Some Regular Patterns in the Distribution of Sediment

Journal of the Oceanographical Vol. 34, pp. 222 to 232, 1978

Some

Society

Regular

Patterns

Contamination Yasushi

Abstract:

of Japan

in the

in the

Coastal

HIRAIZUMI**, Takehiko

Observations

of sediment

When the pollutant concentration regular pattern is observed in the

Distribution

of Sediment

Waters

along

Japan*

MANABE*** and Hajime NISHIMURA**

contamination

is divided quantitative

along

the

coast

of Japan

were

analyzed.

by the fine particle fraction in the sediment, a relationship among the degree and the area of

contamination and the discharge rate of pollutant released continuously into the water along the coast. This regularity was observed with respect to COD, n-hexane soluble substances and heavy metals, and could be expressed by a formula. Polluted and thus dispersion

particles

were

supposed

their distribution in the in the surface water.

Introduction In coastal waters enter, contamination extending out from

to disperse surface

1.

where industrial effluents of sediments are observed the fixed sources of the

pollutants. This is known empirically to be closely related to the contamination of the aquatic ecosystem of that region. In environmental impact assessment to predict the contamination of the aquatic ecosystem, it is necessary to predict quantitatively the extent and intensity of contamination of the sediment; therefore, it would be useful to find a regular pattern of bed sediment contamination from analysis of field data. For the cases referred to in Table 1, regional dispersion of pollutants in the sediment are found to be described by the following empirical equation,

(1) where surface value, tration

C is the pollutant concentration in the of the sediment, C. is its background and S is the polluted area with concenhigher than C. The parameters n and

/3 appear to become constant for given location and pollutant, according to the above mentioned * Received

Aug .

11,

1975,

revised

Oct.

30

and

accepted Oct. 31, 1978. ** University of Tokyo , Department of Chemical Engineering, Bunkyo-ku, Tokyo 113, Japan *** Hyogo Prefectual Fisheries Experimental Station, Nakasaki-cho,

Akashi,

Hyogo

673, Japan

through

sediment

suspension

is expected

in the bottom

to become

similar

water

layer,

to effluent

observations. In this paper, we examine the general relationship between pollutant concentration, distribution in the sediment and release rate of the pollutant. 2.

Relationship among pollutant concentration in sediment, dispersed area and release rate of pollutant In the surface sediment, the distributions of pollutants released from a source are always similar irrespective of the kind of pollutant. This tendency was observed in Osaka Bay with respect to heavy metals, COD and oils (JOH et al . , 1974). From this it is inferred that essentially the same process controls the distribution of pollutants in the sediment. As for the extent of sediment contamination, the pollutant concentrations in the sediment surface were found roughly proportional to the rate of pollutant influx. Based upon this, the following equation is introduced, (2) where M is the rate of heavy metal discharge (kg (1-9, and a and n are constant parameters. Of the earlier study carried out in Osaka Bay, values of 1.56 and 0.4 were respectively obtained for a and n (NISHIMURA and KUMAGAI, 1975). We now proceed to ascertain this relationship in other offshore areas, for other pollutants. (A) COD (in this paper we use the COD as

Regular

Table

1.

Patterns

of Sediment

Studies

of sediment

Table

* (1) (2) (3) (4)

2.

Influx

rate

Contamination

223

contamination.

of COD.

COD influx was estimated

on basis of SS (suspended solids) influx . Economic Planning Agency, Japan (1966): Observation on Water Quality in Coastal Waters of Otake, Iwakuni. 217 pp. Japan Aquatic Resources Conservation Society (1971): Investigation on Environmental Pollution in Eastern Hiuchi-nada. 34 pp. Economic Planning Agency, Japan (1970): Observation on Water Quality in Coastal Waters of Mishima, Kawanoe. 79 pp. Conference on Utilization and Development of the Seto Inland Sea (1972): Analysis on Pollutant Influx to the Seto Inland Sea. ed. by Chugoku Areal Business and Finance Association. 92 pp.

an index for organic pollutants): Distributions of organic pollutants in the sediment were studied in Osaka Bay, the eastern part of Hiuchi-nada, and the offshore region of OtakeIwakuni district. Release rates of COD in these areas are shown in Table 2. Based upon observational results with respect to COD as shown in Fig. 1, the parameters a and n of Eq. (2) were found to be 1.5 and 0.75 respectively. Here C is expressed in mg g-1, M in ton d-1 and S in km2. (B) n-hexane soluble substances (oils): The distributions of oils in the sediment were studied in Osaka Bay, the area off Otake-Iwakuni and off Yokkaichi. The rates of oils discharge in these waters are shown in Table 3. The observational results shown in Fig. 2 give 2.4 and 0.55 respectively for the values of a and n. However, we must note the fact that, not every n-hexane soluble substance in the sediment is attributable to oils. In Osaka Bay, which is

Fig.

