The Calapooia River, a tributary of the Willamette River in Western Oregon, has been reported to have high levels of dissolved nitrogen (DN) by the National Water Quality Assessment Program and the Oregon Department of Environmental Quality.  Research has demonstrated a relative lack of nitrate-N and ammonium-N in surface waters in areas managed for timber production in the steep upper portion of the Calapooia Basin when compared to the flat, lower portion of the basin that is managed for agricultural production.  Additionally, strong seasonal relationships between land use/land cover and sub-basin DN concentration have been identified in the Calapooia Basin.  The role of riparian-zone vegetation and soils in releasing or retaining N is being investigated using in situ net N mineralization incubations across a range of soil and vegetation types.  Incubations are being performed for one year using the buried-bag method at 32 riparian-zone plots along the length of the Calapooia River.  Patterns of seasonal and cumulative net N mineralization across the study area are being analyzed and related to vegetation and soil characteristics using regression analysis.  Preliminary results from seven 20-35-day incubation periods indicate no discernable spatial pattern of net N mineralization across the study sites with net N mineralization values of the soil fraction ranging from -1.48 mg N kg^-1 d^-1 to 2.94 mg N kg^-1 d^-1 with estimates of individual study site standard deviations ranging from 0.05 to 1.10 mg N kg^-1 d^-1.