BIOREMEDIATION OF NITRATE-CONTAMINATED SHALLOW SOILS USING WATER TABLE MANAGEMENT TECHNIQUES: NITRATE REMOVAL EFFICIENCY

Abstract

Nitrate (NO3-N), in excess of plant uptake during crop production, may move below the crops rooting zone.In order to protect groundwater quality, water table management (WTM) has been proposed as a way to remove, viastimulation of denitrification, this excess NO3-N. We conducted a simulation experiment for 130 days to evaluate theeffectiveness of WTM for such purpose. In this experiment, undisturbed soil columns (90 cm long 30 cm diameter) fromthree soils were used. The soils were Blount (somewhat poorly drained Aeric Ochraqualf), Clermont (poorly drainedTypic Glossaqualf) and Huntington (well-drained Fluventic Hapludoll). A band (< 1 cm thick) of NO3-N (2.11 g KNO3-Ncolumn1) treated soil was created 10 cm below the soil surface and removal of that NO3-N was attempted using twodifferent WTM schemes: static (WTM1) and dynamic (WTM2). We also repeated WTM2 using 15N to measure Ntransformations and this treatment, applied to the Huntington soil only, was designated WTM3. Based on denitrificationgases (N2, N2O) emitted, from 9 to 14% of the added NO3-N was removed from soil columns using WTM1 during the130 day test period. With WTM2, 24 to 43% of the added NO3-N was removed. A comparable NO3-N removal estimate(40%) was obtained for the 15N-treated (WTM3) Huntington columns using a mass balance approach. Removal ofNO3-N was faster when the water table was near the soil surface. Maximum rates of in situ NO3-N losses weregenerally 2 to 7 times lower than soil denitrification potenti…