Dating Recent (200 Years) Events in Sediments from Lakes, Estuaries

17

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Dating Recent (200 Years) Events in Sediments from Lakes, Estuaries, and Deep Ocean Environments Using Lead-210 WILLIAM R. SCHELL University of Washington, Laboratory of Radiation Ecology, College of Fisheries, WH-10, Seattle, WA 98195

Sediments from lakes, continental margins and deep oceans record events caused by man and by natural processes and, by using radioactive tracers, their chronological record can be determined. The rhythmic pattern of sedimentation rates and benthic mixing processes has been determined using Pb at lowland lakes of Washington State, at the Puget Sound Estuary and at two deep ocean sites - one 60 km off San Francisco at 1000 m and the other 350 km off New York City at 4000 m. The Pb input as a function of time is shown, for example, to increase from background to some 30 times background at Lake Washington (Seattle), and 13 times background at Sinclair Inlet (near a naval shipyard) of Puget Sound. The dates for maximum inputs of other trace metals into Sinclair Inlet were established; their relative enrichments above background were Cu..8.0 Zn..2.7, Ni..1.9, Cr..2.2. Man's effect on the Lake Washington watershed due to deforestation and urban development has resulted in three changes in sedimentation rates since 1850. The Pb profiles in cores collected at the mouth of the Hudson Canyon (4000 m deep) show wide variations which may be due to sediment redistribution by deep currents and by biological mixing. An episodic event in the canyon may be registered synchronously, 100 years ago, at two stations; one at 2800 m and one at 4000 m deep. By measuring Pu in deep sea cores together with Pb, the past 30 years since the bomb testing can be identified since i t is generally assumed that both Pb and Pu are associated with particulate matter. The deposition inventory for Pb and Pu shows that redistribution processes are active at the deep ocean stations and that Pb serves as a time dependent tracer for both advective transport and biological mixing of sediments. 210

210

239,240

210

210

239,240

210

239,240

210

0097-6156/82/0176-0331 $07.75/0 © 1982 American Chemical Society Currie; Nuclear and Chemical Dating Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982.


332

NUCLEAR AND

C H E M I C A L DATING T E C H N I Q U E S

Recent events s i n c e t h e i n d u s t r i a l r e v o l u t i o n have s i g n i f i c a n t l y a l t e r e d t h e environmental c o n d i t i o n s e x i s t i n g a t many l o c a t i o n s o f our planet. Man has profoundly a c c e l e r a t e d t h e e r o s i o n of the land due t o c l e a r i n g of f o r e s t s and c o n s t r u c t i o n o f roads; he has contaminated the environment by emission of p o l l u t i n g p a r t i c l e s and gases through the processes o f winning metals from o r e s , by the p r o d u c t i o n of energy and by the d i s p o s a l of h i s wastes. Natural changes i n t h e environment a r e c o n t i n u a l l y o c c u r r i n g by t h e changing c l i m a t i c c o n d i t i o n s and by e p i s o d i c events such as v o l c a n i c and t e c t o n i c a c t i v i t y . Dating o f these events over the past 200 years can g i v e some i n s i g h t on what we can expect i n the f u t u r e . This d a t i n g can be accomplished using the rhythmical accumulation of sediments i n a v a i l a b l e r e p o s i t o r i e s such as l a k e s , e s t u a r i e s , a t o l l s , and deep ocean environments together w i t h r a d i o a c t i v e t r a c e r chronometers. The purpose o f t h i s paper i s t o o u t l i n e the methods and t o i l l u s t r a t e the use o f r a d i o a c t i v e chronometers i n s o l v i n g environmental problems which have occurred over the past 150 y e a r s . Experimental Methods 2 1 0

Assumptions i n the P b Method. The method f o r u s i n g decay products o f n a t u r a l l y o c c u r r i n g R a f o r sediment c h r o n o l o g i e s was f i r s t o u t l i n e d by Goldberg (1963). The decay c h a i n o f R a proceeds through several s h o r t h a l f - l i f e r a d i o n u c l i d e s t o long lived P b as: 2 2 6

2 2 6

2 1 0

226

R a

>

222

( t =1620 y r )

R n

>

218p

0

(3.8 d)

214p

>

(3.05 m)

b

214

>

B i

(26.8 m)

