U-238/Th-234 Tracer Studies of Sediment Resuspension and Horizontal Transport in Nearshore Lake...

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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: Brian Eadie 3 , John Robbins 3 , Barry Lesht 2 , Dave Schwab 3 1 University of Wisconsin-Milwaukee 2 Argonne National Laboratory

Transcript of U-238/Th-234 Tracer Studies of Sediment Resuspension and Horizontal Transport in Nearshore Lake...

Page 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.

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

Page 2: 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.

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 ??

Page 3: 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.

1

2

n-1

mean flow

Cross-margin transport during a “plume event”

n+1

Zone of finaldeposition

shore

open lake

Plume

= new sediment inputs

= particle transport

Org C < 0.5%Cs-137 = 0Pb-210 = 0

Org C > 5 %Cs-137 ~ 5 pCi/gPb-210 ~ 20 pCi/g

Page 4: 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.

Seasonal changes in spatial distributions -- 1998-99

238U 234Th

excess 234Thderived from water column

half life = 24.1 days

rapid particle scavenging, deposition, & resuspension

Tres = I water col.

J sediment

= [ 234Th ]part z water

Ised

=fCi m-2

fCi m-2 d-1= days

Page 5: 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.

vehicle

sampling

samplefiltering

Sampler mk1

Page 6: 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.

4

5

6

pump

Sampling sequence

1

2

3

Page 7: 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.

sediment inventory vs. depth

resuspendible sediment inventory, g/m2

0 10000 20000 30000 40000

dept

h, m

eter

s

0

10

20

30

40

50

60

Sep 98Apr 99 May 99Aug 99

mass – pool of resuspendible sed

0 10 20 30 40 50

mas

s in

vent

orie

s, g

/m2

0

10000

20000

30000

40000

west ------> east

alongshore sed inventories

depth alongshore

Page 8: 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.

0 10 20 30 40 50

Th-

234

inve

ntor

ies,

fCi/c

m2

0

500

1000

1500

2000

2500

3000

3500

0 10 20 30 40 50

part

icle

res

iden

ce ti

me,

day

s

0

200

400

600

800

as move from west to east:

Inventories Particle residence times

Tres = Iwater/Jsed = Iwater/ Ised

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Box ---> "downstream"

1 2 3 4

Th

-23

4 In

v.,

fCi/c

m2

0

100

200

300

400

500

Box ---> "downstream"

1 2 3 4

Pa

rtic

le r

esi

de

nce

tim

e,

da

ys

0

50

100

150

200

“downstream” enrichment of Th-234

Inventories Particle residence times

Page 10: 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.

"downstream" enrichment of exTh-234

Box ---> "downstream"

1 2 3 4

I e

xT

h-2

34/I U

-23

8

0

1

2

3

post plume

f = I[234Thex]/ I[238U]

Box ---> "downstream"

1 2 3 4

focu

sin

g f

acto

r

0

1

2

3

Box ---> "downstream"

1 2 3 4

focu

sin

g f

acto

r

0

1

2

3

Box ---> "downstream"

1 2 3 4

focu

sin

g f

acto

r

0

1

2

3

sediment suspended part. dissolved

1 = secular equil w/ 238U

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“Two Box” transport model:

x = distanceAA11 AA22

f n = I Th-234 / I U238water

An = area of nth box

Vn = volume of nth box zn = depth of nth box U238 = U238water = 100 fCi/ L

Th–234n=1 exported = (1-f 1)* A1 * U238 * z1

Th-234 n=2 = Thsupported + Thimported = A2 * U238 * z2 + [(1-f 1)* A1 * U238 * z1] exp(-t) = V2 * U238 + [(1-f 1)* V1 * U238 ] exp(-t) f 2 = [Th-234n=2/ A2 ] / U238 * z2 = 1 + (1-f 1)*(V1/ V2)*exp(-t) transport time to attain observed downstream excess f rom observed upstream deficiency :

t = -1/ * ln[(f 2-1)/ (1-f 1)/ (V1/ V2)] mean transport velocity = x / t

Page 12: 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.

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  

)1(

)1(ln

1

11

22

fI

fIt

Page 13: 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.
Page 14: 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. 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

t) )exp(f(1

1f

V

V

Sink

Source

1

2

2

1

D. Schwab & D Beletsky

Page 15: 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.

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]

Page 16: 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.

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

Page 17: 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.

Special thanks to: Dave Lovalvo, the R/V Neeskay

NSF-CoOP NOAA COP

Page 18: 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.

www.uwm.edu/Dept/GLWI

Page 19: 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.