『Abstract
　Increased levels of phosphorus (P) in freshwater systems generally cause eutrophication leading to algal blooms, fish kills, and decreased biodiversity. Point sources have been fairly well characterized; however, non-point sources (NPS), such as agricultural fields, require further study to ascertain the origin and physicochemical forms of P. During a single storm event in June 2008 in a small Wisconsin agricultural watershed (12.4 km²), a comprehensive study was performed to characterize sediment and P transport dynamics. In addition to standard analytical techniques to quantify sediment and P transport, the atmospheric fallout radionuclides (⁷Be, ²¹⁰ Pbxs, and ¹³⁷Cs) were employed to determine sediment origin and in-stream transport parameters. Sediments originated primarily from surficial upland soils, or cultivated fields, with minor contributions of resuspended streambed sediments and no discernible stream bank contributions. Sediments were deposited onto the streambed during this event, creating a temporary store, which could be resuspended during subsequent flow events. While for this moderate storm event the stream channels exhibited a short-term depositional behavior they appeared erosional in nature over longer time periods. Particulate-bound P was found to be 33-46％ of the total P (TP) transported in the stream channel. The mean dissolved P and TP concentrations at the two stream sites ranged from 0.99±0.32 mg L^-1 to 1.14±0.63 mg L^-1 and 1.77±0.78 mg L^-1 to 1.83±0.78 mg L^-1, respectively. During baseflow conditions, the mean dissolved reactive P (DRP) and TP concentrations were quite high, 027±0.02 mg L^-1 and 0.33±0.04 mg L^-1, respectively, exceeding recommended USEPA TP levels (0.08 mg L^-1; USEPA, 2000) for eutrophication threshold. Overall, significant transport of P in both dissolved and particulate forms occurred during this moderate stormflow event. We assert that improved upland conservation practices are necessary to minimize P export from this agricultural watershed.

Keywords: Particulate and dissolved phosphorus; Atmospheric fallout radionuclides; Sediment sourcing; Stream sediment transport; Agricultural headwater watershed』

1. Introduction
2. Methods
　2.1. Study area
　2.2. Rainfall event
　2.3. Flow collection and analysis
　2.4. Suspended sediment and soil cores collection and analysis
　2.,5. Precipitation collection
3. Results and discussion
　3.1. Soil and sediment characteristics
　3.2. Short- and long-term sediment fluxes
　3.3. ⁷Be/²¹⁰ Pbxs ratio, sediment age, and percent new sediment
　3.4. Sediment origin
　3.5. Soil and sediment phosphorus
　3.6. Phosphorus transport in stream flow
4. Summary
Acknowledgments
Appendix A. Supplementary material
References