『Abstract
　Lake St. Croix is a natural impoundment of the lowermost 37 km of the St. Croix River in Minnesota and Wisconsin, making this one of a few large river systems in the world possessing a long-term depositional basin at its terminus. The river's relatively pristine condition led to its designation as a National Scenic Riverway in 1968, but increasing urbanization in its lower reaches has raised concerns about impacts on water quality. This study was initiated to reconstruct historical loadings of suspended sediment and phosphorus (P) from the sediment record in Lake St. Croix. Twenty-four piston cores, with an average length of 2 m, were collected along eight transects of the lake. Dated chronologies from ²¹⁰Pb, ¹³⁷Cs and ¹⁴C were used to calculate the rate of sediment accumulation in the lake over the past 100+ years. Diatom microfossil analysis was used to reconstruct historical lakewater P concentrations over the same time period, and sediment P analysis quantified the amount of P trapped in lake sediments. Using a whole-lake mass balance approach, the loading of sediment and P to Lake St. Croix over the last 100+ years was calculated. Beginning in 1850, sediment accumulation increased dramatically to a peak in 1950-1960 of eight times background rates prior to European settlement. The peak is driven largely by sediment contributions from small side-valley catchment tributaries to the downstream half of the lake. The total P load to the lake increased sharply after 1940 and remain high, at around four times the level of pre-European settlement conditions. The timing of peak sediment and P loading to the lake shows that early settlement activities, such as logging and the conversion of forest and prairie to agricultural land between 1850 and 1890, had only modest impacts on the lake. By contrast, the mid-1900S brought major increases in sediment and P loading to the lake, suggesting that relatively recent activities on the landscape and changes to nutrient balances in the watershed have caused the current eutrophic condition of this important recreational and natural resource.

Keywords: St. Croix River; Sediment loading; Phosphorus loading; Paleolimnology; Human impact; Mississippi River』

Introduction
Site description
Methods
　Coring
　Core lithology
Sediment dating
Sediment phosphorus
Diatom analysis and lakewater P reconstruction
Results and discussion
　Magmatic susceptibility
　Loss-on-ignition
　Cesium-137
　Lead-210 dating by alpha spectrometry
　Lead-210 dating by gamma spectrometry
　Carbon-14
　Sediment accumulation
　Sediment phosphorus
　Whole-lake fluxes
　Lakewater P reconstruction
　Phosphorus mass balance
Synthesis
　Sediment
　Phosphorus
　Uncertainties
Conclusions
Acknowledgements
References