Testing a Simple Field Method for Assessing Nitrate Removal in Riparian Zones

Being able to identify riparian sites that function better for nitrate removal from groundwater is critical to using efficiently the riparian zones for water quality management. For this purpose, managers need a method that is quick, inexpensive, and accurate enough to enable effective management decisions. This study assesses the precision and accuracy of a simple method using three ground water wells and one measurement date for determining nitrate removal characteristics of riparian buffer zones. The method is a scaled-down version of a complex field research method that consists of a large network of wells and piezometers monitored monthly for over two years. Results using the simplified method were compared to those from the reference research method on a date-by-date basis on eight sites covering a wide range of hydrogeomorphic settings. The accuracy of the three-well, 1 day measurement method was relatively good for assessing nitrate concentration depletion across riparian zones, but poor for assessing the distance necessary to achieve a 90% nitrate removal and for estimating water and nitrate fluxes compared to the reference method. The simplified three-well method provides relatively better estimates of water and nitrate fluxes on sites where ground-water flow is parallel to the water table through homogeneous aquifer material, but such conditions may not be geographically widespread. Despite limited overall accuracy, some parameters that are estimated using the simplified method may be useful to water resource managers. Nitrate depletion information may be used to assess the adequacy of existing buffers to achieve nitrate concentration goals for runoff. Estimates of field nitrate runoff and buffer removal fluxes may be adequate for prioritizing management toward sites where riparian buffers are likely to have greater impact on stream water quality. (KEY TERMS: Ground water; nitrate removal; riparian zone; riparian management; agricultural streams; Ontario.) Vidon, Philippe and Michael G. Dosskey, 2008. Testing a Simple Field Method for Assessing Nitrate Removal in Riparian Zones. Journal of the American Water Resources Association (JAWRA) 44(2):523-534. DOI: 10.1111 ⁄ j.1752-1688.2007.00155.x