Monitoring Trends In Sediment Loss and Transport: Combining Three Investigative Methods for Tracking Changes In Upslope Erosion and Stream Sediment after Farmland Conversion to No-till and CREP Protection

The Fifteenmile Creek Basin encompasses 236,700 acres in north-central Oregon. Approximately 53% of the basin is actively farmed, and the majority of the farmed ground is planted in dryland wheat. Historically, upslope and streambank erosion has transported large sediment loads into the streams draining the basin, leading to degradation of aquatic habitat. Starting in the mid 1990's farmers began switching to no-till production of wheat, and enrolling riparian areas into the CREP program. In 2006 we began a project to measure the changes in erosion and stream sediment resulting from improved land use practices. Our monitoring objects were threefold: (1) determine how sediment loads are changing in the basin, (2) determine the effect of land management changes on erosion rates, and (3) document any changes in stream geomorphology.

To accomplish these objectives we used three approaches. For measuring upslope erosion we used cesium-137 dating techniques to compare erosion from fields in conventional tillage to fields that were early adopters of no-till. For stream sediment, we used the relative bed stability (RBS) survey technique developed by the US EPA. We also conducted channel cross-section surveys to assess changes in stream geomorphology. Though this is an ongoing project designed to look at long-term (i.e. twenty year) changes in the basin, the first two years of the project have already revealed differences in the sub-basins based on the relative number of acres in no-till and CREP.