214p

>

Q

(19.7 m) 4

(1.6xl0" s) 206p

b

210p

P u

0 u n c

a

2

2

2 1 0

u

m e

2 1 0

1

2 1 0

o

f

2

22.35 y r s ) would decay t o background l e v e l s i n 200 y r s , the time of mixing o f the upper sediment l a y e r s can be estimated. The value f o r the d e p o s i t i o n r a t e was expected t o be constant, o r reasonably constant f o r the l o c a l area a t a depth o f 4000 m. How ever, as shown i n Table 2, v a r i a t i o n s o f between 0.5 t o 5.9 dpm*cm" *yr~ were observed. Benninger e t a K , [3] found values o f about 1 dpm*cm" *yr f o r the d e p o s i t i o n r a t e o f P b i n s o i l s and sediments near New Haven, Connecticut and Long I s l a n d . Recent measurements i n Puget Sound a t S i n c l a i r I n l e t by W. R. S c h e l l (unpublished data), i n d i c a t e d t h a t the d e p o s i t i o n r a t e was about 0.35 dpm*cnr *yr. Thus, t o e x p l a i n t h e very high and v a r i a b l e values f o r the Pb d e p o s i t i o n r a t e a t t h e deep ocean s t a t i o n s , one must propose a mechanism whereby m a t e r i a l from t h e topmost l a y e r s o f sediments near the A t l a n t i c Disposal S i t e i s t r a n s p o r t e d and re-deposited a t these s t a t i o n s . By combining the f i n d i n g s o f Cacchione, Drake and the r e s u l t s reported here, a coherent model can be proposed t o e x p l a i n the deposition inventory o f the r a d i o n u c l i d e s . The down-canyon c u r r e n t t r a n s p o r t s l a r g e q u a n t i t i e s o f sediment toward the r a d i o a c t i v e waste d i s p o s a l s i t e a t 4000 m. W i t h i n the upper canyon, f i n e m a t e r i a l i s t r a n s p o r t e d the f u r t h e s t . Near the mouth o f the canyon, sediment e r o s i o n o f the w a l l s occurs due t o the downcanyon c u r r e n t s meeting a proposed opposing on-shore bottom cur rent. The eroded m a t e r i a l from t h e w a l l s i s t r a n s p o r t e d and t h e f i n e r m a t e r i a l i s deposited i n eddies formed where the two c u r r e n t s meet. 2

1

2

2 1 0

2

2 1 0

Currie; Nuclear and Chemical Dating Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

17.

SCHELL

Table 2.

Dating Recent Events in Sediments by


Pb

2 1 0

D e p o s i t i o n o f P b and 2 3 9 , 2 4 0 · Sediment Cores C o l l e c t e d a t t h e U. S. R a d i o a c t i v e Disposal S i t e Near the F a r a l l o n I s l a n d s , 60 km o f f San F r a n c i s c o and a t the Hudson Canyon, 350 km o f f New York C i t y . P u

Ί

η

210pb

No.

357

210

Station Location

Depth (m)

D e p o s i t i o n Rate dpm»cnr yr 2

239 240p >

u

Integrated D e p o s i t i o n mCi*km~ (30 y r ) 2

F a r a l l o n I s l a n d Box Cores 13A

37°38.10*N 123°08.00'W

39

37°38.10'N 123°08.00'W

1043

2.9

4.3

1469

3.5

1.3

Hudson Canyon Box Cores 3

37°49.30'N 70°36.7TW

4015

5.9

.40

4

37°45.03'N 70°35.75'W

3950

3.8

.24

5

37°46.75'N 70°34.0TW

3945

0.7

.12

6

37°54.65'N 70°32.69'W

3740

—

.20

7

37°48.10'N 70°37.11'W

3885

0.5

.09

8

37°49.79'N 70°36.13'W

3995

2.9

.31

15

37°04.24'N 70°26.38'W

3655

0.6

.11

39°02'N 42°36'W

4810

II

4810

0.17 : (0.40)

C o l l e c t i o n made i n 1969, Noshkin and Bowen (1973). e x t r a p o l a t e d t o 1978 from Noshkin and Bowen (1973) estimate o f f a l l o u t deposited a t 4000 m on t h e i r s i n k i n g r a t e model.


