ABSTRACT
This chapter presents results and preliminary interpretations of a regional survey of dissolved nitrite plus nitrate in shallow groundwater in the Willamette Basin. Several local, state, and federal agencies conduct groundwater-quality monitoring in the Willamette Basin, and extensive, targeted groundwater sampling efforts have been conducted by the Oregon Department of Environmental Quality. Seventy randomly distributed shallow wells in alluvial deposits were sampled for nitrate as part of an appraisal of regional groundwater quality in the Willamette Basin. Groundwater underlying irrigated agricultural land generally contained higher nitrate concentrations than did groundwater underlying nonirrigated agricultural land. Nitrate concentrations in groundwater may be related to hydrogeologic factors that affect transport of nitrate in groundwater. Shallow groundwater underlying areas dominated by irrigated agriculture generally receives greater inputs of nitrogen than underlying areas dominated by nonirrigated agriculture. Effective nitrogen management will require an understanding of factors controlling source, transport, and fate of nitrogen in groundwater, in addition to current groundwater nitrate concentrations.