1.

divided

Relationship by influx

between rate

of COD

the concentration in bottom

sedi-

ment and its dispersed area based on COD influx summarized in Table 2. Symbols are explained in the

table.

IIIRAIZUMI, MANABE and NISHIMUIZA

224

Table

(5)

3.

Influx

of n-hexane

soluble

substances.

NAGAI, U., K. KAWAMURA, S. NAKANISHI and K. FUKATSU (1964): Special Survey Report on Fishes Tainted with Oils. pp. 70-85. Science and Technology Agency, Japan. Table

(6)

rate

Environment

4.

Influx

rate

of heavy

metals.

Agency, Japan (1973): Inspection on Environmental

Contamination

by Mercury

in Japan.

Fig. 3. Relationship between the concentration divided by influx rate of heavy metals in bottom sediment

Fig.

2.

divided

Relationship by influx

between rate

the

concentration

of n-hexane

soluble

and

dispersed

area

based

summarized in Table in the table.

4.

Symbols

X,

correlation line shima Bay.

of

distributions

of distributions

sub-

data

in

Mizu-

stances in bottom sediment and dispersed area based on data summarized in Table 3. Symbols

Y,

correlation

are explained

Z,

Osaka Bay. expected correlation

line on basis

of heavy

metals

in fine particle

fraction

in the table.

Chain

a correlation line for the distribution fraction of oil in sediment.

line indicates of the net

line

on

are explained

concentration

of sediment.

mainly

of

Regular

Patterns

of Sediment

always affected by severe organic pollution, 50-80 % of the n-hexane soluble substances in the sediment were observed to be elementary sulfur or sulfide (JoH et al., 1974). In addition, the waters of chronic oil pollution in the present paper are also affected by chronic organic pollution. We will assume that the net concentration of oils in the sediment accounts for approximately half of the n-hexane soluble substances, and we therefore find the value of 1.2 to a in Fig. 2. (C) Heavy metals : Horizontal distributions of heavy metals have been studied in detail for Osaka Bay (JoH et al., 1974); for the eastern part of Hiuchi-nada (YANAGI, 1973); and for the waters off Mizushima, Niihama and Tokuyama by the Environment Agency of Japan (Table 4). We now consider the relationship between these distributions and the discharge rates of heavy metals. First, the discharge rates of pollutant heavy metals are given in Table 4. From these data, relationships can be obtained between the concentration divided by influx rate of heavy metals and the area of the heavy metals distribution on the surface of the sediment (Fig. 3). In this figure, the slope of the correlation line is large for the case of Mizushima (X), and small for the cases of Osaka Bay and eastern Hiuchi-nada (Y). The difference may be explained as follows. In the inner part of Mizushima Bay the water is relatively stagnant, while at the entrance it flows faster due to the tidal current. This results in pollutant particles settling more densely

Fig.

4.

Solid

lines

Cd concentration (MANABE, tours for fraction

indicate

contours

in sediment

1974a). Broken Cd concentration

of sediment.

ppm

for overall

in Harima-nada lines indicate conin fine particle in dry

mud.

Contamination

225

in the nearshore region of the inner bay than at the entrance. In contrast, for Osaka Bay and Hiuchi-nada, the average sediment particle size is larger at the inner regions and smaller at the entrance, far offshore, reflecting the difference of the water depth. This explains why the pollutants are more liable to settle and accumulate offshore and at the center of the bay than at the interior region and near the shore. If the sediment particle size distribution were uniform over the whole area, the pollutant particles would not be liable to settle and accumulate locally, and the slopes of the correlation lines would be identical for any region. As for the case in Fig. 3, the scattered points of data are expected to approach a single correlation line (Z), provided that the areal variance of the sediment size distribution could be cancelled. Thus the correlation line may give 0.9 and 0.6 respectively for the values of a and n. Here C is in lig M is in kg c1-1 and S is in km2. 3.

