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Analysis of Suspended-Sediment Concentrations and Radioisotope Levels in the Wild Rice River Basin, Northwestern Minnesota, 1973-98

U.S. Geological Survey Water Resources Investigations Report 01-4192

 

M.E. Brigham, C.J. McCullough, and P. Wilkinson

 

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Abstract

We examined historical suspended-sediment data and activities of fallout radioisotopes (lead-210 [210Pb], cesium-137 [137Cs], and beryllium-7 [7Be]) associated with suspended sediments and source-area sediments (cultivated soils, bank material, and reference soils) in the Wild Rice River Basin, a tributary to the Red River of the North, to better understand sources of suspended sediment to streams in the region. Multiple linear regression analysis of suspended-sediment concentrations from the Wild Rice River at Twin Valley, Minnesota indicated significant relations between suspended-sediment concentrations and streamflow. Flow-adjusted sediment concentrations tended to be slightly higher in spring than summer-autumn. No temporal trends in concentration were observed during 1973-98. The fallout radioisotopes were nearly always detectable in suspended sediments during spring-summer 1998. Mean 210Pb and 7Be activities in suspended sediment and surficial, cultivated soils were similar, perhaps indicating little dilution of suspended sediment from low-isotopic-activity bank sediments. In contrast, mean 137Cs activities in suspended sediment indicated a mixture of sediment originating from eroded soils and from eroded bank material, with bank material being a somewhat more important source upstream of Twin Valley, Minnesota; and approximately equal fractions of bank material and surficial soils contributing to the suspended load downstream at Hendrum, Minnesota. This study indicates that, to be effective, efforts to reduce sediment loading to the Wild Rice River should include measures to control soil erosion from cultivated fields.

Contents

Abstract

Introduction

Environmental setting

Hydrologic conditions during 1998 sampling

Acknowledgements

Analysis of historical suspended-sediment data

Suspended-sediment data

Relation to streamflow, season, and time

Background

Regression model and results of sediment analysis

Sediment loads

Radioisotope levels of sediments

Background on use of radioisotope methods

Sources of isotopes

Behavior of 210Pb, 137Cs, and 7Be in soils

Radioisotope study approach

Sampling methods

Laboratory analysis of radioisotopes

Radioisotope levels of sediments

Implications for sediment sources

Implications and limitations of study

Summary

References


 

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