Nitrate-nitrogen removal in disturbed and undisturbed wetland microcosms subjected to vertical-flow and surface-flow hydrology and the affects hydrology, storage temperature, and incubation temperature exert on denitrification kinetics

Experiments on disturbed and undisturbed wetland microcosms were conducted to determine the effect that wetland hydrology, hydraulic loading rate, and temperature have on nitrate removal rates, denitrification kinetics, and potential denitrification. Wetland microcosms were constructed using Webster soil from the Southern Research and Outreach Center in Waseca, Minnesota. Two hydrologic flow regimes were used: vertical-flow, where drainage water flowed vertically through the sediment in the microcosm, and surface-flow, where drainage water flow was horizontal over the surface of wetland sediment. Hydraulic loading rates were 8, 25, and 75 cm day-1. The acetylene block method was used to determine the effect temperature and hydrology has on potential denitrification and denitrification kinetics. Tests were conducted on soil slurries produced from undisturbed soil microcosm stored at 10, 15, and 20°C and subjected to vertical-flow or stagnant no-flow conditions.; My results indicated that nitrate removal rates in disturbed (40.9 to 180.3 ng NO3-N g-1 hr-1) and undisturbed (47.7 to 122.4 ng NO3-N g-1 hr-1) vertical-flow wetland microcosms were significantly greater than rates observed in disturbed (-5.8 to 3.8 ng NO3-N g-1 hr-1) and undisturbed (12.1--46.7 ng NO3-N g-1 hr-1) surface-flow wetland microcosms.; Results of the kinetic experiment indicated that denitrification in soil slurries follows a Michaelis-Menten-like model. The values determined for Vmax ranged from 201.6 to 439.8 ng NO3-N g-1 hr-1, and significantly increased with temperature. Hydrology did not have a significant effect on limiting rates overall, but hydrology did have a significant effect on limiting rates for soils stored at 15 and 20°C. The Michaelis Constant (Km) ranged from 10.5--58.0 uM and increased significantly with temperature. The effect of hydrology was insignificant on the Michaelis Constant.; Potential denitrification rates had a significant direct relationship with incubation temperature, and varied inversely with storage temperature. The highest rates of potential denitrification (1,409 ng NO3-N g-1 hr-1) were observed in soil stored at cold temperatures and incubated at warm temperatures. The effect of hydrology was insignificant overall; however, hydrology did have a significant effect when considering only the soils stored at 15 and 20°C.