Effect of particle size distribution on sediment contamination 3.1. Distribution of pollutant in surface sediment As mentioned briefly in the previous section, the horizontal distribution of pollutant in the surface sediment appears to be greatly influenced by geographical and topographical features, current and tide. In the northern part of Hiuchi-nada, the distribution of heavy metals in the sediment is seen to extend out from the sources on

Fig. 5. Solid lines indicate contours for overall Cr concentration in sediment in Harima-nada (MANABE, 1974a). Broken lines indicate contours for Cr concentration in fine particle fraction in sediment.

HIRAIZUMI,

226

the

northern

coast,

located

in

where

an

there

A

is

similar with

no

source

and

KUMAGAI,

to

be

and

size

tween

the

the

in

1972a).

of

sediment

of

in nated

Bay with

In

PCB

addition,

is

generally

of

the

each

where

particle

pollutants

sediment.

in

particle

true

for

PCB

contamidata).

heavy

metals

particle in

fraction

the

findings

at

content

in

metals of

the

and

sediment

(3) where

Ca

is the

pollutant

concentration

in the

was

KUMAGAI,

divided

cations

where

the

1975;

offshore

fine

occupies

sediment

than

in

apparently

in

an

tration

in

the

We

now

between

a

proceed

to

It

is

the

size

remains that

fine

particle of

area, pollutant

consider

the

the

coastal

the

and

this

concen-

fine

in

Harima-nada that

source particle

constant the

contamifound

distribution

on

the

an of

with

coast in

when the

area. the

an

pollutant

decreases

fraction over

in as

the

sediment

the

relationship

water

relationship out

the

from of

lo-

example,

percentage

noteworthy

in

distance

the

that carried

concentration the

At

for

higher

and

studies

example.

fraction.

surrounding

particularly

earlier

net concen-

sediment.

offshore

nation,

total

stagnant,

higher

the

"the

for

Harima-nada,

fraction

fraction

define

particle is

assumed

particle

here

water

of

be

fine

pollutant"

by the

results

generally the

We of

tration

suggests

fine

heavy

in

concentration

ment

the

may

concentrated

the

far

also

pollutant concentration in the fine particle fraction of the sediment will reflect the actual process of pollutant dispersion in the sediment. Of the previously mentioned studies at Harimanada, we now describe the distribution of pollutant with the concept of "the net concentration of pollutant", which corresponds to assume that the pollutant concentrates almost entirely in the fine particle fraction of the sediment (particle diameter less than 50 pm). We then obtain distribution patterns shown by the broken lines in Figs. 4 and 5 that indicate sediment contamination by the heavy metals d, Cr-Stretching far south offshore -Cfrom the northern coast at Harima-nada. Applying the same method to the distribution of the other heavy metals, the following equation is obtained for describing the distribution of pollutant in the fine particle fraction in the sediment (Fig. 6),

1977).

Most be

distribution

pm

of

fraction

the were

unpublished

(NISHIMURA

KUMAGAI,

(a

strongly

shown

the

size

determined

of

in as

Bay

is

region

highest

ƒÊ

in

the 10

concentration

sediment,

Beppu

to than

(HIRAIzuMI,

the

50

Hiuchi-nada

this

where

than (MANABE,

chlorophyll-a)

closely less

beand

pheophytine-a

and

Apparently

Beppu

to

Bay

sediment

found metals

(less

of of

Beppu

diameter.

was

Harima-nada

degradation

fine

sediment.

particles

at

corresponding the

relationship

heavy

distributions

of

found

in

fine

off heavy

concentration

of

of

to

clear

relationship

sediment

Also,

product

A

concentration

the

and and

respect

distribution

percentage

m)

1977),

pollutant

linear

Beppu

(NisHimuRA

with

1972).

a

5). at

data),

also

between

particle Recently

and

metals

unpublished

expected

offshore,

KUMAGAI,

Hiuchi-nada (YANAGI,

can

4

NISHIMURA

in the sediment is controlled by the mixing and diffusion processes of the pollutant in the fine particle fraction. This means that the pollutant distribution in the sediment described by the

being

far

observed

heavy

1975;

(HIRAIzuMI,

Kannonji,

pattern

(Figs. was

respect

metals

another position

situation

Bay

PCB

with

isolated

MANABE and

sediThis

pollutant

Fig. 6. Relationship between trations in fine sediment dispersed

areas

concentration.

bounded

heavy metals concenin Harima-nada and by

the contour

of that

Regular Table

5.

