2007 Annual Report 1a.Objectives (from AD-416) Increase knowledge of sediment erosion and transport by determining the sources of fine sediment that reach the channels in CEAP benchmark watersheds. 1b.Approach (from AD-416) ARS-NSL and University of Iowa researchers will work together to collect samples of potential source material, precipitation, and transported sediment in CEAP watersheds and determine the amount of naturally-occurring radionuclides using a gamma spectrometer. Work will be conducted at ARS locations in Ohio, Indiana, Missouri, Texas, Iowa, and New York. The signature of the transported sediment will reveal its source by comparison to the signatures of the source samples. Data will be available to all cooperators for analysis and reports will be generated as appropriate. 3.Progress Report This report serves to document research conducted under a Specific Cooperative Agreement between ARS and the University of Iowa. Additional details of research can be found in the report for the in-house project 6408-13000-017-00D, "Integrated Assessment and Analysis of Physical Landscape Processes that Impact the Management Of Agricultural Watersheds." The SCA was monitored by meetings, phone and e-mail communications between the ADODR and principle investigator. In the past year samples were collected at four Conservation Effects Assessment Project (CEAP) watersheds. These samples were processed and analyzed. A manuscript has been prepared and will be presented at the annual meeting of the Soil and Water Conservation Society. Agricultural practices often lead to changes in the amount and character of sediment in surface waters which results in erosion or deposition on channel boundaries and to the destruction of valuable land and infrastructure and disruptions of the aquatic environment. Ratios of naturally occurring radionuclides attached to the sediment were used as indicators of the source of sediment to the channels of five CEAP watersheds. It was determined that the dominant source of sediment reaching the channels was derived from the channel boundary on three of the five CEAP watersheds studied. Knowledge of the dominant sources of sediment is critical information needed by watershed model developers and land managers to design effective management practices to reduce erosion and sedimentation on agricultural watersheds. This research supports National Program 201 Water Quality and Management, Problem area #1 Effectiveness of Conservation Practices.