358

N U C L E A R AND

C H E M I C A L DATING T E C H N I Q U E S

2 1 0

I f m a t e r i a l which contains n u t r i e n t s , P b and 2 3 9 , 2 4 0 p a r t i c u l a t e matter i s r a i n i n g down from the water column t o the sediment and i s i n i t i a l l y deposited on r i d g e s a t the ocean bottom, c u r r e n t s may subsequently t r a n s p o r t p a r t of t h i s m a t e r i a l and d e p o s i t i t a t other l o c a t i o n s . The low d e p o s i t i o n r a t e found a t S t a t i o n s 5, 7, and 15 (Table 2) may be due t o the i n i t i a l deposi t i o n on r i d g e s a t the bottom where only a small f r a c t i o n of the m a t e r i a l i s r e t a i n e d i n the topmost l a y e r s . The remainder of the m a t e r i a l i s t r a n s p o r t e d t o s e t t l i n g zones of the submerged v a l l e y such as a t S t a t i o n s 3, 4, 8, 813, and 816. At S t a t i o n 3, a mixed zone occurs to a depth of 12 cm as i n d i c a t e d by the P b profile. At t h i s s t a t i o n , the highest d e p o s i t i o n r a t e of P b i s found compared t o the other e i g h t sampling s t a t i o n s . If this P b p r o f i l e represents b i o l o g i c a l mixing, the s t a t i o n should be r i c h i n benthic organisms because of the d e p o s i t i o n of p a r t i c u l a t e matter i n c l u d i n g n u t r i e n t s from a wide area of bottom. This s t a t i o n a l s o has the highest i n t e g r a t e d d e p o s i t i o n of 2 3 9 2 4 0 ^ Q.4 mCVkm" and one would expect t h a t t h i s higher c o n c e n t r a t i o n could be from the waste d i s p o s a l c a n i s t e r s i n t h i s area. However, i t i s p o s s i b l e t h a t the 239 240p i37 atmospheric f a l l o u t , l i k e P b , i s being concentrated at t h i s area and i s mixed by b i o l o g i c a l organisms t o a depth of 12 cm. Thus, the high l e v e l s of 2 3 9 , 2 4 o i3? and P b r e q u i r e t h a t p h y s i c a l or b i o l o g i c a l mixing occurs and t h a t a d d i t i o n a l m a t e r i a l i s being t r a n s p o r t e d a d v e c t i v e l y and deposited a t t h i s s t a t i o n . The high c o n c e n t r a t i o n s found may not n e c e s s a r i l y be due to leakage from waste d i s p o s a l c a n i s t e r s . According to Dr. D. Rice ( C a l i f o r n i a State U n i v e r s i t y ) (personal communication), the b i o l o g i c a l species d i v e r s i t y shows t h a t a t the s t a t i o n s which have high P b and 2 3 9 2 4 o i f o r sediment d e p o s i t i o n , namely S t a t i o n s 8, 4, and 3, there were 25, 20, and 15 s p e c i e s , r e s p e c t i v e l y ; a t the low sediment depo s i t i o n S t a t i o n s 15, 7, and 5, there were 6, 6, and 10 s p e c i e s , respectively. These b i o l o g i c a l data do not disagree w i t h the a d v e c t i v e mechanism f o r sediment t r a n s p o r t proposed t o e x p l a i n the high sediment d e p o s i t i o n data f o r Pb, C s , and 2 3 9 , 2 4 0 The organisms would be more concentrated i n regions where the a v a i l a b l e p a r t i c u l a t e matter, i n c l u d i n g n u t r i e n t s , would be deposited. Thus, the higher l e v e l s of r a d i o n u c l i d e s a t c e r t a i n s t a t i o n s may not be due to leakage of r a d i o a c t i v e wastes from the c a n i s t e r s but to r e d i s t r i b u t i o n of p a r t i c u l a t e matter deposited from the water column. The 2 3 9 2 4 0 b accounted f o r as being from nuclear weapons-produced f a l l o u t over the past 30 y e a r s , and not from the waste d i s p o s a l c a n i s t e r s . The mechanism must be by t r a n s p o r t and r e d i s t r i b u t i o n of the f i n e f l o c u l e n t sediment a t the sedimentwater i n t e r f a c e . Because of the s i g n i f i c a n t amount of sediment which i s being t r a n s p o r t e d down-canyon, any leakage from the c a n i s t e r s would probably be scavenged l o c a l l y by the environmental sediment m a t e r i a l .


Pu

o n

2 1 0

2 1 0

2 1 0

2

5

Pu

a

2 1 0

3

u

a n d

C s

f r o m

Pu>

C S j

2 1 0

2 1 0

>

2 1 0

Pu

v a

u e s

1 3 7

Pu#

3

Pu

c a n

e


17.

