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NITRATE REMOVAL EFFECTIVENESS OF A RIPARIAN BUFFER ALONG A SMALL AGRICULTURAL STREAM IN WESTERN OREGON
Citation:
WIGINGTON JR, P. J., S. M. Griffith, J. A. Field, J. E. Baham, W. R. Horwath, J. Owen, J. H. Davis, S. C. Rain, AND J. J. Steiner. NITRATE REMOVAL EFFECTIVENESS OF A RIPARIAN BUFFER ALONG A SMALL AGRICULTURAL STREAM IN WESTERN OREGON. JOURNAL OF ENVIRONMENTAL QUALITY. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Madison, WI, 32(1):162-170, (2003).
Description:
We established two study sites with similar soils and hydrology but contrasting riparian vegetation along Lake Creek, an intermittent stream that drains perennial ryegrass fields in the Willamette Valley of western Oregon. One site had a non-cultivated riparian zone with a plant community comprised of grasses, forbs, sedges and rushes, and the other site had cultivated riparian zone in which the perennial ryegrass field extended to the edge of the stream. We instrumented the site with a series of stilling wells to record stream stage and piezometers to record water table elevations. To examine the changes in water quality parameters of groundwater as it moved from the grass seed fields through the riparian zones, we installed a series of nested piezometers along three transects at each site. Each piezometer nest consisted of one piezometer in the A horizon and one in the C horizon at a given location.
Results showed that the non-cultivated riparian zone can significantly reduce the NO3-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/herbaceous vegetation, the potential was not fully realized because only a small proportion of the Lake Creek stream flow interacts with riparian zone soils. Consequently, 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.