Nearly all nutrients lost from forested ecosystems pass through riparian zones where they may be accumulated or lost to downstream transport. However, the function of riparian forests in regulating exchanges of nutrients between ground-water and streams is poorly understood. This research will examine the role of riparian forests in regulating nitrogen flux between hillslope forests, riparian forests and streams using a nitrogen budget approach. Data required will be (1) direction and rate of ground-water flow and (2) concentrations of dissolved organic and inorganic nitrogen in ground-water. A study site located on a wide valley floor along a third-order stream in H.J. Andrews Experimental Forest will be used for this project. MODFLOW, a finite-difference ground-water flow model will be paramaterized with data from a network of piezometers and used to simulate flow paths of water; a tracer study will be used to validate model predictions. Water samples will be collected from transects of wells and analyzed for concentrations of dissolved nitrogen. These data will be used to calculate changes in dissolved nitrogen concentrations along ground-water flow paths in the shallow aquifer beneath the riparian forest and calculate a budget of nitrogen flux, via ground-water flow, between the riparian forest and stream ecosystems. The research program at H.J. Andrews Experimental Forest is recognized at national and international levels as a leader in forest ecosystem research. Institutional support for this research is exceptional.
