium nitrogen was simulated using NH4Cl tracer in horizontal soil columns from Erbaifangzi floodplain wetland located on the lower reach of Huolin River,in order to study the horizontal diffusion of ammonium nitrogen in wetland soils from the floodplains and to reveal the effects of water diffusion rates and volumetric water contents on ammonium nitrogen movement.Results showed that movement fluxes of ammonium nitrogen decreased exponentially with increasing distances far away from water head.The highest movement fluxes of ammonium nitrogen were observed at 10~20 cm soil horizons,followed by 20~60 cm,and the lowest for 0~10 cm soil horizons.The higher movement fluxes of ammonium nitrogen occurred at the distances from 0 to 6 cm,and then showed a rapid decrease at the distances from 6 to 18 cm.After that they kept constant and nearly approached to zero at the distances exceeding 18 cm.The movement fluxes of ammonium nitrogen at all soil horizons were closely linked to water diffusion rates and volumetric water contents,and they increased exponentially with increasing water diffusion rates and volumetric water contents.The movement fluxes of ammonium nitrogen at each soil horizon showed a slow increase,but increased rapidly after water diffusion rates or volumetric water contents reached a certain level.Therefore,it is very necessary for water quality security of Huolin River to monitor and control ammonium movement in subsurface soils.