Distribution of ammonium-N in the water-soil interface of a surface-flow constructed wetland for swine wastewater treatment.
Most livestock wastewaters treated in constructed wetlands are typically rich in ammonium N. The objective of this study was to evaluate the soil-water ammonium distribution and the diffusive flux through the soil-water interface. Wetland system 1 (WS1) was planted to rush and bulrushes, and wetland system 2 (WS2) was planted to bur-reed and cattails. Nitrogen was applied at a rate of 2.5 g m(-2) d(-1). Interstitial soil water was sampled at 9, 24, 50, and 70 m from the inlet. In both wetlands, we found that NH4+ diffusion gradient and N losses were highest in the wetland system with lowest water depth. From other studies, we knew that shallower depths may have promoted a more effective interfacing of nitrifying and denitrifying environments. In turn, this N reduction in the water column may be the reason for steady NH4+-N upward diffusion fluxes. The assumed mechanism for N removal has been nitrification and denitrification but ammonia volatilization could also have occurred. Although diffusion may explain a significant portion of the material transport between the soil-water interface, the large differences in concentrations between outlet and inlet need further explanation.
Szögi
A A
AA
Washington State University, Cooperative Extension, Yakima 98901, USA.
Hunt
P G
PG
D000383:Agriculture; D000818:Animals; D004058:Diffusion; D017753:Ecosystem; D008372:Manure; D009584:Nitrogen / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000032:analysis* / Q000737:chemistry; D012037:Refuse Disposal / Q000379:methods*; D012987:Soil; D013552:Swine; D014872:Water Movements
D008372:Manure; D000644:Quaternary Ammonium Compounds; D012987:Soil; D009584:Nitrogen