Estimated

released nada.

from

influx the

rate

Patterns

of heavy

northern

coast

of Sediment

Contamination

227

metals

of Harima-

These influx rate figures were originally estimated by the authors from material balance calculations and observations fine

particle

is

the

of urban

fraction

of

background

equation

to

constant

always

be

take of The

of

the

same and

in

fine

and

patterns at Harima-nada and of Osaka Bay. In summary, it was found that the distribution of pollutant in sediment can be generally expressed as

pollutant

rate

of

pollutant

discharge In

Section

for

the is

that

not

may

be

the

generally

area

We

may

from in as

concentration

of

estimated

on

The

between

which

is

pollutant

concentration

is

in

shown

used

for

bution

along

above in of

(JOH

is in

a

coastal

be

calcu-

background is

earlier

reasonably findings

and

The

the

a

the

fine

in same

3, fine

1974).

Osaka

area

of

decreases In

Fig.

distriBay.

than

7

The of

99

%

the

bay

to

about we

4. was

fraction

show

where Ca is the net pollutant concentration in the fine particle fraction f in the sediment (mg kg-1), c/f, Ca,00 is the background pollutant concentration in the fine particle fraction of the sediment (mg kg-1), S is the contaminated area bounded by the contours for equal pollutant concentration Ca (km2) and M is the rate of pollutant discharge (kg d-1). The average value of the power n is about 0.65 and n ranges between 0.4 and 0.9 for heavy metals and oils. The corresponding n for COD is greater than this average value probably because of biodegradation. The average value of aa is 1.5 and it ranges between 0.5 and :3. The correlation coefficient for these data is 0.98 for the empirically determined equation shown in Fig. 7.

of

sediment,

procedure

particle

small

the

contour

pollutant for

higher

it

and

by

mentioned

coast :al.,

(Ca -Ca,•‡)/M

Fig.

generally

very

the et

7.

the

percentage

but

the

The

bounded Ca

Fig.

pattern

sdiment

to

metals of

at

pollutant

features.

relation S,

of

can 5.

basis

even

features

rate sources

heavy

the

geological

area

regular

Table

(2)

pollutant

sediment.

Harima-nada in

Eq. the

of

The

terrestrial

shown

sediment,

fraction,

size

6).

northern

use

particle

these

(Fig.

waters

the

fine

observe

concentrated the

fraction. we

varying

frac-

discussion,

in

if

(4)

area

particle

more

particle

the

with

Harima-nada discharge

are

stated in

the

fine

hold

the

previous

fraction

coarse

to in

the

the

pollutants

concentration

lated

of

particle

in

ascertained

pollutant

From

fine

and

was

distribution

seen

the

for

(2) of

uniform.

was

in

Eq.

distribution

where tion it

2.,

the

pollutant by influx dispersed pollutant

of

condition.

between

sediment

but almost

irrespective

bed

Fig. 7. Relationship between the net concentration in fine sediment divided rate of pollutant (Ca-Ca.00)/M and area S bounded by the contour of concentration Ca.

.

This

Eq.(1), may

value sea

Ca,

Ca.

to here

relationship

content

and

similar n

area

effluent.

sediment

parameter

differences 3.2.

the

concentration

appears

the

and industrial

the

there, bottom 50

% the

Discussion Here we give a physical interpretation for the results of the preceeding section. 4.1. Processes controlling contamination of bed sediment in coastal waters The following processes are supposed to be the mechanisms controlling the contamination pattern of sediment: 1) The discharged pollutant, for the most part,

228

HIRAIZUMI,

MANABE

settles in an area comparatively close to the site of pollutant release. 2) The settling fine particles mix and disperse in a dense suspension of grain-fluid mixture just above the bottom. 3) The fine sediment particles settle and deposit to form contamination patterns in the bed sediment. 4) The deposited pollutant fine particles are stirred again, mixed in a dense suspension above the bottom and redispersed in the sediment by a shear stress strong enough to cause movement. Let us investigate these proposed processes. (A) Sedimentation of pollutant particles: First let us describe the sedimentation pattern. Suspended solids (SS) discharged from paper mills is observed to disperse as far as 1 km from the source. At a distance beyond 1 km a sharp decrease in concentration in the surface water is observed. Vertically, at the

