Ground Water Discharge from Riparian Zones and Implications for Buffer Strip Widths to Protect Surface Water

Tuesday, April 21, 2009: 3:10 p.m.
Agave Ballroom (Hilton Tucson El Conquistador Golf & Tennis Resort )
Mark K. Waldick , Department of Earth and Environmental Science, University of Waterloo, Waterloo, ON, Canada
Brewster Conant Jr., Ph.D. , Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON, Canada
David L. Rudolph, Ph.D., PE , University of Waterloo, Waterloo, ON, Canada
In many cases, groundwater can contribute the majority of water and nutrients to surface water bodies in agricultural environments yet the role that riparian buffer strips play in controlling groundwater nutrient loads to streams is poorly understood. Riparian zone width is believed to be a significant factor in the overall performance of these buffer strips; however, little has been done to quantify the influence of buffer width on groundwater quality. Preferential groundwater flow pathways through the riparian zone, which may reduce the beneficial effects of the zone, could influence the minimum buffer width required to remove nitrate contamination from groundwater. The influence of buffer width and preferential flow on riparian zone groundwater quality was investigated over a 14 month period along a 0.5 km reach of a stream adjacent to an agricultural field in Kintore, Ontario, Canada. At the site, three transects consisting of up to 25 wells each were used to evaluate changes in groundwater quality across the riparian zone where it was 6.5, 10, and 20 m wide and subsurface materials consisted of intermingled glacial silt tills and sandy glaciofluvial deposits. Preferential pathways discharging into the stream (i.e., springs and seeps) were identified using infrared thermography and streambed temperature surveys. Groundwater and nitrate mass fluxes into the stream were quantified using a variety of techniques including: differential stream gauging with surface water quality analyses; streambed water quality with temperature modeling of streambed flux; and Darcy and mass flux calculations using 48 streambed piezometers.  Groundwater quality results indicated significant nitrate removal occurred within the first six meters of the riparian zone, which suggests that even narrow riparian zones can be effective at attenuating agricultural nutrients in groundwater. Preliminary results also indicated that nutrient loads through some of the preferential pathways might be significant depending on the hydrogeologic setting.
See more of: Nitrates in Ground Water II
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