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U-238/Th-234 Tracer Studies of Sediment Resuspension and Horizontal Transport in Nearshore Lake Michigan J. Val Klump 1

U-238/Th-234 Tracer Studies of Sediment Resuspension and Horizontal Transport in Nearshore Lake Michigan J. Val Klump 1 , James T. Waples 1 , Kent A. Orlandini 2 , David N. Edgington 1 , Kim Weckerly 1 , Don Szmania 1 , & Richard A. MacKenzie 1 With the collaboration of :

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U-238/Th-234 Tracer Studies of Sediment Resuspension and Horizontal Transport in Nearshore Lake Michigan J. Val Klump 1

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  1. U-238/Th-234 Tracer Studies of Sediment Resuspension and Horizontal Transport in Nearshore Lake Michigan J. Val Klump1, James T. Waples1, Kent A. Orlandini2, David N. Edgington1, Kim Weckerly1, Don Szmania1, & Richard A. MacKenzie1 With the collaboration of: Brian Eadie3, John Robbins3, Barry Lesht2, Dave Schwab3 1University of Wisconsin-Milwaukee 2Argonne National Laboratory 3NOAA GLERL

  2. Th-U disequilibria: application to studies of particle dynamics • Basin scale distribution and particle transport: 1998-99 • Q: can we track particle movement on a time scale of weeks ? • how much mass is available ?? • how long do particles remain in the water column ?? • can we estimate the direction & rate of horizontal advection ??

  3. Cross-margin transport during a “plume event” Plume n+1 open lake 1 shore Zone of final deposition Org C < 0.5% Cs-137 = 0 Pb-210 = 0 Org C > 5 % Cs-137 ~ 5 pCi/g Pb-210 ~ 20 pCi/g 2 mean flow n-1 = new sediment inputs = particle transport

  4. Seasonal changes in spatial distributions -- 1998-99 234Th 238U half life = 24.1 days rapid particle scavenging, deposition, & resuspension I water col. Tres = J sediment excess 234Th derived from water column [ 234Th ]part z water = l Ised fCi m-2 = = days fCi m-2 d-1

  5. Sampler mk1 vehicle sampling sample filtering

  6. pump 1 4 2 5 3 6 Sampling sequence

  7. mass – pool of resuspendible sed alongshore depth

  8. as move from west to east: Inventories  Particle residence times  Tres = Iwater/Jsed = Iwater/  Ised

  9. “downstream” enrichment of Th-234 Inventories  Particle residence times 

  10. 1 = secular equil w/ 238U f = I[234Thex]/ I[238U] sediment suspended part. dissolved

  11. “Two Box” transport model: A2 A1 Dx = distance

  12. 1. Estimate transport times: Isupported = V  U-238 = A z  U-238 U-238 = 100 fCi L-1 z = 20 meters V1 (source) ~ 1800 km2 0.02 ~ 3600 km3 V2 (sink) ~ 425 km2 0.02 ~ 8.5 km3 V1/V2 = A1/A2 ~ 4.2 May 99: f1 = 0.88 f2 = 1.17 t ~ 38 days Aug 99: f1 = 0.79 f2 = 1.46 t ~ 23 days ? transport velocity ~ 100 to 150 km  30 days ~ 3 – 5 km/day

  13. 2. Estimate of source area: if dist. ~ 100 km & velocity ~ 4 km d-1 (B. Lesht) 25 days ~ one ½ life for f1 = 0.85 f2 = 1.45 V1/V2  6 i.e. the longer it takes the greater the source area D. Schwab & D Beletsky

  14. 3. Estimate of mass transport required: • for 234Thex of 50%, i.e. f = 1.5 • area of temporary sink ~ 500 km2 • z = 20 meters •  excess Th-234 ~ 0.5 Curies ~ 1 x 1012 dpm • if [Th-234]susp part ~ 35 pCi g-1 ~ 80 dpm g-1 •  a rapid transport “event” • 13 x 103 MT (w/o decay) • 25 x 103 MT (one ½ life) i.e. the longer it takes the more you need • ~ 1% of total susp. particulates in the plume • 50-100 “half lives” to transport amt ~ total annual deposition ? • ~ several years ?? [~ 4-8 yrs]

  15. Sediments in the Lake = the ultimate sink via burial Where are they being buried ? How quickly do materials move from source to sink ? ~ years to decades Chart of sediment thickness

  16. Special thanks to: Dave Lovalvo, the R/V Neeskay NSF-CoOP NOAA COP

  17. www.uwm.edu/Dept/GLWI

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