Fig. 8. Horizontal distribution pattern of SS in each layer in coastal waters. ** off Iwakuni coast -June 15, 1965-(based on JEPA, 1966) Al, ebb tide, surface 0.75 m depth layer; layer; B2, flood tide, ** off Tagonoura -Nov.

layer; A2, ebb tide, Bl, flood tide, surface 0.75 m depth layer. 22, 1970-

Cl, surface layer; C2, 2 m depth layer; C3, 5 m depth layer.

and NISHIMURA

front of distribution, the layer of highest concentration of SS shifts from the surface layer to the middle, and finally may descend to the bottom (Fig. 8). Most SS are deposited on the sea bed within 5 km from the discharge source on the coast. At Minamata, the amount of accumulated mercury in the bay area within 2 km from the coastal source was about 200 tons in 1963 at which time the discharge from the source had already ceased (HANYA et al., 1973). This was about 50 % of the total released mercury. At Tokuyama, within the bay area, the accumulated mercury in the sediment was estimated to be 15 tons in 1972 (NAKANISHI et al., 1973), which is 15,-20 % of the total estimated discharge. These examples suggest that a fair amount of the discharged mercury settles and deposits in the area near the source. The average diameter of polluted particles in the sediment appears to be 50 pm or less (NISHIMURA and KUMAGAI, 1974), the settling velocity of which is around 18 mor less. However, most of the finer particles seem to settle rapidly to the bottom, by agglomeration of particles. The above situation may be explained in this way. (B) Motion and depositing process of the pollutant on the sea bed: The horizontal distribution of the contaminated suspension is formed as the result of the interaction of two processes, referred to above as 2) and 4). Then the horizontal distribution of contaminant in the sediment is governed by process 3). The horizontal and settling velocities of the sediment control these processes. The critical velocity for initiating sediment movement has been studied by many researchers. In this paper, we select certain contributions and review the relationship between particle size, critical velocity and settling velocity (Fig. 9). From this figure the behavior of sediment particles can be devided into four categories, according to the region defined by water velocity and particle size. Region 1: After erosion, sediment is suspended again. Region 2: Sediment rolls or saltates on the bottom without being suspended again. Region 3: Suspended matter settles and de-

Regular

Patterns

of Sediment

Contamination

229

To estimate the horizontal mixing of pollutant in sediment on the sea bed, the results of studies on the dispersion and stranding of radioactive labelled sand (INOUE, 1956; SATO, 1962, 1963) can be utilized. To interpret the studies, the basic equation for horizontal mixing from a radially symmetric source will be used as an analogy. For an instantaneous point release of contaminant of amount M, the general solution was given by OKUBO (1962) with diffusion coefficient K(=Arm). In case of m=1, the solution was Fig. 9. Relationship between particle size:and motion on sea bottom. Uer.(V), critical velocity after VANNONI(1964); Ucr.(W), critical velocity after WHITE (1970); Usettling, settling velocity of particles with specific density 2.5. Circle numbers indicate regions. posits to the bottom. Suspended matter is maintained in a suspension without erosion, rolling, saltation or settling. Very small particles of diameter less than 50 gm, which are now being discussed, mix and disperse in the sediment by repeating the processes of Region 1, 3 and 4, but not of Region 2. Thus the transport of pollutants in the fine sediment will go through the following process : Pollutants and polluted fine particles remain in suspension and are dispersed by water movement, stay for a long time in the water near the bottom and spread over a wide area. Once the particles settle and form a deposit, a surface contamination pattern soon appears on the bottom sediment corresponding to the contamination pattern of the floating particles in the water above. Under such conditions, removal of the deposited pollutant takes place very slowly because a velocity (Ucr in Fig. 9) greater than the critical shear is not as likely to occur as often as the condition which allows particles to float. This means that when compared with the rate of contamination process, recovery process will be slow. The above mentioned conditions may bring about formation of a highly contaminated suspension layer just above the bottom, as observed in polluted waters. 4.2. Diffusion of pollutant in sediment

(JOSEPH and SENDER, 1958) and m=4/3,

(5)

the solution was

(6)

(OZMIDOV, 1958)

Region 4:

where the

CI

is

the

distance

time, is

p the

is

the

the the

of

and

2/3 Of

the

n

results

employed

(Fig.

assumed

transition

of

From

former

power

r of

the

solution

dispersed

area

sand.