SCHELL

Dating Recent Events in Sediments by

210

Pb

359

Conclusions Dating o f recent (200 y e a r ) events i n a wide v a r i e t y o f f r e s h and s a l t water environments has been made by measuring n a t u r a l l e v e l s o f unsupported P b c o n c e n t r a t i o n s i n s e c t i o n s o f sediment core samples. I f the atmospheric P b i n p u t has been determined, a s i n g l e o r few l a y e r s can be used t o f i n d the age o f d e p o s i t i o n a t a given depth i n shallow waters. However, a s e r i e s of measure ments o f core s e c t i o n s can b e t t e r d e f i n e the sedimentation r a t e s . Where man's a c t i v i t i e s o r natural events have a l t e r e d the deposi t i o n h i s t o r y , t h e P b p r o f i l e has been used t o determine t h e magnitude o f the changes i n the sedimentary regime and t o d e f i n e the time when these changes occurred. Increases i n Pb c o n c e n t r a t i o n s o f 30 times have been measured i n Lake Washington caused mainly through the burning o f leaded f u e l i n i n t e r n a l combusion engines. S i g n i f i c a n t i n c r e a s e s i n the c o n c e n t r a t i o n s o f Zn (6 t i m e s ) , Pb (13 t i m e s ) , and Cu (8 times) have been i n t r o d u c e d by man's a c t i v i t y near S i n c l a i r I n l e t , probably as a r e s u l t of shipyard's a c t i v i t i e s . By measuring other elements i n the same core p r o f i l e s , t h e i r d i f f u s i o n as compared t o P b have been observed. Biological mixing and p o s s i b l e sedimentation r a t e s have been determined from the c o n c e n t r a t i o n p r o f i l e s , assuming t h a t the P b t r a c e r i s f i x e d s t r o n g l y t o t h e sediment p a r t i c l e s a t t h e deep ocean s t a t i o n s . The P b t r a c e r o f sediments has been shown t o compare times when anthropogenic events occurred w i t h times obtained from the r a d i o a c t i v e chronology i n f r e s h , e s t u a r i n e , and marine waters. These s t u d i e s i n t r o d u c e and u t i l i z e a n a t u r a l biogeochemical t r a c e r o f sedimentary processes. The use o f P b t o t r a c e deep ocean c u r r e n t s where f l o c c u l e n t m a t e r i a l i s t r a n s p o r t e d i n one region and deposited i n another may p r o v i d e v a l u a b l e i n f o r m a t i o n on deep sea t r a n s p o r t . However, more work i s r e q u i r e d t o v e r i f y these i n i t i a l findings. A d d i t i o n a l work a l s o i s needed t o evaluate mechanisms r e s p o n s i b l e f o r the d i f f e r e n c e s i n d i f f u s i o n of c e r t a i n elements i n sediments compared t o lead and t o i d e n t i f y i f two types o f b i o l o g i c a l mixing may indeed be r e s p o n s i b l e f o r the high sedimentation r a t e s found i n the deep ocean. 2 1 0


2 1 0

2 1 0

2 1 0

2 1 0

2 1 0

2 1 0

I would l i k e t o acknowledge t h e a s s i s t a n c e given by Robert S. Barnes f o r the Lake Washington S t u d i e s , by the students i n 1979, 1980 F i s h e r i e s 477, 478 c l a s s e s f o r the S i n c l a i r I n l e t s t u d i e s and by Susan Sugai and Ahmad N e v i s s i f o r the radiochemical measurements i n the ocean s t u d i e s .


360

NUCLEAR AND CHEMICAL DATING TECHNIQUES

Literature Cited [1] Aller, R. C., and Cochran, J. Κ., Th/ U disequilibrium in nearshore sediment: particle reworking and diagenic time scales, Earth and Planet. Sci. Lett., 29, 37-50 (1976). [2] Barnes, R. S., Birch, P. Β., Spiridakis, D. C., and Schell, W. R., Changes in the sedimentation history of lakes using Pb as a tracer of sinking particulate matter, In: Isotope Hydrology - 1978, IAEA-STI/PUB/493, 875-8981 (1978). [3] Benninger, Κ. Ε., Lewis, D. Μ., and Turekian, Κ. Κ., The use of natural Pb-210 as a heavy metal tracer in the river estuarine system, Marine Chem., 12, 202-210 (1975). [4] Bruland, K. W., Lead-210 Geochronology in the Coastal Marine Environment, PhD Dissertation, University of California, San Diego (1974). [5] Cacchione, D. Α., Rowe, G. T., and Malakoff, Α., In: Sedi mentation in Submarine Canyons, F. Stanley and G. Kelling, eds., Dowden, Hutchinson & Ross, Stroudsburg, Pa., Chapt. 4, (1977). [6] Crecelius, Ε. Α., Arsenic geochemical cycle in Lake Washing ton, Limnol. Oceanog., 20, 441-451 (1975). [7] Crecelius, Ε. Α., Piper, D. Ζ., Particulate lead contamina tion recorded in sedimentary cores from Lake Washington, Seattle, Environ. Sci. Technol., 6, 274-278 (1973). [8] Donaldson, J. R., The Phosphorous Budget of Iliaamna Lake, Alaska, as Related to the Cyclic Abundance of Sockeye Salmon, PhD Dissertation, University of Washington, Seattle (1967). [9] Doyle, L. J., Woo, C. C., and Pilkey, O. Η., Sediment flux through the inter canyon slope areas: U. S. Atlantic Continental Margin, Abst., Geol. Soc., AW Prog., 8, 8-843 (1976). [10] Drake, D. Ε., Hatcher, P., and Keller, G., Suspended parti culate matter and mud deposition in the upper Hudson submarine canyon, F. Stanley and G. Kelling, eds., Dowden, Hutchinson & Ross, Stroudsburg, Pa., Chapt. 3 (1977). [11] Eakins, J. D. and Morrison, R. T., United Kingdom Atomic Energy, Auth, Harwell, AERE-R8475 (1976). [12] Edmondson, W. T., and Allison, D. Ε., Recording densitometry of X radiographs for the study of cryptic laminations in the sediments of Lake Washington, Limnol. Oceanog., 15, 138-144 (1970). [13] Εl-Daoushy, M. F. A. F., The determination of Pb and Ra in lake sediments and dating application, Uppsala, Sweden report UUIP-979 (1976). [14] Goldberg, E. D., Geochronology with lead-210, In: Radio active Dating IAEA STI/PUB, 68, 121-131 (1963). [15] Gould, H. R., and Budinger, T. F., Control of sedimentation and bottom configuration by convection currents, Lake Washington, J. Mar. Res., 17, 183-198 (1958). 234

