IMPLICATIONS OF LEGACY AND LAG EFFECTS FOR CONNECTING WATERSHED SEDIMENT YIELDS TO MODELED FIELD EROSION, AGRICULTURAL BMPs, RIPARIAN BUFFERS, AND STREAM RESTORATION, DRIFTLESS AREA, WISCONSIN

Much time and money has been spent over the last 40 years in the U.S. by farmers, soil scientists, hydrologists, geomorphologists, engineers, and ecologists attempting to document how agricultural best management practices, natural vegetation in riparian corridors, and stream rehabilitation or bank stabilization reduces sediment yields and improves ecological conditions at watershed outlets. These issues are especially pertinent in the steep erodible landscape of the Driftless Area in southwest Wisconsin, where many miles of world-class spring-fed trout streams remain on state impaired waters lists from excessive sedimentation and degraded habitat even though this area was the birthplace of the conservation movement 75 years ago. In between fields and watershed outlets lies a vast repository of sediment in overbank areas and small channels that has been deposited over the last 100 years or more. These agricultural streams generally have slopes between 0.1 and 0.3 percent, and streams with this slope range have the ability to store or move sediment depending on localized low flows, floods, and hydraulic conditions. Historical fine-grained, organic-rich sediment stored in valley bottoms, banks, and in channels, even in small watersheds of about 20 square miles, likely contributes a substantial portion of the suspended sediment and phosphorus loading to the upper Mississippi River Basin and Gulf of Mexico. Streambanks, made overly high by accelerated rates of overbank sedimentation during the late 19^th and most of the 20^th century, are now major sources of sediment, especially in channelized and straightened stream reaches. Tree-lined channels also are prone to collect sediment because of the increase in roughness; thus it is important to look beyond vegetation type and into the sediment record to understand the usefulness of vegetative filter strips along riparian corridors. This presentation will synthesize results from historical sedimentation and channel change studies in the Driftless Area with modern studies of bank erosion and fine sediment deposition in channels and modern rates of soil loss from fields and pastures under various best management and cropping practices. Specifically, results from the targeted implementation study on Pleasant Valley, Pecatonica watershed, will be highlighted.