Nitrate transport in shallow groundwater at the stream-riparian interface in an urbanizing catchment

Drive point peizometers were installed at the stream-riparian interface in a small urbanizing southern Ontario catchment to measure the effect of buffers (presence/ absence) and land use (urban/agricultural) on the movement of NO-3-N in shallow groundwater from the riparian area to the stream. Mean NO-3-N concentrations ranged from 1.0 to 1.3 mg L-1 with maximum values of 9.4 mg L-1. Holding land use constant, there was no significant difference (p>0.05) in NO-33-N concentration between buffered and unbuffered sites. Nitrate-N levels were not significantly different (p>0.05) as a function of land use. The lack of difference between sites as a function of buffer absence/presence and land use is probably due to the placement of some peizometers in low conductivity materials that limited groundwater flow from the riparian zone to the stream. Subsurface factors controlling the hydraulic gradient are important in defining buffer effectiveness and buffer zones should not be used indiscrim inately as a management tool in urban and agricultural landscapes to control nitrate-N loading in shallow groundwater to streams without detailed knowledge of the hydrogeo logic environment.