238


210

210


226

210

17. SCHELL Dating Recent Events in Sediments by Pb 361


210

[16] Lewis, D. Μ., The use of Pb as a heavy metal tracer i n the Susquehana River system, Geochem. et Cocmochin. Acta, 41, 1557-1564 (1977). [17] Nevissi, Α., Beck, J . Ν., and Kuroda, P. Κ., Long lived radon daughters as atmospheric radioactive tracers, Health Phys. 27, 181-188 (1974). [18] Noshkin, V. Ε., and Bowen, V. T., Concentrations and distri butions of long lived fallout radionuclides in open ocean sediments, In: Radioactive Contamination of the Marine Environment, IAEA - STI/PUB, 313, 631-686 (1973). [19] Poet, S. Ε . , Moore, Η. Ε . , and M a r t e l l , Ε. Α., Lead-210, Bismuth-210, and polonium-210 i n the atmosphere: accurate radio measurement and application to aerosol residence time determination, J . Geophys. Res., 77, 6515-6527 (1972). [20] Powers, Η. Α., Wilcox, R. Ε., Volcanic ash from Mount Mazama (Crater Lake) and from Glacier Park, Science, 144, 13341336 (1964). [21] Rama, M. Koide, and Goldberg, E. D . , Pb-210 in Natural Waters, Science, 134, 98-99 (1961). [22] Rangarajan, C. S., Gopalakrishnan, S., and Eapen, C. D . , Global variation of lead-210 in surface a i r and p r e c i p i t a t i o n , USAERDA, Health and Safety Laboratory Environmental Quarterly Report, HASL-298, UC-11, I-63-82 (1976). [23] S c h e l l , W. R., Jokelo, T . , and Eagle, R., Natural Pb and Po in a marine environment, IAEA-STI/PUB, 313, 701-711 (1973). [24] S c h e l l , W. R., and Barnes, R. S., Lead and Mercury in the aquatic environment of Western Washington State, In: Aqueous Environmental Chemistry of Metals, A. J . Rubin, ed., Ann Arbor Science, Ann Arbor, Michigan, 129-165 (1974). [25] S c h e l l , W. R., and Watters, R., Plutonium in aqueous systems Health Phys., 29, 589-597 (1975). [26] S c h e l l , W. R., Concentrations, Physical-Chemical states and mean residence times of Pb and Po i n marine and estuarine waters, Geochem. Cosmochim. Acta, 41, 1019-1031 (1977). [27] S c h e l l , W. R., and Sugai, S., Radionuclides at the U. S. Radioactive waste disposal s i t e near the Farallon Islands, Health Physics, 39:475-496 (1980). [28] S c h e l l , W. R., Lowman, F. G . , and Marshall, R. P . , Geochem istry of the Transuric elements at Bikini Atoll, In: Trans uranic Elements in the Environment, W. C. Hanson, ed., DOE/ TIC 22800, 541-577 (1980). [29] Turekian, Κ. Κ., Oceans, Prentice H a l l , Englewood Cliffs, New York, 120 (1968). 210

210

210

RECEIVED

210

July 23, 1981.


Dating Recent (200 Years) Events in Sediments from Lakes, Estuaries

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