Little

value

it

may

than

an

discussed

tracer

either and

less

1956),

of

of

of

n

reasonably

1

of

can

sediment

diffusion

area

In

the

grains

and

above

than by

150ƒÊm) rolling of

area

is be

lies

around

shown

that

of

diffusion

m

the (1

experiment, so

coarse

the

sand

than

by

this

the

surface

upon

exponent

mentioned were

the

depend

the

for

the

11).

that

may and

in

(Fig.

assume

rather particles

also

tracer

employed

disperse behavior

are

other

we of

greater

The

C

(INOSE,

radioactive

the

this,

coefficient

sand

s-1).

distance

relationship

patterns of

sediment

3/4).

nth

is

the

the

when

n

and ƒÁ

1/3.

distribution

scale

of

is the

solution.

10),

that and

linear

concentration

radioactivity

difference

s-1)

relationship

linear

the

is

a

data the

r t

(cm2/3

for

experimental

the

The

1

patch,

(cm

n, the

latter

between

and

is

the

verifies

above

1/2

power, of

S;

for

analysis

S

nth

a patch,

parameter imply

logarithm

contour

of

velocity

solutions

between

in

center

dissipation

above

and

the diffusion

energy

The

concentration

from

size

and the

(diameter seemed suspension. are

classified

to

HIRAIZUMI,

230

MANABE

and NISHIMURA

Eq. (4), expressing the regular pattern controlling the contamination of coastal sediment. As was shown in the preceding, this process is similar to diffusion of pollutant in the surface water layer. Assuming that the polluted particles disperse in the nepheloid layer or in the suspension layer on the bottom of thickness H, the following equation can be derived, (7) where r is the the dispersion

distance from the source, K is coefficient, M is the rate of

pollutant discharge, C is the pollutant content in the sediment and c is the ratio of settling Fig.

10.

Examination

of

dispersion

radioactive sand on sea, bed with time-at Tomakomai, 1955-count activity root

to area

8, or the

of S bounded

cube

patterns

of

portion is that

of

pollutant.

the elapse of C of radioroot

by the contour

The

boundary

condition

(7a)

or square

for count

C.

If

we

assume

(7b) The

solution

becomes

(8)

Fig. 11. Typical example showing extension of dispersion area of radioactive labelled sand on sea bed with the elapse of time-at Kashima, 11.1 m depth-based on the data of SATO (1962).

into Regions 2 and 3 of Fig. 9. For a smaller disperion range r, the coarse particles may be suspended in eddies and this dispersion seems to be controlled by eddy diffusion. For a larger diffusion range r, the sand particles probably settle before completing dispersion in the larger eddy. This suggests that even the dispersion of coarse grain sediment may partly be accounted for by eddy diffusion. 4.3. A formula describing the distribution of polluted sediment In Section 3 we found an empirical equation,

where S is the area bounded by the contour, of the pollutant concentration C, and n and A are constants. In Eq. (8), C represents the pollutant content in the sediment as a whole. Now we use Ca as a pollutant concentration in the fine sediment fraction f, and reduce Eq. (8) to the following equation, assuming that the product Af is equal to a constant parameter A' , (9) From the above discussion, the exponent of the diffusion coefficient in Eq. (7b) appears- to be in the range of 1 to 4/3 and we expect K at about the value Ar1.0 on the basis of the above analysis of Eqs. (5) and (6), and the observations. On the other hand, from the results of the preceding, Sec. 3.2., we estimated that n/2 of Eq. (9) averaged to 0.65 and ranged from 0.4 and 0.9. Therefore we know that. it ranges from 0.8 to 1.8. This result implies that

Regular

Patterns

of Sediment-

the physical processes leading to Eq. (9) are similar to those leading to Eq. (4) 5.

