Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2002
Publication Date: 2/28/2003
Citation: WIGINGTON, P.J., GRIFFITH, S.M., FIELD, J.A., BAHAM, J.E., HORWATH, W.R., OWEN, J.S., DAVIS, J.H., RAIN, S.C., STEINER, J.J. EFFECTIVENESS OF A RIPARIAN WATER QUALITY BUFFER ALONG A SMALL AGRICULTURALSTREAM IN WESTERN OREGON. JOURNAL OF ENVIRONMENTAL QUALITY. 2003. v. 32(1). p. 162-170. Interpretive Summary: Much of the land in Willamette Valley, Oregon where grass seed production occurs, is marginally productive for most other crops because of the poorly drained soil conditions. The role of riparian areas bordering grass seed fields in moderating surface water and groundwater quality is not well understood. A study site in western Oregon was instrumented to determine how riparian areas bordering grass seed fields process N and thereby influence water quality. The research site consisted of a perennial ryegrass seed field, a grass riparian area, and an intermittent creek. Lake Creek study site hydrology and water chemistry data indicated that considerable processing of inorganic N occurred in these riparian areas and thus maintained almost undetectable shallow groundwater nitrate concentrations. Despite the fact that the Lake Creek riparian area was very effective in diminishing shallow groundwater nitrate levels, most of the ground and surface waters bypassed the rooting zones of the riparian areas during the year. It is suggested that the use of prudent agricultural practices is the most promising approach for management of stream water quality along streams in poorly drained landscapes of Willamette Valley.
Technical Abstract: Two study riparian sites with similar soils and hydrology but contrasting vegetation were established along Lake Creek in western Oregon to determine their water quality function. One site had a non-cultivated riparian zone with a plant community comprised of primarily herbaceous plants and the other site had a cultivated riparian zone in which the ryegrass seed production field extended to the edge of the creek. Stream stage and water table elevations were recorded. Groundwater quality was monitored as water moved from the grass seed fields through the riparian zones. The non-cultivated riparian zone can significantly reduce the nitrate-N concentrations of shallow groundwater moving from grass seed fields. Darcy=s Law based estimates of shallow groundwater flow through riparian zone A horizons revealed that this water flowpath could account for only a very small percentage of the streamflow. Two flowpaths are proposed as the primary source of streamflow: 1) groundwater rising to watershed surfaces and exfiltrating into stream channels, swales, and ponded areas, and 2) rainfall on saturated watershed surfaces with rapid movement to swales, channels and saturated depressions. Even though there is great potential for nitrogen and other pollutants to be reduced as water moves through the non cultivated riparian zone with grass or herbaceous vegetation, the potential was not fully realized because only a small proportion of the Lake Creek stream flow interacted with riparian zone soils. Effective nutrient water quality management in poorly drained landscapes similar to the Lake Creek watershed is primarily dependent on implementation of sound agricultural practices within grass seed fields and is less influenced by riparian zone vegetation.