Conclusion Based on a treatment of the fine particle fraction, a formula has been deduced which expresses the relationship between the continuous influx of pollutant from a fixed source and the extent and the intensity of sea bed contamination. The horizontal dispersion of the contaminated sediment resembles that of the effluent from a coastal source in the surface water and a similar correlation formula could be derived for the contamination of the sediment. The behavior of the fine sediment suggests that when compared with the process of contamination, once settled sediment is supposed not to be easily suspended again, and natural elimination of the polluted sediment takes place slowly. These findings make it possible to fairly accurately predict and assess the degree of contamination of bottom sediment once the amount of pollutant discharge at the coast is known. Acknowledgement The authors wish to express their gratitude to their colleague, Dr. Mikio KUMAGAI, for his constructive criticisms and suggestions. Also, the authors wish to express sincere appreciation to Dr. Nicholas C. KRAUS, Nearshore Environment Research Center, for his helpful review of the manuscript. References HANYA, T. and T. AIZAWA (1973): Accumulation of mercury in Minamata Bay. In, Mechanism of Water Pollution, ed. by Kyoritsu Publ. Co., Tokyo, pp. 92-117 (in Japanese). HIRAIZUMI,Y., T. MANABE, M. TAKAHASHI,K. NISHIDA, H. JOH and H. NISHIMURA (1975): Analysis of PCBs contamination of sediment in the coastal waters of the Seto Inland Sea. La mer, 13, 163-169. HIRAIZUMI,Y. (1976): PCBs pollution in the Seto Inland Sea-Its pathways and influxes-Kagaku (Science, Japan), 46, 314-322 (in Japanese). INOSE, Y. (1956): Observation on stranded sand

Contamination

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using radioactive tracer. Proceeding of 2nd Coastal Engineering Conference, Tokyo, pp. 163-167. JOH, H., S. YAiviocHi and T. ABE (1974): Condition of heavy metal pollution in Osaka Bay. Bull. Osaka Fish. Exper. Stat., No. 4, pp. 1-41 (in Japanese). JOSEPH, T. and H. SENDER (1958): ilber die horizontale Diffusion im Meere. Dt. Hydrogr., 2., 11, 49. KUMAGAI, M. (1977): A Study on the pollution of coastal marine environment. Doctoral dissertation, Department of Chemical Enginnering, University of Tokyo, Japan, 257 pp. . MANABE, T. and T. TAKESUE (1974): Contamination of bed sediment in Harima-nada. Bull. Fish. Exp. Stat. of Hyogo-ken. No. 14, 61-67 (in Japanese). MANABE, T., H. SAKAGUCHI and T. TAKESUE (1974): Observation about heavy metals distribution in sediment of Harima-nada. Annual Report of Hyogo Fisheris Experimental Station, No. 48, 281-286 (in Japanese). NISHIMURA, H. (1973): Pollution in Seto Inland Sea-Oil pollutionKagaku (Science, Japan), 43, 171-179 (in Japanese). NISHIMURA, H. and M. KUMAGAI (1974): Heavy metals pollution in Seto Inland Sea. Kagaku (Science, Japan), 44, 103-109 (in Japanese). NAKANISHI, H., M. UKITA and K. MAEDA (1973): Mercury accumulation in sediment of Tokuyama Bay. Effluent Treatment Technology, 14, 915925 (in Japanese). OKUBO, A. (1962): Review of theoretical model for turbulent diffusion in the sea. J. Oceanogr. Soc. Japan, 20th anniversary vol., 286-320. OZMIDOV, R. V. (1958): On the calculation of horizontal turbulent diffusion of the pollutant patches in the sea. Doklady Acad. Nauk SSSR, 120, 761. SATO, S. (1962): Environmental setting of Kashima Industrial Port. vol. 2, ed. by Ministry of Transportation, Tokyo, 201 pp. (in Japanese). SATO, S. (1963): Observation and analysis of stranding sand by isotope technique. Technical Note of Port and Harvour Technical Res. Inst., No. 5, 1-200 (in Japanese). VANNONI, V. A. (1964): Measurement of critical shear stress. Calif. Inst. Tech. Rep., No. KH-R-7. WHITE, S. J. (1970): Plain bed thresholds of fine grained sediments. Nature, 228, p. 152. YANAGI, T. (1973): Current and sediment of Hiuchinada. Research Note on Coastal Oceans, 11, 8-11 (in Japanese).

HIRAIZUMI,

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MANABE

and NISHIMURA

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